linux-hardening - Re: [PATCH for-next 16/25] fortify: Explicitly disable Clang support

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Date:   Wed, 25 Aug 2021 12:41:56 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Daniel Micay <danielmicay@...il.com>,
        Francis Laniel <laniel_francis@...vacyrequired.com>,
        Bart Van Assche <bvanassche@....org>,
        David Gow <davidgow@...gle.com>, linux-mm@...ck.org,
        clang-built-linux@...glegroups.com, linux-hardening@...r.kernel.org
Subject: Re: [PATCH for-next 16/25] fortify: Explicitly disable Clang support

On Sun, Aug 22, 2021 at 12:57 AM Kees Cook <keescook@...omium.org> wrote:
>
> Clang has never correctly compiled the FORTIFY_SOURCE defenses due to
> a couple bugs:
>
>         Eliding inlines with matching __builtin_* names
>         https://bugs.llvm.org/show_bug.cgi?id=50322
>
>         Incorrect __builtin_constant_p() of some globals
>         https://bugs.llvm.org/show_bug.cgi?id=41459
>
> In the process of making improvements to the FORTIFY_SOURCE defenses, the
> first (silent) bug (coincidentally) becomes worked around, but exposes
> the latter which breaks the build. As such, Clang must not be used with
> CONFIG_FORTIFY_SOURCE until at least latter bug is fixed (in Clang 13),
> and the fortify routines have been rearranged.
>
> Update the Kconfig to reflect the reality of the current situation.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Acked-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  security/Kconfig | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/security/Kconfig b/security/Kconfig
> index 0ced7fd33e4d..fe6c0395fa02 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -191,6 +191,9 @@ config HARDENED_USERCOPY_PAGESPAN
>  config FORTIFY_SOURCE
>         bool "Harden common str/mem functions against buffer overflows"
>         depends on ARCH_HAS_FORTIFY_SOURCE
> +       # https://bugs.llvm.org/show_bug.cgi?id=50322
> +       # https://bugs.llvm.org/show_bug.cgi?id=41459
> +       depends on !CC_IS_CLANG
>         help
>           Detect overflows of buffers in common string and memory functions
>           where the compiler can determine and validate the buffer sizes.
> --
> 2.30.2
>
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-- 
Thanks,
~Nick Desaulniers