core: rpmb: select the provisioning target by CID

When several RPMB-capable devices are present, key provisioning must not
land on an arbitrary one: writing the key to the wrong device is hard to
undo and leaves the intended device unprovisioned. CFG_RPMB_WRITE_KEY_CID
lets a controlled (factory) setup pin provisioning to a known device so
the outcome is deterministic.

Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez@oss.qualcomm.com>

Author: ldts

core/tee/tee_rpmb_fs.c

@@ -1186,6 +1186,28 @@ static TEE_Result rpmb_set_dev_info(const struct rpmb_dev_info *dev_info)
 	return TEE_SUCCESS;
 }
 
+#ifdef CFG_RPMB_WRITE_KEY_CID
+static bool rpmb_cid_match(const uint8_t *cid)
+{
+	char *hs = (char *)TO_STR(CFG_RPMB_WRITE_KEY_CID);
+	uint8_t want[RPMB_CID_SIZE] = { };
+	uint32_t n = 0;
+
+	n = tee_hs2b((uint8_t *)hs, want, strlen(hs), sizeof(want));
+	if (n != RPMB_CID_SIZE) {
+		EMSG("Invalid CFG_RPMB_WRITE_KEY_CID");
+		return false;
+	}
+
+	return !memcmp(cid, want, RPMB_CID_SIZE);
+}
+#else
+static bool rpmb_cid_match(const uint8_t *cid __unused)
+{
+	return true;
+}
+#endif
+
 static TEE_Result legacy_rpmb_init(void)
 {
 	TEE_Result res = TEE_SUCCESS;
@@ -1240,7 +1262,10 @@ static TEE_Result legacy_rpmb_init(void)
 			 * Need to write the key here and verify it.
 			 */
 			DMSG("RPMB INIT: Auth key not yet written");
-			res = tee_rpmb_write_and_verify_key();
+			if (rpmb_cid_match(rpmb_ctx->cid))
+				res = tee_rpmb_write_and_verify_key();
+			else
+				EMSG("CID mismatch, CFG_RPMB_WRITE_KEY_CID");
 		} else {
 			EMSG("Verify key failed! %#"PRIx32, res);
 			EMSG("Make sure key here matches device key");
@@ -1257,8 +1282,12 @@ static bool rpmb_ctx_list_empty(void)
 
 static TEE_Result add_rpmb_ctx_to_list(void)
 {
-	struct rpmb_ctx_candidate *cand = calloc(1, sizeof(*cand));
+	struct rpmb_ctx_candidate *cand = NULL;
+
+	if (!rpmb_cid_match(rpmb_ctx->cid))
+		return TEE_SUCCESS;
 
+	cand = calloc(1, sizeof(*cand));
 	if (!cand)
 		return TEE_ERROR_OUT_OF_MEMORY;
 

mk/config.mk

@@ -231,6 +231,10 @@ CFG_RPMB_TESTKEY ?= n
 # - RPMB key provisioning in a controlled environment (factory setup)
 CFG_RPMB_WRITE_KEY ?= n
 
+# Restricts RPMB key provisioning to the device whose CID matches this
+# upper-case hex string (2 * RPMB_CID_SIZE chars). Unset: provision the first.
+# CFG_RPMB_WRITE_KEY_CID ?= 112233445566778899AABBCCDDEEFF00
+
 # For the kernel driver to enable in-kernel RPMB routing it must know in
 # advance that OP-TEE supports it. Setting CFG_RPMB_ANNOUNCE_PROBE_CAP=y
 # will announce OP-TEE's capability for RPMB probing to the kernel and it