[PATCH] x86/entry/32: Add missing ASM_CLAC in general_protection entry

[PATCH] x86/entry/32: Add missing ASM_CLAC in general_protection entry

[Thomas Gleixner]

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@linutronix.de>
Cc: stable@vger.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)

Re: [PATCH] x86/entry/32: Add missing ASM_CLAC in general_protection entry

[Brian Gerst]

On Wed, Feb 19, 2020 at 4:58 AM Thomas Gleixner <tglx@linutronix.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@linutronix.de>
> Cc: stable@vger.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

Re: [PATCH] x86/entry/32: Add missing ASM_CLAC in general_protection entry

[Thomas Gleixner]

Brian Gerst <brgerst@gmail.com> writes:

> On Wed, Feb 19, 2020 at 4:58 AM Thomas Gleixner <tglx@linutronix.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@linutronix.de>
>> Cc: stable@vger.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