crypto: inside-secure - add support for 0 length HMAC messages

This patch adds support for the specific corner case of performing HMAC
on an empty string (i.e. payload length is zero). This solves the last
failing cryptomgr extratests for HMAC.
Signed-off-by: Pascal van Leeuwen <pvanleeuwen@verimatrix.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/inside-secure/safexcel_hash.c

@@ -29,6 +29,8 @@ struct safexcel_ahash_req {
 	bool finish;
 	bool hmac;
 	bool needs_inv;
+	bool hmac_zlen;
+	bool len_is_le;
 
 	int nents;
 	dma_addr_t result_dma;
@@ -117,7 +119,7 @@ static void safexcel_context_control(struct safexcel_ahash_ctx *ctx,
 	if (req->finish) {
 		/* Compute digest count for hash/HMAC finish operations */
 		if ((req->digest == CONTEXT_CONTROL_DIGEST_PRECOMPUTED) ||
-		    req->processed[1] ||
+		    req->hmac_zlen || req->processed[1] ||
 		    (req->processed[0] != req->block_sz)) {
 			count = req->processed[0] / EIP197_COUNTER_BLOCK_SIZE;
 			count += ((0x100000000ULL / EIP197_COUNTER_BLOCK_SIZE) *
@@ -136,6 +138,8 @@ static void safexcel_context_control(struct safexcel_ahash_ctx *ctx,
 		}
 
 		if ((req->digest == CONTEXT_CONTROL_DIGEST_PRECOMPUTED) ||
+		    /* Special case: zero length HMAC */
+		    req->hmac_zlen ||
 		    /* PE HW < 4.4 cannot do HMAC continue, fake using hash */
 		    ((req->processed[1] ||
 		      (req->processed[0] != req->block_sz)))) {
@@ -144,11 +148,18 @@ static void safexcel_context_control(struct safexcel_ahash_ctx *ctx,
 				CONTEXT_CONTROL_SIZE((req->state_sz >> 2) + 1) |
 				CONTEXT_CONTROL_TYPE_HASH_OUT |
 				CONTEXT_CONTROL_DIGEST_PRECOMPUTED;
+			/* For zero-len HMAC, don't finalize, already padded! */
+			if (req->hmac_zlen)
+				cdesc->control_data.control0 |=
+					CONTEXT_CONTROL_NO_FINISH_HASH;
 			cdesc->control_data.control1 |=
 				CONTEXT_CONTROL_DIGEST_CNT;
 			ctx->base.ctxr->data[req->state_sz >> 2] =
 				cpu_to_le32(count);
 			req->digest = CONTEXT_CONTROL_DIGEST_PRECOMPUTED;
+
+			/* Clear zero-length HMAC flag for next operation! */
+			req->hmac_zlen = false;
 		} else { /* HMAC */
 			/* Need outer digest for HMAC finalization */
 			memcpy(ctx->base.ctxr->data + (req->state_sz >> 2),
@@ -701,8 +712,37 @@ static int safexcel_ahash_final(struct ahash_request *areq)
 	} else if (unlikely(req->hmac && !req->len[1] &&
 			    (req->len[0] == req->block_sz) &&
 			    !areq->nbytes)) {
-		/* TODO: add support for zero length HMAC */
-		return 0;
+		/*
+		 * If we have an overall 0 length *HMAC* request:
+		 * For HMAC, we need to finalize the inner digest
+		 * and then perform the outer hash.
+		 */
+
+		/* generate pad block in the cache */
+		/* start with a hash block of all zeroes */
+		memset(req->cache, 0, req->block_sz);
+		/* set the first byte to 0x80 to 'append a 1 bit' */
+		req->cache[0] = 0x80;
+		/* add the length in bits in the last 2 bytes */
+		if (req->len_is_le) {
+			/* Little endian length word (e.g. MD5) */
+			req->cache[req->block_sz-8] = (req->block_sz << 3) &
+						      255;
+			req->cache[req->block_sz-7] = (req->block_sz >> 5);
+		} else {
+			/* Big endian length word (e.g. any SHA) */
+			req->cache[req->block_sz-2] = (req->block_sz >> 5);
+			req->cache[req->block_sz-1] = (req->block_sz << 3) &
+						      255;
+		}
+
+		req->len[0] += req->block_sz; /* plus 1 hash block */
+
+		/* Set special zero-length HMAC flag */
+		req->hmac_zlen = true;
+
+		/* Finalize HMAC */
+		req->digest = CONTEXT_CONTROL_DIGEST_HMAC;
 	} else if (req->hmac) {
 		/* Finalize HMAC */
 		req->digest = CONTEXT_CONTROL_DIGEST_HMAC;
@@ -1667,6 +1707,7 @@ static int safexcel_hmac_md5_init(struct ahash_request *areq)
 	req->digest = CONTEXT_CONTROL_DIGEST_PRECOMPUTED;
 	req->state_sz = MD5_DIGEST_SIZE;
 	req->block_sz = MD5_HMAC_BLOCK_SIZE;
+	req->len_is_le = true; /* MD5 is little endian! ... */
 	req->hmac = true;
 
 	return 0;