linux-kernel - Re: [PATCH v4] poly1305: generic C can be faster on chips with slow unaligned access

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Message-ID: <20161108172626.GA99078@google.com>
Date:   Tue, 8 Nov 2016 09:26:26 -0800
From:   Eric Biggers <ebiggers@...gle.com>
To:     Martin Willi <martin@...ongswan.org>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        René van Dorst <opensource@...rst.com>
Subject: Re: [PATCH v4] poly1305: generic C can be faster on chips with slow
 unaligned access

On Tue, Nov 08, 2016 at 08:52:39AM +0100, Martin Willi wrote:
> 
> 
> Not sure what the exact alignment rules for key/iv are, but maybe we
> want to replace the same function in chacha20_generic.c as well?
> 
> Martin

chacha20-generic provides a blkcipher API and sets an alignmask of sizeof(u32)
- 1.  This applies to the key buffer for ->setkey() and to the mapped addresses
for the input/output buffers and IV during the blkcipher walk.  So it does not
appear to have the problems that poly1305 has.  

I do however see one small problem which is that
'u8 stream[CHACHA20_BLOCK_SIZE];' is, strictly speaking, not guaranteed to be
aligned to u32.

Eric