linux-kernel - [PATCH v4 1/6] crypto: lib/sha256 - Use memzero

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Message-Id: <20201025143119.1054168-2-nivedita@alum.mit.edu>
Date:   Sun, 25 Oct 2020 10:31:14 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        Eric Biggers <ebiggers@...nel.org>,
        David Laight <David.Laight@...lab.com>
Cc:     linux-kernel@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>
Subject: [PATCH v4 1/6] crypto: lib/sha256 - Use memzero_explicit() for clearing state

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>
---
 lib/crypto/sha256.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/crypto/sha256.c b/lib/crypto/sha256.c
index 2321f6cb322f..d43bc39ab05e 100644
--- a/lib/crypto/sha256.c
+++ b/lib/crypto/sha256.c
@@ -265,7 +265,7 @@ static void __sha256_final(struct sha256_state *sctx, u8 *out, int digest_words)
 		put_unaligned_be32(sctx->state[i], &dst[i]);
 
 	/* Zeroize sensitive information. */
-	memset(sctx, 0, sizeof(*sctx));
+	memzero_explicit(sctx, sizeof(*sctx));
 }
 
 void sha256_final(struct sha256_state *sctx, u8 *out)
-- 
2.26.2