feat(auth): compare platform and certificate ROTPK for authentication

Compared the full ROTPK with the ROTPK obtained from the certificate
when the platform supports full ROTPK instead of hash of ROTPK.

Additionally, changed the code to verify the ROTPK before relying on
it for signature verification.

Change-Id: I52bb9deb1a1dd5b184d3156bddad14c238692de7
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>

2 files changed, 57 insertions, 34 deletions

diff --git a/drivers/auth/auth_mod.c b/drivers/auth/auth_mod.c
index 1bf03d409..f15306537 100644
--- a/drivers/auth/auth_mod.c
+++ b/drivers/auth/auth_mod.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2022, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2023, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -33,7 +33,6 @@
 #pragma weak plat_set_nv_ctr2
 #pragma weak plat_convert_pk
 
-
 static int cmp_auth_param_type_desc(const auth_param_type_desc_t *a,
 		const auth_param_type_desc_t *b)
 {
@@ -150,8 +149,8 @@ static int auth_signature(const auth_method_param_sig_t *param,
 			  const auth_img_desc_t *img_desc,
 			  void *img, unsigned int img_len)
 {
-	void *data_ptr, *pk_ptr, *pk_hash_ptr, *sig_ptr, *sig_alg_ptr;
-	unsigned int data_len, pk_len, pk_hash_len, sig_len, sig_alg_len;
+	void *data_ptr, *pk_ptr, *pk_plat_ptr, *sig_ptr, *sig_alg_ptr;
+	unsigned int data_len, pk_len, pk_plat_len, sig_len, sig_alg_len;
 	unsigned int flags = 0;
 	int rc = 0;
 
@@ -173,52 +172,69 @@ static int auth_signature(const auth_method_param_sig_t *param,
 	/* Get the public key from the parent. If there is no parent (NULL),
 	 * the certificate has been signed with the ROTPK, so we have to get
 	 * the PK from the platform */
-	if (img_desc->parent) {
+	if (img_desc->parent != NULL) {
 		rc = auth_get_param(param->pk, img_desc->parent,
 				&pk_ptr, &pk_len);
+		return_if_error(rc);
 	} else {
-		rc = plat_get_rotpk_info(param->pk->cookie, &pk_ptr, &pk_len,
-				&flags);
-	}
-	return_if_error(rc);
-
-	if (flags & (ROTPK_IS_HASH | ROTPK_NOT_DEPLOYED)) {
-		/* If the PK is a hash of the key or if the ROTPK is not
-		   deployed on the platform, retrieve the key from the image */
-		pk_hash_ptr = pk_ptr;
-		pk_hash_len = pk_len;
-		rc = img_parser_get_auth_param(img_desc->img_type,
-					param->pk, img, img_len,
-					&pk_ptr, &pk_len);
+		/*
+		 * Root certificates are signed with the ROTPK, so we have to
+		 * get it from the platform.
+		 */
+		rc = plat_get_rotpk_info(param->pk->cookie, &pk_plat_ptr,
+					 &pk_plat_len, &flags);
 		return_if_error(rc);
 
-		/* Ask the crypto module to verify the signature */
-		rc = crypto_mod_verify_signature(data_ptr, data_len,
-						 sig_ptr, sig_len,
-						 sig_alg_ptr, sig_alg_len,
-						 pk_ptr, pk_len);
+		assert(is_rotpk_flags_valid(flags));
+
+		/* Also retrieve the key from the image. */
+		rc = img_parser_get_auth_param(img_desc->img_type,
+					       param->pk, img, img_len,
+					       &pk_ptr, &pk_len);
 		return_if_error(rc);
 
-		if (flags & ROTPK_NOT_DEPLOYED) {
+		/*
+		 * Validate the certificate's key against the platform ROTPK.
+		 *
+		 * Platform may store key in one of the following way -
+		 * 1. Hash of ROTPK
+		 * 2. Hash if prefixed, suffixed or modified ROTPK
+		 * 3. Full ROTPK
+		 */
+		if ((flags & ROTPK_NOT_DEPLOYED) != 0U) {
 			NOTICE("ROTPK is not deployed on platform. "
 				"Skipping ROTPK verification.\n");
-		} else {
-			/* platform may store the hash of a prefixed, suffixed or modified pk */
+		} else if ((flags & ROTPK_IS_HASH) != 0U) {
+			/*
+			 * platform may store the hash of a prefixed,
+			 * suffixed or modified pk
+			 */
 			rc = plat_convert_pk(pk_ptr, pk_len, &pk_ptr, &pk_len);
 			return_if_error(rc);
 
-			/* Ask the crypto-module to verify the key hash */
+			/*
+			 * The hash of the certificate's public key must match
+			 * the hash of the ROTPK.
+			 */
 			rc = crypto_mod_verify_hash(pk_ptr, pk_len,
-				    pk_hash_ptr, pk_hash_len);
+						    pk_plat_ptr, pk_plat_len);
+			return_if_error(rc);
+		} else {
+			/* Platform supports full ROTPK */
+			if ((pk_len != pk_plat_len) ||
+			    (memcmp(pk_plat_ptr, pk_ptr, pk_len) != 0)) {
+				ERROR("plat and cert ROTPK len mismatch\n");
+				return -1;
+			}
 		}
-	} else {
-		/* Ask the crypto module to verify the signature */
-		rc = crypto_mod_verify_signature(data_ptr, data_len,
-						 sig_ptr, sig_len,
-						 sig_alg_ptr, sig_alg_len,
-						 pk_ptr, pk_len);
 	}
 
+	/* Ask the crypto module to verify the signature */
+	rc = crypto_mod_verify_signature(data_ptr, data_len,
+					 sig_ptr, sig_len,
+					 sig_alg_ptr, sig_alg_len,
+					 pk_ptr, pk_len);
+
 	return rc;
 }
 
diff --git a/include/plat/common/platform.h b/include/plat/common/platform.h
index a14d77504..72d316018 100644
--- a/include/plat/common/platform.h
+++ b/include/plat/common/platform.h
@@ -44,10 +44,17 @@ enum fw_enc_status_t;
  * plat_get_rotpk_info() flags
  ******************************************************************************/
 #define ROTPK_IS_HASH			(1 << 0)
+
 /* Flag used to skip verification of the certificate ROTPK while the platform
    ROTPK is not deployed */
 #define ROTPK_NOT_DEPLOYED		(1 << 1)
 
+static inline bool is_rotpk_flags_valid(unsigned int flags)
+{
+	unsigned int valid_flags = ROTPK_IS_HASH;
+	return (flags == ROTPK_NOT_DEPLOYED) || ((flags & ~valid_flags) == 0);
+}
+
 /*******************************************************************************
  * plat_get_enc_key_info() flags
  ******************************************************************************/