Patent Application
20220214881
Embodiments described herein generally relate to bounds checking in computing systems. In particular, embodiments described herein relate to cryptographic enforcement of bounds checking in executing programs by computing hardware.
Memory safety and concurrency errors have afflicted computer systems for decades, with no sign of sustained improvement. This has motivated the development of programming languages with strict checking of type systems that mitigate those concerns. Rust is rapidly gaining acceptance as one such language that strictly enforces a novel type system based on borrow-checking that draws on linear typing, ownership typing, and region-based memory management. Rust defines data types with byte-granular bounds. Existing byte-granular bounds checks are not enforced cryptographically. Non-cryptographic bounds checks depend on unencrypted bounds not being corrupted, which may occur via various ways such as physical attacks, unsafe code, and bit errors.
Various examples in accordance with the present disclosure will be described with reference to the drawings.
The present disclosure relates to methods, apparatus, systems, and non-transitory computer-readable storage media for enforcing byte-granular bounds checking of programs in computing hardware to provide resilience when one or more assumptions are violated. The technology described herein maintains metadata necessary for byte-granular bounds checking in a pair of encrypted 64-bit values and checks it automatically in hardware when memory is accessed. This technology also introduces new instructions for updating that metadata and compiler techniques for inserting those instructions at necessary points in the program.
Memory safety is becoming more important for customers hardening the security of their software. Strictly typed languages such as Rust are an increasingly popular tool for achieving memory safety. The technology described herein cryptographically enforces byte-granular bounds checks as are needed by Rust in computing hardware. This provides defense-in-depth and support for stronger threat models, including support for enforcing byte-granular bounds checks, even in unsafe code.
In the following description, numerous specific details are set forth. However, embodiments may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail to avoid obscuring the understanding of the description.
Some examples described herein discuss the Rust programming language. Rust is a multi-paradigm, general-purpose programming language, developed by the Rust Foundation, designed for performance and safety, especially safe concurrency. Rust is syntactically similar to C++ but can guarantee memory safety by using a borrow checker to validate references. Rust achieves memory safety without garbage collection, and reference counting is optional. Although discussed with reference to Rust, one or more implementations described herein may also be adapted for use with other type checking programming languages.
Rust's type system eliminates spatial safety errors (e.g., Out-Of-Bounds (OOB) accesses) by checking bounds of memory objects. Rust also eliminates temporal safety errors. The error called “Use After Free” (UAF) is prevented by tracking all references to each object so that the object is only freed after the object is no longer referenced. Uninitialized use is avoided directly by refusing to compile programs with objects that are not initialized prior to use. Type confusion is mitigated by strict type checking. Data races are avoided by only permitting a single reference to each mutable object to be active at any given point in time.
Table 1 shows an example of code that does not pass type checking due to an invalid ownership transfer. This code is rejected by the Rust compiler for attempting to create multiple, simultaneously active references to a mutable object.
The Rust compiler statically determines the lifetimes of many objects, sometimes with assistance from program developers in the form of annotations (e.g., to indicate the lifetime of a reference-typed return value from a function that accepts multiple input references). Rust also provides support for dynamic reference counting when necessary. Rust's type system avoids the need for garbage collection since Rust destroys objects as soon as they are no longer referenced.
However, Rust permits the use of unsafe code that bypasses type safety checks as well as linkage with code written in languages other than Rust, since Rust adheres to the Application Binary Interface (ABI) that is also used by languages such as C and C++. ABIs specify how functions interact with each other (e.g., to save and restore register values, pass parameters, and return data). The term “unsafe code” is used herein to cover both unsafe code in Rust and all code written in other languages. Unsafe code even appears within the Rust standard library. These interactions with unsafe code have led to a variety of bugs in Rust-based software stacks. Even for safe Rust code, security depends on the assumptions listed above.
The technology described herein prevents unsafe code from undermining safe code with an enhanced ABI that enforces borrow-checking in computing hardware, referred to herein as the borrow-checking ABI, or BC-ABI. The BC-ABI may be used within unsafe code to extend borrow-checking to a subset of unsafe, non-Rust code that is compatible with the constraints of borrow-checking. Furthermore, BC-ABI interoperates with other unsafe code that does not adhere to the constraints of borrow-checking. The effect of compiler bugs within safe code can be contained by enforcing the BC-ABI in computing hardware even within safe code. BC-ABI can likewise contain the effects of other threats, e.g., from incorrect system software including libraries, a compromised OS kernel or virtual machine manager (VMM); physical attacks; and bit flips (e.g., due to radiation).
Some unsafe code may legitimately need to bypass borrow-checking, so overrides are supported when necessary. For example, a keyword may indicate “dyn_safe” (for “dynamically-checked safe”) sections of code, in addition to unsafe sections, so that “dyn_safe” may be used when the expectation is that the type system will not actually be violated, but Rust is unable to statically verify it. The “unsafe” code may be reserved for situations in which the program developer actually needs to bypass the type system. The technology herein also describes how a cryptographic implementation of the BC-ABI satisfies the requirements to mitigate risks from lower layers of the system enumerated in one or more of the assumptions of correctness of system software including libraries, the OS kernel, and the VMM; absence of physical attacks; and absence of bit flips with high efficiency and minimal hardware and software touchpoints. The increased static type information that is available in strictly typed languages such as Rust can also create opportunities for optimizing dynamic type checking.
In one implementation, the BC-ABI is an interoperable extension of the x86-64 ABI, so the BC-ABI adopts the same conventions as the x86-64 ABI (e.g., which registers are used for selected numbered parameters, how extra parameters are arranged on the stack, and which registers are caller- vs. callee-saved) and includes additional hardening operations. The characteristics of each operation are highlighted below since there may be multiple ways to implement them based on different underlying hardware mechanisms. In one implementation, the hardening operations may be implemented using Cryptographic Computing (CC) 216 of
In general, computing hardware 200 may include processing cores, caches, registers, translation lookaside buffers (TLBs), memory management units (MMUs), other processor hardware, input/output (I/O) devices, main memory, secondary memory, other system-level hardware, and other hardware found in processors and computer systems (e.g., as shown in the other processors and computer systems disclosed below). In particular, computing hardware 200 includes an instruction set architecture (ISA) 202. As extended herein, ISA 202 includes mark immutable instruction 204, transfer ownership instruction 206, and assert immutable instruction 208. CC compiler 104 generates these instructions by code generator 110 as needed. CC 216 includes circuitry as described, for example, in “Cryptographic Computing Using Encrypted Base Addresses and Used in Multi-Tenant Environments”, United States Patent Publication Number US20200201789A1, published on Jun. 25, 2020, and incorporated herein by reference. LEVI 218 includes circuitry as described, for example, in “Data Relocation for Inline Metadata”, US Patent Publication US20210405896, published Dec. 30, 2021, and incorporated herein by reference. Computing hardware 200 also includes circuitry as described in “Pointer Based Data Encryption”, US Patent Publication No. 20200125501A1, published Apr. 23, 2020, and incorporated herein by reference.
Memory 210 includes a plurality of objects 214 allocated as a result of executing CC enforced binary code 118. Objects 214 are referenced by a plurality of pointers 212, respectively.
In one implementation, memory safety check unit 220 implements borrow checking in computing hardware 200, as described below in
To be able to enforce the BC-ABI in computing hardware 200, the design must move beyond representing a pointer as a reference into an undifferentiated, flat memory space. The architecture of computing hardware 200 uniquely identifies each object as well as the object's current owner, which is the sole variable through which the object can be referenced at that time in the program if the object is mutable. If the object is immutable, the object still has an owner, but one or more additional references may exist that can be used to read from the object.
To represent ownership using CC 216, an ownership ID is inserted into unused bits within each pointer. The processor can check the ownership ID of a pointer against the current ownership ID for the object being referenced.
One option for storing an ownership ID is to use Linear Inline Metadata (LIM) 218 (as disclosed in US Patent Publication US20210405896), which stores metadata inline within each object. Specifically, since every object crosses the midpoint of the slot that fits it best, that midpoint is a convenient location to store metadata such as an ownership ID. The compact pointer encoding only specifies the slot containing the object, not the precise bounds of the object. Thus, even though it is infeasible to store metadata at more obvious locations, such as at the beginning or end of an allocation, a processor of computing hardware 200 can locate metadata in constant time at the midpoint of the slot. Bounds can also be stored in that manner to support byte-granular bounds checks with synchronous exception reporting as required by languages such as Rust. Tags can be stored as well to mitigate spatial safety vulnerabilities that may be missed by bounds checks. The ownership ID and tag checks together also support generating synchronous exceptions for UAF exploits, and the tag is also incorporated into the pointer encryption, which in turn binds the data encryption to the tag.
Similarly, other memory tagging approaches may be used to hold the ownership ID in memory, for example, by having a separate table of ownership IDs stored in memory where each entry in the table represents the ownership ID of a corresponding granule of memory. For example, the location of every 16 bytes of data in memory may correspond to an entry in the ownership ID table for the memory address of those 16 bytes of data. On a load or store operation to the address of a data granule, the processor may then lookup the corresponding ownership ID for that address in the table, where the address of the 16 bytes of data is used as an index into the ownership ID table, identifying the current ownership ID for the data granule.
In various implementations, the size data field 410 may include any number of bits. For example, the size data may include: 2-bits or more; 4-bits or more; 6-bits or more; or 8-bits or more. The size data field 410 provides an indication of the size of the memory allocation. The tag data field 420 may include any number of bits. For example, the tag data field 420 may include: 4-bits or more, 6-bits or more; 8-bits or more, 16-bits or more, or 32-bits or more. The encoded pointer 400 also includes a pointer arithmetic field 440. The pointer arithmetic field 440 may include any number of bits. For example, the pointer arithmetic field 440 may include: 4-bits or more, 6-bits or more; 8-bits or more, 16-bits or more, or 32-bits or more.
As depicted in
One property that is to be ensured by the technology described herein is exclusive mutability. This is achieved by updating the ownership ID of an object whenever a dataflow is observed dynamically between two references (that is, p=&mut q). In this way, the transferred reference (on the right-hand side of the expression) loses the ownership of the object and is not allowed to be used to modify the object since the ownership ID will be mismatched. The destination of the dataflow (on the left-hand side of the expression), however, will hold the most recent ownership ID, which is the same ID as encoded in the object metadata, and thus becomes the only valid reference to access the object.
The technology described herein relies, in one implementation, on LIM 218 to encode ownership ID in both pointer and object metadata. When the borrow is transferred (when a dataflow between two references are detected), the metadata of the object is updated and only the destination reference's metadata is updated accordingly, thus invalidating the previous reference after the transfer. Later, LIM 218 relies on computing hardware 200 to locate the inline metadata in constant time and compare tags between pointers and objects to raise exceptions when mismatches are found.
In one implementation, an ownership transfer operation is implemented by randomizing the ownership ID metadata for an object and generating a new pointer with the updated ownership ID, after checking that the supplied input pointer has an ownership ID and tag matching that of the referenced object. For example, the ownership transfer operation may be implemented in a new instruction such as transfer ownership instruction 206.
Table 2 shows an end-to-end example of unsafe coding containing a bug. This sample code violates the borrow checking rules in Rust. An existing compiler would accept this code even though the code's runtime behavior violated the borrow checking rules. The technology described herein, including BC-ABI, mitigates this violation.
The dynamic error indication generated by enforcement of BC-ABI highlights the presence of the bug to the program developer (e.g., by CC compiler 104). The program developer could correct the program as shown in Table 3 so that the program will be executed without error with BC-ABI enforcement in effect.
Rust defines separate ownership transfers and bounds checking for fields within structures as shown in the example in Table 4, so it is necessary to store separate metadata for each field individually to which a reference may be generated.
In Table 4, ownership is tracked separately for distinct fields within a structure. The ampersand operator borrows a reference to its operand, and the “mut” modifier is used to borrow a mutable reference. References to be dereferenced use the asterisk operator.
The CC compiler 104 generates pointers both to overall structures as well as to individual fields within structures (e.g., as illustrated in
Ownership ID fields may be set for fields in an object structure and then reset after a borrow.
This provides the CC compiler 104 with an opportunity to synchronize the ownership IDs within all the fields (e.g., set them all to the same value) so that a pointer to any field can be generated from a pointer to the first field within the structure. For example, this may be implemented using an instruction that accepts a specified next ownership ID rather than a random next ownership ID such that the same ID can be used across multiple fields. This may be used whenever transferring ownership of the overall structure, even if not immediately preceded by operations that establish separate ownership of distinct fields.
It may also be necessary to set the tag/version values across all the fields such that a pointer to any of them can be generated from a pointer to the first field. To help enforce spatial safety, different tag values may be used for different fields, but their relationship needs to be predictable (e.g., strictly incrementing for each consecutive field) to permit generating pointers to fields from the pointer to the first field.
BC-ABI can enforce per-field borrow-checking in unsafe code. The example code is shown in Table 5.
When performing a move operation from one variable to another, ownership of the referenced data transfers from the source variable to the destination variable, and the ownership will not be returned after that point.
When borrowing a mutable reference to data, the ownership of the data is first transferred to the destination variable, and the ownership is later transferred back to the source variable.
When borrowing immutable references to data (there may be multiple that are simultaneously active), the ownership of the data remains with the source variable, since the original variable may still be used to read the data even while other immutable references exist. However, the data is not permitted to be updated while any immutable references exist.
In one implementation, three additional instructions are added to the instruction set architecture (ISA) of computing hardware 200: 1) Mark Immutable instruction 204; 2) Transfer Ownership instruction 206; and 3) Assert Immutable instruction 208. Each of these instructions are generated by CC compiler 104 as needed. Each of these instructions accepts a pointer as an operand.
A new Mark Immutable instruction 204 should be used to mark an object as immutable in the object's associated metadata the first time an immutable reference is generated after the data was referenced mutably. The object is referenced by a pointer as an operand to the Mark Immutable instruction 204.
The same ownership ID as was used for the mutable reference can be used for all the simultaneously valid immutable references. The only way to clear the immutability marking is to transfer ownership, which will invalidate previous pointers (by randomizing the object's ownership ID) to prevent undetected use of mutated data via immutable references. This may be accomplished by the Transfer Ownership instruction 206. The object is referenced by a pointer as an operand to the Transfer Ownership instruction 206. An ownership ID may be supplied as an optional parameter. The Transfer Ownership instruction 206 may be used for a move or a borrow of a pointer reference.
A new Assert Immutable instruction 204 may be used to generate a fault if the supplied reference is to a mutable object. The CC compiler 104 may insert such instructions when accessing immutable references supplied by untrusted code to ensure that the code marked the data as immutable, or the CC compiler can intersperse them throughout code to provide defense-in-depth. The object is referenced by a pointer as an operand to the Assert Immutable instruction 204.
In one implementation, another protection that can be provided by CC hardening for Rust is to ensure access rights of a pointer in Rust programs dynamically by allowing only mutable references that can modify the memory and no reference can modify an immutable object. This may be implemented by adding an extra bit in the metadata to indicate whether the object is mutable (when allocated). The writable bit of an object is determined when the object is allocated (let mut o=1) and cannot be altered later. While the writable bit encoded in the pointer can be altered, the bit can only be switched from writable to read only (i.e., 1->0 if 1 represents writable, and 0 represents read only). This also follows Rust typing rules which allows a mutable reference to be safely cast to an immutable reference but not vice versa.
Move and borrow operations may need to be performed for an entire hierarchy of objects referenced from an initial object to mitigate attempts to save pointers to interior objects and use them later after ownership of a higher-level object has already been transferred. Thus, CC compiler 104 may generate code to walk object hierarchies and perform those updates.
For each parameter moved into or mutably borrowed by a callee, the callee must perform that operation to avoid the requirement for the callee to trust the caller to transfer ownership. For each parameter immutably borrowed by a callee, the caller must mark that object as immutable to avoid the requirement for the caller to trust the callee to not mutate the object.
Ownership of data returned by a reference needs to be transferred from the callee to the caller such that subsequent references to the original pointer that may have been saved by the callee are disallowed.
The BC-ABI caller should transfer ownership back to itself for each pointer that is returned from a callee. The caller should not trust the callee to perform the transfer, since the callee may omit the transfer and save a pointer with a valid ownership ID that could be used later without authorization.
Some languages already include constructs embodying ownership transfer, e.g., unique_ptr in C++. Other languages could be extended similarly. Such constructs may be extended to be hardened using CC analogously to how the similar constructs in Rust can be hardened.
The base ABI entrusts the callee with saving and restoring certain register values, which may be undesirable in some cases, e.g., when calling a function in an untrusted library. One risk is that the values of those registers may be used by the callee in an unauthorized manner, and a second risk is that the callee may corrupt the values of registers upon return with an intent to corrupt the operation of the caller. Such interfaces between functions that are not in the same trust domain (e.g., different tenants) may avoid treating any registers as callee-saved. Furthermore, the general-purpose registers other than those containing function parameters may be sanitized (e.g., zeroed) prior to invoking the untrusted callee.
Untrusted code may attempt to forge arbitrary pointers to bypass BC-ABI restrictions. To mitigate this, mechanisms are needed to constrain memory accesses from untrusted code. These controls do not need to be so precise as those on references to objects that are subject to borrow-checking (except for accesses from unsafe code to borrow-checked objects), but they should be sufficiently strict to block unauthorized access to borrow-checked memory regions. For example, CC encrypts data, and unencrypted pointers do not provide plaintext access to encrypted data. CC cryptographically mitigates attempts to forge encrypted pointers.
An access from unsafe code should only be permitted if the access satisfies one of the following rules. 1) The access is specifically authorized via a pointer with associated per-object security metadata. The object may be in any region of memory (e.g., heap, stack, or global). Pointer encryption mitigates attempted pointer forgeries granting unauthorized access. 2) The access is to a limited range of register: stack pointer (RSP)- or register: instruction pointer (RIP)-relative offsets that a static code validator determines does not violate security policy, (stays within the current stack frame and the portion of the preceding stack frame containing on-stack arguments or within the bounds of an authorized global variable). There may be tradeoffs between compatibility with unsafe code and enforcing these checks, so administrators may be responsible for making those tradeoffs when deciding which code to run. For example, some unsafe code may include complex memory accesses that are infeasible to analyze statically. 3) The access is to a range of memory in which sensitive data is cryptographically protected such that an unauthorized access does not result in information disclosure or adversary-controlled data corruption, that is, the data would at least be garbled in ways that are unpredictable to the adversary. This obviates the need for a static validator to check the code and hence avoids the tradeoffs between code compatibility and security mentioned above. 4) The access is authorized via a pointer with associated region-specific security metadata (e.g., to restrict the access to a particular stack frame). This supports dynamic enforcement to avoid the compatibility limitations of static code validation as described above, and it may be enforced cryptographically.
Any code pointer that a tenant depends upon should be protected from tampering by any other tenant. For example, return address encryption in combination with stack bounds checks as described above or a shadow stack may be used to protect return addresses. Forward code pointers may also be encrypted.
To further harden boundaries between tenants, separate keys can be used for each of a tenant's objects. However, controlled sharing can still be allowed. The pointer may contain an embedded key ID so that a tenant can generate a pointer authorizing a different tenant to access just that object with the granting tenant's key.
Strictly typed languages such as Rust that provide convenient alternatives to polymorphism, e.g., Rust traits, may have more type information available statically to CC compiler 104 compared to loosely typed languages or those that rely more on polymorphism. This may allow optimizations in which that type information is supplied statically to the processor in computing hardware 200, e.g., using new, typed load and store instructions that accept a type ID operand, so that the type information does not need to be stored separately. The processor could then enforce that the correct type of object is being accessed to mitigate type confusion, even during transient execution, e.g., by comparing the supplied type ID to one stored using LIM or by binding data encryption to the type ID. The latter concept of binding data encryption to the type ID may be implemented as disclosed in US Patent Publication Number US202000201789A1, as part of the Ld/StEP instructions.
Alternatively, when type information cannot be determined statically, it may be stored as dynamic metadata, e.g., using LIM, and new type-checking instructions may assert that the stored metadata for a supplied object is within the set of acceptable types for the method being run on that object. TypeChk and TypeJmp instructions and a design for using them for dynamic type checking are described in “Hardware Apparatuses, Methods, and Systems for Individually Revocable Capabilities for Enforcing Temporal Memory Safety”, US Patent Publication Number US20210200546, published, Jul. 1, 2021, and incorporated herein by reference, but the described method specifies that type metadata is stored in a separate table. In contrast, the technology disclosed herein envisions the type metadata being stored in line with allocations.
Enforcing the BC-ABI cryptographically in a way that binds encryption of data and metadata (e.g., bounds, ownership ID, and immutability) to the security context that is relevant for BC-ABI (e.g., object identity, tag/version, and type) helps to ensure that the BC-ABI security policy is enforced even in the presence of attacks or data corruption pertaining to lower layers of the system. For example, a bit flip due to radiation could change unencrypted metadata for an object so that it is incorrectly marked as mutable, but that change could be detected if it occurred to the same location in the ciphertext for encrypted metadata, e.g., using integrity checking. Even without integrity checking, applying a block cipher with diffusion to the metadata will cause corruption to propagate to other bits where it may be detected indirectly, e.g., due to corrupted bounds no longer matching valid accesses. Physical attacks may corrupt even more bits and perform more sophisticated forms of corruption, such as moving or replaying data. Cryptography is useful in these cases as well, especially since cryptographic enforcement of the BC-ABI binds the object's encryption to its location/identity in the linear/virtual address space upon which program semantics are based directly. In combination with additional controls over changes to processor state, e.g., registers, cryptographic enforcement of BC-ABI can also defend against interference from untrusted privileged software.
At some point during execution of the program, if an object is associated with a different variable, then at block 1508 memory safety check unit 220 updates the ownership ID in the metadata for the object (e.g., to reflect the “borrowing”). In one implementation, updating the ownership ID in the metadata for the object is accomplished by executing a Transfer Ownership instruction 206 as described above. At block 1510, memory safety check unit 220 sets the matching updated ownership ID in the pointer to the allocated object. In one implementation, updating the ownership ID in the pointer is accomplished by executing a Transfer Ownership instruction 206 as described above. Next, at block 1512, if the updated ownership ID of the object does not match the ownership ID in the pointer when the object is accessed, then an exception is generated at block 1514. Otherwise, this processing completes. The actions described in
In CC 216 hardened for Rust (CC-Rust), most of the analyses are done at Mid-level intermediate representation (IR) (MIR) level. This is because while Rust MIR is relatively close to low level virtual machine (LLVM) IR, Rust MIR contains much richer type information of the compiled program (e.g., lifetime of references) that are essential for analyzing a Rust program but are lost after being translated into LLVM IR. Herein, two analyses used by CC-Rust are introduced, which are borrow expire analysis (to analyze when a certain borrow expires) and borrow transfer analysis (to analyze the set of borrows that has not been transferred thus might need to be expired at each program point).
The purpose of borrow expire analysis is to infer a set of possible locations that a given borrow expires. Invalidating the borrow at correct expiration locations ensures CC-Rust guarantees avoidance of temporal errors by preventing the use of dangling pointers dynamically. Meanwhile, the expiration of a certain borrow might revive the previously transferred reference.
Table 6 shows how an expired borrow revives other references.
The sample code of Table 6 illustrates how an expired borrow ‘b’ can revive the references that ‘b’ reborrowed from. After goes out the scope, ‘x’ then again becomes a valid pointer that can be used to access ‘a’.
Rust currently uses Non-Lexical Lifetime (NLL) to verify whether the compiling program follows the borrow checking rules. In NLL, the lifetime of a borrow (reference) is represented as a set, which contains all the program points (in MIR) where the borrow is alive. Each program point is a pair of a basic block ID and a statement index, which uniquely identify a statement in MIR. For example, {B, 0} represents the first statement in basic block B.
Conceptually, the borrow expire analysis works by performing a depth-first search on a control-flow graph followed by the items in the lifetime. The traversal terminates at every invalid program point (which are not included in the lifetime).
While borrow expire analysis helps CC-Rust to determine when a given borrow expires, it does not compute which borrow need to be expired. As the borrows that are transferred are implicitly invalidated during runtime, they should not be expired again. For this purpose, another analysis called a borrow transfer analysis is run by analyzer 106 to compute a set of expirable borrows that have not been transferred at every program point.
In one implementation, the borrow transfer analysis is a classical Gen/Kill Data flow analysis that can be described by defining a top (), bottom (
) and a monotonic transfer function (f) based on kill and gen sets. For borrow transfer analysis, they are defined as following:
): the set of all variables in the code.
): the empty set.
The final result can then be computed by applying the transfer function to each statement in the MIR repeatedly until a fixed point is reached.
It is possible for a previously transferred reference to revive due to the expiration of the destinated reference. Thus, CC-Rust needs to provide support to revive a desired reference safely. Note that a set of new primitives should not be introduced to revive an arbitrary reference because those primitives are likely to be used by the malicious user to forge a valid pointer. Instead, a strict handoff of ownership should be enforced by computing hardware 200.
Table 7 shows an example on how a reference should be revived after the borrow passed to a function expires.
CC-Rust revives ‘x’ in the example by rewriting the CC-enforced function to follow BC-ABI. BC-ABI transfers within the callee the ownership ID of the parameter passed in before use to ensure that a valid reference is passed in from an untrusted caller. The callee returns extra values to the caller for the transferred parameter, and the caller receives the extra return value and revives a desired reference by transferring from the extra return value. As the result, the example in Table 7 will be rewritten into the code in Table 8.
Apart from function calls, references can also revive due to the expiration of a reborrow. A reborrow takes place using a statement such as let p=&(*q). After the statement, p and q will point to the same object, but q will be invalidated as it is transferred to p and has lost the ownership of the object. In the simple scenario, when the control flow does not diverge, the source and destination of the transfer can be easily determined. As shown in the example code in Table 9, when there is not divergence (no branches), the source and destination of the reborrow can be static determined.
Thus, to revive a reference, CC-Rust simply transfers the ownership from the ‘reborrower’ back to the previously transferred reference. The nested reborrow of the same object can be handled by maintaining a stack of reborrowed references statically and revive the reference at the top when the current ‘reborrower’ expires.
In more complicated cases, where the control flow diverges and the source and destination of the borrow transfer cannot be uniquely determined, CC-Rust requires more instrumentation to figure out which path has been taken during runtime.
As shown in Table 10, CC-Rust needs to determine which path is taken during runtime to revive the desired reference when there is a control flow divergence.
The technology described herein also further provides new instructions and implementation of those new instructions for cryptographically enforcing “ratcheting pointers” (also called ratchet pointers herein) that harden byte-granular checks for slices within overall memory allocations for objects. A ratchet pointer is a cryptographically enforced address that additionally includes an upper bound to be used to keep memory accesses within a bounded range. The lower bound implicitly specified in the cryptographically enforced address can only be increased, and the upper bound computed from the address and a size of a slice can only be decreased, thus keeping accesses within the authorized range at each point in program execution. Thus, the bounded range can be “ratcheted” downward in size (that is, narrowed) through one or more adjustments from the initial base address and size, but once ratcheted, the size of the bounded range cannot be increased. If a request to access the object attempts to access memory outside of the bounded range (as ratcheted), this request will be prevented from being performed and an exception will be raised.
Rust frequently uses slice types that represent a narrowed view into a larger allocation. Slice base addresses and sizes may be computed dynamically. For a simple example, consider the code of Table 11.
This program generates the output shown in Table 12.
Note that dynamic bounds checks are performed during execution of the program by computing hardware 200, since the size of each slice is unknown at compile time.
Rust represents a slice as a pair of 64-bit values: a pointer to the beginning of the slice (the base address) and the length of slice. This utilizes byte-granular bounds for slices of overall allocations. The programming language is often required to generate a panic if the bounds check fails. Programs also require the ability to query bounds for certain constructs that do not result in a panic, as illustrated in the second statement in proc_slice.
There is a distinction between the language requirement for performing byte-granular bounds checks and security hardening requirements (e.g., to cryptographically isolate distinct allocations). These requirements can potentially be satisfied separately by distinct mechanisms. For example, existing arithmetic instructions can continue to be used by the Rust compiler for byte-granular checks, and non-byte-granular cryptographic isolation between allocations can serve as a hardening mechanism for advanced threat models (e.g., against compiler bugs, hardware-based trojans, side channels, physical attacks, etc.).
Consider byte-granular checks being performed by arithmetic instructions atop cryptographically isolated allocations. Transient execution may permit an out-of-bound (OOB) access to proceed speculatively beyond the byte-granular bounds check. However, if the OOB access extends so far that the requested access would reach a different allocation, then the cryptographic isolation would protect the data in that other allocation. Eventually, once the mis-speculation is resolved, the byte-granular bounds check failure would be detected and processed.
However, it may be desirable to cryptographically harden even the byte-granular bounds checks. Furthermore, the compiler and runtime may find the ability to generate an exception in response to a byte-granular bounds check failure convenient, even if the bounds are set to cover the entire allocation.
To represent byte-granular bounds efficiently, the existing representation in the Rust compiler (base address: 64-bit pointer, length: 64-bit size) can be extended. The base address and size can both be limited to the address space size supported by computing hardware 200.
The base address pointer will already be in an encrypted format by default with CC 216 activated, but that default format permits pointer arithmetic within the power-of-two slot specified in the pointer. To enforce lower bounds, this should be revised to prevent the program from decreasing pointer values that are designated as ratchet pointers. This can be accomplished by encrypting the entire pointer such that the pointer can only be modified using a dedicated instruction, which will be defined to only increase the value of the pointer. This avoids the need for storing a lower bound. If the software needs to increase the pointer value and then later decrease the pointer value, this may be accomplished by saving a copy of the relatively lower value of the pointer prior to generating the higher pointer value. Furthermore, the semantics could be reversed such that the address in the main pointer serves as the upper bound and the additional bound is the lower bound. A flag in the pointer could indicate which semantics are applicable if both are supported by the same computing hardware 200. Adding support for the reverse semantics would lead to corresponding changes in the instructions for encoding and updating pointers. Another possibility is for both lower and upper bounds to be stored separately from the main pointer (e.g., as separate 64-bit values or as a compressed encoding to pack both bounds into a single, additional 64-bit value).
In some implementations, power 1902 may be left unencrypted so that ratchet pointers may be automatically distinguished from non-ratchet pointers based on the power field. For example, a range of power field values may be reserved for ratchet pointers. A mapping may be defined from ratchet pointer power values to power values for pointers encrypted in a non-ratcheting format (e.g., the format shown in
In other implementations, the entire 64 bits of the ratchet pointer 1900, including the power field, may be encrypted for maximum strength. Instruction encodings may be modified to specify that a ratchet pointer is in use, as is described below, rather than relying on the power field to distinguish ratchet pointers from non-ratchet pointers.
CCEncodeRatchetPointer (CCEncRPtr) dest_ptr:r64, dest_limit:r64, src_ptr:r64, src_limit:r64
Where dest_ptr is the ratchet pointer, dest_limit is the size of the slice, src_ptr is the non-ratchet pointer, and src_limit is the size of the allocation.
A limit can be expressed either as a distance relative to a base address as described above, e.g., to the last byte that is allowed to be accessed or one past that last byte, or alternatively as an absolute address, e.g., of the last byte that is allowed to be accessed or one past that last byte. The limit checks described herein may thus take forms such as a check that an address is less than or equal to the limit if it references the last byte that is allowed to be accessed or as a check that an address is less than the limit if it references one past that last byte. Anywhere herein that a limit is mentioned, it can be interpreted in either of those ways.
At block 2002, memory safety check unit 220 decrypts the non-ratchet pointer in the first source (src_ptr) operand, which is in an encrypted format. At block 2004, memory safety check unit 220 re-encrypts the non-ratchet pointer into a ratchet pointer indicated by the first destination (dst_ptr) operand in the ratchet pointer format shown in
CCIncreaseLowerBoundRatchetPtr (CCILBRPtr) dest_ptr:r64, dest_limit:r64, src_ptr:r64, src_limit:r64, amount:r64/imm8/16/32
Where dest_ptr is the new ratchet pointer, dest_limit is the new size of the slice, src_ptr is the source ratchet pointer, src_limit is the size of the source slice (expressed as a size or an absolute upper bound), and amount is the change (increase) in the lower bound.
At block 2102, memory safety check unit 220 decrypts the ratchet pointer in the first source operand (src_ptr) and the second source operand (src_limit), which are in an encrypted format. At block 2104, memory safety check unit 220 adds the value indicated by the amount operand to the decrypted ratchet pointer value to generate an updated pointer value. At block 2106, memory safety check unit 220 determines if the updated pointer value is less than the original ratchet pointer value (as indicated by the first source (src_ptr) operand). If yes, at block 2108, memory safety check unit 220 generates an exception. If not, at block 2110, memory safety check unit 220 encrypts the updated pointer value and stores the updated pointer value in the ratchet pointer indicated by the first destination (dst_ptr) operand. At block 2112, memory safety check unit 220 re-encrypts the limit value of the destination limit in the second destination (dest_limit) operand) based at least in part on the encrypted, updated (base) pointer value.
The source limit determines the value of the destination limit. In embodiments in which the limit is encoded as an absolute address, it's the same plaintext value for the destination limit as it was for the source limit. On the other hand, in embodiments that encode the limit as a relative distance from the base address (i.e., as a length), then the amount operand is subtracted from the plaintext value of the source limit to produce the plaintext value of the destination limit. Regardless of how the destination limit plaintext is generated, it is then encrypted and placed in the dest_limit operand.
Note that CCILBRPtr does not check the limit. If the pointer ends up being incremented beyond the limit, that will be detected when the pointer is dereferenced. However, CCILBRPtr may be extended to check the limit and detect OOB conditions more quickly to enhance debuggability. In one implementation, CCILBRPtr may be implemented as a compacted encoding (e.g., by requiring the pointers and limits to be in adjacent registers according to some defined ordering, or by using combined src/dest operands).
The limit value may also be encrypted to mitigate forgery and corruption attempts. The limit value may be encrypted using the same cipher that is used to encrypt the base address. In some embodiments, the limit value may be represented as an absolute limit (e.g., an address) rather than a relative length so that the limit does not need to be updated in tandem with the base address. This avoids the need for some subtractions to save power. Furthermore, representing the upper bound as a limit reduces the number of additions or subtractions during bounds checks associated with pointer dereferences. In other embodiments, the limit value may be represented as a relative length.
The encryption of the limit value is linked to the encrypted base pointer to avoid mixing and matching base and limit values to expand access. For example, the encrypted base address can be input as a tweak while encrypting the limit. A tweak is a cryptographic input in addition to the key that needs to match across both the encryption and decryption operations for decryption to succeed. Furthermore, the limit encryption is bound to the encrypted base pointer encoding that cryptographically protects all offset bits rather than the underlying power-of-two-aligned encrypted pointer format that would permit modification of offset bits. Otherwise, if malicious or buggy code receives two pointers specifying different, non-adjacent slices of a single allocation, then the code could combine the lower base address with the higher limit and gain unauthorized access to the intervening portion of the allocation, since they both share the same underlying power-of-two-aligned encrypted pointer representation. This also has the benefit of permitting limit decryption to be parallelized with the base pointer decryption. A drawback is that the limit needs to be re-encrypted whenever pointer arithmetic occurs, but that is generally less frequent than pointer dereferences. Thus, this approach is more secure and performant. In another implementation, a “slice version” value may be incorporated in addition to the slot version to prevent replay of limits with multiple instances of the same slice base address.
The number of encrypted bits may be synchronized with that of the slice base address, or the numbers and positions of bits may differ between them. Unlike the base address, the unencrypted field, if any, is not needed for distinguishing pointer formats. That distinction is only needed for base addresses.
Other embodiments may use other mechanisms for protecting the pointer information (e.g., base and limit addresses) from being corrupted. For example, each memory word (or set of memory words) that may contain a ratchet pointer may have one or more tag bits associated with it to indicate whether that memory word does in fact contain a ratchet pointer. That tag bit information may be propagated to and from the register file to indicate whether each register (or set of registers) that may contain a ratchet pointer does contain a ratchet pointer at the current time. Only valid ratchet pointers, i.e., those marked with the corresponding tag value, will be accepted for use in memory accesses that require a ratchet pointer. Any use of an unauthorized instruction to attempt to modify a ratchet pointer may result in the tag information being reset such that the pointer is no longer recognized by the processor as a valid ratchet pointer, or it may result in an exception being generated by the processor.
An additional instruction is defined to reduce the encrypted limit (thereby decreasing the upper bound).
CCDecreaseUpperBoundRatchetPtr (CCDUBRPtr) dest_ptr:r64, dest_limit:r64, src_ptr:r64, src_limit:r64, amount:r64/imm8/16/32
Where dest_ptr is the new ratchet pointer, dest_limit is the new size of the slice (either an absolute upper bound or relative size), src_ptr is the source ratchet pointer, src_limit is the size of the source slice, and amount is the change (decrease) in the upper bound.
At block 2302, memory safety check unit 220 decrypts the limit value of the source limit of the second source (src_limit) operand associated with the ratchet pointer in the first source (src_ptr) operand, which is in an encrypted format. At block 2304, memory safety check unit 220 subtracts the value indicated by the amount operand from the decrypted source limit value to generate an updated limit value. At block 2306, memory safety check unit 220 determines if the updated limit value is greater than the original source limit value. If yes, at block 2308, memory safety check unit 220 generates an exception. If not, at block 2310, memory safety check unit 220 encrypts the updated limit value and stores the updated limit value in the destination limit of the second destination operand (dst_limit) associated with the ratchet pointer indicated by the first destination (dst_ptr) operand. As in CCILBRPtr, the instruction processing may be extended trivially to check that the limit does not drop below the base address for enhanced debuggability.
The technology described herein provides a mechanism for checking memory accesses against ratchet pointers during execution of the program by computing hardware 200. Memory operands using ratchet pointers specify both the base pointer as well as the limit, both in registers, along with any other operands as part of the selected memory operand type (e.g., scale, index, and/or displacement).
If ratchet pointers reuse the same power field (e.g., power 1902 of
Defining a prefix has an advantage of not requiring new instructions and supporting the full range of complex instruction set computing (CISC) instructions that accept memory operands directly. However, prefixes are increasingly scarce. This would also require the prefix to either specify within itself what register contains the limit or register allocation would need to be restricted so that base pointers and limits are always stored in adjacent registers (e.g., RCX paired with RDX) for some defined register ordering.
Defining new load and store instructions would exhibit the inverse of the advantages and disadvantages of prefix-based embodiments. In one implementation, it may be simpler to generate micro-operations to perform the new checks associated with ratchet pointers from a completely new instruction as compared to existing instructions modified with a prefix.
Regardless of the instruction encoding for specifying a memory operand, the additional operations 2400 resulting from the use of a ratchet pointer access to perform memory access checks are shown in
At block 2412, memory safety check unit 220 checks that the entire access to be performed is below the limit (that is, accesses to all memory locations in the request are within the upper bound). That is, one or more addresses of a requested access to the object must be below the limit. If not, memory safety check unit 220 generates an exception at block 2408. If the access is below the limit at block 2412, at block 2414, computing hardware 200 continues with memory pipeline operations.
Sometimes the program needs to query bounds without generating exceptions. A new instruction can be defined for this purpose.
CCLimitQuery mem:m64, limit:r64
Where mem is an address in memory, and limit is the upper bound.
Implementation of the CCLimitQuery instruction computes the effective address for the memory operand and compare the effective address to the limit. A flag (e.g., over flag (OF)), dependent on the outcome of the limit check, is set.
Note that the temporal safety properties of ratchet pointers are equivalent to those of the underlying non-ratchet pointers, since the ratchet pointers get converted to non-ratchet pointers during pointer dereferences.
There may be other potential usages and optimizations for ratchet pointers.
The slice pointers are essentially the same as Rust references, that is, when needed they will be lowered to both a pointer and bounds but when the compiler can prove correctness, the compiler will just retain the pointer. Thus, ratchet pointers may potentially be useful for any pointers in Rust.
The Rust compiler by default lowers a reference argument (such as slc in the print_slice function included in Table 11) to a pointer and separate bounds. This could potentially be converted to a compound structure that can then be treated as a whole (e.g., to simplify compiler enabling to handle ratchet pointers by reusing existing compiler support for compound structures rather than needing to add specialized ratchet pointer support).
The compiler may optimize by removing redundant checks (e.g., hoisting checks out of loops) and performing non-checked dereferences wherever possible. This may increase the usefulness of adding explicit check instructions or function calls instead of prefixing all memory instructions, since adding prefixes increases the size of code relative to including few check instructions or function calls. It may be useful to permit use of at least some ratchet pointers as ordinary cryptographic pointers in certain cases, (e.g., by using a CCConvertRatchetToNonRatchetPtr instruction that converts a ratchet pointer into a non-ratcheting cryptographic pointer and then using that in some subsequent accesses), so that compiler static analysis can elide byte-granular bounds checks based on static analysis showing that certain accesses are always safe. However, this presents a tradeoff between needing to trust code to optimize performance and providing defense-in-depth and resisting malicious or buggy code.
Ratchet pointers may also be used for polymorphic objects, such as trait objects in Rust and polymorphic classes in C++, since those are dynamically sized. A single object may be accessed relative to multiple traits or classes defining its usable data and functionality, so ratchet pointers may be useful for enforcing that only appropriate data fields can be used based on the current trait or class being used to access the object. It may be necessary for the program to expand the bounds of an object, e.g., when casting to a subclass type, so CCDUBRPtr and CCILBRPtr may accept an operand to override the default bounds checks in those cases, e.g., reverting instead to the bounds of the power-of-two slot encoded in the pointer.
Considering other languages, std::string and std::array could be implemented using ratchet pointers. Projects such as Checked C also introduce a checked pointer type that behaves essentially the same as references in Rust.
Exemplary Computer Architectures.
Detailed below are describes of exemplary computer architectures. Other system designs and configurations known in the arts for laptop, desktop, and handheld personal computers (PC)s, personal digital assistants, engineering workstations, servers, disaggregated servers, network devices, network hubs, switches, routers, embedded processors, digital signal processors (DSPs), graphics devices, video game devices, set-top boxes, micro controllers, cell phones, portable media players, hand-held devices, and various other electronic devices, are also suitable. In general, a variety of systems or electronic devices capable of incorporating a processor and/or other execution logic as disclosed herein are generally suitable.
Processors 2570 and 2580 are shown including integrated memory controller (IMC) unit circuitry 2572 and 2582, respectively. Processor 2570 also includes as part of its interconnect controller unit point-to-point (P-P) interfaces 2576 and 2578; similarly, second processor 2580 includes P-P interfaces 2586 and 2588. Processors 2570, 2580 may exchange information via the point-to-point (P-P) interconnect 2550 using P-P interface circuits 2578, 2588. IMCs 2572 and 2582 couple the processors 2570, 2580 to respective memories, namely a memory 2532 and a memory 2534, which may be portions of main memory locally attached to the respective processors.
Processors 2570, 2580 may each exchange information with a chipset 2590 via individual P-P interconnects 2552, 2554 using point to point interface circuits 2576, 2594, 2586, 2598. Chipset 2590 may optionally exchange information with a coprocessor 2538 via a high performance interface 2592. In some examples, the coprocessor 2538 is a special-purpose processor, such as, for example, a high throughput processor, a network or communication processor, compression engine, graphics processor, general purpose graphics processing unit (GPGPU), embedded processor, or the like.
A shared cache (not shown) may be included in either processor 2570, 2580 or outside of both processors, yet connected with the processors via P-P interconnect, such that either or both processors' local cache information may be stored in the shared cache if a processor is placed into a low power mode.
Chipset 2590 may be coupled to a first interconnect 2516 via an interface 2596. In some examples, first interconnect 2516 may be a Peripheral Component Interconnect (PCI) interconnect, or an interconnect such as a PCI Express interconnect or another I/O interconnect. In some examples, one of the interconnects couples to a power control unit (PCU) 2517, which may include circuitry, software, and/or firmware to perform power management operations with regard to the processors 2570, 2580 and/or co-processor 2538. PCU 2517 provides control information to a voltage regulator (not shown) to cause the voltage regulator to generate the appropriate regulated voltage. PCU 2517 also provides control information to control the operating voltage generated. In various examples, PCU 2517 may include a variety of power management logic units (circuitry) to perform hardware-based power management. Such power management may be wholly processor controlled (e.g., by various processor hardware, and which may be triggered by workload and/or power, thermal or other processor constraints) and/or the power management may be performed responsive to external sources (such as a platform or power management source or system software).
PCU 2517 is illustrated as being present as logic separate from the processor 2570 and/or processor 2580. In other cases, PCU 2517 may execute on a given one or more of cores (not shown) of processor 2570 or 2580. In some cases, PCU 2517 may be implemented as a microcontroller (dedicated or general-purpose) or other control logic configured to execute its own dedicated power management code, sometimes referred to as P-code. In yet other examples, power management operations to be performed by PCU 2517 may be implemented externally to a processor, such as by way of a separate power management integrated circuit (PMIC) or another component external to the processor. In yet other examples, power management operations to be performed by PCU 2517 may be implemented within BIOS or other system software.
Various I/O devices 2514 may be coupled to first interconnect 2516, along with a bus bridge 2518 which couples first interconnect 2516 to a second interconnect 2520. In some examples, one or more additional processor(s) 2515, such as coprocessors, high throughput many integrated core (MIC) processors, GPGPUs, accelerators (such as graphics accelerators or digital signal processing (DSP) units), field programmable gate arrays (FPGAs), or any other processor, are coupled to first interconnect 2516. In some examples, second interconnect 2520 may be a low pin count (LPC) interconnect. Various devices may be coupled to second interconnect 2520 including, for example, a keyboard and/or mouse 2522, communication devices 2527 and a storage circuitry 2528. Storage circuitry 2528 may be a disk drive or other mass storage device which may include instructions/code and data 2530, in some examples. Further, an audio I/O 2524 may be coupled to second interconnect 2520. Note that other architectures than the point-to-point architecture described above are possible. For example, instead of the point-to-point architecture, a system such as multiprocessor system 2500 may implement a multi-drop interconnect or other such architecture.
Exemplary Core Architectures, Processors, and Computer Architectures.
Processor cores may be implemented in different ways, for different purposes, and in different processors. For instance, implementations of such cores may include: 1) a general purpose in-order core intended for general-purpose computing; 2) a high performance general purpose out-of-order core intended for general-purpose computing; 3) a special purpose core intended primarily for graphics and/or scientific (throughput) computing. Implementations of different processors may include: 1) a CPU including one or more general purpose in-order cores intended for general-purpose computing and/or one or more general purpose out-of-order cores intended for general-purpose computing; and 2) a coprocessor including one or more special purpose cores intended primarily for graphics and/or scientific (throughput) computing. Such different processors lead to different computer system architectures, which may include: 1) the coprocessor on a separate chip from the CPU; 2) the coprocessor on a separate die in the same package as a CPU; 3) the coprocessor on the same die as a CPU (in which case, such a coprocessor is sometimes referred to as special purpose logic, such as integrated graphics and/or scientific (throughput) logic, or as special purpose cores); and 4) a system on a chip (SoC) that may include on the same die as the described CPU (sometimes referred to as the application core(s) or application processor(s)), the above described coprocessor, and additional functionality. Exemplary core architectures are described next, followed by descriptions of exemplary processors and computer architectures.
Thus, different implementations of the processor 2600 may include: 1) a CPU with the special purpose logic 2608 being integrated graphics and/or scientific (throughput) logic (which may include one or more cores, not shown), and the cores 2602(A)-(N) being one or more general purpose cores (e.g., general purpose in-order cores, general purpose out-of-order cores, or a combination of the two); 2) a coprocessor with the cores 2602(A)-(N) being a large number of special purpose cores intended primarily for graphics and/or scientific (throughput); and 3) a coprocessor with the cores 2602(A)-(N) being a large number of general purpose in-order cores. Thus, the processor 2600 may be a general-purpose processor, coprocessor or special-purpose processor, such as, for example, a network or communication processor, compression engine, graphics processor, GPGPU (general purpose graphics processing unit circuitry), a high throughput many integrated core (MIC) coprocessor (including 30 or more cores), embedded processor, or the like. The processor may be implemented on one or more chips. The processor 2600 may be a part of and/or may be implemented on one or more substrates using any of a number of process technologies, such as, for example, bipolar complementary metal oxide semiconductor (CMOS) (BiCMOS), CMOS, or N-type metal oxide semiconductor (NMOS).
A memory hierarchy includes one or more levels of cache unit(s) circuitry 2604(A)-(N) within the cores 2602(A)-(N), a set of one or more shared cache unit(s) circuitry 2606, and external memory (not shown) coupled to the set of integrated memory controller unit(s) circuitry 2614. The set of one or more shared cache unit(s) circuitry 2606 may include one or more mid-level caches, such as level 2 (L2), level 3 (L3), level 4 (L4), or other levels of cache, such as a last level cache (LLC), and/or combinations thereof. While in some examples ring-based interconnect network circuitry 2612 interconnects the special purpose logic 2608 (e.g., integrated graphics logic), the set of shared cache unit(s) circuitry 2606, and the system agent unit circuitry 2610, alternative examples use any number of well-known techniques for interconnecting such units. In some examples, coherency is maintained between one or more of the shared cache unit(s) circuitry 2606 and cores 2602(A)-(N).
In some examples, one or more of the cores 2602(A)-(N) are capable of multi-threading. The system agent unit circuitry 2610 includes those components coordinating and operating cores 2602(A)-(N). The system agent unit circuitry 2610 may include, for example, power control unit (PCU) circuitry and/or display unit circuitry (not shown). The PCU may be or may include logic and components needed for regulating the power state of the cores 2602(A)-(N) and/or the special purpose logic 2608 (e.g., integrated graphics logic). The display unit circuitry is for driving one or more externally connected displays.
The cores 2602(A)-(N) may be homogenous or heterogeneous in terms of architecture instruction set architecture (ISA); that is, two or more of the cores 2602(A)-(N) may be capable of executing the same ISA, while other cores may be capable of executing only a subset of that ISA or a ISA.
Exemplary Core Architectures—In-Order and Out-of-Order Core Block Diagram.
In
By way of example, the exemplary register renaming, out-of-order issue/execution core architecture may implement the pipeline 2700 as follows: 1) the instruction fetch 2738 performs the fetch and length decoding stages 2702 and 2704; 2) the decode circuitry 2740 performs the decode stage 2706; 3) the rename/allocator unit circuitry 2752 performs the allocation stage 2708 and renaming stage 2710; 4) the scheduler(s) circuitry 2756 performs the schedule stage 2712; 5) the physical register file(s) circuitry 2758 and the memory unit circuitry 2770 perform the register read/memory read stage 2714; the execution cluster(s) 2760 perform the execute stage 2716; 6) the memory unit circuitry 2770 and the physical register file(s) circuitry 2758 perform the write back/memory write stage 2718; 7) various circuitry may be involved in the exception handling stage 2722; and 8) the retirement unit circuitry 2754 and the physical register file(s) circuitry 2758 perform the commit stage 2724.
The front end unit circuitry 2730 may include branch prediction circuitry 2732 coupled to an instruction cache circuitry 2734, which is coupled to an instruction translation lookaside buffer (TLB) 2736, which is coupled to instruction fetch circuitry 2738, which is coupled to decode circuitry 2740. In one example, the instruction cache circuitry 2734 is included in the memory unit circuitry 2770 rather than the front-end circuitry 2730. The decode circuitry 2740 (or decoder) may decode instructions, and generate as an output one or more micro-operations, micro-code entry points, microinstructions, other instructions, or other control signals, which are decoded from, or which otherwise reflect, or are derived from, the original instructions. The decode circuitry 2740 may further include an address generation unit circuitry (AGU, not shown). In one example, the AGU generates an LSU address using forwarded register ports, and may further perform branch forwarding (e.g., immediate offset branch forwarding, LR register branch forwarding, etc.). The decode circuitry 2740 may be implemented using various different mechanisms. Examples of suitable mechanisms include, but are not limited to, look-up tables, hardware implementations, programmable logic arrays (PLAs), microcode read only memories (ROMs), etc. In one example, the core 2790 includes a microcode ROM (not shown) or other medium that stores microcode for certain macroinstructions (e.g., in decode circuitry 2740 or otherwise within the front end circuitry 2730). In one example, the decode circuitry 2740 includes a micro-operation (micro-op) or operation cache (not shown) to hold/cache decoded operations, micro-tags, or micro-operations generated during the decode or other stages of the processor pipeline 2700. The decode circuitry 2740 may be coupled to rename/allocator unit circuitry 2752 in the execution engine circuitry 2750.
The execution engine circuitry 2750 includes the rename/allocator unit circuitry 2752 coupled to a retirement unit circuitry 2754 and a set of one or more scheduler(s) circuitry 2756. The scheduler(s) circuitry 2756 represents any number of different schedulers, including reservations stations, central instruction window, etc. In some examples, the scheduler(s) circuitry 2756 can include arithmetic logic unit (ALU) scheduler/scheduling circuitry, ALU queues, arithmetic generation unit (AGU) scheduler/scheduling circuitry, AGU queues, etc. The scheduler(s) circuitry 2756 is coupled to the physical register file(s) circuitry 2758. Each of the physical register file(s) circuitry 2758 represents one or more physical register files, different ones of which store one or more different data types, such as scalar integer, scalar floating-point, packed integer, packed floating-point, vector integer, vector floating-point, status (e.g., an instruction pointer that is the address of the next instruction to be executed), etc. In one example, the physical register file(s) circuitry 2758 includes vector registers unit circuitry, writemask registers unit circuitry, and scalar register unit circuitry. These register units may provide architectural vector registers, vector mask registers, general-purpose registers, etc. The physical register file(s) circuitry 2758 is overlapped by the retirement unit circuitry 2754 (also known as a retire queue or a retirement queue) to illustrate various ways in which register renaming and out-of-order execution may be implemented (e.g., using a reorder buffer(s) (ROB(s)) and a retirement register file(s); using a future file(s), a history buffer(s), and a retirement register file(s); using a register maps and a pool of registers; etc.). The retirement unit circuitry 2754 and the physical register file(s) circuitry 2758 are coupled to the execution cluster(s) 2760. The execution cluster(s) 2760 includes a set of one or more execution unit(s) circuitry 2762 and a set of one or more memory access circuitry 2764. The execution unit(s) circuitry 2762 may perform various arithmetic, logic, floating-point or other types of operations (e.g., shifts, addition, subtraction, multiplication) and on various types of data (e.g., scalar floating-point, packed integer, packed floating-point, vector integer, vector floating-point). While some examples may include a number of execution units or execution unit circuitry dedicated to specific functions or sets of functions, other examples may include only one execution unit circuitry or multiple execution units/execution unit circuitry that all perform all functions. The scheduler(s) circuitry 2756, physical register file(s) circuitry 2758, and execution cluster(s) 2760 are shown as being possibly plural because certain examples create separate pipelines for certain types of data/operations (e.g., a scalar integer pipeline, a scalar floating-point/packed integer/packed floating-point/vector integer/vector floating-point pipeline, and/or a memory access pipeline that each have their own scheduler circuitry, physical register file(s) circuitry, and/or execution cluster—and in the case of a separate memory access pipeline, certain examples are implemented in which only the execution cluster of this pipeline has the memory access unit(s) circuitry 2764). It should also be understood that where separate pipelines are used, one or more of these pipelines may be out-of-order issue/execution and the rest in-order.
In some examples, the execution engine unit circuitry 2750 may perform load store unit (LSU) address/data pipelining to an Advanced Microcontroller Bus (AMB) interface (not shown), and address phase and writeback, data phase load, store, and branches.
The set of memory access circuitry 2764 is coupled to the memory unit circuitry 2770, which includes data TLB circuitry 2772 coupled to a data cache circuitry 2774 coupled to a level 2 (L2) cache circuitry 2776. In one exemplary example, the memory access circuitry 2764 may include a load unit circuitry, a store address unit circuit, and a store data unit circuitry, each of which is coupled to the data TLB circuitry 2772 in the memory unit circuitry 2770. The instruction cache circuitry 2734 is further coupled to a level 2 (L2) cache circuitry 2776 in the memory unit circuitry 2770. In one example, the instruction cache 2734 and the data cache 2774 are combined into a single instruction and data cache (not shown) in L2 cache circuitry 2776, a level 3 (L3) cache circuitry (not shown), and/or main memory. The L2 cache circuitry 2776 is coupled to one or more other levels of cache and eventually to a main memory.
The core 2790 may support one or more instructions sets (e.g., the x86 instruction set architecture (with some extensions that have been added with newer versions); the MIPS instruction set architecture; the ARM instruction set architecture (with optional additional extensions such as NEON)), including the instruction(s) described herein. In one example, the core 2790 includes logic to support a packed data instruction set architecture extension (e.g., AVX1, AVX2), thereby allowing the operations used by many multimedia applications to be performed using packed data.
Exemplary Execution Unit(s) Circuitry.
Exemplary Register Architecture.
In some examples, the register architecture 2900 includes writemask/predicate registers 2915. For example, in some examples, there are 8 writemask/predicate registers (sometimes called k0 through k7) that are each 16-bit, 32-bit, 64-bit, or 128-bit in size. Writemask/predicate registers 2915 may allow for merging (e.g., allowing any set of elements in the destination to be protected from updates during the execution of any operation) and/or zeroing (e.g., zeroing vector masks allow any set of elements in the destination to be zeroed during the execution of any operation). In some examples, each data element position in a given writemask/predicate register 2915 corresponds to a data element position of the destination. In other examples, the writemask/predicate registers 2915 are scalable and consists of a set number of enable bits for a given vector element (e.g., 8 enable bits per 64-bit vector element).
The register architecture 2900 includes a plurality of general-purpose registers 2925. These registers may be 16-bit, 32-bit, 64-bit, etc. and can be used for scalar operations. In some examples, these registers are referenced by the names RAX, RBX, RCX, RDX, RBP, RSI, RDI, RSP, and R8 through R15.
In some examples, the register architecture 2900 includes scalar floating-point (FP) register 2945 which is used for scalar floating-point operations on 32/64/80-bit floating-point data using the x87 instruction set architecture extension or as MMX registers to perform operations on 64-bit packed integer data, as well as to hold operands for some operations performed between the MMX and XMIM registers.
One or more flag registers 2940 (e.g., EFLAGS, RFLAGS, etc.) store status and control information for arithmetic, compare, and system operations. For example, the one or more flag registers 2940 may store condition code information such as carry, parity, auxiliary carry, zero, sign, and overflow. In some examples, the one or more flag registers 2940 are called program status and control registers.
Segment registers 2920 contain segment points for use in accessing memory. In some examples, these registers are referenced by the names CS, DS, SS, ES, FS, and GS.
Machine specific registers (MSRs) 2935 control and report on processor performance. Most MSRs 2935 handle system-related functions and are not accessible to an application program. Machine check registers 2960 consist of control, status, and error reporting MSRs that are used to detect and report on hardware errors.
One or more instruction pointer register(s) 2930 store an instruction pointer value. Control register(s) 2955 (e.g., CR0-CR4) determine the operating mode of a processor (e.g., processor 2570, 2580, 2538, 2515, and/or 2600) and the characteristics of a currently executing task. Debug registers 2950 control and allow for the monitoring of a processor or core's debugging operations.
Memory (mem) management registers 2965 specify the locations of data structures used in protected mode memory management. These registers may include a GDTR, IDRT, task register, and a LDTR register.
Alternative examples may use wider or narrower registers. Additionally, alternative examples may use more, less, or different register files and registers.
Instruction set architectures.
An instruction set architecture (ISA) may include one or more instruction formats. A given instruction format may define various fields (e.g., number of bits, location of bits) to specify, among other things, the operation to be performed (e.g., opcode) and the operand(s) on which that operation is to be performed and/or other data field(s) (e.g., mask). Some instruction formats are further broken down though the definition of instruction templates (or sub-formats). For example, the instruction templates of a given instruction format may be defined to have different subsets of the instruction format's fields (the included fields are typically in the same order, but at least some have different bit positions because there are less fields included) and/or defined to have a given field interpreted differently. Thus, each instruction of an ISA is expressed using a given instruction format (and, if defined, in a given one of the instruction templates of that instruction format) and includes fields for specifying the operation and the operands. For example, an exemplary ADD instruction has a specific opcode and an instruction format that includes an opcode field to specify that opcode and operand fields to select operands (source1/destination and source2); and an occurrence of this ADD instruction in an instruction stream will have specific contents in the operand fields that select specific operands.
Exemplary Instruction Formats.
Examples of the instruction(s) described herein may be embodied in different formats. Additionally, exemplary systems, architectures, and pipelines are detailed below. Examples of the instruction(s) may be executed on such systems, architectures, and pipelines, but are not limited to those detailed.
The prefix(es) field(s) 3001, when used, modifies an instruction. In some examples, one or more prefixes are used to repeat string instructions (e.g., 0xF0, 0xF2, 0xF3, etc.), to provide section overrides (e.g., 0x2E, 0x36, 0x3E, 0x26, 0x64, 0x65, 0x2E, 0x3E, etc.), to perform bus lock operations, and/or to change operand (e.g., 0x66) and address sizes (e.g., 0x67). Certain instructions require a mandatory prefix (e.g., 0x66, 0xF2, 0xF3, etc.). Certain of these prefixes may be considered “legacy” prefixes. Other prefixes, one or more examples of which are detailed herein, indicate, and/or provide further capability, such as specifying particular registers, etc. The other prefixes typically follow the “legacy” prefixes.
The opcode field 3003 is used to at least partially define the operation to be performed upon a decoding of the instruction. In some examples, a primary opcode encoded in the opcode field 3003 is one, two, or three bytes in length. In other examples, a primary opcode can be a different length. An additional 3-bit opcode field is sometimes encoded in another field.
The addressing field 3005 is used to address one or more operands of the instruction, such as a location in memory or one or more registers.
The content of the MOD field 3142 distinguishes between memory access and non-memory access modes. In some examples, when the MOD field 3142 has a value of b11, a register-direct addressing mode is utilized, and otherwise register-indirect addressing is used.
The register field 3144 may encode either the destination register operand or a source register operand or may encode an opcode extension and not be used to encode any instruction operand. The content of register index field 3144, directly or through address generation, specifies the locations of a source or destination operand (either in a register or in memory). In some examples, the register field 3144 is supplemented with an additional bit from a prefix (e.g., prefix 3001) to allow for greater addressing.
The R/M field 3146 may be used to encode an instruction operand that references a memory address or may be used to encode either the destination register operand or a source register operand. Note the R/M field 3146 may be combined with the MOD field 3142 to dictate an addressing mode in some examples.
The SIB byte 3104 includes a scale field 3152, an index field 3154, and a base field 3156 to be used in the generation of an address. The scale field 3152 indicates scaling factor. The index field 3154 specifies an index register to use. In some examples, the index field 3154 is supplemented with an additional bit from a prefix (e.g., prefix 3001) to allow for greater addressing. The base field 3156 specifies a base register to use. In some examples, the base field 3156 is supplemented with an additional bit from a prefix (e.g., prefix 3001) to allow for greater addressing. In practice, the content of the scale field 3152 allows for the scaling of the content of the index field 3154 for memory address generation (e.g., for address generation that uses 2scale*index+base).
Some addressing forms utilize a displacement value to generate a memory address. For example, a memory address may be generated according to 2scale*index+base+displacement, index*scale+displacement, r/m+displacement, instruction pointer (RIP/EIP)+displacement, register+displacement, etc. The displacement may be a 1-byte, 2-byte, 4-byte, etc. value. In some examples, a displacement 3007 provides this value. Additionally, in some examples, a displacement factor usage is encoded in the MOD field of the addressing field 3005 that indicates a compressed displacement scheme for which a displacement value is calculated by multiplying disp8 in conjunction with a scaling factor N that is determined based on the vector length, the value of a b bit, and the input element size of the instruction. The displacement value is stored in the displacement field 3007.
In some examples, an immediate field 3009 specifies an immediate value for the instruction. An immediate value may be encoded as a 1-byte value, a 2-byte value, a 4-byte value, etc.
Instructions using the first prefix 3001(A) may specify up to three registers using 3-bit fields depending on the format: 1) using the reg field 3144 and the R/M field 3146 of the Mod R/M byte 3102; 2) using the Mod R/M byte 3102 with the SIB byte 3104 including using the reg field 3144 and the base field 3156 and index field 3154; or 3) using the register field of an opcode.
In the first prefix 3001(A), bit positions 7:4 are set as 0100. Bit position 3 (W) can be used to determine the operand size but may not solely determine operand width. As such, when W=0, the operand size is determined by a code segment descriptor (CS.D) and when W=1, the operand size is 64-bit.
Note that the addition of another bit allows for 16 (24) registers to be addressed, whereas the MOD R/M reg field 3144 and MOD R/M R/M field 3146 alone can each only address 8 registers.
In the first prefix 3001(A), bit position 2 (R) may an extension of the MOD R/M reg field 3144 and may be used to modify the ModR/M reg field 3144 when that field encodes a general purpose register, a 64-bit packed data register (e.g., a SSE register), or a control or debug register. R is ignored when Mod R/M byte 3102 specifies other registers or defines an extended opcode.
Bit position 1 (X) X bit may modify the SIB byte index field 3154.
Bit position B (B) B may modify the base in the Mod R/M R/M field 3146 or the SIB byte base field 3156; or it may modify the opcode register field used for accessing general purpose registers (e.g., general purpose registers 2925).
In some examples, the second prefix 3001(B) comes in two forms—a two-byte form and a three-byte form. The two-byte second prefix 3001(B) is used mainly for 128-bit, scalar, and some 256-bit instructions; while the three-byte second prefix 3001(B) provides a compact replacement of the first prefix 3001(A) and 3-byte opcode instructions.
Instructions that use this prefix may use the Mod R/M R/M field 3146 to encode the instruction operand that references a memory address or encode either the destination register operand or a source register operand.
Instructions that use this prefix may use the Mod R/M reg field 3144 to encode either the destination register operand or a source register operand, be treated as an opcode extension and not used to encode any instruction operand.
For instruction syntax that support four operands, vvvv, the Mod R/M R/M field 3146 and the Mod R/M reg field 3144 encode three of the four operands. Bits[7:4] of the immediate 3009 are then used to encode the third source register operand.
Bit[7] of byte 2 3417 is used similar to W of the first prefix 3001(A) including helping to determine promotable operand sizes. Bit[2] is used to dictate the length (L) of the vector (where a value of 0 is a scalar or 128-bit vector and a value of 1 is a 256-bit vector). Bits[1:0] provide opcode extensionality equivalent to some legacy prefixes (e.g., 00=no prefix, 01=66H, 10=F3H, and 11=F2H). Bits[6:3], shown as vvvv, may be used to: 1) encode the first source register operand, specified in inverted (1s complement) form and valid for instructions with 2 or more source operands; 2) encode the destination register operand, specified in 1s complement form for certain vector shifts; or 3) not encode any operand, the field is reserved and should contain a certain value, such as 1111b.
Instructions that use this prefix may use the Mod R/M R/M field 3146 to encode the instruction operand that references a memory address or encode either the destination register operand or a source register operand.
Instructions that use this prefix may use the Mod R/M reg field 3144 to encode either the destination register operand or a source register operand, be treated as an opcode extension and not used to encode any instruction operand.
For instruction syntax that support four operands, vvvv, the Mod R/M R/M field 3146, and the Mod R/M reg field 3144 encode three of the four operands. Bits[7:4] of the immediate 3009 are then used to encode the third source register operand.
The third prefix 3001(C) can encode 32 vector registers (e.g., 128-bit, 256-bit, and 512-bit registers) in 64-bit mode. In some examples, instructions that utilize a writemask/opmask (see discussion of registers in a previous figure, such as
The third prefix 3001(C) may encode functionality that is specific to instruction classes (e.g., a packed instruction with “load+op” semantic can support embedded broadcast functionality, a floating-point instruction with rounding semantic can support static rounding functionality, a floating-point instruction with non-rounding arithmetic semantic can support “suppress all exceptions” functionality, etc.).
The first byte of the third prefix 3001(C) is a format field 3511 that has a value, in one example, of 62H. Subsequent bytes are referred to as payload bytes 3515-3519 and collectively form a 24-bit value of P[23:0] providing specific capability in the form of one or more fields (detailed herein).
In some examples, P[1:0] of payload byte 3519 are identical to the low two mmmmm bits. P[3:2] are reserved in some examples. Bit P[4] (R′) allows access to the high 16 vector register set when combined with P[7] and the ModR/M reg field 3144. P[6] can also provide access to a high 16 vector register when SIB-type addressing is not needed. P[7:5] consist of an R, X, and B which are operand specifier modifier bits for vector register, general purpose register, memory addressing and allow access to the next set of 8 registers beyond the low 8 registers when combined with the ModR/M register field 3144 and ModR/M R/M field 3146. P[9:8] provide opcode extensionality equivalent to some legacy prefixes (e.g., 00=no prefix, 01=66H, 10=F3H, and 11=F2H). P[10] in some examples is a fixed value of 1. P[14:11], shown as vvvv, may be used to: 1) encode the first source register operand, specified in inverted (1s complement) form and valid for instructions with 2 or more source operands; 2) encode the destination register operand, specified in is complement form for certain vector shifts; or 3) not encode any operand, the field is reserved and should contain a certain value, such as 1111b.
P[15] is similar to W of the first prefix 3001(A) and second prefix 3011(B) and may serve as an opcode extension bit or operand size promotion.
P[18:16] specify the index of a register in the opmask (writemask) registers (e.g., writemask/predicate registers 2915). In one example, the specific value aaa=000 has a special behavior implying no opmask is used for the particular instruction (this may be implemented in a variety of ways including the use of a opmask hardwired to all ones or hardware that bypasses the masking hardware). When merging, vector masks allow any set of elements in the destination to be protected from updates during the execution of any operation (specified by the base operation and the augmentation operation); in other one example, preserving the old value of each element of the destination where the corresponding mask bit has a 0. In contrast, when zeroing vector masks allow any set of elements in the destination to be zeroed during the execution of any operation (specified by the base operation and the augmentation operation); in one example, an element of the destination is set to 0 when the corresponding mask bit has a 0 value. A subset of this functionality is the ability to control the vector length of the operation being performed (that is, the span of elements being modified, from the first to the last one); however, it is not necessary that the elements that are modified be consecutive. Thus, the opmask field allows for partial vector operations, including loads, stores, arithmetic, logical, etc. While examples are described in which the opmask field's content selects one of a number of opmask registers that contains the opmask to be used (and thus the opmask field's content indirectly identifies that masking to be performed), alternative examples instead or additional allow the mask write field's content to directly specify the masking to be performed.
P[19] can be combined with P[14:11] to encode a second source vector register in a non-destructive source syntax which can access an upper 16 vector registers using P[19]. P[20] encodes multiple functionalities, which differs across different classes of instructions and can affect the meaning of the vector length/rounding control specifier field (P[22:21]). P[23] indicates support for merging-writemasking (e.g., when set to 0) or support for zeroing and merging-writemasking (e.g., when set to 1).
Exemplary examples of encoding of registers in instructions using the third prefix 3001(C) are detailed in the following tables.
Program code may be applied to input instructions to perform the functions described herein and generate output information. The output information may be applied to one or more output devices, in known fashion. For purposes of this application, a processing system includes any system that has a processor, such as, for example, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), or a microprocessor.
The program code may be implemented in a high-level procedural or object-oriented programming language to communicate with a processing system. The program code may also be implemented in assembly or machine language, if desired. In fact, the mechanisms described herein are not limited in scope to any particular programming language. In any case, the language may be a compiled or interpreted language.
Examples of the mechanisms disclosed herein may be implemented in hardware, software, firmware, or a combination of such implementation approaches. Examples may be implemented as computer programs or program code executing on programmable systems comprising at least one processor, a storage system (including volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device.
One or more aspects of at least one example may be implemented by representative instructions stored on a machine-readable medium which represents various logic within the processor, which when read by a machine causes the machine to fabricate logic to perform the techniques described herein. Such representations, known as “IP cores” may be stored on a tangible, machine readable medium and supplied to various customers or manufacturing facilities to load into the fabrication machines that actually make the logic or processor.
Such machine-readable storage media may include, without limitation, non-transitory, tangible arrangements of articles manufactured or formed by a machine or device, including storage media such as hard disks, any other type of disk including floppy disks, optical disks, compact disk read-only memories (CD-ROMs), compact disk rewritables (CD-RWs), and magneto-optical disks, semiconductor devices such as read-only memories (ROMs), random access memories (RAMs) such as dynamic random access memories (DRAMs), static random access memories (SRAMs), erasable programmable read-only memories (EPROMs), flash memories, electrically erasable programmable read-only memories (EEPROMs), phase change memory (PCM), magnetic or optical cards, or any other type of media suitable for storing electronic instructions.
Accordingly, examples also include non-transitory, tangible machine-readable media containing instructions or containing design data, such as Hardware Description Language (HDL), which defines structures, circuits, apparatuses, processors and/or system features described herein. Such examples may also be referred to as program products.
Emulation (including binary translation, code morphing, etc.).
In some cases, an instruction converter may be used to convert an instruction from a source instruction set architecture to a target instruction set architecture. For example, the instruction converter may translate (e.g., using static binary translation, dynamic binary translation including dynamic compilation), morph, emulate, or otherwise convert an instruction to one or more other instructions to be processed by the core. The instruction converter may be implemented in software, hardware, firmware, or a combination thereof. The instruction converter may be on processor, off processor, or part on and part off processor.
References to “one example,” “an example,” etc., indicate that the example described may include a particular feature, structure, or characteristic, but every example may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same example. Further, when a particular feature, structure, or characteristic is described in connection with an example, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other examples whether or not explicitly described.
Moreover, in the various examples described above, unless specifically noted otherwise, disjunctive language such as the phrase “at least one of A, B, or C” is intended to be understood to mean either A, B, or C, or any combination thereof (e.g., A, B, and/or C). As such, disjunctive language is not intended to, nor should it be understood to, imply that a given example requires at least one of A, at least one of B, or at least one of C to each be present.
The following examples pertain to further embodiments. Specifics in the examples may be used anywhere in one or more embodiments. Example 1 is an apparatus including a memory to store an object referenced by a ratchet pointer; and a processor to provide access to a slice of the object by decrypting a base address and a limit of the ratchet pointer, generating a cryptographic address in an encrypted format bound to an identity of the object and not the slice; and performing effective address generation for the cryptographic address based at least in part on the base address and the limit.
In Example 2, the subject matter of Example 1 can optionally include the processor to generate an exception when the effective address generation for the cryptographic address decreases the cryptographic address below the base address. In Example 3, the subject matter of Example 1 can optionally include the processor to generate an exception when one or more addresses of a requested access to the object are not less than the limit. In Example 3, the subject matter of Example 1 can optionally include the processor to encode the ratchet pointer from a non-ratchet pointer by executing an encode ratchet pointer instruction of an instruction set architecture (ISA) of the processor. In Example 5, the subject matter of Example 4 can optionally include the processor to execute the encode ratchet pointer instruction to decrypt a non-ratchet pointer of a first source operand, re-encrypt the non-ratchet pointer in a format of a ratchet pointer and store the ratchet pointer as a first destination operand, and encrypt a source limit of a second source operand and store the encrypted limit in a destination limit of a second destination operand, the destination limit associated with the ratchet pointer of the first destination operand.
In Example 6, the subject matter of Example 5 can optionally include the processor to execute the encode ratchet pointer instruction to generate an exception when the source limit of the second source operand is not within a power of two slot of the object. In Example 7, the subject matter of Example 1 can optionally include the processor to increase a lower bound of the ratchet pointer by executing an increase lower bound ratchet pointer instruction of an instruction set architecture (ISA) of the processor. In Example 8, the subject matter of Example 7 can optionally include the processor to execute the increase lower bound ratchet pointer instruction to decrypt the ratchet pointer of a first source operand, add an amount to a decrypted pointer value of the decrypted ratchet pointer to generate an updated pointer value, encrypt the updated pointer value and store the encrypted, updated pointer value in the ratchet pointer of a first destination operand, and re-encrypt a source limit associated with the ratchet pointer of the first source pointer operand as a destination limit of a second destination operand, the destination limit associated with the ratchet pointer of the first destination operand.
In Example 9, the subject matter of Example 8 can optionally include the processor to execute the increase lower bound ratchet pointer instruction to generate an exception when the updated pointer value is less than the decrypted pointer value of the decrypted ratchet pointer. In Example 10, the subject matter of Example 1 can optionally include the processor to decrease an upper bound of the ratchet pointer by executing a decrease upper bound ratchet pointer instruction of an instruction set architecture (ISA) of the processor. In Example 11, the subject matter of Example 10 can optionally include the processor to execute the decrease upper bound ratchet pointer instruction to decrypt a limit value of a source limit of a second source pointer operand associated with a source ratchet pointer of a first source operand, subtract an amount from the decrypted limit value to generate an updated limit value, encrypt the updated limit value and store the encrypted, updated limit value in a destination limit of a second destination operand, the destination limit associated with a ratchet pointer of a first destination operand. In Example 12, the subject matter of Example 11 can optionally include the processor to execute the decrease upper bound ratchet pointer instruction to generate an exception when the updated limit value is more than the decrypted limit value.
Example 13 is a method including storing an object referenced by a ratchet pointer in a memory; and providing access to a slice of the object by decrypting a base address and a limit of the ratchet pointer, generating a cryptographic address in an encrypted format bound to an identity of the object and not the slice; and performing effective address generation for the cryptographic address based at least in part on the base address and the limit. In Example 14, the subject matter of Example 13 can optionally include generating an exception when the effective address generation for the cryptographic address decreases the cryptographic address below the base address. In Example 15, the subject matter of Example 13 can optionally include generating an exception when one or more addresses of a requested access to the object are not less than the limit. In Example 16, the subject matter of Example 13 can optionally include encoding the ratchet pointer from a non-ratchet pointer by executing an encode ratchet pointer instruction of an instruction set architecture (ISA) of a processor.
In Example 17, the subject matter of Example 16 can optionally include executing the encode ratchet pointer instruction to decrypt a non-ratchet pointer of a first source operand, re-encrypt the non-ratchet pointer in a format of a ratchet pointer and store the ratchet pointer as a first destination operand, and encrypt a source limit of a second source operand and store the encrypted limit in a destination limit of a second destination operand, the destination limit associated with the ratchet pointer of the first destination operand. In Example 18, the subject matter of Example 17 can optionally include executing the encode ratchet pointer instruction to generate an exception when the source limit of the second source operand is not within a power of two slot of the object. In Example 19, the subject matter of Example 13 can optionally include increasing a lower bound of the ratchet pointer by executing an increase lower bound ratchet pointer instruction of an instruction set architecture (ISA) of a processor.
In Example 20, the subject matter of Example 19 can optionally include executing the increase lower bound ratchet pointer instruction to decrypt the ratchet pointer of a first source operand, add an amount to a decrypted pointer value of the decrypted ratchet pointer to generate an updated pointer value, encrypt the updated pointer value and store the encrypted, updated pointer value in the ratchet pointer of a first destination operand, and re-encrypt a source limit associated with the ratchet pointer of the first source pointer operand as a destination limit of a second destination operand, the destination limit associated with the ratchet pointer of the first destination operand. In Example 21, the subject matter of Example 20 can optionally include executing the increase lower bound ratchet pointer instruction to generate an exception when the updated pointer value is less than the decrypted pointer value of the decrypted ratchet pointer. In Example 22, the subject matter of Example 13 can optionally include decreasing an upper bound of the ratchet pointer by executing a decrease upper bound ratchet pointer instruction of an instruction set architecture (ISA) of a processor.
In Example 23, the subject matter of Example 22 can optionally include executing the decrease upper bound ratchet pointer instruction to decrypt a limit value of a source limit of a second source pointer operand associated with a source ratchet pointer of a first source operand, subtract an amount from the decrypted limit value to generate an updated limit value, encrypt the updated limit value and store the encrypted, updated limit value in a destination limit of a second destination operand, the destination limit associated with a ratchet pointer of a first destination operand. In Example 24, the subject matter of Example 23 can optionally include executing the decrease upper bound ratchet pointer instruction to generate an exception when the updated limit value is more than the decrypted limit value.
Example 25 is a system including a ratchet pointer; an address generation unit (AGU); a memory to store an object referenced by the ratchet pointer; and a processor to provide access to a slice of the object by decrypting a base address and a limit of the ratchet pointer, generating a cryptographic address in an encrypted format bound to an identity of the object and not the slice; and performing effective address generation for the cryptographic address by the AGU based at least in part on the base address and the limit. In Example 26, the subject matter of Example 25 can optionally include the processor to generate an exception when the effective address generation for the cryptographic address decreases the cryptographic address below the base address. In Example 27, the subject matter of Example 25 can optionally include the processor to generate an exception when one or more addresses of a requested access to the object are not less than the limit. In Example 28, the subject matter of Example 25 can optionally include the processor to encode the ratchet pointer from a non-ratchet pointer by executing an encode ratchet pointer instruction of an instruction set architecture (ISA) of the processor. In Example 29, the subject matter of Example 28 can optionally include the processor to execute the encode ratchet pointer instruction to decrypt a non-ratchet pointer of a first source operand, re-encrypt the non-ratchet pointer in a format of a ratchet pointer and store the ratchet pointer as a first destination operand, and encrypt a source limit of a second source operand and store the encrypted limit in a destination limit of a second destination operand, the destination limit associated with the ratchet pointer of the first destination operand.
Example 30 is an apparatus operative to perform the method of any one of Examples 13 to 24. Example 31 is an apparatus that includes means for performing the method of any one of Examples 13 to 24. Example 32 is an apparatus that includes any combination of modules and/or units and/or logic and/or circuitry and/or means operative to perform the method of any one of Examples 13 to 24. Example 33 is an optionally non-transitory and/or tangible machine-readable medium, which optionally stores or otherwise provides instructions that if and/or when executed by a computer system or other machine are operative to cause the machine to perform the method of any one of Examples 13 to 24.
The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the disclosure as set forth in the claims.
