Effective verification of confidentiality for multi-threaded programs

This paper studies how confidentiality properties of multi-threaded programs can be verified efficiently by a combination of newly developed and existing model checking algorithms. In particular, we study the verification of scheduler-specific observational determinism (SSOD), a property that characterizes secure information flow for multi-threaded programs under a given scheduler. Scheduler-specificness allows us to reason about refinement attacks, an important and tricky class of attacks that are notorious in practice. SSOD imposes two conditions: (SSOD-1) all individual public variables have to evolve deterministically, expressed by requiring stuttering equivalence between the traces of each individual public variable, and (SSOD-2) the relative order of updates of public variables is coincidental, i.e., there always exists a matching trace. We verify the first condition by reducing it to the question whether all traces of each public variable are stuttering equivalent. To verify the second condition, we show how the condition can be translated, via a series of steps, into a standard strong bisimulation problem. Our verification techniques can be easily adapted to verify other formalizations of similar information flow properties. We also exploit counter example generation techniques to synthesize attacks for insecure programs that fail either SSOD-1 or SSOD-2, i.e., showing how confidentiality of programs can be broken.