+/**
+ * restrict_link_to_builtin_trusted - Restrict keyring addition by built in CA
+ *
+ * Restrict the addition of keys into a keyring based on the key-to-be-added
+ * being vouched for by a key in the built in system keyring.
+ */
+int restrict_link_by_builtin_trusted(struct key *keyring,
+ const struct key_type *type,
+ const union key_payload *payload)
+{
+ return restrict_link_by_signature(builtin_trusted_keys, type, payload);
+}
+
+#ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
+/**
+ * restrict_link_by_builtin_and_secondary_trusted - Restrict keyring
+ * addition by both builtin and secondary keyrings
+ *
+ * Restrict the addition of keys into a keyring based on the key-to-be-added
+ * being vouched for by a key in either the built-in or the secondary system
+ * keyrings.
+ */
+int restrict_link_by_builtin_and_secondary_trusted(
+ struct key *keyring,
+ const struct key_type *type,
+ const union key_payload *payload)
+{
+ /* If we have a secondary trusted keyring, then that contains a link
+ * through to the builtin keyring and the search will follow that link.
+ */
+ if (type == &key_type_keyring &&
+ keyring == secondary_trusted_keys &&
+ payload == &builtin_trusted_keys->payload)
+ /* Allow the builtin keyring to be added to the secondary */
+ return 0;
+
+ return restrict_link_by_signature(secondary_trusted_keys, type, payload);
+}
+#endif
+