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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Mon, 7 Nov 2016 20:02:35 +0100
Message-ID: <CAHmME9rzBST8Lqapzykwf2rUyxLXuyOF0wX+Sy259Qtx9a4YSg@mail.gmail.com>
Subject: Re: [PATCH] poly1305: generic C can be faster on chips with slow
 unaligned access
To: Eric Biggers <ebiggers@google.com>
Cc: David Miller <davem@davemloft.net>,
        Herbert Xu <herbert@gondor.apana.org.au>, linux-crypto@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Martin Willi <martin@strongswan.org>,
        WireGuard mailing list <wireguard@lists.zx2c4.com>,
        =?UTF-8?Q?Ren=C3=A9_van_Dorst?= <opensource@vdorst.com>
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On Mon, Nov 7, 2016 at 7:26 PM, Eric Biggers <ebiggers@google.com> wrote:
>
> I was not referring to any users in particular, only what users could do.  As an
> example, if you did crypto_shash_update() with 32, 15, then 17 bytes, and the
> underlying algorithm is poly1305-generic, the last block would end up
> misaligned.  This doesn't appear possible with your pseudocode because it only
> passes in multiples of the block size until the very end.  However I don't see
> it claimed anywhere that shash API users have to do that.

Actually it appears that crypto/poly1305_generic.c already buffers
incoming blocks to a buffer that definitely looks aligned, to prevent
this condition!

I'll submit a v2 with only the inner unaligned operations changed.