linux-kernel - Re: [PATCH v2 04/19] crypto: x86/sha

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Date:   Wed, 12 Oct 2022 23:08:53 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Robert Elliott <elliott@....com>, davem@...emloft.net,
        tim.c.chen@...ux.intel.com, ap420073@...il.com, ardb@...nel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 04/19] crypto: x86/sha - limit FPU preemption

On Thu, Oct 13, 2022 at 02:04:43PM +0800, Herbert Xu wrote:
> On Wed, Oct 12, 2022 at 10:57:04PM -0700, Eric Biggers wrote:
> >
> > 'len' can't be 0 at the beginning of this loop, so the 'if (chunk)' check isn't
> > needed.  And it wouldn't make sense even if 'len' could be 0, since a while loop
> > could just be used in that case.
> 
> I don't see anything preventing len from being zero if this gets
> called directly by a user of the Crypto API through crypto_shash_update.
> But yes a while loop would be a lot cleaner.
> 

When len == 0, the following path is taken instead:

        if (!crypto_simd_usable() ||
            (sctx->count % SHA1_BLOCK_SIZE) + len < SHA1_BLOCK_SIZE)
                return crypto_sha1_update(desc, data, len);

- Eric