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Date:   Tue, 31 Oct 2023 12:25:58 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc:     peterz@infradead.org, linux-kernel@vger.kernel.org,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Kees Cook <keescook@chromium.org>,
        Mike Rapoport <rppt@kernel.org>,
        Pengfei Xu <pengfei.xu@intel.com>,
        John Allen <john.allen@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        linux-kbuild@vger.kernel.org
Subject: Re: [PATCH] x86: Let AS_WRUSS depend on X86_64
Message-ID: <20231031112558.GAZUDkRrkEStZqDnz4@fat_crate.local>
References: <20231031102111.32142-1-jirislaby@kernel.org>
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+ linux-kbuild@vger.kernel.org

On Tue, Oct 31, 2023 at 11:21:11AM +0100, Jiri Slaby (SUSE) wrote:
> Since commit 18e66b695e78 ("x86/shstk: Add Kconfig option for shadow
> stack"), AS_WRUSS is set even in 32-bit .configs. It is due to how
> Kbuild works. .config is not considered during make oldconfig (and other
> make *config), so standard (64-bit) gcc is invoked from 'as-instr'
> Kbuild tests. And such gcc indeed reports that wruss is supported, so
> AS_WRUSS=y is set.
> 
> Provided the wruss instruction is 64-bit only (and used in pure 64-bit
> X86_USER_SHADOW_STACK), it has little sense to have AS_WRUSS=y set on
> 32-bit.
> 
> Therefore, make the whole test dependent on X86_64 to ensure it's set
> only on 64-bit.
> 
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
> Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Borislav Petkov (AMD) <bp@alien8.de>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Mike Rapoport (IBM) <rppt@kernel.org>
> Cc: Pengfei Xu <pengfei.xu@intel.com>
> Cc: John Allen <john.allen@amd.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> ---
>  arch/x86/Kconfig.assembler | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/Kconfig.assembler b/arch/x86/Kconfig.assembler
> index 8ad41da301e5..a5b5241711e3 100644
> --- a/arch/x86/Kconfig.assembler
> +++ b/arch/x86/Kconfig.assembler
> @@ -27,5 +27,6 @@ config AS_GFNI
>  
>  config AS_WRUSS
>  	def_bool $(as-instr,wrussq %rax$(comma)(%rbx))
> +	depends on X86_64
>  	help
>  	  Supported by binutils >= 2.31 and LLVM integrated assembler
> -- 
> 2.42.0
> 

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette