kCPA: Towards Sensitive Pointer Full Life Cycle Authentication for OS Kernels

Nowadays, code reuse attacks impose a substantial threat to the security of operating system kernels. Control-flow graph-based CFI techniques, while effective, bring considerable performance overhead, thus limiting their practical adoption in real-world products. As an alternative approach, recent research suggests safeguarding the integrity of sensitive pointers as a countermeasure against manipulation attempts. Unfortunately, existing pointer integrity protection schemes only protect sensitive pointers partially and ignore assembly code, leaving protection gaps. To fill up these protection gaps, we propose a novel security concept named full life-cycle integrity, which enforces the integrity of a sensitive pointer at every step on its value flow chain. To realize full life-cycle integrity, we propose three novel techniques, including assembly-aware sensitivity for analyzing assembly code, Merkle PAC tree for protecting interrupt context securely and efficiently, and pointer-grained authentication for defeating spatial substitution attacks. We have developed a practical implementation of comprehensive life-cycle integrity for the Linux kernel, called ”kernel Code Pointer Authentication” (kCPA), which leverages the ARM Pointer Authentication (PAuth) mechanism. This implementation has been extended to the Apple M1 architecture for real-world evaluation on PAuth hardware. Our assessment demonstrates that kCPA effectively mitigates a range of real-world attacks while incurring a minimal 2.5% performance overhead for the Phoronix Test Suite and nearly negligible performance impact for SPEC2017 benchmarks.