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

Kees Cook
2021-08-19T06:29:14Z

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@chromium.org>

-Kees

>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.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)) \
> > $@.symversions; \
> + else \
> + rm -f $@.symversions; \
> fi;
> else
> cmd_modversions_c = \
> --
> 2.30.2
>

--
Kees Cook