cf-protection

This option enables control-flow enforcement technology (CET) on x86; a more detailed description of CET is available here. Similar to clang, this flag takes one of the following values:

  • none - Disable CET completely (this is the default).
  • branch - Enable indirect branch tracking (IBT).
  • return - Enable shadow stack (SHSTK).
  • full - Enable both branch and return.

This flag only applies to the LLVM backend: it sets the cf-protection-branch and cf-protection-return flags on LLVM modules. Note, however, that all compiled modules linked together must have the flags set for the compiled output to be CET-enabled. Currently, Rust's standard library does not ship with CET enabled by default, so you may need to rebuild all standard modules with a cargo command like:

$ RUSTFLAGS="-Z cf-protection=full" RUSTC="rustc-custom" cargo +nightly build -Z build-std --target x86_64-unknown-linux-gnu

Detection

An ELF binary is CET-enabled if it has the IBT and SHSTK tags, e.g.:

$ readelf -a target/x86_64-unknown-linux-gnu/debug/example | grep feature:
      Properties: x86 feature: IBT, SHSTK

Troubleshooting

To display modules that are not CET enabled, examine the linker errors available when cet-report is enabled:

$ RUSTC_LOG=rustc_codegen_ssa::back::link=info rustc-custom -v -Z cf-protection=full -C link-arg="-Wl,-z,cet-report=warning" -o example example.rs
...
/usr/bin/ld: /.../build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-d73f7266be14cb8b.rlib(std-d73f7266be14cb8b.std.f7443020-cgu.12.rcgu.o): warning: missing IBT and SHSTK properties