linux-kernel - Re: [PATCH 05/13] kbuild: remove stale *.symversions

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Message-ID: <202108182328.5CF89AC2@keescook>
Date:   Wed, 18 Aug 2021 23:29:10 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH 05/13] kbuild: remove stale *.symversions

On Thu, Aug 19, 2021 at 09:57:36AM +0900, Masahiro Yamada wrote:
> cmd_update_lto_symversions merges all the existing *.symversions, but
> some of them might be stale.
> 
> If the last EXPORT_SYMBOL is removed from a C file, the *.symversions
> file is not deleted or updated. It contains stale CRCs, which will be
> used for linking the vmlinux or modules.
> 
> It is not a big deal when the EXPORT_SYMBOL is really removed. However,
> when the EXPORT_SYMBOL is moved to another file, the same __crc_<symbol>
> will appear twice in the merged *.symversions, possibly with different
> CRCs if the function argument is changed at the same time. It would
> cause potential breakage of module versioning.
> 
> If no EXPORT_SYMBOL is found, let's remove *.symversions explicitly.

Ah, and this was an issue for non-LTO builds too? Regardless, nice
catch.

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

-Kees

> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
> 
>  scripts/Makefile.build | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 279363266455..585dae34746a 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -177,6 +177,8 @@ cmd_modversions_c =								\
>  	if $(NM) $@ 2>/dev/null | grep -q __ksymtab; then			\
>  		$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
>  		    > $@...mversions;						\
> +	else									\
> +		rm -f $@...mversions;						\
>  	fi;
>  else
>  cmd_modversions_c =								\
> -- 
> 2.30.2
> 

-- 
Kees Cook