June 20, 2021

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Examiner: Automatically Locating Inconsistent Instructions Between Real Devices and CPU Emulators for ARM. (arXiv:2105.14273v1 [cs.CR])

Emulator is widely used to build dynamic analysis frameworks due to its
fine-grained tracing capability, full system monitoring functionality, and
scalability of running on different operating systemsand architectures.
However, whether the emulator is consistent with real devices is unknown. To
understand this problem, we aim to automatically locate inconsistent
instructions, which behave differently between emulators and real devices.

We target ARM architecture, which provides machine readable specification.
Based on the specification, we propose a test case generator by designing and
implementing the first symbolic execution engine for ARM architecture
specification language (ASL). We generate 2,774,649 representative instruction
streams and conduct differential testing with these instruction streams between
four ARM real devices in different architecture versions (i.e., ARMv5, ARMv6,
ARMv7-a, and ARMv8-a) and the state-of-the-art emulators (i.e., QEMU). We
locate 155,642 inconsistent instruction streams, which cover 30% of all
instruction encodings and 47.8% of the instructions. We find undefined
implementation in ARM manual and implementation bugs of QEMU are the major
causes of inconsistencies. Furthermore, we discover four QEMU bugs, which are
confirmed and patched by thedevelopers, covering 13 instruction encodings
including the most commonly used ones (e.g.,STR,BLX). With the inconsistent
instructions, we build three security applications and demonstrate
thecapability of these instructions on detecting emulators, anti-emulation, and
anti-fuzzing.