From: Arvind Sankar <nivedita@alum.mit.edu>
To: Herbert Xu <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>,
"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
Eric Biggers <ebiggers@kernel.org>,
David Laight <David.Laight@aculab.com>
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH v3 2/5] crypto: lib/sha256 - Don't clear temporary variables
Date: Fri, 23 Oct 2020 15:22:00 -0400 [thread overview]
Message-ID: <20201023192203.400040-3-nivedita@alum.mit.edu> (raw)
In-Reply-To: <20201023192203.400040-1-nivedita@alum.mit.edu>
The assignments to clear a through h and t1/t2 are optimized out by the
compiler because they are unused after the assignments.
Clearing individual scalar variables is unlikely to be useful, as they
may have been assigned to registers, and even if stack spilling was
required, there may be compiler-generated temporaries that are
impossible to clear in any case.
So drop the clearing of a through h and t1/t2.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
lib/crypto/sha256.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/lib/crypto/sha256.c b/lib/crypto/sha256.c
index d43bc39ab05e..099cd11f83c1 100644
--- a/lib/crypto/sha256.c
+++ b/lib/crypto/sha256.c
@@ -202,7 +202,6 @@ static void sha256_transform(u32 *state, const u8 *input)
state[4] += e; state[5] += f; state[6] += g; state[7] += h;
/* clear any sensitive info... */
- a = b = c = d = e = f = g = h = t1 = t2 = 0;
memzero_explicit(W, 64 * sizeof(u32));
}
--
2.26.2
next prev parent reply other threads:[~2020-10-23 19:22 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-23 19:21 [PATCH v3 0/5] crypto: lib/sha256 - cleanup/optimization Arvind Sankar
2020-10-23 19:21 ` [PATCH v3 1/5] crypto: Use memzero_explicit() for clearing state Arvind Sankar
2020-10-23 20:50 ` Herbert Xu
2020-10-23 19:22 ` Arvind Sankar [this message]
2020-10-23 22:11 ` [PATCH v3 2/5] crypto: lib/sha256 - Don't clear temporary variables Eric Biggers
2020-10-23 19:22 ` [PATCH v3 3/5] crypto: lib/sha256 - Clear W[] in sha256_update() instead of sha256_transform() Arvind Sankar
2020-10-23 19:22 ` [PATCH v3 4/5] crypto: lib/sha256 - Unroll SHA256 loop 8 times intead of 64 Arvind Sankar
2020-10-23 22:31 ` Eric Biggers
2020-10-23 19:22 ` [PATCH v3 5/5] crypto: lib/sha256 - Unroll LOAD and BLEND loops Arvind Sankar
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