TimeDice: Schedulability-Preserving Priority Inversion for Mitigating Covert Timing Channels Between Real-time Partitions

Timing predictability is a precondition for successful communication over a covert timing channel. Real-time systems are particularly vulnerable to timing channels because real-time applications can easily have temporal locality due to limited uncertainty in schedules. In this paper, we show that real-time applications can create hidden information flow even when the temporal isolation among the time partitions is strictly enforced. We then introduce an online algorithm that randomizes time-partition schedules to reduce the temporal locality, while guaranteeing the schedulability of, and thus the temporal isolation among, time partitions. We also present an analysis of the cost of the randomization on the responsiveness of real-time tasks. From an implementation on a Linux-based real-time operating system, we validate the analysis and evaluate the scheduling overhead as well as the impact on an experimental real-time system.