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 <[e-mail]>
Reviewed-by: Eric Biggers <[e-mail]>
Acked-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

lib/crypto/sha256.c

···
 		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)