Facing the Safety-Security Gap in RTES: the Challenge of Timeliness

Safety-critical real-time systems, including real-time cyber-physical and industrial control systems, need not be solely correct but also timely. Untimely (stale) results may have severe consequences that could render the control system’s behaviour hazardous to the physical world. To ensure predictability and timeliness, developers follow a rigorous process, which essentially ensures real-time properties a priori, in all but the most unlikely combinations of circumstances. However, we have seen the complexity of both real-time applications, and the environments they run on, increase. If this is matched with the also increasing sophistication of attacks mounted to RTES systems, the case for ensuring both safety and security through aprioristic predictability loses traction, and presents an opportunity, which we take in this paper, for discussing current practices of critical realtime system design. To this end, with a slant on low-level task scheduling, we first investigate the challenges and opportunities for anticipating successful attacks on real-time systems. Then, we propose ways for adapting traditional fault- and intrusiontolerant mechanisms to tolerate such hazards. We found that tasks which typically execute as analyzed under accidental faults, may exhibit fundamentally different behavior when compromised by malicious attacks, even with interference enforcement in place