powerpc/powernv: Fix the overflow of OPAL message notifiers head array

Fixes the condition check of incoming message type which can
otherwise shoot beyond the message notifiers head array.

Signed-off-by: Neelesh Gupta <neelegup@linux.vnet.ibm.com>
Reviewed-by: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>
Reviewed-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/powernv/opal.c

@@ -308,16 +308,12 @@ void opal_notifier_disable(void)
 int opal_message_notifier_register(enum OpalMessageType msg_type,
 					struct notifier_block *nb)
 {
-	if (!nb) {
-		pr_warning("%s: Invalid argument (%p)\n",
-			   __func__, nb);
-		return -EINVAL;
-	}
-	if (msg_type > OPAL_MSG_TYPE_MAX) {
-		pr_warning("%s: Invalid message type argument (%d)\n",
+	if (!nb || msg_type >= OPAL_MSG_TYPE_MAX) {
+		pr_warning("%s: Invalid arguments, msg_type:%d\n",
 			   __func__, msg_type);
 		return -EINVAL;
 	}
+
 	return atomic_notifier_chain_register(
 				&opal_msg_notifier_head[msg_type], nb);
 }
@@ -354,7 +350,7 @@ static void opal_handle_message(void)
 	type = be32_to_cpu(msg.msg_type);
 
 	/* Sanity check */
-	if (type > OPAL_MSG_TYPE_MAX) {
+	if (type >= OPAL_MSG_TYPE_MAX) {
 		pr_warning("%s: Unknown message type: %u\n", __func__, type);
 		return;
 	}