Sapper: a language for hardware-level security policy enforcement

Privacy and integrity are important security concerns. These concerns are addressed by controlling information flow, i.e., restricting how information can flow through a system. Most proposed systems that restrict information flow make the implicit assumption that the hardware used by the system is fully ``correct'' and that the hardware's instruction set accurately describes its behavior in all circumstances. The truth is more complicated: modern hardware designs defy complete verification; many aspects of the timing and ordering of events are left totally unspecified; and implementation bugs present themselves with surprising frequency. In this work we describe Sapper, a novel hardware description language for designing security-critical hardware components. Sapper seeks to address these problems by using static analysis at compile-time to automatically insert dynamic checks in the resulting hardware that provably enforce a given information flow policy at execution time. We present Sapper's design and formal semantics along with a proof sketch of its security. In addition, we have implemented a compiler for Sapper and used it to create a non-trivial secure embedded processor with many modern microarchitectural features. We empirically evaluate the resulting hardware's area and energy overhead and compare them with alternative designs.