1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * livepatch-sample.c - Kernel Live Patching Sample Module
4  *
5  * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
6  */
7 
8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9 
10 #include <linux/module.h>
11 #include <linux/kernel.h>
12 #include <linux/livepatch.h>
13 
14 /*
15  * This (dumb) live patch overrides the function that prints the
16  * kernel boot cmdline when /proc/cmdline is read.
17  *
18  * Example:
19  *
20  * $ cat /proc/cmdline
21  * <your cmdline>
22  *
23  * $ insmod livepatch-sample.ko
24  * $ cat /proc/cmdline
25  * this has been live patched
26  *
27  * $ echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
28  * $ cat /proc/cmdline
29  * <your cmdline>
30  */
31 
32 #include <linux/seq_file.h>
33 static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
34 {
35 	seq_printf(m, "%s\n", "this has been live patched");
36 	return 0;
37 }
38 
39 static struct klp_func funcs[] = {
40 	{
41 		.old_name = "cmdline_proc_show",
42 		.new_func = livepatch_cmdline_proc_show,
43 	}, { }
44 };
45 
46 static struct klp_object objs[] = {
47 	{
48 		/* name being NULL means vmlinux */
49 		.funcs = funcs,
50 	}, { }
51 };
52 
53 static struct klp_patch patch = {
54 	.mod = THIS_MODULE,
55 	.objs = objs,
56 };
57 
58 static int livepatch_init(void)
59 {
60 	return klp_enable_patch(&patch);
61 }
62 
63 static void livepatch_exit(void)
64 {
65 }
66 
67 module_init(livepatch_init);
68 module_exit(livepatch_exit);
69 MODULE_LICENSE("GPL");
70 MODULE_INFO(livepatch, "Y");
71