HFL: Hardware Fuzzing Loop with Reinforcement Learning

As hardware systems grow increasingly complex, ensuring their security becomes more critical. This complexity often introduces difficult and costly vulnerabilities to address after fabrication. Traditional verification methods, such as formal and dynamic approaches, encounter limitations in scalability and efficiency when applied to complex hardware designs. While hardware fuzzing presents a promising solution for efficient and effective vulnerability detection, current methods face several challenges, including coverage saturation, long simulation times, and limited vulnerability detection capabilities. This paper introduces Hardware Fuzzing Loop (HFL), a novel fuzzing framework designed to address these limitations. We demonstrate that Long Short-Term Memory (LSTM), a machine learning model commonly used in natural language processing, can effectively capture the semantics of test cases and accurately predict hardware coverage. Building on this insight, we leverage reinforcement learning to optimize the test generation strategy dynamically within a hardware fuzzing loop. Our approach utilizes a multi-head LSTM to generate sophisticated RISC-V assembly instruction sequences, along with an LSTM-based predictor that evaluates the quality of these instructions. By dynamically interacting with the hardware, HFL efficiently explores complex instruction sequences with minimal fuzzing iterations, allowing it to uncover hard-to-detect vulnerabilities. We evaluated HFL on three RISC-V cores, and the results show that it achieves higher coverage using fewer than 1% of the test cases required by leading hardware fuzzers, effectively mitigating the issue of coverage saturation. Furthermore, HFL identified all known vulnerabilities in the tested systems and discovered four previously unknown high-severity issues, demonstrating its significant potential in improving hardware security assessments.