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

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Message-ID: <87r1yooo7f.fsf@nanos.tec.linutronix.de>
Date:   Fri, 21 Feb 2020 00:04:20 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Brian Gerst <brgerst@...il.com>
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

Brian Gerst <brgerst@...il.com> writes:

> 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.

Agreed, but that's a seperate cleanup. The fix is the right thing also
for backports.

Aisde of that this mindlessly copied code will be gone in the
foreseeable future. Just lacks some testing and changelog writing :)

Thanks,

        tglx