ES-FUZZ: Improving the Coverage of Firmware Fuzzing with Stateful and Adaptable MMIO Models

Grey-box fuzzing is widely used for testing embedded systems (ESes). The fuzzers often test the ES firmware in a fully emulated environment without real peripherals. To achieve decent code coverage, some state-of-the-art (SOTA) fuzzers infer the memory-mapped I/O (MMIO) behavior of peripherals from the firmware binary. We find the thus-generated MMIO models stateless, fixed, and poor at handling ES firmware's MMIO reads for retrieval of a data chunk. This leaves ample room for improving the code coverage.