Formal verification of integrity-Preserving countermeasures against cache storage side-channels

Abstract

Formal verification of systems-level software such as hypervisors and operating systems can enhance system trustworthiness. However, without taking low level features like caches into account the verification may become unsound. While this is a well-known fact w.r.t. timing leaks, few works have addressed latent cache storage side-channels, whose effects are not limited to information leakage. We present a verification methodology to analyse soundness of countermeasures used to neutralise these channels. We apply the proposed methodology to existing countermeasures, showing that they allow to restore integrity of the system. We decompose the proof effort into verification conditions that allow for an easy adaption of our strategy to various software and hardware platforms. As case study, we extend the verification of an existing hypervisor whose integrity can be tampered using cache storage channels. We used the HOL4 theorem prover to validate our security analysis, applying the verification methodology to a generic hardware model.