Verifying Safety for Resilient Cyber-Physical Systems via Reactive Software Restart

Resilient cyber-physical systems (CPS) must ensure safety and per-form required tasks in the presence of malicious cyber attacks. Recently, restart-based defenses have been proposed in which a CPS mitigates attacks by reverting to an initial safe state. In this paper, we consider a class of reactive restart approaches for CPS under malicious attacks with verifiable safety guarantees. We consider a setting where the controllers are engineered to crash and reboot following faults or attacks. We present a hybrid system model that captures the trade-off between security, availability, and safety of the CPS due to the reactive restart. We develop sufficient conditions under which an affine controller provides verifiable safety guar-antees for the physical plant using a barrier certificate approach. We synthesize safety-critical controllers using control barrier functions to guarantee system safety under given timing parameters. We present two case studies on the proposed approach using a warehouse temperature control system and a two-dimensional non-linear system. Our proposed approach guarantees the safety for both cases.