Separation Logic-Based Verification Atop a Binary-Compatible Filesystem Model

Abstract

Filesystems have held the interest of the formal verification community for a while, with several high-performance filesystems constructed with accompanying proofs of correctness. However, the question of verifying an existing filesystem and incorporating filesystem-specific guarantees remains unexplored, leaving those application developers underserved who need to work with a specific filesystem known to be fit for their purpose. In this work, we present an implementation of a verified filesystem which matches the specification of an existing filesystem, and with our new model AbsFAT tie it to the reasoning framework of separation logic in order to verify properties of programs which use the filesystem. This work is intended to match the target filesystem, FAT32, at a binary level and return the same data and error codes returned by mature FAT32 implementations, considered canonical. We provide a logical framework for reasoning about program behavior when filesystem calls are involved in terms of separation logic, and adapt it to simplify and automate the proof process in ACL2. By providing this framework, we encourage and facilitate greater adoption of software verification by application developers.