linux-kernel - Re: [PATCH] x86/entry/32: Add missing ASM_CLAC in general

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Date:   Wed, 19 Feb 2020 15:10:49 -0500
From:   Brian Gerst <brgerst@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH] x86/entry/32: Add missing ASM_CLAC in general_protection entry

On Wed, Feb 19, 2020 at 4:58 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> All exception entry points must have ASM_CLAC right at the
> beginning. The general_protection entry is missing one.
>
> Fixes: e59d1b0a2419 ("x86-32, smap: Add STAC/CLAC instructions to 32-bit kernel entry")
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: stable@...r.kernel.org
> ---
>  arch/x86/entry/entry_32.S |    1 +
>  1 file changed, 1 insertion(+)
>
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -1681,6 +1681,7 @@ SYM_CODE_START(int3)
>  SYM_CODE_END(int3)
>
>  SYM_CODE_START(general_protection)
> +       ASM_CLAC
>         pushl   $do_general_protection
>         jmp     common_exception
>  SYM_CODE_END(general_protection)

How about moving ASM_CLAC to common_exception instead?  That would
save a few bytes (kernel text + alternatives), and the AC bit has no
effect on kernel stack pushes.

--
Brian Gerst