1 /*
2  * livepatch-sample.c - Kernel Live Patching Sample Module
3  *
4  * Copyright (C) 2014 Seth Jennings <[email protected]>
5  *
6  * This program is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public License
8  * as published by the Free Software Foundation; either version 2
9  * of the License, or (at your option) any later version.
10  *
11  * This program is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14  * GNU General Public License for more details.
15  *
16  * You should have received a copy of the GNU General Public License
17  * along with this program; if not, see <http://www.gnu.org/licenses/>.
18  */
19 
20 #include <linux/module.h>
21 #include <linux/kernel.h>
22 #include <linux/livepatch.h>
23 
24 /*
25  * This (dumb) live patch overrides the function that prints the
26  * kernel boot cmdline when /proc/cmdline is read.
27  *
28  * Example:
29  * $ cat /proc/cmdline
30  * <your cmdline>
31  * $ insmod livepatch-sample.ko
32  * $ cat /proc/cmdline
33  * this has been live patched
34  * $ echo 0 > /sys/kernel/livepatch/klp_sample/enabled
35  * <your cmdline>
36  */
37 
38 #include <linux/seq_file.h>
39 static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
40 {
41 	seq_printf(m, "%s\n", "this has been live patched");
42 	return 0;
43 }
44 
45 static struct klp_func funcs[] = {
46 	{
47 		.old_name = "cmdline_proc_show",
48 		.new_func = livepatch_cmdline_proc_show,
49 	}, { }
50 };
51 
52 static struct klp_object objs[] = {
53 	{
54 		/* name being NULL means vmlinux */
55 		.funcs = funcs,
56 	}, { }
57 };
58 
59 static struct klp_patch patch = {
60 	.mod = THIS_MODULE,
61 	.objs = objs,
62 };
63 
64 static int livepatch_init(void)
65 {
66 	int ret;
67 
68 	ret = klp_register_patch(&patch);
69 	if (ret)
70 		return ret;
71 	ret = klp_enable_patch(&patch);
72 	if (ret) {
73 		WARN_ON(klp_unregister_patch(&patch));
74 		return ret;
75 	}
76 	return 0;
77 }
78 
79 static void livepatch_exit(void)
80 {
81 	WARN_ON(klp_disable_patch(&patch));
82 	WARN_ON(klp_unregister_patch(&patch));
83 }
84 
85 module_init(livepatch_init);
86 module_exit(livepatch_exit);
87 MODULE_LICENSE("GPL");
88