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Date: Mon, 10 Oct 2016 10:51:14 -0700
From: Joe Perches <joe@...ches.com>
To: Eric Biggers <ebiggers@...gle.com>
Cc: herbert@...dor.apana.org.au, davem@...emloft.net,
linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: cmac - fix alignment of 'consts'
On Mon, 2016-10-10 at 10:37 -0700, Eric Biggers wrote:
> On Mon, Oct 10, 2016 at 10:29:55AM -0700, Joe Perches wrote:
> > On Mon, 2016-10-10 at 10:15 -0700, Eric Biggers wrote:
> > > The per-transform 'consts' array is accessed as __be64 in
> > > crypto_cmac_digest_setkey() but was only guaranteed to be aligned to
> > > __alignof__(long). Fix this by aligning it to __alignof__(__be64).
> > []
> > > diff --git a/crypto/cmac.c b/crypto/cmac.c
> > []
> > > @@ -57,7 +57,8 @@ static int crypto_cmac_digest_setkey(struct crypto_shash *parent,
> > > unsigned long alignmask = crypto_shash_alignmask(parent);
> > > struct cmac_tfm_ctx *ctx = crypto_shash_ctx(parent);
> > > unsigned int bs = crypto_shash_blocksize(parent);
> > > - __be64 *consts = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
> > > + __be64 *consts = PTR_ALIGN((void *)ctx->ctx,
> > > + (alignmask | (__alignof__(__be64) - 1)) + 1);
> >
> >
> > Using a bitwise or looks very odd there. Perhaps:
> >
> > min(alignmask + 1, __alignof__(__be64))
> >
>
>
> Alignment has to be a power of 2. From the code I've read, crypto drivers work
> with alignment a lot and use bitwise OR to mean "the more restrictive of these
> alignmasks". So I believe the way it's written is the preferred style.
>
> Eric
Hey Eric.
I don't see any PTR_ALIGN uses in crypto/ or drivers/crypto/ that
use a bitwise or, just mask + 1, but I believe the effect is the
same. Anyway, your choice, but I think using min is clearer.
cheers, Joe
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