Re: [PATCH v26 6/9] x86/vdso: Insert endbr32/endbr64 to vDSO

[Kees Cook]

On Tue, Apr 27, 2021 at 01:47:17PM -0700, Yu-cheng Yu wrote:
> From: "H.J. Lu" <hjl.tools@xxxxxxxxx>
> 
> When Indirect Branch Tracking (IBT) is enabled, vDSO functions may be
> called indirectly, and must have ENDBR32 or ENDBR64 as the first
> instruction.  The compiler must support -fcf-protection=branch so that it
> can be used to compile vDSO.

If you respin this, you can maybe rephrase this since CONFIG_X86_IBT
has already tested for the compiler support.

> 
> Signed-off-by: H.J. Lu <hjl.tools@xxxxxxxxx>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
> v24:
> - Replace CONFIG_X86_CET with CONFIG_X86_IBT to reflect splitting of shadow
>   stack and ibt.
> 
>  arch/x86/entry/vdso/Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 05c4abc2fdfd..a773a5f03b63 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -93,6 +93,10 @@ endif
>  
>  $(vobjs): KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
>  
> +ifdef CONFIG_X86_IBT
> +$(vobjs) $(vobjs32): KBUILD_CFLAGS += -fcf-protection=branch
> +endif
> +
>  #
>  # vDSO code runs in userspace and -pg doesn't help with profiling anyway.
>  #
> -- 
> 2.21.0
> 

-- 
Kees Cook