linux-kernel - Re: [PATCH v5 10/15] x86/purgatory: Disable CFI

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Date:   Wed, 13 Oct 2021 12:05:59 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     x86@...nel.org, Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v5 10/15] x86/purgatory: Disable CFI

On Wed, Oct 13, 2021 at 11:16:53AM -0700, Sami Tolvanen wrote:
> Disable CONFIG_CFI_CLANG for the stand-alone purgatory.ro.

If there's a v6, this commit log might do well to have a "why" added. I
assume it'd be something like:

... because purgatory is not running with a full kernel mapping with
jump tables, etc...

Reviewed-by: Kees Cook <keescook@...omium.org>

> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Tested-by: Sedat Dilek <sedat.dilek@...il.com>
> ---
>  arch/x86/purgatory/Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 95ea17a9d20c..911954fec31c 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -55,6 +55,10 @@ ifdef CONFIG_RETPOLINE
>  PURGATORY_CFLAGS_REMOVE		+= $(RETPOLINE_CFLAGS)
>  endif
>  
> +ifdef CONFIG_CFI_CLANG
> +PURGATORY_CFLAGS_REMOVE		+= $(CC_FLAGS_CFI)
> +endif
> +
>  CFLAGS_REMOVE_purgatory.o	+= $(PURGATORY_CFLAGS_REMOVE)
>  CFLAGS_purgatory.o		+= $(PURGATORY_CFLAGS)
>  
> -- 
> 2.33.0.1079.g6e70778dc9-goog
> 

-- 
Kees Cook