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@alum.mit.edu>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/lib/crypto/sha256.c b/lib/crypto/sha256.c
index 2321f6c..d43bc39 100644 (file)
--- 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)