Orpheus: Enforcing Cyber-Physical Execution Semantics to Defend Against Data-Oriented Attacks

Recent studies have revealed that control programs running on embedded devices suffer from both control-oriented attacks (e.g., code-injection or code-reuse attacks) and data-oriented attacks (e.g., non-control data attacks). Unfortunately, existing detection mechanisms are insufficient to detect runtime data-oriented exploits, due to the lack of runtime execution semantics checking. In this work, we propose Orpheus, a security methodology for defending against data-oriented attacks by enforcing cyber-physical execution semantics. We address several challenges in reasoning cyber-physical execution semantics of a control program, including the event identification and dependence analysis. As an instantiation of Orpheus, we present a new program behavior model, i.e., the event-aware finite-state automaton (eFSA). eFSA takes advantage of the event-driven nature of control programs and incorporates event checking in anomaly detection. It detects data-oriented exploits if physical events and eFSA's state transitions are inconsistent. We evaluate our prototype's performance by conducting case studies under data-oriented attacks. Results show that eFSA can successfully detect different runtime attacks. Our prototype on Raspberry Pi incurs a low overhead, taking 0.0001s for each state transition integrity checking, and 0.063s~0.211s for the cyber-physical contextual consistency checking.