The last mile: An empirical study of timing channels on seL4

Abstract

Storage channels can be provably eliminated in well-designed, highassurance kernels. Timing channels remain the last mile for confidentiality and are still beyond the reach of formal analysis, so must be dealt with empirically. We perform such an analysis, collecting a large data set (2,000 hours of observations) for two representative timing channels, the locally-exploitable cache channel and a remote exploit of OpenSSL execution timing, on the verified seL4 microkernel. We also evaluate the effectiveness, in bandwidth reduction, of a number of black-box mitigation techniques (cache colouring, instruction-based scheduling and deterministic delivery of server responses) across a number of ha..