[PATCH v5 1/7] crypto: qce - Fix HMAC self-test failures for empty messages

[Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>]

BAM DMA cannot process zero-length transfers. For plain hashes this is
handled by returning the precomputed hash of the empty message
(tmpl->hash_zero), but for keyed HMAC the result depends on the key and
cannot be a constant. As a result, hmac(sha256) produced an incorrect
digest for an empty message and the crypto self-tests failed.

Use the preallocated fallback ahash for the HMAC transforms to compute
the digest whenever the message is empty (in both the .final() and
.digest() paths).

Cc: stable@vger.kernel.org
Fixes: ec8f5d8f6f76 ("crypto: qce - Qualcomm crypto engine driver")
Tested-by: Kuldeep Singh <kuldeep.singh@oss.qualcomm.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
---
 drivers/crypto/qce/sha.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/crypto/qce/sha.c b/drivers/crypto/qce/sha.c
index 0a3f88aaf5169ea7b47a549bbc10ea87d3ae7a2b..03b58a83e540802e88fbf1394108da35188b68bc 100644
--- a/drivers/crypto/qce/sha.c
+++ b/drivers/crypto/qce/sha.c
@@ -270,6 +270,25 @@ static int qce_ahash_update(struct ahash_request *req)
 	return qce->async_req_enqueue(tmpl->qce, &req->base);
 }
 
+/*
+ * BAM DMA cannot handle zero-length transfers. For plain hashes the result of
+ * an empty message is a known constant (hash_zero), for keyed HMAC it depends
+ * on the key, so compute it with the software fallback.
+ */
+static int qce_ahash_hmac_zero(struct ahash_request *req)
+{
+	HASH_FBREQ_ON_STACK(fbreq, req);
+	struct scatterlist sg;
+	int ret;
+
+	sg_init_one(&sg, NULL, 0);
+	ahash_request_set_crypt(fbreq, &sg, req->result, 0);
+	ret = crypto_ahash_digest(fbreq);
+	HASH_REQUEST_ZERO(fbreq);
+
+	return ret;
+}
+
 static int qce_ahash_final(struct ahash_request *req)
 {
 	struct qce_sha_reqctx *rctx = ahash_request_ctx_dma(req);
@@ -280,6 +299,8 @@ static int qce_ahash_final(struct ahash_request *req)
 		if (tmpl->hash_zero)
 			memcpy(req->result, tmpl->hash_zero,
 					tmpl->alg.ahash.halg.digestsize);
+		else if (IS_SHA_HMAC(rctx->flags))
+			return qce_ahash_hmac_zero(req);
 		return 0;
 	}
 
@@ -317,6 +338,8 @@ static int qce_ahash_digest(struct ahash_request *req)
 		if (tmpl->hash_zero)
 			memcpy(req->result, tmpl->hash_zero,
 					tmpl->alg.ahash.halg.digestsize);
+		else if (IS_SHA_HMAC(rctx->flags))
+			return qce_ahash_hmac_zero(req);
 		return 0;
 	}
 

-- 
2.47.3