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 (≈0%-1.94% in SPEC CPU2017 and
≈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