IBM at USENIX Security Symposium 2025

Instruction set architectures (ISAs) are complex, with hundreds of registers and instructions that can modify dozens of them during execution, variably on each instance. Prose-style ISA specifications struggle to capture these intricacies of the ISAs, where often the important details about a single register are spread out across hundreds of pages of documentation. Ensuring that all ISA-state is swapped in context switch implementations of privileged software requires meticulous examination of these pages. This manual process is tedious and error-prone. We propose a tool called Sailor that leverages machine-readable ISA specifications written in Sail and Isla symbolic execution engine for Sail to automate this task. Sailor determines the ISA-state that must be swapped during the context switch using the data collected from Isla and a novel algorithm to identify all the ISA-state that must be swapped during context switches. We use Sailor to assess the context switch code of multiple systems: from regular user process context switching code in the RISC-V Linux kernel on the StarFive VisionFive2 board, to the enclave context switching code in confidential computing frameworks, Keystone and Komodo. We identify multiple mishandled security-sensitive ISA-state. This research exposes an often overlooked attack surface that stems from mishandled ISA-state, enabling unprivileged adversaries to exploit system vulnerabilities.