linux-kernel - Re: [PATCH v2 1/6] crypto: Use memzero

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Message-ID: <20201023153927.GA217686@rani.riverdale.lan>
Date:   Fri, 23 Oct 2020 11:39:27 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        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 1/6] crypto: Use memzero_explicit() for clearing state

On Wed, Oct 21, 2020 at 09:36:33PM -0700, Eric Biggers wrote:
> On Tue, Oct 20, 2020 at 04:39:52PM -0400, Arvind Sankar wrote:
> > Without the barrier_data() inside memzero_explicit(), the compiler may
> > optimize away the state-clearing if it can tell that the state is not
> > used afterwards. At least in lib/crypto/sha256.c:__sha256_final(), the
> > function can get inlined into sha256(), in which case the memset is
> > optimized away.
> > 
> > Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
> 
> Reviewed-by: Eric Biggers <ebiggers@...gle.com>
> 
> Maybe get the one in arch/arm64/crypto/sha3-ce-glue.c too?
> 
> - Eric

Hm, there are a few more as well like that. But now I'm thinking it's
only the generic sha256.c that may be problematic. The rest of them are
in _final() functions which will be stored as function pointers in a
structure, so there should be no risk of them getting optimized away?