linux-kernel - Re: [PATCH] randstruct: temporarily disable clang support

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Message-ID: <63deacb1.170a0220.f078.6779@mx.google.com>
Date:   Sat, 4 Feb 2023 11:06:25 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-hardening@...r.kernel.org, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] randstruct: temporarily disable clang support

On Fri, Feb 03, 2023 at 11:42:01AM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> Randstruct with clang is currently unsafe to use in any clang release
> that supports it, due to a clang bug that is causing miscompilations:
> "-frandomize-layout-seed inconsistently randomizes all-function-pointers
> structs" (https://github.com/llvm/llvm-project/issues/60349).  Disable
> it temporarily until the bug is fixed and the fix is released in a clang
> version that can be checked for.
> 
> Fixes: 035f7f87b729 ("randstruct: Enable Clang support")
> Cc: stable@...r.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> ---
>  security/Kconfig.hardening | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index 53baa95cb644..aad16187148c 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -280,7 +280,8 @@ config ZERO_CALL_USED_REGS
>  endmenu
>  
>  config CC_HAS_RANDSTRUCT
> -	def_bool $(cc-option,-frandomize-layout-seed-file=/dev/null)
> +	# Temporarily disabled due to https://github.com/llvm/llvm-project/issues/60349
> +	def_bool n
>  
>  choice
>  	prompt "Randomize layout of sensitive kernel structures"
> 
> base-commit: 7b753a909f426f2789d9db6f357c3d59180a9354
> -- 
> 2.39.1

This should be fixed with greater precision -- i.e. this is nearly fixed
in Clang now, and is likely to be backported. So I think we'll need
versioned checks here.

-- 
Kees Cook