Patent Grant
10447728
The present disclosure relates to virtualization architectures and, more specifically, to protection of guest processes using a virtualization layer of a virtualization architecture.
Data communication in a network involves the exchange of data between two or more entities interconnected by communication links and sub-networks (segments). The entities are typically software processes executing in operating systems of computers, such as endpoint nodes (endpoints) and intermediate nodes. The intermediate nodes interconnect the communication links and segments to enable transmission of data between the endpoints. A local area network (LAN) is an example of segment that provides relatively short distance communication among the interconnected nodes, whereas a wide area network (WAN) enables long distance communication over links provided by telecommunications facilities. The Internet is an example of a WAN that connects disparate computer networks throughout the world, providing global communication between nodes on various networks.
Malicious software (malware) has become a pervasive problem for nodes coupled to networks, such as the Internet. Malware is often embedded within downloadable content intended to adversely influence or attack normal operations of a node. Whereas operating system vulnerabilities have traditionally been common targets of such malware content, attackers have broadened their attack to exploit vulnerabilities in processes or applications, such as web browsers as well as operating system data structures. For example, malware content may be embedded within objects associated with a web page hosted by a malicious web site.
Various types of security enhanced nodes are often deployed at different segments of the networks. These nodes often employ virtualization systems to provide enhanced security needed to uncover the presence of malware embedded within ingress content propagating over the different segments. The enhanced security may include anti-virus scanning software that scans the ingress content for viruses and other forms of malware, as well as virtual machines that replay the content to monitor its behavior during execution so as to detect anomalies that may indicate the presence of malware. However, increasingly sophisticated malware may be able to infect the virtual machines to avoid detection by, e.g., altering states of resources of the nodes, such as operating system data structures. Moreover, strict specifications for some nodes (e.g., endpoints) may require execution of software, despite known vulnerabilities and potential of infection by malware. Thus, a technique to protect the processes executing (as well as operating system data structures) in the virtual machines of the nodes is needed.
The above and further advantages of the embodiments herein may be better understood by referring to the following description in conjunction with the accompanying drawings in which like reference numerals indicate identically or functionally similar elements, of which:
The embodiments described herein provide a technique for protecting guest processes of a guest operating system kernel using a virtualization layer of a virtualization architecture executing on a node of a network environment. The virtualization layer may include a user mode portion having hyper-processes and a kernel portion having a micro-hypervisor (i.e., a type of hypervisor operating at a highest privilege level of a physical processor of the node) that cooperate to virtualize the guest operating system kernel within a virtual machine and to make hardware resources of the node available for use by the guest operating system kernel, either as pass-through resources, emulated resources, or a combination thereof. Illustratively, the micro-hypervisor may cooperate with the hyper-processes of the virtualization layer to protect the guest processes against attack by one or more exploits that may employ malware. To that end, the guest process protection technique enables the micro-hypervisor and/or hyper-processes of the virtualization layer to determine (i) when the guest operating system switches to a guest process for execution, (ii) an identity of the guest process, and (iii) a protection policy to be associated with the guest process identity.
In an embodiment, each guest process runs in its own guest address space and has one or more guest page tables in the form of a guest page table hierarchy associated with that address space. The guest operating system kernel employs the guest page table hierarchy to perform a first address space translation from a guest-virtual address to a guest-physical address. The virtualization layer performs a second address space translation nested (i.e., layered) with the first translation that employs one or more nested page tables in a form of a nested page table hierarchy to, e.g., perform the second translation from the guest-physical address to a host-physical address used to access main memory of the node (i.e., a view of main memory as seen by the virtual machine). The translation of guest-physical address to host-physical address may be flexible, i.e., such translation may be implemented on a per page basis to determine how each guest-physical address is translated to a host-physical address.
A root address for each page table hierarchy is stored in a control register of a central processing unit (CPU) of the node. As a hardware resource, the control register is virtualized by the virtualization layer as a virtual control register for use by the guest operating system kernel. When switching guest processes (and address spaces) for execution on the CPU during a context switch, the guest operating system kernel swaps a prior guest page table hierarchy (i.e., a prior address space) for the guest page table hierarchy of the guest process (i.e., a current address space) to be executed by loading the root address of the guest page table hierarchy into the virtual control register to activate the guest page table hierarchy (i.e., the current address space). According to the technique, switching among guest processes for execution on the CPU may be determined using the content of the virtual control register, which represents the root address of the guest page table hierarchy. Specifically, the virtualization layer may be configured to intercept write accesses to the virtual control register to determine switching of guest processes. That is, upon detecting a new root address (value) loaded into the virtual control register, the virtualization layer may determine that the guest operating system is switching from a prior guest process associated with the prior guest page table hierarchy to the (current) guest process associated with the guest page table hierarchy.
The virtualization layer may then determine the identity of the guest process associated with the guest page table hierarchy using various approaches. One such approach involves content analysis of the guest process, wherein one or more code pages of the process, as marked by the guest page table hierarchy, are hashed to identify the process. The virtualization layer may perform the content analysis by examining the guest page table hierarchy to select the one or more code pages (e.g., entries in the guest page table hierarchy that are marked executable) of the guest process and hashing those code pages to effectively hash the code section of the process. Accordingly, hashing any instance of the guest process code pages should produce a hash value that is identical to a pre-computed hash value for the process, as each instance of the guest process has an identical code section. As a result, if a hash function having a substantially low collision rate is used to hash the code section of a guest process to produce a hash value that is known (e.g., via a pre-computed hash value for the process), then the identity of the guest process can be determined from the known hash value.
Another approach for determining the identity of the guest process associated with the guest page table hierarchy involves an in-guest component (agent) that cooperates with the virtualization layer to inform about guest process creation and destruction. Illustratively, for each newly created guest process, the agent may inform the virtualization layer of the identity of the new guest process and of the corresponding value of the virtual control register that points to the guest page tables of that guest process. Upon destruction of the (new) guest process, the agent may inform the virtualization layer to no longer track the value of the virtual control register corresponding to the guest process, because that process has been destroyed.
Upon determining the identity of a guest process, the virtualization layer may associate a protection policy, embodied as a protection profile, to the guest process. According to the technique, the protection profile may (i) contain information about process events that may be intercepted by the virtualization layer, wherein the intercepted events may involve certain instructions or accesses, (ii) contain a reference to a nested page table hierarchy associated with the guest process, and (iii) specify restrictions (e.g., embodied as permissions of nested page tables of the nested page table hierarchy) to be applied when the process is active (e.g., run). For example, assume that the guest process may have known vulnerabilities, wherein exploits that target the process may exhibit similar behavior, such as overflowing a buffer on a process stack. As a result, the protection profile applied to the process by the virtualization layer may state that when the process is created or activated, permissions that render the stack non-executable are applied. More generally, the virtualization layer may apply the protection profile to override the permissions configured by the guest operating system kernel in the guest page tables (for the guest-virtual address to guest-physical address translations) with the permissions configured by the virtualization layer in the nested page tables (for the guest-physical address to host-physical address translations) on a per-page and per-process basis.
Advantageously, the guest process protection technique provides protection at the granularity of memory pages (or sub-pages) for a guest process running in a guest operating system. To that end, the virtualization layer (including the micro-hypervisor) may monitor the switching of the guest page table hierarchy in the guest operating system kernel to determine when the guest process executes and then identify the guest process through hashing of its code pages. The virtualization layer may thereafter utilize the nested page table hierarchy to apply protections for the process at the granularity of code pages, as opposed to protecting a general address space of the entire guest operating system kernel. In other words, the technique enables identification of a particular guest process and application of a protection profile to that process alone.
In an embodiment, the endpoints may illustratively include, e.g., client/server desktop computers, laptop/notebook computers, process controllers, medical devices, data acquisition devices, mobile devices, such as smartphones and tablet computers, and/or any other intelligent, general-purpose or special-purpose electronic device having network connectivity and, particularly for some embodiments, that may be configured to implement a virtualization system. The nodes 200 illustratively communicate by exchanging packets or messages (i.e., network traffic) according to a predefined set of protocols, such as the Transmission Control Protocol/Internet Protocol (TCP/IP); however, it should be noted that additional protocols, such as the HyperText Transfer Protocol Secure (HTTPS), may be advantageously used with the embodiments herein. In the case of private network 130, the intermediate node 200I may include a firewall or other network device configured to limit or block certain network traffic in an attempt to protect the endpoints from unauthorized users. Unfortunately, such conventional attempts often fail to protect the endpoints, which may be compromised.
The memory 220 may include a plurality of locations that are addressable by the CPU(s) 210 via a memory management unit (MMU 215), as well as the network interface(s) 260 and device(s) 270 via an I/O MMU (IOMMU 255). Note that accesses to/from memory 220 by the CPU(s) 210 may occur directly through the MMU 215 and over the system interconnect 250, whereas accesses to/from the memory by the network interface(s) 260 and device(s) 270 may occur directly through the IOMMU 255 of the system interconnect. That is, a first data path may occur directly from the CPU to the memory 220 via the system interconnect 250 and a second (independent) data path may occur directly from the I/O devices 270 to the memory 220 also via the system interconnect 270. The memory locations may be configured to store software program code (including application programs) and data structures associated with the embodiments described herein. The CPU 210 may include processing elements or logic adapted to execute the software program code, such as modules of a virtualization architecture 300, and manipulate the data structures, such as a process control block (PCB) 235 and a process table 245. Exemplary CPUs may include families of instruction set architectures based on the x86 CPU from Intel Corporation of Santa Clara, Calif., the x64 CPU from Advanced Micro Devices of Sunnyvale, Calif., and the ARM CPU from ARM Holdings, plc of the United Kingdom.
A (guest) operating system kernel 230, portions of which are typically resident in memory 220 and executed by the CPU, functionally organizes the node by, inter alia, invoking operations in support of the software program code and application programs executing on the node. A suitable guest operating system kernel 230 may include the Windows® series of operating systems from Microsoft Corp of Redmond, Wash., the MAC OS® and IOS® series of operating systems from Apple Inc. of Cupertino, Calif., the Linux operating system and versions of the Android™ operating system from Google, Inc. of Mountain View, Calif., among others. Suitable application programs may include Adobe Reader® from Adobe Systems Inc. of San Jose, Calif. and Microsoft Word from Microsoft Corp of Redmond, Wash. Illustratively, the software program code may be executed as guest processes 240 of the kernel 230. As used herein, a process (e.g., a guest process) is an instance of software program code (e.g., an application program) executing in the operating system that may be separated (decomposed) into one or more threads, wherein each thread is a sequence of execution within the process.
It will be apparent to those skilled in the art that other types of processing elements and memory, including various computer-readable media, may be used to store and execute program instructions pertaining to the embodiments described herein. Also, while the embodiments herein are described in terms of software program code, processes, and computer applications or programs stored in memory, alternative embodiments may also include the code, processes and programs being embodied as components, logic, and/or modules consisting of hardware, software, firmware, or combinations thereof.
Virtualization Architecture
The micro-hypervisor 320 (i.e., a type of hypervisor operating at a highest privilege level of a physical processor of the node) may be embodied as a light-weight module configured to facilitate run-time security analysis, including exploit and malware detection and threat intelligence, of the guest processes 240 executing on the node 200. As described herein, the micro-hypervisor 320 may cooperate with corresponding hyper-processes 350 of the virtualization layer 310 to virtualize the hardware and control privileges (i.e., access control permissions) to hardware resources of the node that are typically controlled by the guest operating system kernel. Illustratively, the hardware resources may include (physical) CPU(s) 210, memory 220, network interface(s) 260, and devices 270. The micro-hypervisor 320 may be configured to control access to one or more of the resources in response to a request by a guest process 240 to access the resource.
A user mode portion of the virtualization layer 310 includes the hyper-processes 350, examples of which include, inter alia, a guest monitor 352, a threat protection component 354, and a policy manager 356. The guest monitor 352 is illustratively a unique virtual machine monitor (VMM), i.e., a type 0 VMM, which includes virtualization functionality that cooperates with the micro-hypervisor 320 to virtualize the guest operating system within the VM and run one or more micro-virtual machines (micro-VMs), such as, in some embodiments, a memory view (as described below). Accordingly, the guest monitor 352 may include computer executable instructions executed by the CPU 210 to perform operations that spawn, configure, and control/implement the VM or any of a plurality of micro-VMs. The guest monitor 352 may further include virtualization functionality that emulates privileged instructions (i.e., an instruction emulator) and devices (i.e., a virtual device emulator) that act as software substitutes for hardware devices not directly assigned to the guest operating system. As such, a set of hardware resources may be virtualized among a plurality of micro-VMs that may access those resources. That is, the guest monitor 352 may create virtual devices (e.g., software state machines) of the hardware resources for use by the micro-VMs that, from the perspective of the guest operating system, appear as physical resources.
As used herein, the term “micro” VM denotes a virtual machine serving as a container that may be restricted to a single guest process (as opposed to the VM which is spawned as a container for the entire guest operating system having many guest processes). In one embodiment, the micro-VMx may be implemented outside of the VM, (i.e., in a separate protection domain) using, e.g., copy-on-write semantics. In another embodiment, the micro-VMi may be implemented inside the VM (i.e., inside a same protection domain as the VM) using, e.g., one or more memory views as described further herein. However, whereas a micro-VM may be restricted to a single guest process, the hardware resources used by that micro-VM, such as memory, may be accessed by a plurality of micro-VMs (and their respective guest processes). As noted, there is only one virtual machine (e.g., the VM) per guest operating system on the endpoint. Typically, the guest operating system running in the VM has one “view” of the memory 220, i.e., “guest-physical” memory, corresponding to one nested page table. Accordingly, as described herein, a same nested page table (i.e., memory view) may be used by a plurality of guest processes, each contained in a separate corresponding micro-VM that uses a same nested page table. However, additional views of memory may be created for each guest process, such as where every view corresponds to a different (i.e., separate) nested page table. Thus, different guest processes may view the guest-physical memory differently (e.g., with different translations or different permissions to the host-physical memory).
In an embodiment, the micro-VM may be implemented as such a view (i.e., a guest-physical memory view) of the memory 220, i.e., controlling the host-physical memory (hardware resource) underlying the guest-physical view of memory. Notably, different guest processes 240 may run in different micro-VMs, each of which is controlled by the (same) guest monitor 352 (also controlling the VM) to thereby enable a global view of execution activity in the guest operating system. The micro-VM thus has properties similar to the typical VM, but with less overhead, i.e., no additional guest monitors. In terms of execution, operation of the guest process is controlled and synchronized by the guest operating system kernel 230; however, in terms of access to hardware resources (managed in host mode), operation of the process is controlled by the guest monitor 352. Access to hardware resources may be synchronized among the micro-VMs and the VM by the guest monitor 352 rather than virtually shared. Notably, certain types of hardware resources, such as memory, may not need express synchronization among micro-VMs. For example, each CPU core may have a single memory view (i.e., set of nested page tables) active at a time, so that express synchronization among memory views is unnecessary. As such, memory views may be assigned to multiple micro-VMs with implicit synchronization.
In an embodiment, the privileged interfaces 305 and 315 may be embodied as a set of defined hyper-calls, each of which is an operation that explicitly calls (explicit transition) into the micro-hypervisor. The hyper-calls may originate from one or more hyper-processes 350 of the virtualization layer 310 and are directed to the micro-hypervisor 320 over the privileged interface 315; alternatively, bi-directional communications may originate from a protected component (e.g., an agent) in the guest operating system directed to the micro-hypervisor (virtualization layer) over the privileged interface 305. A transition from the guest operating system to the virtualization layer 310 is called a VM exit. Such a transition may be implicit, e.g., an intercepted operation or page-protection violation, or explicit, such as a VMCALL instruction from guest mode to host mode. Further, as used herein, an inter-process communication (IPC) message between two hyper-processes requires two hyper-calls (i.e., one for each process) for bi-directional communication.
The policy manager 356 may contain computer executable instructions executed by the CPU 210 to perform operations that associate a protection policy with each guest process 240, as described further herein. The threat protection component 354 may include instrumentation logic implemented as heuristics configured to determine the presence of an exploit or malware in any suspicious guest operating system process (kernel or user mode). To that end, the threat protection component 354 may include software program code (e.g., executable machine code) in the form of instrumentation logic (including decision logic) configured to analyze one or more interception points originated by one or more guest processes 240 to invoke the services, e.g., accesses to the hardware resources, of the guest operating system kernel 230. Illustratively, the threat protection component 354 may contain computer executable instructions executed by the CPU 210 to perform operations that initialize and implement the instrumentation logic.
As used herein, an interception point is a point in an instruction stream where control passes to (e.g., is intercepted by) the virtualization layer 310, e.g., the micro-hypervisor 320. Illustratively, the micro-hypervisor can intercept execution inside the guest operating system at arbitrary points such as (i) inside any guest process, (ii) inside the guest operating system kernel, and/or (iii) on transitions between guest processes and the guest operating system kernel. Malicious behavior may then be analyzed by the virtualization layer (e.g., the threat protection component 354), wherein the behavior may occur anywhere in the guest operating system, including in any guest process or in the guest operating system kernel. The virtualization layer 310 may, thus, place interception points at appropriate instruction stream points, whether in a process or in the kernel.
The guest operating system kernel 230 may be configured to include an operating system (OS) specific extension or agent 360 adapted to communicate with the threat protection component 354. The agent 360 illustratively contains executable machine code in the form of logic configured to provide an interface to the threat protection component 354 that allows introspection (examination and/or interception) of contents of internal structures of the guest operating system kernel 230, as well as semantic context associated with such contents, as described herein. Such virtual machine introspection (VMI) may involve examination of data structures of the guest operating system kernel 230 in a manner that obviates duplication of (i.e., without copying) those structures between the guest and host modes of the virtualization architecture. To that end, the agent 360 may run in host mode ring 3 or guest mode ring 0; however, in an embodiment described herein, the agent 360 illustratively runs in guest mode ring 3. Accordingly, the agent 360 may contain computer executable instructions executed by the CPU 210 to perform operations that implement communication with, and introspection by, the threat protection component 354. For example, identification (ID) of each guest process 240 running in the guest operating system may be obtained from process IDs stored in a data structure, e.g., the process table 245, of the guest operating system. Instead of having to probe that data structure and with knowledge to extract its contents, the threat protection component 354 can instruct the agent to examine the process table 245 and provide the ID of the guest process 240. That is, the agent 360 operating in the guest mode may act on behalf callers (e.g., guest monitor 352) operating in the host mode to access (i.e., probe) data structures in the guest mode with knowledge to extract its contents. Accordingly, the agent may be configured with knowledge of the guest O/S data structures. Alternatively, the threat protection component may examine directly the memory used by the guest O/S (i.e., virtual machine introspection) to determine locations (and layout) of the process table 245 so as to determine the ID of the guest process 240. Illustratively, threat protection component 354 may communicate with the guest operating system (i.e., the agent 360) over a defined application programming interface (API) 365.
As a light-weight module, the micro-hypervisor 320 may provide a virtualization layer having less functionality than a typical hypervisor. Therefore, as used herein, the micro-hypervisor 320 is a module that is disposed or layered beneath (underlying, i.e., directly on native hardware and operating at a highest privilege level of that native hardware) the guest operating system kernel 230 and includes the functionality of a micro-kernel (e.g., protection domains, execution contexts, capabilities and scheduling), as well as a subset of the functionality of a hypervisor (e.g., management of virtual CPUs and their states, management of the MMU, IOMMU and other security-critical devices, as well as hyper-calls to implement a virtual machine monitor). Accordingly, the micro-hypervisor 320 may cooperate with the guest monitor 352 to provide additional virtualization functionality in an operationally and resource efficient manner. Unlike a type 1 or type 2 VMM (hypervisor), the guest monitor 352 is illustratively a type 0 VMM (VMM 0) that does not fully virtualize the hardware resources of the node 200, while supporting execution of one entire operating system/instance inside one virtual machine, i.e., the VM. The guest monitor 352 may thus instantiate the VM as a container for the guest processes 240, as well as the guest operating system kernel 230 and its hardware resources. Illustratively, the guest monitor 352 is a pass-through module configured to expose the hardware resources of the node (as controlled by micro-hypervisor) to the guest operating system kernel 230. Yet, virtualization processing in response to a VM exit (and a resulting transition of control flow from the guest operating system to the micro-hypervisor) may be performed by the guest monitor. To that end, the micro-hypervisor 320 may enable communication between the guest operating system (i.e., the VM) and the guest monitor over privileged interfaces 305 and 315.
In an embodiment, the micro-hypervisor 320 may include a plurality of data structures, such as objects 330 and capabilities 342, configured to provide security and isolation features associated with the virtualization architecture 300. Illustratively, the objects 330 include one or more protection domains 332, execution contexts 334 and scheduling contexts 336. As used herein, a protection domain 332 is a kernel mode object that implements spatial isolation among the hyper-processes of the virtualization layer and includes a representation of a security privilege associated with each hyper-process 350 that is enforced by the micro-hypervisor 320. Illustratively, each hyper-process 350 in the virtualization layer 310 runs in a separate protection domain 332. An execution context 334 is illustratively a representation of a thread associated with the hyper-process 350 and, to that end, defines a state of the thread for execution on the CPU 210. In an embodiment, the execution context 334 may include inter alia (i) contents of CPU registers, (ii) pointers/values on a stack, (iii) a program counter, and/or (iv) allocation of memory via, e.g., memory pages. The execution context 334 is thus a static view of the state of thread and, therefore, its associated hyper-process 350. For the thread to execute on a CPU, its execution context is tightly linked to a scheduling context 336, which may be configured to provide information for scheduling the execution context 334 for execution on the CPU 210. Illustratively, the scheduling context information may include a priority and a quantum time for execution of its linked execution context on CPU 210.
The micro-hypervisor 320 also includes a per-protection domain (PD) capability space 340 that contains capabilities 342A-N, wherein each capability 342 is a pointer to an object 330 having associated permissions (i.e., privileges). Hyper-processes 350 of the virtualization layer 310 do not have the ability to work with the capabilities 342 directly, i.e., they cannot read the pointer or privileges directly and can only refer to those capabilities using a capability selector 345, e.g., an integral number. To invoke a specific capability, a hyper-process 350, such as the guest monitor 352, may issue a hyper-call request (e.g., over interface 315) to the micro-hypervisor 320, wherein the request includes an action (e.g., “send a message” or “delegate a capability”) along with a corresponding capability selector, i.e., an index such as N, that identifies (names) the object 330 involved in the hyper-call. Illustratively, the capabilities 342 are used to name the object on which the hyper-call operates and, at the same time, convey the access permissions of the calling hyper-process on that object. In response to the request, the micro-hypervisor may access the per-PD capability space 340 to select the requested capability 342N, which names (e.g., points to) the object (e.g., scheduling context 336) on which the action is performed.
Illustratively, a capability 342 is a concept that is only known in the virtualization layer 310, i.e., the guest operating system is unaware of the capability. The capability 342 is essentially a mechanism to enforce security privileges among the hyper-processes 350 of the virtualization layer 310. Notably, each hyper-process 350 is provided only a minimal set of capabilities 342 necessary for that component to perform its assigned function. For example, the guest monitor 352 may have the capability to access the VM, while only the threat protection component 354 may have the capability to communicate with the guest monitor 352 and policy manager 356. Thus, an attacker that is able to compromise a hyper-process (protection domain 332) would only be able to inflict damage associated with the capabilities 342 held by that protection domain 332.
As described herein, certain events or activities, e.g., attempted access to hardware resources, of a guest process 240 may be treated as interception points that allow the virtualization layer 310 to further monitor or instrument the process using a spawned micro-VM. A system call is an example of an interception point at which a change in privilege modes or levels occurs in the guest operating system, i.e., from guest mode ring 3 (a lowest level of guest mode privilege) of the guest process 240 to guest mode ring 0 (a highest mode of guest mode privilege) of the guest operating system kernel 230. The guest monitor 352 may intercept the system call and examine a state of the process issuing (sending) the call. The instrumentation logic of threat protection component 354 may analyze the system call to determine whether the call is suspicious and, if so, instruct the guest monitor 352 to instantiate (spawn) one or more micro-VMs, managed by the guest monitor in cooperation with the threat protection component, to detect anomalous behavior which may be used in determining an exploit or malware.
As used herein, an exploit may be construed as information (e.g., executable code, data, one or more commands provided by a user or attacker) that attempts to take advantage of a computer program or system vulnerability, often employing malware. Typically, a vulnerability may be a coding error or artifact of a computer program that allows an attacker to alter legitimate control flow during processing of the computer program by an electronic device and, thus, causes the electronic device to experience undesirable or unexpected behaviors. The undesired or unexpected behaviors may include a communication-based or execution-based anomaly which, for example, could (1) alter the functionality of the electronic device executing application software in a malicious manner; (2) alter the functionality of the electronic device executing the application software without any malicious intent; and/or (3) provide unwanted functionality which may be generally acceptable in another context. To illustrate, a computer program may be considered a state machine where all valid states (and transitions between states) are managed and defined by the program, in which case an exploit may be viewed as seeking to alter one or more of the states (or transitions) from those defined by the program. Malware may be construed as computer code that is executed by an exploit to harm or co-opt operation of an electronic device or misappropriate, modify or delete data. Conventionally, malware may often be designed with malicious intent, and may be used to facilitate an exploit. For convenience, the term “malware” may be used herein to describe a malicious attack, and encompass both malicious code and exploits detectable in accordance with the disclosure herein.
Memory Virtualization
Virtualization provides one or more additional page tables, i.e., nested page tables (NPT) 430, layered underneath (i.e., nested with) the GPT 410. The nested page tables 430 may be utilized to perform a second translation from the guest-physical address 425 to a host-physical address 435, wherein the host-physical address 435 is an address used to access (physical) main memory 220. The translation of guest-physical address 425 to host-physical address 435 may be flexible, i.e., such translation may be implemented on a per page basis to determine how each guest-physical address 425 is translated to a host-physical address 435. Illustratively, translation from guest-physical addresses to host-physical addresses is controlled by the virtualization layer 310 to establish a mapping from the guest-physical addresses used in a VM (e.g., the VM) to a host-physical address in main memory 220.
In an embodiment, guest page tables 410 are part of a guest page table hierarchy that is controlled by the guest operating system kernel 230, and the nested page tables 430 are part of a nested page table hierarchy that is controlled by the virtualization layer 310, e.g., managed by the micro-hypervisor 320 in cooperation with the guest monitor 352. In one arrangement where the MMU hardware supports nested paging, the page table hierarchies may be organized as a two-stage (i.e., layered) translation arrangement of the (physical) MMU 215 (supporting a virtualized MMU via two-level page table hierarchies), where the page tables define the translation of a guest-virtual address 415 to a guest-physical address 425 (a first stage defined by the GPT) and, ultimately, to a host-physical address 435 (a second stage defined by the NPT). There, the guest operating system kernel 230 manages the guest page tables 410, the virtualization layer 310 manages the nested page tables 430, and the nested page tables are consulted by the MMU after the guest page tables. Hence, the nested page tables may be used to override permissions.
In an alternative arrangement where the MMU hardware does not support nested paging (e.g., it can only perform one-level translation), the guest page tables may be organized as a shadow page table arrangement synchronized with the nested page table hierarchy such that the shadow page tables provide guest-virtual address to host-physical address translations that are updated with changes to the guest page table hierarchy or nested page table hierarchy. The virtualization layer 310 is responsible for folding the guest page tables 410 (managed by the guest operating system kernel 230) and the nested page tables 430 (managed by the virtualization layer) together to create the shadow page tables so as to perform end-to-end translation from guest-virtual addresses to host-physical addresses. The MMU 215 then uses the shadow page tables for translating guest-virtual addresses to host-physical addresses as a single level translation. Accordingly, the shadow page tables are updated when the guest page tables or nested page tables change. It should be noted that either arrangement may provide additional functionality, wherein each translation stage may define access permissions on a page granularity. That is, for each page referenced by a page table, access permissions may be specified as to whether the page is readable (r) writeable (w), or executable (x). Note that sub-page protection may implemented when the MMU only provides page-granularity by write protecting a page having the sub-page to be protected and for any write violations that occur to non-protected portions of the page (i.e., outside the sub-page being protected), perform the write operation to that portion of the page on behalf of the guest O/S.
In an embodiment, the “ultra” (ultimate) translation to physical memory of the two-stage arrangement, i.e., the translation from guest-physical address 425 to host-physical address 435, may be employed to overwrite any page permissions that the guest operating system kernel 230 has defined. For example, assume the guest operating system kernel 230 has defined, using the GPT, a certain read (r), write (w), execute (x) mapping for a guest-virtual address 415 to guest-physical address 425 of a page accessible by a guest process 240, so that the guest process 240 may expect that it can actually read, write and execute that page. Yet, using the nested page tables 430 (i.e., layered beneath the GPT), the virtualization layer 310 may alter or change those permissions to be write protected, i.e., read-only (r) and execute (x) with no write permission, for the actual (host) physical page that the guest operating system kernel 230 (and guest process 240) may attempt to access. Therefore, any time that the guest process 240 attempts a write access to the page, an access violation of the nested page tables occurs, resulting in a VM exit (e.g., a transition) that returns control to the virtualization layer 310. Note that for the shadow page table arrangement, the violation occurs for a shadow page acting as a condensed two-stage address translation. In response to determining that the attempted write access is to a physical page that is write protected, the virtualization layer 310 may take action, such as emulating the access, making the page writeable, shadow copying the write, or completely nullifying the effects of that access. As another example, assume the guest operating system kernel 230 has marked the page as non-executable. The virtualization layer 310 may render the page executable or emulate the instruction that would have been executed if the page had been executed.
Memory Views
As noted, the micro-VM may be implemented as a view of the memory 220 (memory view) embodied as nested page table address mappings that control the host-physical memory underlying the guest-physical view of memory. Accordingly, the memory view is a hardware resource (i.e., a set of NPT tables) used by the micro-VM as a container (i.e., constraining access to memory) for one or more guest processes. The address space of each guest process 240 may be represented by the combination of the GPT and a memory view (e.g., NPT address mappings). Different guest processes 240 may run in different memory views, each of which is controlled by the guest monitor 352 associated with the VM to thereby enable a global view of execution activity in the guest operating system. In an embodiment, each memory view may have its own nested page table hierarchy that describes the guest-physical memory layout of the view (i.e., micro-VM); accordingly, the VM may implement one or more micro-VMs as memory views through different NPTs 430 of the nested page table hierarchies. A protection profile of each guest process, as described further herein, defines in which memory view (micro-VM) that guest process runs. The guest operating system kernel 230 and hardware resources may then be mapped into the memory views to ensure synchronization when accessing the guest operating system kernel and resources.
Illustratively, each memory view 510 has its own set of NPTs 430 of a nested page table hierarchy associated with a micro-VM that describes the guest-physical memory layout of that view as controlled by the virtualization layer 310, e.g., managed by micro-hypervisor 320 in cooperation with the guest monitor 352. For example, memory view 510a has NPTs 430a associated with micro-VM 0, memory view 510b has NPTs 430b associated with micro-VM 1, and memory view 510c has NPTs 430c associated with micro-VM 2. As such, the VM may include one or more micro-VMs each having different nested page table hierarchies. Accordingly, one or more guest processes 240 along with the guest operating system kernel 230 run in a micro-VM, i.e., guest processes 240a,b,c and guest O/S kernel 230 run in micro-VM 0, guest processes 240d,e and guest O/S kernel 230 run in micro-VM 1, and agent 360 and guest O/S kernel 230 run in micro-VM 2.
When the guest operating system kernel 230 switches from one guest process 240 to another, the guest monitor 352 (VMM) observes the guest process switch and, in response, instructs the micro-hypervisor to swap (switch) to the NPT 430 that implements the memory view to which the switched process is assigned. Thus, if the guest monitor 352 observes a guest process switch from guest process 240a to guest process 240c (or from guest process 240d to guest process 240e), no NPT switching occurs and the memory view remains unchanged. However, in response to observing a guest process switch from guest process 240c to guest process 240e, the guest monitor 352 (in cooperation with the micro-hypervisor) switches from NPT 430a to NPT 430b. Likewise, in response to observing a switch from guest process 240d to the agent 360, the guest monitor switches from NPT 430b to NPT 430c. Because the guest operating system kernel 230 is mapped in all nested page table hierarchies, a change from one memory view (micro-VM) to another does not change the state of the guest operating system kernel, i.e., it appears as if the guest operating system kernel 230 “moves” from one memory view to another.
Advantageously, the assignment of guest processes to memory views (micro-VMs) is flexible and efficient. For example, guest processes that belong to a particular (default) protection profile may run in memory view 510a where the entire memory is visible, e.g., in guest mode, and no permissions have been overridden. Certain other guest processes may require a higher degree of protection/monitoring and may be assigned to memory view 510b where the guest monitor 352 may tighten (i.e., restrict) permission to certain memory pages. Likewise, certain trusted processes, such as agent 360, may be assigned to memory view 510c where certain memory pages are visible (i.e., accessible) that are not visible in the other memory views. In sum, one or more guest processes may be assigned to each memory view and a guest process may also be reassigned from one memory view to another.
Guest Process Protection
The embodiments described herein provide a technique for protecting guest processes 240 of guest operating system kernel 230 on a virtual machine (e.g., the VM) using the virtualization layer 310. As noted, the virtualization layer 310 may include a user mode portion having hyper-processes 350 and a kernel portion having the micro-hypervisor 320. Illustratively, the micro-hypervisor may cooperate with the hyper-processes of the virtualization layer 310 to protect the guest processes 240 against attack by one or more exploits that may employ malware. To that end, the guest process protection technique enables the micro-hypervisor and/or hyper-processes of the virtualization layer to determine (i) when the guest operating system switches to a guest process for execution, (ii) an identity of the guest process, and (iii) a protection policy to be associated with the guest process identity.
Switching to a guest process 240 for execution on CPU 210 may be determined using a control register of the CPU that is associated with a guest page table hierarchy.
In an embodiment, each processor core of CPU 210 has its own virtualized control register to enable access to the guest address space of the guest process 240. Thus, each value of the virtual control register (CR3) may reference (point to) a hierarchy of guest page tables, which list or enumerate all memory pages 660 in the guest virtual (linear) address space of the process 240. For example, the virtual control register 610 points to the base address of the page directory 620 of the hierarchy 600 and a first field 415A (e.g., predetermined high-order bits) of a guest-virtual address 415 points to a page directory entry of the page directory 620. The page directory entry 622 then points to the base address of a page table 640, while a second field 415B of the guest-virtual address 415 points to a page table entry 642 of the page table 640. The page table entry 642, in turn, points to the base address of a memory page 660 and a third field 415C (e.g., predetermined low-order bits) of the guest-virtual address 415 points to the guest-physical address 425 (offset) within the page 660. A similar hierarchy may be provided for the nested page tables 430 to translate the guest-physical address 425 to a host-physical address 435. In addition, the x86 CPU may support virtualized MMUs via a two-level page table hierarchy that provides layering (i.e., nesting) such that the virtual control register (CR3) provides a root for a first level of page tables (i.e., guest page table hierarchy) and a nested page table control register (EPT/NPT pointer) provides a root for a second level of page tables (i.e., nested page table hierarchy). Illustratively, the nested page tables are extended page tables (EPT) in x86 CPU from Intel and the NPT control register is an EPT base pointer register in the x86 CPU. As such, the EPT pointer may be accessible (i.e., visible) only to the virtualization layer, i.e., the root pointer of the second level of page tables (NPT) is not virtualized in the VM, so that the NPT control register (e.g., EPT base pointer) is invisible in the guest mode. Note that other CPU architectures, such as the x64 CPU from Advanced Micro Devices and the ARM CPU from ARM Holdings, may provide a similar two-level page table hierarchy with separate root pointer registers for each level.
In accordance with the guest process protection technique, the virtualization layer 310 (micro-hypervisor 320) is configured to intercept write accesses by the guest operating system kernel 230 to the virtual control register 610 to record changes to the content (value) of the register. That is, the virtual control register 610 is used to detect, e.g., at the virtualization layer 310, switching of guest processes 240 in the guest operating system. Specifically, the guest process protection technique is directed to use of a virtualized hardware resource, i.e., control register 610 whose content is changed (altered) on every guest process context switch in a VM (e.g., the VM), wherein a VM exit to the virtualization layer 310 is triggered when the content of that register changes. Illustratively, the control register is CR3 of x86 CPUs, although the technique may apply similarly to other CPU architectures (e.g., the x64 CPU from Advanced Micro Devices), because operating systems generally run each guest process in a separate virtual address space and the virtual-to-physical address space translation uses page tables hierarchies.
Switching from one process to another therefore requires switching page tables, which are rooted in the virtual control register 610. In an embodiment, intercepting access to that register enables determination of a switch from one guest page table hierarchy to another, which can be interpreted as a guest process switch. That is, upon detecting the guest operating system loading a new root address (value) into the virtual control register CR3, the virtualization layer 310 may determine that the guest operating system is activating a new set of guest page tables 410 and, thus, switching from a prior guest process associated with the prior guest page table hierarchy to the (new) guest process associated with the (new) guest page table hierarchy. The virtualization layer 310 may then determine the identity of the guest process associated with the guest page table hierarchy to enable a decision of whether to, e.g., protect or monitor the process.
Determination of the identity of the guest process requires, inter alia, distinguishing among other guest processes executing in the guest operating system. The virtualization layer 310 typically cannot determine the memory pages used by the guest processes 240, so as to distinguish among those processes by, e.g., determining their type or associated data structures, because the memory pages used for each guest process are stored in data structures known only to the guest operating system. However, the virtualization layer may obtain semantic context, such as read or write information, about a memory page 660 when accessed by a guest process 240 so as to determine the identity of that guest process. As such, in one or more embodiments, the guest process protection technique described herein may employ various approaches to determining the identity of the guest process using such semantic context.
A first approach involves the use of the agent 360 (i.e., an in-guest operating system component) to probe the guest processes 240 and communicate with the virtualization layer 310 (i.e., the threat protection component 354) regarding location and semantics of certain guest operating system data structures. As noted, the agent 360 is an operating system extension module that cooperates with the virtualization layer 310 to provide certain information, such as process creation and destruction. For example, when a new guest process is created in the guest operating system, the agent 360 may identify the process to the virtualization layer via activation of a guest page table hierarchy 600. That is, the agent may examine the process table 245 to acquire the identity of the new guest process 240 and then inform the virtualization layer 310 that the corresponding value of the virtual control register that points to the guest page table hierarchy 600 belongs to the new guest process 240. Upon destruction of the process, the agent may inform the virtualization layer to no longer track the value of the virtual control register because the corresponding process has been destroyed. Note that any process (including the agent) running at the guest mode privilege level operates at a same privilege level of the virtualization architecture 300 as an attacker and, thus, may be compromised (e.g., infiltrated) by the attacker. However, as described herein, the guest process protection technique may protect the agent 360 when operating in the guest mode privilege level.
A second approach to determining a guest process involves implementation of guest operating system specific knowledge in the virtualization layer. Illustratively, this approach may involve the use of virtual machine introspection (VMI) by the virtualization layer 310 to probe the memory of a VM for purposes of examining (i.e., parsing) guest operating system specific data structures to determine their layouts and linkages (i.e., memory forensics). For example, assume the virtualization layer 310 probes the VM memory (i.e., memory allocated to the VM) to parse guest operating system internal data structures, such as the PCB 235. Parsing of the PCB 235 for a guest address space may reveal a field having a path that includes a name for a guest process 240. The virtualization layer 310 may then deduce the identity of the guest process from the process name. Such sematic parsing may be implemented in the threat protection component 354 of the virtualization layer 310, which operates in host mode privilege level of the virtualization architecture 300 and, thus, beyond the privilege level of an attacker, which is typically at the privilege level of guest operating system. However, this approach is also operating system specific and, therefore, may be unreliable because a guest operating system upgrade or patch that changes the layouts of the data structures may result in misinterpretation of their content.
A third approach involves content analysis of the guest process 240, wherein one or more code pages of the process as marked by the guest page table hierarchy 600 are hashed to identify the process, i.e., the one or more code pages may be “fingerprinted” (hashed) so as to identify the process.
It should be noted that the content analysis approach may be difficult to implement because hashing often cannot be performed on the entire guest process. As noted, the guest operating system has the ability to page the guest process 240; accordingly, a portion (not all) of the code pages 710 for the process may reside in main memory 220. For example, when the virtualization layer 310 first detects switching of the process into memory, the guest operating system may have only loaded one page from disk, i.e., the entire guest process image may not be present in memory 220. Nevertheless, during a VM exit or transition (switch) in privilege levels from guest mode to host mode, the virtualization layer 310 may use a current instruction pointer (e.g., via a program counter in a processor core of the VM) in the guest mode to determine from which code page 710 the process is executing. A hash value 730 may then be computed on a per page basis, wherein the hash values 730 of code pages 710 at particular guest (virtual) addresses are compared with hash values of codes pages at similar addresses of other guest processes to substantially reduce a number of candidate guest process identities, i.e., multiple candidate identities of a process from differing portions of the codes pages for that process.
Although the content analysis approach may include comparison of code page hashes with corresponding hashes of known (benign) guest processes to determine the identity of a guest process, the approach may be extended to determine when the guest process has been (suspiciously) modified. Such modification may trigger a raising of a suspiciousness level of the virtualization layer 310 if the comparison with known hashes does not match and, consequently, possible initiation of further instrumentation of the suspiciously modified process. For example, assume an attacker copies a code page 710 that was previously identified as a code page of a guest page table 410 for a guest process 240 and makes a minor change to the new (copied) page, as well as alters the page table to point to the new code page, i.e., effectively swapping the code page with the new modified code page. Since the technique described herein hashes pages and not page tables, the content of the different page that the altered page table references may be hashed to identify the process assuming, e.g., that the new code page is recently loaded from disk and, thus, is authentically part of the process. However, if the modified content of the code page includes the same code as the original code of the original page, the resulting hash value 730 may be the same. Moreover, the behavior of the guest process 240 is the same because the original code was replaced with a copy of that code, albeit on a separate memory page, i.e., the process still behaves in an expected way. Yet, if the attacker sufficiently modifies content of the guest process, e.g., changes a jump target to another address location, the modification may be reflected in the code page 710 and as a change in the resulting hash value 730. Although the changed hash value may not be known and may be assumed to be a recently loaded authentic code page, the virtualization layer 310 may monitor (instrument) multiple different pages to compute a likelihood of a particular identity of the guest process, e.g., where a substantial number (99%) of the pages appear to resemble the guest process. As such, when one or more pages (i.e., a threshold of pages) appear odd (i.e., do no match an existing hash for a code page of the process), the virtualization layer 310 may surmise (i.e., determine) that the guest process 240 is being attacked.
Once the identity of one or more guest processes are determined, mappings may be established and maintained in the virtualization layer 310 that associate particular instances of the processes with particular values of the virtual control register (CR3) 610. Such mappings enable the virtualization layer to name the different guest process instances solely by their virtual control register (CR3) values and, thus, distinguish the processes. The mapping may be established using any of the approaches described herein upon detecting (for the first time) the guest operating system switching to a virtual control register value that is unknown to the virtualization layer. For example, upon detecting creation of a new guest process, the agent 360 may inform the virtualization layer 310 as to the value of the virtual control register for the process 240. Since the guest process is unknown, the virtualization layer may perform an analysis on the guest page tables 410 or data structures to determine the identity of the process and then map the process to the virtual control register value.
Upon determining an identity of a guest process, the virtualization layer 310 may associate a protection policy with the guest process identity.
More generally, the virtualization layer 310 may apply the protection profile 830a to override permissions 815aa of a page 710aa as defined by the guest page table (GPT) hierarchy 410a using higher priority permissions 825aa enforced by the nested page table (NPT) hierarchy 430a for that page on a per process (e.g., 240a,b) basis. For example, even though the guest operating system kernel 230 may mark the stack executable (i.e., pages of the stack have permissions in the GPT allowing execution) for a particular guest process 240, the virtualization layer 310 may render the stack non-executable (i.e., the pages of the stack have permissions in the NPT preventing execution) in host mode for that process. Alternatively, if the guest operating system kernel marks certain code pages 710aa of the process as writeable (e.g., permissions 815aa), the virtualization layer 310 may write protect those pages (i.e., mark the pages non-writable in permissions 825aa) in host mode. Although the protection profile 830a,b may apply different permissions (restrictions) for different instances of the guest process 240a,b, it is possible to apply similar restrictions for all instances of the process (e.g., a same protection profile enforcing identical permissions 825 of NPT 430). Note that whereas GPT permissions 815aa,ba may be associated with the GPT 410a,b for each guest process 240a,b along with a virtual control register value (i.e., root pointer to the respective GPT), the NPT 430a may be associated with a memory view (micro-VM) of the virtual machine (e.g., the VM) running the guest operating system so that the NPT permissions 725aa,ba may be applied to the NPT 430a of a nested page table hierarchy.
As noted, certain events or activities, e.g., attempted access to kernel resources, of a guest process 240 may be treated as interception points that allow the virtualization layer 310 to further monitor or instrument the process using a spawned micro-VM. In an embodiment, a hyper-breakpoint may be employed in connection with the protection profile to trigger an interception point. For example, upon activation of the guest process in the guest operating system, a hyper-breakpoint may be inserted in a code page 710 at an entry location (address) of a certain function, e.g., to check if the stack is intact or if a function is being called correctly from the proper address. If insertion of the breakpoint in the code page is detected, an attacker may refrain from any malicious activity, which is desirable as it deters that activity. However, if the hyper-breakpoint is not detected, the guest process protection technique described herein may employ the protection profile for the guest process to specify restrictions to be applied to the nested page table 430 when the process is active. For example, the virtualization layer 310 may modify the nested page table 430 to render the code page 710 execute-only, but not readable nor writeable, and insert a hyper-breakpoint in the page. When accessing the page, the guest process (or a version thereof that is compromised by an attacker) may traverse the hyper-breakpoint, which triggers an exit or switch to the virtualization layer. In particular, when the compromised process attempts to read the page, e.g., to detect whether it has been modified or instrumented, an interception point, such as a trap (e.g., NPT violation), may be invoked into the virtualization layer 310.
Upon trapping, the virtualization layer 310 may proceed in accordance with one or more options. One option may be to undo the breakpoint, restore the original content of the code page 710 and allow the compromised guest process to read the original content. The attacker may then determine that the content of the page is as expected and proceed accordingly. A second option may be to leave the page execute-only and emulate the effects of the read access (instruction) using, e.g., the instruction emulator of the guest monitor 352 for device accesses. Software emulation of the read instruction may obviate native execution of the instruction on the CPU 210, but may also allow the virtualization layer 310 to simulate the original content of the code location (i.e., return the original content as a result for the read of the location), thereby masking the hyper-breakpoint from the guest mode. For both options, the attacker may observe the expected value, while the hyper-breakpoint remains invisible to the guest process (or other processes) within the guest operating system (i.e., in guest mode).
In another embodiment, the hyper-breakpoint may be used in a situation where certain processes are activated. Here, the breakpoint may be applied not only in a user-space code section of the process (i.e., guest mode ring 3) but also in kernel-space (i.e., guest mode ring 0) to determine whether a guest process is calling certain APIs. For example, assume that the guest process 240 is not expected to access the network, e.g., via network interface 260. The virtualization layer 310 may insert a hyper-breakpoint on all systems calls to the guest operating system kernel 230 that have network-related functionality. If the process exhibits deviant (i.e., anomalous or malicious) behavior and attempts to access the network interface 260, the virtualization layer 310 may observe the process 240 issuing a system call related to the network and may classify this access as suspicious and, thus, respond accordingly.
The protection profile may also be used to protect certain properties of a guest process. Assume the in-guest component, i.e., the agent 360, is configured to call into and inform the virtualization layer 310 when a suspicious guest process 240 is activated (switched) in the guest operating system so that the virtualization layer can monitor the process. The agent 360 may also be configured to notify the virtualization layer when the guest process 240 is terminated or destroyed so that the virtualization layer can stop monitoring the process. However, an attacker could compromise the agent 360 and replace the call to the virtualization layer with other code that avoids announcing the process as suspicious, thereby evading detection. In other words, the attacker could modify the agent code in such a way that a process created by the attacker is not announced to the virtualization layer 310. However, such evasion may be innocuous because once the process is created and activated, a resulting change to the virtual control register (CR3) value may be detected by the virtualization layer. Nevertheless the attacker could further modify the agent code to inform the virtualization layer that the guest process associated with a particular CR3 value is benign so that the virtualization layer would only apply minimal protection and monitoring of the process. Thus, there is need to protect the agent against tampering, illustratively through use of the protection profile 830.
In an embodiment, the agent 360 may identify itself, e.g., upon initialization or startup in the guest operating system by issuing a call into the virtualization layer 310. In response, the virtualization layer may confirm the identity of the agent by comparing a hash value 730 of the entire code section 740 (executable code pages 710) of the agent with an expected hash value of that code section (i.e., a hash of all code pages of the agent). Once the identity of the agent is confirmed (thus indicating that the code is authentic and unmodified), the virtualization layer 310 may apply a protection profile 830 to the agent code that protects all of the code pages 710 of the agent 360 against modification by, e.g., rendering the pages execute-only. As a result, an attacker in the guest operating system is unable to write to those code pages, even though the guest page tables 410 may grant the pages write permission or the attacker may elevate the permissions to grant such write permission in the guest operating system. In other words, the nested page tables 430 would still enforce the protection profile that renders the pages write-protected, thus obviating the ability of the attacker to modify the agent code. Note that even if an attacker made a copy of the agent, e.g., prior to confirming the agent, that copy would include the same code with the same hash value and exhibit the same expected behavior, so the identity of the agent can be equally confirmed.
In another embodiment, the protection profile may be used to render a guest process (e.g., the agent process) visible when active, but invisible when inactive. Illustratively, in response to detecting a context switch to the agent process, the virtualization layer 310 marks the nested page table 430 to render the agent code pages readable and certain agent data structures writeable. Moreover, in response to detecting a context switch away from the agent, the nested page table 430 may be marked to render all of the agent code pages completely invisible, i.e., remove read, write and execute permissions in the NPT for those code pages. Thus, when inactive on a processor core, the agent's code pages appear “unplugged” from a main memory perspective, i.e., the pages seem to be not resident in memory 220. When the guest operating system switches back to the agent, the code pages may be made to reappear by again altering permissions (now allowing access) for those code pages in the NPT. Note that permissions for the code pages in the GPT, which is subject to attack in the guest mode, need not be altered other than pages used to translate access to the code pages themselves (i.e., pages storing portions of the GPT translating addresses of the code pages).
It should be noted that the agent 360 is an example of a unique guest process running in the guest operating system that cooperates with and is controlled by the virtualization layer 310. The unique guest process may be protected by altering the permissions of its pages (i.e., in the NPT) at the virtualization layer (micro-hypervisor) level between the time when the process is swapped into memory for execution (e.g., the pages are marked writeable and executable) and when the process is swapped out of memory (e.g., the pages are marked read-only or even rendered invisible by preventing all access) in order to protect the guest process against nefarious behavior in the guest operating system. Also the type of protection specified (and applied) by the protection profile 830 may vary depending on a desired level of security. That is, to protect the integrity of the unique guest process, it would be sufficient to render the pages write protected, which may allow an attacker to read the content of the pages. However, to also protect the confidentiality of the guest process, the pages would be rendered invisible to protect against reading of their content by the attacker.
Yet, the guest process protection technique described herein may be extended to apply the protection profile 830 to an arbitrary guest process 240 executing in the guest operating system. For example, the virtualization layer 310 may apply a protection profile to such a guest process wherein its code pages 710 are always render non-writable. Thus, if an attacker wants to modify code and the pages are not writable, the attacker cannot alter the code. In addition, the guest operating system may load a guest process into memory, at which point its memory pages 660 may be writeable. Once loaded into the memory pages, the virtualization layer 310 may employ the nested page table 430 to render the code pages 710 executable but without write permission, i.e., the pages are executable but the code in those pages are not alterable. Assume now that an attacker wants to modify the code of the guest process. Since the code is protected against writes, the attacker cannot modify the code because any writes attempted to those code pages 710 will result in a (NPT) page fault. Assume further that the attacker has guest mode kernel privileges in the guest operating system and, as such, adds write permission to the guest page table 410 for the code pages 710 of that guest process 240 to thereby allow the attacker to write to those code pages. Even in this scenario, the virtualization layer 310 may override the write permission in the GPT for those pages using the layered permissions in the nested page table 430. In another scenario, assume the attacker adds new code or data pages (as opposed to modifying existing permissions to the guest page table for the code pages). In this other scenario, the virtualization layer may detect additions to the GPT and again override any write permission in the GPT for those pages using the layered permissions in the nested page table. As such, the guest process protection technique may protect against: (i) pages being removed, (ii) pages being added; (iii) page permissions being modified; and (iv) translations (i.e., GPT address translations) being modified. Note that the technique may also be extended to protect equally guest operating system data structures in guest-physical memory.
In an embodiment, the protection profile 830 may apply to a guest process that is performance critical, wherein interception of any events for that process is not allowed. Accordingly, when the guest operating system kernel 230 switches to that guest process, the protection profile may specify that the virtualization layer 310 disable all intercepts and not apply any additional protection. Such a protection profile 830 may be part of a platform policy that extends from the appliance 200M to the endpoint 200E, similar to virus signatures that define policy which specifies actions for specific processes. Note that the policy (and protection profile) could change at run-time. For example, if many false positives are generated for a particular guest process 240 because the protection profile is sub-optimal, that protection profile could be updated (refined) and the updated profile distributed to all endpoints 200E to reduce the occurrence of false positives. Distribution of protection profiles may be further extended to updated policies defined for particular guest processes 240 that may be attacked by, e.g., a newly discovered exploit. The policy updates pushed to the endpoints 200E may specify that, for a particular application created as a guest process at the endpoints, a particular memory location targeted by the new exploit should be protected and, in response to a write request to that location, a specified action should be performed.
The guest process protection technique described herein generally requires precision in the protection profiles 830 applied to memory pages 660 because over-protection of a guest process 240 in the guest operating system may cause a plurality of traps to the virtualization layer 310, many of which may be false positives. For example, if a data page (rather than a code page) of a guest process is write-protected, then any legitimate writing of data in the process will trap to the virtualization layer, forcing the micro-hypervisor 320 to determine whether the access is allowable (a legitimate write) or not (a malicious write). However, such determinations are generally not performed efficiently. It is thus desirable to distinguish between data pages and code pages, and protect only the code pages 710 against writing (because writing to the data pages may be legitimate). Yet, the guest process protection technique is sufficiently flexible to render data pages write-protected for a particular guest process 240 and not for another, thus allowing the virtualization layer 310 on a per-process basis to sort data page writes and determine which of them are legitimate and which are malicious.
In order to make the protection of a guest process effective and complete, it may not be sufficient to just protect certain memory pages 660 via the CPU 210 (i.e., MMU 215) against modification by an attacker; other hardware may independently access and modify the memory (e.g., device 270 via I/O transactions to main memory 220). In an embodiment, upon making one or more memory pages write-protected at the nested page tables 430 of the MMU 215, the virtualization layer 310 may also render the pages write-protected at the IOMMU 255 so that an attacker is also unable to write to the page via a direct memory access (DMA) transaction. In general, the IOMMU 255 only allows read and write permissions for a device 270; thus the attacker cannot execute code from the device, although it can read and write a page in main memory 220. Assume the nested page table 430 is modified to mark a code page 710 with read and execute permissions (i.e., but not write permission), such that the attacker can execute the code page on the CPU 210, but cannot write to the code page 710 from the CPU. However, the attacker could configure the device 270 (or a system DMA controller) to issue a DMA transaction to write to the page 710 from the device 270 whose control it may have co-opted. Marking the code page 710 read-only in the IOMMU 255 would close such an attack avenue. Similarly, the page 710 may be marked non-readable in the IOMMU 255 to protect the page against reads for confidentiality purposes, i.e., to prevent the attacker from reading that page via a DMA transaction.
Advantageously, the guest process protection technique provides protection at the granularity of code pages (or sub-pages) for a guest process running in a guest operating system. To that end, the virtualization layer (including the micro-hypervisor) may monitor the switching of the guest page table hierarchy in the guest operating system kernel to determine when the guest process executes and then may identify the guest process through hashing of its code pages. The virtualization layer may thereafter utilize the nested page table hierarchy to apply protections for the process at the granularity of code pages (or sub-pages), as opposed to protecting a general address space of the entire guest operating system kernel. In other words, the technique enables identification of a particular process and application of a protection profile to that process alone.
While there have been shown and described illustrative embodiments for protecting a guest process of a guest operating system using a virtualization layer executing on a node of a network environment, it is to be understood that various other adaptations and modifications may be made within the spirit and scope of the embodiments herein. For example, embodiments have been shown and described herein with relation to deployment of the virtualization architecture 300 in endpoint 200E of network 130. However, the embodiments in their broader sense are not so limited, and may, in fact, provide for deployment of the virtualization architecture 300 in an appliance, such as MDS appliance 200M, of the network. In such a deployment, the virtualization layer 310 of the architecture may include the micro-hypervisor 320 and hyper-processes 350 described herein. However, instead of one or more micro-VMs, the virtualization architecture may employ one or more full VMs, wherein each VM may run a guest operating system (kernel and guest processes) associated with a guest monitor 352 and thread protection component 354. The use of a separate guest monitor 352 per VM isolates any error in the virtualization functionality that could be exploited by malware (triggered by an attacker) running in the VM to only the protection domain of the guest monitor, thereby preventing spread of the malware and obviating any performance impact on the other VMs. In addition, use of a separate threat protection component 354 for each VM facilitates use of different guest operating systems having different structures and organizations.
Moreover, the embodiments described herein may extend the guest process protection technique to allow protection of certain kernel data structures. For example, assume the virtualization layer is aware of the location of a run queue data structure of the guest operating system. The virtualization layer may write-protect that data structure to observe when changes occur to the run queue, such as writes that add a process or delete a process. However, there may again be a need to distinguish between legitimate and malicious writes. Furthermore, the virtualization layer 310 may protect a memory page containing the PCB 235 for a guest process 240 to observe an attempt to elevate privileges by modifying, e.g., user credentials. By protecting the page, the virtualization layer can observe accesses to the page and emulate any legitimate (permitted) accesses.
The foregoing description has been directed to specific embodiments. It will be apparent, however, that other variations and modifications may be made to the described embodiments, with the attainment of some or all of their advantages. For instance, it is expressly contemplated that the components and/or elements described herein can be implemented as software encoded on a tangible (non-transitory) computer-readable medium (e.g., disks, electronic memory, and/or CDs) having program instructions executing on a computer, hardware, firmware, or a combination thereof. Moreover, the embodiments or aspects thereof can be implemented in hardware, firmware, software, or a combination thereof. In the foregoing description, for example, in certain situations, terms such as “engine,” “component” and “logic” are representative of hardware, firmware and/or software that is configured to perform one or more functions. As hardware, engine (or component/logic) may include circuitry having data processing or storage functionality. Examples of such circuitry may include, but is not limited or restricted to a microprocessor, one or more processor cores, a programmable gate array, a microcontroller, an application specific integrated circuit, semiconductor memory, or combinatorial logic. Accordingly this description is to be taken only by way of example and not to otherwise limit the scope of the embodiments herein. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the embodiments herein.
The present application claims priority from commonly owned Provisional Patent Application No. 62/265,751, entitled TECHNIQUE FOR PROTECTING GUEST PROCESSES USING A LAYERED VIRTUALIZATION ARCHITECTURE, filed on Dec. 10, 2015, the contents of which are incorporated herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 62265751 | Dec 2015 | US |
