linux-kernel - Re: [PATCH] crypto: x86/polyval - Fix crashes when keys are not 16-byte aligned

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Date:   Mon, 17 Oct 2022 16:02:29 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Nathan Huckleberry <nhuck@...gle.com>
Cc:     Bruno Goncalves <bgoncalv@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: x86/polyval - Fix crashes when keys are not
 16-byte aligned

On Mon, Oct 17, 2022 at 03:26:20PM -0700, Nathan Huckleberry wrote:
> The key_powers array is not guaranteed to be 16-byte aligned, so using
> movaps to operate on key_powers is not allowed.
> 
> Switch movaps to movups.
> 
> Fixes: 34f7f6c30112 ("crypto: x86/polyval - Add PCLMULQDQ accelerated implementation of POLYVAL")
> Reported-by: Bruno Goncalves <bgoncalv@...hat.com>
> Signed-off-by: Nathan Huckleberry <nhuck@...gle.com>
> ---
>  arch/x86/crypto/polyval-clmulni_asm.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/crypto/polyval-clmulni_asm.S b/arch/x86/crypto/polyval-clmulni_asm.S
> index a6ebe4e7dd2b..32b98cb53ddf 100644
> --- a/arch/x86/crypto/polyval-clmulni_asm.S
> +++ b/arch/x86/crypto/polyval-clmulni_asm.S
> @@ -234,7 +234,7 @@
>  
>  	movups (MSG), %xmm0
>  	pxor SUM, %xmm0
> -	movaps (KEY_POWERS), %xmm1
> +	movups (KEY_POWERS), %xmm1
>  	schoolbook1_noload
>  	dec BLOCKS_LEFT
>  	addq $16, MSG

I thought that crypto_tfm::__crt_ctx is guaranteed to be 16-byte aligned,
and that the x86 AES code relies on that property.

But now I see that actually the x86 AES code manually aligns the context.
See aes_ctx() in arch/x86/crypto/aesni-intel_glue.c.

Did you consider doing the same for polyval?

If you do prefer this way, it would be helpful to leave a comment for
schoolbook1_iteration that mentions that the unaligned access support of
vpclmulqdq is being relied on, i.e. pclmulqdq wouldn't work.

- Eric