Symbolic Verification of Cache Side-Channel Freedom

Cache timing attacks allow third-party observers to retrieve sensitive information from program executions. But, is it possible to automatically check the vulnerability of a program against cache timing attacks and then, automatically shield program executions against these attacks? For a given program, a cache configuration and an attack model, our CacheFix framework either verifies the cache side-channel freedom of the program or synthesizes a series of patches to ensure cache side-channel freedom during program execution. At the core of our framework is a novel symbolic verification technique based on automated abstraction refinement of cache semantics. The power of such a framework allows symbolic reasoning over counterexample traces and combines it with runtime monitoring for eliminating cache side channels during program execution. Our evaluation with routines from OpenSSL, libfixedtimefixedpoint, GDK, and FourQlib libraries reveals that our CacheFix approach (dis)proves cache side-channel freedom within an average of 75 s. In nearly all test cases, CacheFix synthesizes all patches within 20 min to ensure cache side-channel freedom of the respective routines during execution.