[PATCH] SoC: cros_ec_codec: switch to library API for SHA-256

[Ard Biesheuvel <ardb@kernel.org>]

The CrOS EC codec driver uses SHA-256 explicitly, and not in a
performance critical manner, so there is really no point in using
the dynamic SHASH crypto API here. Let's switch to the library API
instead.

Cc: Cheng-Yi Chiang <cychiang@chromium.org> 
Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: Benson Leung <bleung@chromium.org>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
Looking at the code, I was wondering if the SHA-256 is really required
here? It looks like it is using it as some kind of fingerprint to decide
whether the provided file is identical to the one that has already been
loaded. If this is the case, we should probably just use CRC32 instead.

Also, do we really need to wipe the context struct? Is there any security
sensitive data in there?

 sound/soc/codecs/Kconfig         |  3 +--
 sound/soc/codecs/cros_ec_codec.c | 21 +++++---------------
 2 files changed, 6 insertions(+), 18 deletions(-)

diff --git a/sound/soc/codecs/Kconfig b/sound/soc/codecs/Kconfig
index e6a0c5d05fa5..c7ce4cc658cf 100644
--- a/sound/soc/codecs/Kconfig
+++ b/sound/soc/codecs/Kconfig
@@ -537,8 +537,7 @@ config SND_SOC_CQ0093VC
 config SND_SOC_CROS_EC_CODEC
 	tristate "codec driver for ChromeOS EC"
 	depends on CROS_EC
-	select CRYPTO
-	select CRYPTO_SHA256
+	select CRYPTO_LIB_SHA256
 	help
 	  If you say yes here you will get support for the
 	  ChromeOS Embedded Controller's Audio Codec.
diff --git a/sound/soc/codecs/cros_ec_codec.c b/sound/soc/codecs/cros_ec_codec.c
index d3dc42aa6825..6bc02c485ab2 100644
--- a/sound/soc/codecs/cros_ec_codec.c
+++ b/sound/soc/codecs/cros_ec_codec.c
@@ -107,24 +107,13 @@ static int send_ec_host_command(struct cros_ec_device *ec_dev, uint32_t cmd,
 static int calculate_sha256(struct cros_ec_codec_priv *priv,
 			    uint8_t *buf, uint32_t size, uint8_t *digest)
 {
-	struct crypto_shash *tfm;
+	struct sha256_state sctx;
 
-	tfm = crypto_alloc_shash("sha256", CRYPTO_ALG_TYPE_SHASH, 0);
-	if (IS_ERR(tfm)) {
-		dev_err(priv->dev, "can't alloc shash\n");
-		return PTR_ERR(tfm);
-	}
-
-	{
-		SHASH_DESC_ON_STACK(desc, tfm);
-
-		desc->tfm = tfm;
-
-		crypto_shash_digest(desc, buf, size, digest);
-		shash_desc_zero(desc);
-	}
+	sha256_init(&sctx);
+	sha256_update(&sctx, buf, size);
+	sha256_final(&sctx, digest);
 
-	crypto_free_shash(tfm);
+	memzero_explicit(&sctx, sizeof(sctx));
 
 #ifdef DEBUG
 	{
-- 
2.17.1