Progress-Sensitive Security for SPARK

SPARK 2014 is a safety critical language subset of Ada developed by Altran and used for developing safe and secure software by major industrial players in the aviation, commercial, medical, space, and military domains. This paper puts a spotlight on the SPARK flow analysis. Articulating the boundaries of what is achievable by the analysis, we spell out attacks to exploit termination, progress, resource exhaustion, and timing channels. We harden the analysis to achieve security against stronger attackers, with the focus on progress-sensitive security as our baseline. Instead of redesigning and reimplementing the enforcement, we leverage known flow analyses for weaker attackers by a transform on program dependence graphs. We establish the soundness of this approach for a core language and demonstrate that it can be applied as a source-to-source transform of SPARK code when modifying the compiler is undesirable. A case study, derived from publicly available code for a control unit of a missile, indicates the usefulness of the approach.