[PATCH 0/3] x86/cfi: Fix a few kCFI issues found with GCC

[Kees Cook <kees@kernel.org>]

Hi!

While testing x86 kernels built by GCC with the coming kCFI patches I
tripped over three problems. Since the kCFI call sequence was optimized
in v7.3-rc1, the trap handler decodes the check one byte off, so a
kCFI failure in a CONFIG_FINEIBT=y kernel running in kCFI mode reports
whatever %rbx holds as the target, with Clang as well as GCC (1/3). GNU
as warns about the "cs" prefix in the FineIBT paranoid caller template,
which Clang's integrated assembler accepts silently (2/3). And objtool's
kCFI check treats GCC's jump-table jump for the BPF interpreter's computed
goto as an unchecked indirect call (3/3).

Thanks!

-Kees

Kees Cook (3):
  x86/kcfi: Decode the kCFI check from the trap address
  x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte
  objtool: Skip jump table jumps in the kCFI indirect call check

 arch/x86/kernel/alternative.c |  3 ++-
 arch/x86/kernel/cfi.c         | 14 +++++++-------
 tools/objtool/check.c         |  8 ++++++++
 3 files changed, 17 insertions(+), 8 deletions(-)

-- 
2.55.0