Verifying Compiled File System Code

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Abstract

This paper presents a case study on retrospective verification of the Linux Virtual File System (VFS), which is aimed at checking for violations of API usage rules and memory properties. Since VFS maintains dynamic data structures and is written in a mixture of C and inlined assembly, modern software model checkers cannot be applied. Our case study centres around our novel verification tool, the SOCA Verifier, which symbolically executes and analyses compiled code. We describe how this verifier deals with complex program features such as memory access, pointer aliasing and computed jumps, while reducing manual modelling to the bare minimum. Our results show that the SOCA Verifier is capable of reliably analysing complex operating system components such as the Linux VFS, thereby going beyond traditional testing tools and into niches that current software model checkers do not reach.