  The deterministic (timing) behavior of real-time systems (RTS) can be used by
adversaries - say, to launch side channel attacks or even destabilize the
system by denying access to critical resources. We propose a protocol (named
REORDER) to obfuscate this predictable timing behavior of RTS, especially ones
designed using dynamic-priority scheduling algorithms (e.g., EDF). We also
present a metric (named "schedule entropy") that measures the levels of
obfuscation introduced into a given real-time system. The REORDER protocol was
integrated into the standard Linux real-time scheduler and evaluated on a
realistic embedded platform (Raspberry Pi) running the MiBench automotive
benchmark workloads. We also demonstrate how designers of RTS can increase the
security of their systems and also quantitatively measure the impact (both in
terms of security and performance) of using this protocol.
