linux-hardening - Re: [PATCH] fortify: Update compile-time tests for Clang 14

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Date:   Mon, 31 Jan 2022 11:09:27 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        linux-hardening@...r.kernel.org, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fortify: Update compile-time tests for Clang 14

On Sun, Jan 30, 2022 at 10:16 AM Kees Cook <keescook@...omium.org> wrote:
>
> Clang 14 introduces support for compiletime_assert(). Update the
> compile-time warning regex to catch Clang's variant of the warning text
> in preparation for Clang supporting CONFIG_FORTIFY_SOURCE.

https://twitter.com/ifosteve/status/1190348262500421634?lang=en
error messages can change over time. More thoughts below.

>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: linux-hardening@...r.kernel.org
> Cc: llvm@...ts.linux.dev
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> I'm splitting this patch out of the main Clang FORTIFY enabling patch.
> ---
>  scripts/test_fortify.sh | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/test_fortify.sh b/scripts/test_fortify.sh
> index a4da365508f0..c2688ab8281d 100644
> --- a/scripts/test_fortify.sh
> +++ b/scripts/test_fortify.sh
> @@ -46,8 +46,12 @@ if "$@" -Werror -c "$IN" -o "$OUT".o 2> "$TMP" ; then
>                 status="warning: unsafe ${FUNC}() usage lacked '$WANT' symbol in $IN"
>         fi
>  else
> -       # If the build failed, check for the warning in the stderr (gcc).
> -       if ! grep -q -m1 "error: call to .\b${WANT}\b." "$TMP" ; then
> +       # If the build failed, check for the warning in the stderr.
> +       # GCC:
> +       # ./include/linux/fortify-string.h:316:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
> +       # Clang 14:
> +       # ./include/linux/fortify-string.h:316:4: error: call to __write_overflow_field declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
> +       if ! grep -Eq -m1 "error: call to .?\b${WANT}\b.?" "$TMP" ; then

Doesn't this depend on -Werror being set? I guess it did so before
hand, too, but couldn't I unset CONFIG_WERROR then this check would
still fail (since instead of `error:` we'd have `warning:`)? If we
used __attribute__((error(""))) then this would always be an error.
Right now, it is only because -Werror is set promoting the warning
diagnostic to an error.

>                 status="warning: unsafe ${FUNC}() usage lacked '$WANT' warning in $IN"
>         fi
>  fi
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers