Preemptive Real-Time Scheduling Incorporating Security Constraint for Cyber Physical Systems

Abstract

SUMMARYSince many cyber-physical systems (CPSs) manipulate security-sensitive data, enhancing the quality of security in a CPS is a critical and challenging issue in CPS design. Although there has been a large body of research on securing general purpose PCs, directly applying such techniques to a CPS can compromise the real-time property of CPSs since the timely execution of tasks in a CPS typically relies on real-time scheduling. Recognizing this property, previous works have proposed approaches to add a security constraint to the real-time properties to cope with the information leakage problem that can arise between real-time tasks with different security levels. However, conventional works have mainly focused on non-preemptive scheduling and have suggested a very naive approach for preemptive scheduling, which shows limited analytical capability. In this paper, we present a new preemptive fixed-priority scheduling algorithm incorporating a security constraint, called lowest security-level first (LSF) and its strong schedulability analysis to reduce the potential of information leakage. Our simulation results show that LSF schedulability analysis outperforms state-of-the-art FP analysis when the security constraint has reasonable timing penalties.

Incorporating Security Constraints into Mixed-Criticality Real-Time Scheduling

“…However, such approaches are dependent on the type of the shared resources and can negatively influence the execution time of task since each task could use the limited shared resource. Instead, some studies used a general flushing mechanism [2]- [4]. Whenever there is a possibility of information leakage, a function to clear the state of the shared resource is invoked, which is called FT.…”

“…Note that we assume the total order of security-levels meaning that all tasks have different securitylevels. In this paper, likewise existing studies [3], [4], we focus on the information leakage arising from τ H to τ L since the information leakage from τ L to τ H is not as critical as that from τ H to τ L and considering two directions of information leakage causes more FTs, which often results in task sets becoming unschedulable. Thus, we incorporate the following security constraint into real-time scheduling to address the information leakage problem; for any two consecutively executing tasks under any real-time scheduler, a FT to cleanse the state of shared resources should be invoked between the two tasks if the former is τ H and the latter is τ L .…”

“…A number of studies in [2]- [4] addressed the problem of information leakage that can arise on the shared resources used by real-time tasks with different security-levels in a RTS. The initial work [3] proposed the Flush Task (FT) mechanism to cleanse the state of shared resources to prevent the sensitive data on the shared resource from being gleaned by attackers.…”

“…It also proposed a real-time scheduling algorithm and a schedulability analysis that take into account the timing overhead of the FT mechanism as a security constraint. There have been following studies designed for preemptive Fixed Priority (FP) and preemptive Dynamic Priority (DP) scheduling for enhancing the timing guarantees [2], [4].…”

A Comprehensive Technological Survey on Dependable Self-Managing CPS: The Decade of Researches on Correctness and Dependability

“…E.g. energy and temporal constraints [99], fault tolerance and temporal constraints [68], security and temporal constraints [100], system and environment states and priority of tasks [101], etc. Furthermore, a recommended method of multithreading multi-agent scheduling was proposed to search the efficient and fast solution of complex problems in real-time featuring rapid dynamic changes and uncertainty [98].…”