From: Ard Biesheuvel <ardb@kernel.org>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: 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>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH v4 1/6] crypto: lib/sha256 - Use memzero_explicit() for clearing state
Date: Mon, 26 Oct 2020 08:59:07 +0100 [thread overview]
Message-ID: <CAMj1kXE618YtdrCg7BRqiD2K4S2x1S7L7gZgS+25WUNM+Q8TFw@mail.gmail.com> (raw)
In-Reply-To: <20201025143119.1054168-2-nivedita@alum.mit.edu>
On Sun, 25 Oct 2020 at 15:31, Arvind Sankar <nivedita@alum.mit.edu> 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@alum.mit.edu>
> Reviewed-by: Eric Biggers <ebiggers@google.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> 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
>
next prev parent reply other threads:[~2020-10-26 7:59 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-25 14:31 [PATCH v4 0/6] crypto: lib/sha256 - cleanup/optimization Arvind Sankar
2020-10-25 14:31 ` [PATCH v4 1/6] crypto: lib/sha256 - Use memzero_explicit() for clearing state Arvind Sankar
2020-10-26 7:59 ` Ard Biesheuvel [this message]
2020-10-25 14:31 ` [PATCH v4 2/6] crypto: " Arvind Sankar
2020-10-26 7:58 ` Ard Biesheuvel
2020-10-25 14:31 ` [PATCH v4 3/6] crypto: lib/sha256 - Don't clear temporary variables Arvind Sankar
2020-10-26 7:59 ` Ard Biesheuvel
2020-10-25 14:31 ` [PATCH v4 4/6] crypto: lib/sha256 - Clear W[] in sha256_update() instead of sha256_transform() Arvind Sankar
2020-10-26 8:00 ` Ard Biesheuvel
2020-10-25 14:31 ` [PATCH v4 5/6] crypto: lib/sha256 - Unroll SHA256 loop 8 times intead of 64 Arvind Sankar
2020-10-26 8:00 ` Ard Biesheuvel
2020-10-25 14:31 ` [PATCH v4 6/6] crypto: lib/sha256 - Unroll LOAD and BLEND loops Arvind Sankar
2020-10-25 18:51 ` David Laight
2020-10-25 20:18 ` Arvind Sankar
2020-10-25 23:23 ` David Laight
2020-10-25 23:53 ` Arvind Sankar
2020-10-26 10:06 ` David Laight
2020-10-26 8:02 ` Ard Biesheuvel
2020-10-30 6:53 ` [PATCH v4 0/6] crypto: lib/sha256 - cleanup/optimization Herbert Xu
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