linux-kernel - Re: [PATCH v2 3/6] crypto: lib/sha256 - Clear W[] in sha256_update() instead of sha256

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Date:   Wed, 21 Oct 2020 21:59:49 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        David Laight <David.Laight@...lab.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/6] crypto: lib/sha256 - Clear W[] in sha256_update()
 instead of sha256_transform()

On Tue, Oct 20, 2020 at 04:39:54PM -0400, Arvind Sankar wrote:
> The temporary W[] array is currently zeroed out once every call to
> sha256_transform(), i.e. once every 64 bytes of input data. Moving it to
> sha256_update() instead so that it is cleared only once per update can
> save about 2-3% of the total time taken to compute the digest, with a
> reasonable memset() implementation, and considerably more (~20%) with a
> bad one (eg the x86 purgatory currently uses a memset() coded in C).
> 
> Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>

Looks good,

Reviewed-by: Eric Biggers <ebiggers@...gle.com>