diff -Naur xattr-a/include/uapi/linux/xattr.h xattr-b/include/uapi/linux/xattr.h
--- xattr-a/include/uapi/linux/xattr.h	2023-12-19 20:22:20.000000000 +1100
+++ xattr-b/include/uapi/linux/xattr.h	2023-12-24 13:31:57.653254146 +1100
@@ -81,5 +81,9 @@
 #define XATTR_POSIX_ACL_DEFAULT  "posix_acl_default"
 #define XATTR_NAME_POSIX_ACL_DEFAULT XATTR_SYSTEM_PREFIX XATTR_POSIX_ACL_DEFAULT
 
+/* User namespace */
+#define XATTR_PAX_PREFIX XATTR_USER_PREFIX "pax."
+#define XATTR_PAX_FLAGS_SUFFIX "flags"
+#define XATTR_NAME_PAX_FLAGS XATTR_PAX_PREFIX XATTR_PAX_FLAGS_SUFFIX
 
 #endif /* _UAPI_LINUX_XATTR_H */
diff -Naur xattr-a/mm/shmem.c xattr-b/mm/shmem.c
--- xattr-a/mm/shmem.c	2023-12-19 20:22:20.000000000 +1100
+++ xattr-b/mm/shmem.c	2023-12-24 13:31:57.803254146 +1100
@@ -3649,6 +3649,14 @@
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
 
+
+	if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
+		if (strcmp(name, XATTR_NAME_PAX_FLAGS))
+			return -EOPNOTSUPP;
+		if (size > 8)
+			return -EINVAL;
+	}
+
 	name = xattr_full_name(handler, name);
 	return simple_xattr_get(&info->xattrs, name, buffer, size);
 }