linux-kernel - Re: [PATCH] poly1305: generic C can be faster on chips with slow unaligned access

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Message-ID: <CAHmME9rzBST8Lqapzykwf2rUyxLXuyOF0wX+Sy259Qtx9a4YSg@mail.gmail.com>
Date:   Mon, 7 Nov 2016 20:02:35 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Eric Biggers <ebiggers@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Martin Willi <martin@...ongswan.org>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>,
        René van Dorst <opensource@...rst.com>
Subject: Re: [PATCH] poly1305: generic C can be faster on chips with slow
 unaligned access

On Mon, Nov 7, 2016 at 7:26 PM, Eric Biggers <ebiggers@...gle.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.