On Thu, Jan 28, 2021 at 03:52:19PM -0600, Josh Poimboeuf wrote:
>
> With retpolines disabled, some configurations of GCC will add Intel CET
> instrumentation to the kernel by default. That breaks certain tracing
> scenarios by adding a superfluous ENDBR64 instruction before the fentry
> call, for functions which can be called indirectly.
>
> CET instrumentation isn't currently necessary in the kernel, as CET is
> only supported in user space. Disable it unconditionally.
>
> Reported-by: Nikolay Borisov <nborisov@xxxxxxxx>
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> ---
> Makefile | 6 ------
> arch/x86/Makefile | 3 +++
> 2 files changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index e0af7a4a5598..51c2bf34142d 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -948,12 +948,6 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)
> # change __FILE__ to the relative path from the srctree
> KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
>
> -# ensure -fcf-protection is disabled when using retpoline as it is
> -# incompatible with -mindirect-branch=thunk-extern
> -ifdef CONFIG_RETPOLINE
> -KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)
> -endif
> -
Why is that even here, in the main Makefile if this cf-protection thing
is x86-specific?
Are we going to move it back there when some other arch gets CET or
CET-like support?
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
