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

From	Eric Biggers <ebiggers@google.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] poly1305: generic C can be faster on chips with slow unaligned access
Date	2016-11-07 20:30 +0100
Message-ID	<sAXMd-7uI-3@gated-at.bofh.it> (permalink)
References	(4 earlier) <szyGe-1ul-21@gated-at.bofh.it> <szQD7-4MR-15@gated-at.bofh.it> <sAWwO-6Ln-29@gated-at.bofh.it> <sAWZP-6Y4-7@gated-at.bofh.it> <sAXsT-7ns-53@gated-at.bofh.it>
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On Mon, Nov 07, 2016 at 08:02:35PM +0100, Jason A. Donenfeld wrote:
> 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!
> 

No it does *not* buffer all incoming blocks, which is why the source pointer can
fall out of alignment.  Yes, I actually tested this.  In fact this situation is
even hit, in both possible places, in the self-tests.

Eric

Thread

[PATCH] poly1305: generic C can be faster on chips with slow unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-02 19:00 +0100
  Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access Herbert Xu <herbert@gondor.apana.org.au> - 2016-11-02 21:20 +0100
    Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access Sandy Harris <sandyinchina@gmail.com> - 2016-11-02 21:50 +0100
    Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-02 22:10 +0100
      Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access Herbert Xu <herbert@gondor.apana.org.au> - 2016-11-02 22:10 +0100
        Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-02 22:30 +0100
          Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access Herbert Xu <herbert@gondor.apana.org.au> - 2016-11-02 22:30 +0100
            Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-02 23:10 +0100
              Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access Herbert Xu <herbert@gondor.apana.org.au> - 2016-11-03 01:50 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-03 08:30 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access David Miller <davem@davemloft.net> - 2016-11-03 18:10 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-03 23:30 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access Eric Biggers <ebiggers@google.com> - 2016-11-04 18:40 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-07 19:10 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-07 19:30 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access Eric Biggers <ebiggers@google.com> - 2016-11-07 19:40 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-07 20:10 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access Eric Biggers <ebiggers@google.com> - 2016-11-07 20:30 +0100
                Re: [PATCH] poly1305: generic C can be faster on chips with slow  unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-07 20:50 +0100
  [PATCH v2] poly1305: generic C can be faster on chips with slow unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-07 20:20 +0100
    [PATCH v3] poly1305: generic C can be faster on chips with slow unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-07 20:50 +0100
    [PATCH v4] poly1305: generic C can be faster on chips with slow unaligned access "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-07 21:00 +0100
      Re: [PATCH v4] poly1305: generic C can be faster on chips with slow  unaligned access Eric Biggers <ebiggers@google.com> - 2016-11-07 21:50 +0100
      Re: [PATCH v4] poly1305: generic C can be faster on chips with slow  unaligned access Martin Willi <martin@strongswan.org> - 2016-11-08 09:10 +0100
        Re: [PATCH v4] poly1305: generic C can be faster on chips with slow  unaligned access Eric Biggers <ebiggers@google.com> - 2016-11-08 18:30 +0100

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