linux-hardening - Re: [PATCH] randstruct: disable Clang 15 support

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Date:   Wed, 8 Feb 2023 10:53:29 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Bill Wendling <morbo@...gle.com>, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] randstruct: disable Clang 15 support

On Tue, Feb 7, 2023 at 10:52 PM Eric Biggers <ebiggers@...nel.org> wrote:
>
> From: Eric Biggers <ebiggers@...gle.com>
>
> The randstruct support released in Clang 15 is unsafe to use due to a
> bug that can cause miscompilations: "-frandomize-layout-seed
> inconsistently randomizes all-function-pointers structs"
> (https://github.com/llvm/llvm-project/issues/60349).  It has been fixed
> on the Clang 16 release branch, so add a Clang version check.
>
> Fixes: 035f7f87b729 ("randstruct: Enable Clang support")
> Cc: stable@...r.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Thanks for the patch and report. Guessing that wasn't fun to debug.
Acked-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  security/Kconfig.hardening | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index 53baa95cb644f..0f295961e7736 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -281,6 +281,9 @@ endmenu
>
>  config CC_HAS_RANDSTRUCT
>         def_bool $(cc-option,-frandomize-layout-seed-file=/dev/null)
> +       # Randstruct was first added in Clang 15, but it isn't safe to use until
> +       # Clang 16 due to https://github.com/llvm/llvm-project/issues/60349
> +       depends on !CC_IS_CLANG || CLANG_VERSION >= 160000
>
>  choice
>         prompt "Randomize layout of sensitive kernel structures"
>
> base-commit: 4ec5183ec48656cec489c49f989c508b68b518e3
> --
> 2.39.1
>
>


-- 
Thanks,
~Nick Desaulniers