Hypervisor-based, hardware-assisted system monitoring

Carsten Willems Ruhr University Bochum
Ralf Hund Ruhr University Bochum

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In the last few years, many different techniques have been introduced to analyse malicious binary executables. Most of these techniques take advantage of Virtual Machine Introspection (VMI), the process of analysing the state of a virtual machine from the outside. On the one hand, many approaches are based on system emulators which enable a tight control over the program execution. Unfortunately, such approaches typically induce a huge performance overhead. On the other hand, there are approaches based on hypervisors. Early implementations were hampered by the missing virtualizability of the x86 instruction set architecture: since the memory management unit (MMU) itself was not virtualized, memory separation needed to be enforced in software with the help of so-called 'shadow page' tables, an approach that again induced performance overhead. However, processor vendors have recently added hardware support for MMU virtualization, and modern CPUs offer so-called 'two-dimensional paging' to overcome such performance bottlenecks.

In our presentation we demonstrate how this processor feature can be utilized to implement a binary analysis framework. More specifically, we introduce an approach to monitor code execution based on the concept of Currently eXecutable Pages (CXP), i.e. we precisely control which memory pages are currently executable to enable the interception of intermodular function calls and their corresponding returns. When an interception occurs, we apply VMI to deduce runtime information such as function parameters. To demonstrate the practical feasibility of the proposed approach, we implemented 'VMMInspector', a framework for binary analysis on 64-bit machines and Windows 7. In several case studies we present different usage scenarios for that framework. Amongst other applications, we demonstrate how the kernel rootkit TDSS/TDL4 can be analysed in an automated way.

VB2013 takes place 2-4 October 2013 in Berlin, Germany.

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