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MAVMM: Lightweight and Purpose Built VMM for Malware Analysis

MAVMM: Lightweight and Purpose Built VMM for Malware Analysis. Yang Feng Jan 6 th 2011. Outline. Introduction Design Implementation Evaluation Conclusion. Introduction. Traditional tools: Disassembling Dynamic black box analysis Debugging Virtualization Technology

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MAVMM: Lightweight and Purpose Built VMM for Malware Analysis

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  1. MAVMM: Lightweight and Purpose Built VMM for Malware Analysis Yang Feng Jan 6th 2011

  2. Outline • Introduction • Design • Implementation • Evaluation • Conclusion

  3. Introduction • Traditional tools: • Disassembling • Dynamic black box analysis • Debugging • Virtualization Technology • Strong isolation, take snapshots and roll back the guest’s state • Monitor virtual machine based rootkits

  4. Introduction • Virtualization Technology • Evade detection and prevent analysis • Side channels, artifacts of platform • General purpose VMM is not suitable for malware analysis • Designed for functionality and performance • Complexity virtual device emulation, expose many vulnerabilities

  5. Introduction • MAVMM • A VMM focus on malware analysis • Hardware-support for virtualization • Keep VMM small and simple • Smaller TCB(trusted computing base) • Function: execution trace, memory dump, system call, disk access and network interaction • Detectability

  6. Design • Independent of virtualization platform and guest operating system • Use hardware virtualization technology • Faster virtualization performance • Simplify VMM implementation • Advantage: • Additional CPU mode for hypervisor • Nested paging-Memory virtualization • Address space identifiers(ASID)-reduce TLB switches • IOMMU-I/O virtualization • Event interception and injection-Instruction virtualization

  7. Design • Special Purpose Hypervisor • Thin and lean->simplicity->transparency and security • Xen, KVM or VMware: too complex->bugs General purpose VMM MAVMM

  8. Design • Boot-strapping the Hypervisor • Start earlier and run at a higher CPU privilege level • Two options: • Boot directly from a boot loader (*) -> small and simple • Run on top of or alongside a host OS • Protecting Hypervisor Memory • Nested paging table(NPT) <-> EPT • input/output memory management unit(IOMMU) <-> VT-d

  9. Design • Feature Extraction • Execution trace -> run-time debugger • TF flag in rflags register, set it to 1 • Memory page • Fetch guest pointers from memory • Guest logical address -> host physical address • Segmentation unit and paging unit, with the help of NPT • System calls • Network and disk access -> system calls

  10. Design • Getting analysis data • Use the same hard disk • Use a separated hard disk • Use an USB flash drive • Use a system port such as serial port • Selective analysis • Compact mode: keep activated a few interceptions • Full mode: all features mentioned • Monitor specific processes: processes list, intercept write to paging base pointer(CR3 register) • Track sub-processes: system call tracing • -> minimize detectability -> bios service or simple driver

  11. Implementation • Use AMD SVM technology • Started with TVMM • http://venus.is.s.u-tokyo.ac.jp/~kaneda/tvmm/ • NPT, IOMMU, AMD Simnow

  12. Implementation • Boot-strapping • Use grub boot loader • Grub starts -> MAVMM -> Grub • Why not MAVMM load the guest OS directly? • Initialize the booting environment expected by Guest OS • Be sure it’s not overwrite the guest OS image • Too complicated • Set initial instruction pointer address of the guest to 0x7c00: • 0x7c00: beginning address of loaded master boot record

  13. Implementation • Protecting Hypervisor Memory • Create NPT and fill with ID mapping • NP fault exception, handle the fault and hide • Use an external USB drive to virtualize VMM region • Hide query of the USB port • Use Device Exclusion Vector(DEV) to protect VMM from being affected by external device DMA

  14. Implementation • Feature Extraction • System call • int 0x80 or sysenter • iret or sysexit • For int 0x80: use control bit in VMCB, read EAX register • Using iret interception with thread ID mapping to handle some system call (useful data is after handler) • For sysenter: modify index in SYSENTER_CS_MSR to point to some unmapped segment -> #GP fault

  15. Implementation • Feature Extraction • Network and File Access • Network: • sys_socketcall -> func and args -> EBX & ECX • sockaddr_in structure • Record IP addresses, port number and data • File • sys_read and sys_write • Mapping from descriptor numbers of opened files to pathnames • sys_open and sys_close

  16. Implementation • Feature Extraction • Getting Analysis Data • Bind a virtual serial port in Simnow to a real port on Host • External USB drive -> hiding device and I/O access mechanism • Selective Analysis • Using a guest program mavmm-u and VMMCALL instructions • Compact mode and full mode • Remove binary file and its existence before executing malware

  17. Implementation • Transparent Event Forwarding • Track system call, no hardware virtualization support • Intercept iret instruction and modification of CR3 • Set TF flag to 1 in rflags register -> DB fault • Works well for most interceptions except interrupt and exception • Forwarding these two events already supported

  18. Evaluation • In AMD Simnow simulator • Simulate a machine with 900MHz processor and 256MB of RAM • Run Simnow on 2.4GHz Intel Core 2 CPU with 2.5GB RAM • On x86_64 Ubuntu Linux 8.04 • Kernel 2.6.24-24

  19. Evaluation • Functionality • Fine-grained tracking • A simple “Hello world” program

  20. Evaluation • Functionality • High-level tracking • Monitor the booting process of tty Linux 8.0 -> 21953 system calls • Rootkit.Linux.Agent.30.Chsh

  21. Evaluation • Detectability • Red Pill: sensitive but not-privileged instruction • Local descriptor tables register check • VMWare I/O Channel • Virtual PC Special Inst. • Machine state word check • Xen CPUID Check

  22. Evaluation • Security • About TLB profiling attack • MAVMM does not support multiple guest VM instances • Smaller, fewer TLB entries written • About external timing attack • Complex and expensive • Root privilege, huge amount of CPU cycles, an external timing source and prior knowledge about target system • About trusted computing base

  23. Evaluation • Performance Overhead • Compact mode and full mode, outside hypervisor • Each program five times and show average • Future: switch to USB logging, batch data dumps

  24. Conclusion • A lightweight VMM designed specially for malware analysis • Hardware virtualization support • Simplicity, security and transparency • Extract useful information • Easy to add new functions

  25. Thanks!

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