diff --git a/Documentation/security/keys.txt b/Documentation/security/keys.txt
index e35de987fc48..5fe04a7cc03d 100644
--- a/Documentation/security/keys.txt
+++ b/Documentation/security/keys.txt
@@ -1445,6 +1445,15 @@ The structure has a number of fields, some of which are mandatory:
      	 The authorisation key.
 
 
+ (*) struct key_restriction *(*lookup_restriction)(const char *params);
+
+     This optional method is used to enable userspace configuration of keyring
+     restrictions. The restriction parameter string (not including the key type
+     name) is passed in, and this method returns a pointer to a key_restriction
+     structure containing the relevant functions and data to evaluate each
+     attempted key link operation. If there is no match, -EINVAL is returned.
+
+
 ============================
 REQUEST-KEY CALLBACK SERVICE
 ============================
diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index eaee981c5558..8496cf64575c 100644
--- a/include/linux/key-type.h
+++ b/include/linux/key-type.h
@@ -147,6 +147,14 @@ struct key_type {
 	 */
 	request_key_actor_t request_key;
 
+	/* Look up a keyring access restriction (optional)
+	 *
+	 * - NULL is a valid return value (meaning the requested restriction
+	 *   is known but will never block addition of a key)
+	 * - should return -EINVAL if the restriction is unknown
+	 */
+	struct key_restriction *(*lookup_restriction)(const char *params);
+
 	/* internal fields */
 	struct list_head	link;		/* link in types list */
 	struct lock_class_key	lock_class;	/* key->sem lock class */