Re: [PATCH 2/2] cfi: fix conditions for HAVE_CFI_ICALL_NORMALIZE_INTEGERS

Sami Tolvanen
2024-10-10T20:21:01Z

On Thu, Oct 10, 2024 at 09:38:27AM +0000, Alice Ryhl wrote:
> The HAVE_CFI_ICALL_NORMALIZE_INTEGERS option has some tricky conditions
> when KASAN or GCOV are turned on, as in that case we need some clang and
> rustc fixes [1][2] to avoid boot failures. The intent with the current
> setup is that you should be able to override the check and turn on the
> option if your clang/rustc has the fix. However, this override does not
> work in practice. Thus, use the new RUSTC_LLVM_VERSION to correctly
> implement the check for whether the fix is available.
>
> Additionally, remove KASAN_HW_TAGS from the list of incompatible
> options. The CFI_ICALL_NORMALIZE_INTEGERS option is incompatible with
> KASAN because LLVM will emit some constructors when using KASAN that are
> assigned incorrect CFI tags. These constructors are emitted due to use
> of -fsanitize=kernel-address or -fsanitize=kernel-hwaddress that are
> respectively passed when KASAN_GENERIC or KASAN_SW_TAGS are enabled.
> However, the KASAN_HW_TAGS option relies on hardware support for MTE
> instead and does not pass either flag. (Note also that KASAN_HW_TAGS
> does not `select CONSTRUCTORS`.)
>
> Link: https://github.com/llvm/llvm-project/pull/104826 [1]
> Link: https://github.com/rust-lang/rust/pull/129373 [2]
> Fixes: 4c66f8307ac0 ("cfi: encode cfi normalized integers + kasan/gcov bug in Kconfig")
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>

This looks correct to me. Checking the LLVM version is definitely a
better option. Thanks!

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>

Sami