Zero footprint guest memory introspection from xen
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The document discusses advancements in memory introspection for virtual machines, particularly focusing on enhancing security against sophisticated malware like rootkits and cyber-espionage. It highlights the limitations of traditional in-guest security solutions and advocates for out-of-guest memory introspection using hypervisor capabilities, specifically within the Xen framework. The presentation outlines various improvements, including hardware acceleration and the implementation of the memory events API, to provide a more robust security architecture with zero in-guest footprint.
![www.bitdefender.com 5/12/2015• 17
XenAccess and mem-events
enhancements
• 2014 – Bitdefender published a set of patches (as RFC) to enhance
the mem-events API
o implements its own version of LibVMI
o simpler API
o nothing [guest] OS specific
o support for other HV-s can be added
o allows to map guest memory (via EPT)
o uses a very simple page cache to optimize (un)maps
o optimized access to specific resources
• Some patches went into mainline, others will follow shortly](https://image.slidesharecdn.com/zero-footprintguestmemoryintrospectionfromxen-150512131105-lva1-app6891/85/Zero-footprint-guest-memory-introspection-from-xen-17-320.jpg)
Zero footprint guest memory introspection from xen
- 1. www.bitdefender.com 5/12/2015• 1 Zero-Footprint Guest Memory Introspection from Xen Xen Project DEVELOPER SUMMIT August 18th, 2014 Mihai DONȚU – Technical Project Manager, Bitdefender Ravi SAHITA – Principal Engineer, Intel Improving VM Introspection Using Hardware Virtualization Extensions
- 2. www.bitdefender.com 5/12/2015• 2 Outline • Security issues • Memory introspection o Operation o Evolution • XenAccess and mem-events enhancements • Sample usages • Hardware Acceleration for memory introspection • Conclusions
- 3. www.bitdefender.com 5/12/2015• 3 Security issues we are facing today • Advanced malware types o Rootkits o Kernel exploits o Zero-days • APTs, botnets, cyber-espionage and so on heavily rely on those…
- 4. www.bitdefender.com 5/12/2015• 4 Security issues we are facing today 2
- 5. www.bitdefender.com 5/12/2015• 5 Security issues we are facing today 3 Malware today execute in the same context and with the same privileges as anti-malware software lack of isolation problem Common Malware Advanced Malware Drivers App1 (Office) OS Kernel ISOLATION Kernel Controlled App2 (Browser) Security Solution Security Filter Drivers App1 (Office) OS Kernel App2 (Browser) Security Solution Security Filter ISOLATION Kernel Controlled Isolation Bypassed & Malware Controlled
- 6. www.bitdefender.com 5/12/2015• 6 Conclusion: advanced attacks evade traditional security solutions
- 7. www.bitdefender.com 5/12/2015• 7 Envision the big picture so… what’s the big difference?... Xen Hypervisor dom0 SVA (domU0) domU1Memory Introspection Engine domU2 domUN Protected area
- 8. www.bitdefender.com 5/12/2015• 8 Memory introspection Envision the big picture Xen Hypervisor dom0 SVA (domU0) domU1Memory Introspection Engine domU2 domUN Protected area Hypervisor Controlled, Hardware Enforced STRONG ISOLATION Introspection Engine Alternative 2 Introspection Engine Alternative 3
- 9. www.bitdefender.com 5/12/2015• 9 • Address a number of security issues from outside the guest OS without relying on functionality that can be rendered unreliable by advanced malware • Analyze raw memory image of guest OS, services and user mode applications, then identify o kernel memory areas o driver objects, driver code, IDT, etc. o user memory areas o process code, process stack, process heap, etc. What is memory introspection? Envision the big picture
- 10. www.bitdefender.com 5/12/2015• 10 • Use existent hardware virtualization extensions (Intel EPT / AMD RVI) • Set hooks on guest OS memory o mark 4K pages as non-execute or non-writable o hooking & notification must be supported efficiently by HV & CPU • Audit access of those areas by the code running in VM (OS or apps) o write attempts (driver objects, fast I/O tables, page tables) o execution attempts • Allow or deny attempts – decision provided by security logic How does it work? Memory introspection
- 11. www.bitdefender.com 5/12/2015• 11 How does it work? 2 Memory introspection EPT protected areas provide detection for various OS level changes (ex. new module load, new process start, …) EPT protected areas provide detection for attempts & protection against integrity violation Guest VM Physical Memory Space OS kernel code kernel driver code and data kernel data SSDT, IDT, … user mode code user mode stacks & heaps
- 12. www.bitdefender.com 5/12/2015• 12 • Building a reliable image of the guest OS state o what objects are inside a guest VM? o what operations are being performed inside a guest VM? o object and event identification and correlation is done by the introspection engine – to decide event and object maliciousness • Using hooks we can detect numerous events, including o a driver / kernel module is loaded or unloaded o a new user process or thread is created o user stack / heap is allocated o memory is being paged in / out How does it work? 3 Memory introspection
- 13. www.bitdefender.com 5/12/2015• 13 How does it work? 4 Memory introspection Traditional in-guest security solution Out-of-guest memory introspection OSKernel TypicalAnti-MalwareKernelModule Read mem by Virtual Addr, read files, registry, … Enum processes, files, … 01010 10011 MZ… Setup well-known callbacks & notifications New process PID 0x1234 HKLM... XENHypervisor MemoryIntrospectionEngine Read mem by Physical Addr Read vCPU registers 01010 10011 Setup EPT hooks on mem pages (by Physical Addr) Write / Execute attempt on PA 0x000A12345678 RAX = 0x1234 RIP = 0x7890
- 14. www.bitdefender.com 5/12/2015• 14 • bridging the semantic gap – obtain rich semantics from only raw physical memory pages and virtual CPU registers o how do we correlate 4K memory pages with semantically rich and meaningful OS specific data structures? o to be solved by security solution vendors • forward lots of mem-event notifications with low overhead to introspection engine o to be solved by hypervisor and CPU vendors Two big challenges Memory introspection
- 15. www.bitdefender.com 5/12/2015• 15 Memory introspection evolution • 2003 – Garfinkel & Rosenblum: “A Virtual Machine Introspection Based Architecture for Intrusion Detection” o the starting point for a considerable amount of academic research • 2006 – Jiang & Wang: “’Out-of-the-box’Monitoring of VM-based High-Interaction Honeypots” • 2008 – Dinaburg et al.: “Ether: MalwareAnalysis via Hardware Virtualization Extensions” o Built on top of Xen 3.1 • 2008 – VMsafe API announced by VMware, which provides access to a guest’s: o CPU, memory, disk, I/O devices etc. o supported memory introspection for vSphere / ESXi • 2010 – VMware vShield Endpoint (as a replacement for VMsafe API) o in-guest agent based o file introspection only • 2012 – VMware deprecates VMsafe
- 16. www.bitdefender.com 5/12/2015• 16 Memory introspection in Xen • 2007 – XenAccess, XenProbes • 2008 – Lares • 2009 – first patches for the mem-events API • 2010 – LibVMI – uses XenAccess and XenStore o targets Xen, but support for other HV-s can be added o insufficient flexibility in changing page permissions o no support for mapping guest memory RW o insufficient information about the guest CPUs o high overhead when reading the vCPU register state o a ‘complete’ initialization requires intimate knowledge about the guest OS o code for handling specific guest OS-s (Windows, with Linux in the works)
- 17. www.bitdefender.com 5/12/2015• 17 XenAccess and mem-events enhancements • 2014 – Bitdefender published a set of patches (as RFC) to enhance the mem-events API o implements its own version of LibVMI o simpler API o nothing [guest] OS specific o support for other HV-s can be added o allows to map guest memory (via EPT) o uses a very simple page cache to optimize (un)maps o optimized access to specific resources • Some patches went into mainline, others will follow shortly
- 18. www.bitdefender.com 5/12/2015• 18 XenAccess and mem-events enhancements 2 mem-event notification Xen Hypervisor SVA (domU0) Memory Introspection Engine domU1 uint32_t flags; uint32_t vcpu_id; uint64_t gfn; … mem_event_regs_t regs;
- 19. www.bitdefender.com 5/12/2015• 19 Example use of the extended API Xen Hypervisor dom0 SVA (domU0) Memory Introspection Engine Protected areas Critical Kernel Module Critical Kernel Module App1 App2 …Code, stacks, heaps, IAT, … Code, stacks, heaps, IAT, … Code, stacks, heaps, IAT, … Mem-events and VMCALLs facilitated by XEN
- 20. www.bitdefender.com 5/12/2015• 20 Example use of the extended API 2 • Bitdefender’s own introspection engine can o protect the kernel from known rootkit hooking techniques o protect user processes (e.g. browsers, MS Office, Adobe Reader, …) from o code injection o function detouring o code execution from stack / heap o unpacked malicious code o inject remediation tools into the guest on-the-fly (no help from ‘within’ needed) • Runs in userspace in a user domain (SVA – Security Virtual Appliance) • Introspection logic has very small overhead o bulk of the overhead is given by sending / receiving events and calls between protected guest VMs and SVA
- 21. 21 Hardware Acceleration for Memory Introspection Ravi Sahita Intel
- 22. 22 Hardware Acceleration for Memory Introspection Factors Limiting VM Memory Monitoring Performance Addressing Lack of Memory Isolation Addressing Performance gaps for execution and data access-control policies Xen Extensions
- 23. 23 Factors Limiting VM Memory Monitoring Performance Round-trip time –Monitoring execution and data accesses –Dynamic data structures imply high frequency events Filtering events –Monitoring data accesses requires filtering non- interesting events due to 4K page sharing Further, round-trip time is amplified with VMMs nesting
- 24. 24 Multiple EPTs as Protection Domains CPU0 Hypervisor Intel® VT-x with EPT VM0 Extended Page Table (EPT) Domains EPT Walker Execution crossing EPT domains or data Accesses causing eventshost physical address Intel® Virtualization Technology for IA-32, Intel® 64 and Intel® Architecture (Intel® VT-x) OS kernel Code/data (RX/RW) Driver Code (RX) Driver Code (RO) OS kernel Code/data (RO/NP) Data (RW) Data (NP)
- 25. 25 Addressing Lack of Isolation… Xen EPT DomainsEPT Domains policy events CPU Hypervisor- derived isolation
- 26. 26 Kernel module Kernel module Security module …Without Sacrificing Performance Must allow for legal execution of components isolated in permission domains Each execution transfer across domains leads to VM exits that the hypervisor must mediate As components isolated via domains, numerous execution transfers are induced High Frequency of such VM exits to the hypervisor causes overhead Process Hypervisor Eliminate these induced VM exits on legal control transfers Legal control transfers
- 27. 27 VM Functions: Hypercalls Without VM Exits VM Functions: Intel® VT-x extensions for services configured by the hypervisor – Different VM Functions correspond to different services Hypervisor configures VM Functions via new fields in VMCS Guest software invokes VM Functions via new instruction (VMFUNC<leaf>) – Value in EAX specifies which VM Function leaf is invoked CPU provides services as configured with no VM exit Intel® Virtualization Technology for IA-32, Intel® 64 and Intel® Architecture (Intel® VT-x)
- 28. 28 VMFUNC-based Domain Switching Paravirtualized software can request protection domain switch via VMFUNC (specifying domain index) Hypervisor pre- configures domain index to EPTPs Hypervisor pre- configures domain boundaries View switching to speed up access control policies CPU0 Hypervisor Intel® VT-x with EPT VM0 Extended Page Table (EPT) domains EPT Walker VMFUNC (EPTP switch) Host physical address Aternate Extended Page Table (EPT) list Intel® Virtualization Technology for IA-32, Intel® 64 and Intel® Architecture (Intel® VT-x)
- 29. 29 Asynchronous Induced VMExits In VM-introspection scenarios critical data is monitored in place Legacy approaches are to VMExit and emulate access Alternatively, VMExit and switch views to single step the guest (MTF) High frequency of writes to monitored data cause high overhead Requires custom logic in the VMM increasing complexity/state in the hypervisor Kernel (Guest) Hypervisor EPT Domains Ring-0 Monitoring Agent Monitored Memory WRITE 2. EPT-V VMexit 3. VMResume to single step access Single Step Memory View 4. VMexit after access completed Access Policy 1. View Policies 5. VMResume EPT Domains Emulation
- 30. 30 Accelerating Induced Events Via Virtualization Exception (#VE) – Mutates EPT violations into a new IA exception – delivered through guest IDT VMM enables EPT violation conversion to #VE Data access monitoring view policies setup in EPT domains Data access causes #VE instead of VMexit Guest monitoring agent can emulate in guest OR use VMFUNC to single step access Hypervisor (VMX-root) Kernel/VMX-non-root EPT Domains Monitoring Service Monitored Memory 1. Handle #VE 3. Complete single step or emulate in guest Single Step Memory View 2. Setup single step or emulate WRITE Access Policy 1. Policies VMFUNC VMFUNC #VE #VE info VMFUNC EPT Domains
- 31. 31 VMFUNC Configuration Hypervisor checks IA32_VMX_VMFUNC MSR for allowed VM-Function controls Opts-in by setting “Enable VM functions” in the secondary processor-based VM- execution controls field Activates “EPTP switching” by setting bit-0 in the VM Function Control Configure alternate EPTP values in memory referenced via VMCS field Guest software uses VMFUNC opcode with leaf selector EAX=0 and ECX containing the index of EPTP (view) selected Errors reported to the hypervisor via VM Exits “Enable VM functions” VM- execution control (bit 13) EPTP-list address 0:Alternate-EPTP 1:Alternate-EPTP 511:Alternate-EPTP “EPTP switching” (bit 0) Secondary processor-based VM-execution controls VMFunction Control (new) In memory VMCS In VMCS (new) IA32_VMX_VMFUNC MSR (index 491H)
- 32. 32 Virtualization Exception (VE) Configuration Enumerated by the VMM via capability MSR Set VMCS “Enable VE” bit Negotiate “VE Info” page with Hypervisor #VE delivered through guest IDT Suppress VE EPTE Bit 63 – Set on pages the VMM does not want to cause a #VE for “Enable VE” VM-execution control (bit 18) VE Information Address Exit Reason Suppress Exit Qualification Secondary processor-based VM-execution controls In memory Virtual Machine Control Structure (VMCS) In VMCS (new) IA32_VMX_PROCBASED_ CTLS2 (48Bh) Bit 50 Guest Linear Address Guest Physical Address EPTP Index
- 33. 33 Xen Extensions 1. Efficiently creating and maintaining alternate EPT views/domains via extension of p2m 2. Hypercalls to edit EPT permissions without conflicting with Xen EPT management 3. Report guest-specific memory events via #VE in a Xen compatible manner (Suppress #VE EPTE bit) 4. Enabling CPU acceleration if VMFUNC and #VE CPU enumerated and opted-in Xen Hypervisor domUN domU0 Security Engine EPT DomainsEPT Domains Security Engine CPU #VE EPT DomainsEPT Domains #VE
- 34. 34 VM Introspection Performance Improvements Round-trip time – VMFUNC to allow safe, fast Memory View (EPT) switches – VMexits mutated to #VE for guest memory monitoring Filtering events – Reduced latency of #VE event handling reduces overhead of filtering events Round-trip time amplification due to VMM nesting – No VMexits to root VMM implies no amplification of VMexits due to EPT violations Scalable Runtime Memory Introspection w/o VT overheads
- 35. www.bitdefender.com 5/12/2015• 35 • Today Xen can be the base for providing a much improved layer of security – serves as a model for other HV vendors o Truly agentless security (zero in guest footprint) o IT Admins can deploy introspection based solutions seamlessly, without changing a single line of config inside the guest VMs • Hardware enforced isolation (against kernel exploits, zero days, …) • Hardware extensions enable intra-VM isolation to enable protected agent based introspection for high frequency access monitoring and agent isolation • Both models require straight-forward Xen infrastructure changes (multi-EPT views, hardware acceleration capabilities) Conclusions
- 36. www.bitdefender.com 5/12/2015• 36 Thank you! enterprise.bitdefender.com