Re: [PATCH crypto-next 06/23] x86/fpu: Remove VLA usage of skcipher

[Kees Cook]

On Mon, Sep 24, 2018 at 4:45 AM, Ard Biesheuvel
<ard.biesheuvel@xxxxxxxxxx> wrote:
> On Wed, 19 Sep 2018 at 04:11, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>>
>> In the quest to remove all stack VLA usage from the kernel[1], this
>> replaces struct crypto_skcipher and SKCIPHER_REQUEST_ON_STACK() usage
>> with struct crypto_sync_skcipher and SYNC_SKCIPHER_REQUEST_ON_STACK(),
>> which uses a fixed stack size.
>>
>> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx
>>
>> Cc: x86@xxxxxxxxxx
>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>
> Doing some archeology on this driver, it turns out that the FPU
> wrapper was introduced to support combining the generic CTR, LRW, XTS
> and PCBC chaining modes with the AES-NI core transform. In the mean
> time, CTR, LRW and XTS support have been implemented natively, which
> leaves pcbc-aes-aesni as the only remaining user of the fpu template.
>
> Since there are no users of pcbc(aes) in the kernel, could we perhaps
> just remove this driver and all the special handling we have for it in
> aesni-intel_glue.c?

Both options get rid of the VLA, so I'm happy either way. ;)

> If not, or in case we prefer to defer that to the next release:
>
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

Thanks!

-Kees

-- 
Kees Cook
Pixel Security