FirmGuide: Boosting the Capability of Rehosting Embedded Linux Kernels through Model-Guided Kernel Execution

Linux kernel is widely used in embedded systems. To understand practical threats to the Linux kernel, we need to perform dynamic analysis with a full-system emulator, e.g., QEMU. However, due to hardware fragmentation, e.g., various types of peripherals, most embedded systems are not currently supported by QEMU. Though some progress has been made on rehosting firmware, it mainly focuses on user space programs or simple real-time operating systems.The goal of this work is to boost the capability of rehosting the embedded Linux kernels in QEMU. By doing so, dynamic analysis systems can be firstly applied on embedded Linux kernels by leveraging off-the-shelf tools upon QEMU. Accordingly, we proposed a new technique called model-guided kernel execution. It combines the peripheral abstractions in the Linux kernel and kernel-peripheral interactions to semi-automatically generate peripheral models that are then used to synthesize new QEMU virtual machines to start the dynamic analysis.We have implemented a prototype called FirmGuide. It generates 9 peripheral models with full functionality and 64 with minimum functionality covering 26 SoCs. Our evaluation with 6,188 firmware images shows that it can successfully rehost more than 95% of Linux kernels in 2 architectures and 22 versions. None of them can be rehosted in the vanilla QEMU. The result of the LTP benchmark shows the reliability and robustness of the rehosted Linux kernels. We further conduct two security applications, i.e., vulnerability analysis and fuzzing, on the rehosted Linux kernels to demonstrate the usage scenarios.