FineIBT: Fine-grain Control-flow Enforcement with Indirect Branch Tracking

We present the design, implementation, and evaluation of FineIBT: a CFI enforcement mechanism that improves the precision of hardware-assisted CFI solutions, like Intel IBT and ARM BTI, by instrumenting program code to reduce the valid/allowed targets of indirect forward-edge transfers. We study the design of FineIBT on the x86-64 architecture, and implement and evaluate it on Linux and the LLVM toolchain. We designed FineIBT's instrumentation to be compact, and incur low runtime and memory overheads, and generic, so as to support a plethora of different CFI policies. Our prototype implementation incurs negligible runtime slowdowns ($\approx$0%-1.94% in SPEC CPU2017 and $\approx$0%-1.92% in real-world applications) outperforming Clang-CFI. Lastly, we investigate the effectiveness/security and compatibility of FineIBT using the ConFIRM CFI benchmarking suite, demonstrating that our nimble instrumentation provides complete coverage in the presence of modern software features, while supporting a wide range of CFI policies (coarse- vs. fine- vs. finer-grain) with the same, predictable performance.