1 /*
2  * livepatch-sample.c - Kernel Live Patching Sample Module
3  *
4  * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
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  *
30  * $ cat /proc/cmdline
31  * <your cmdline>
32  *
33  * $ insmod livepatch-sample.ko
34  * $ cat /proc/cmdline
35  * this has been live patched
36  *
37  * $ echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
38  * $ cat /proc/cmdline
39  * <your cmdline>
40  */
41 
42 #include <linux/seq_file.h>
43 static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
44 {
45 	seq_printf(m, "%s\n", "this has been live patched");
46 	return 0;
47 }
48 
49 static struct klp_func funcs[] = {
50 	{
51 		.old_name = "cmdline_proc_show",
52 		.new_func = livepatch_cmdline_proc_show,
53 	}, { }
54 };
55 
56 static struct klp_object objs[] = {
57 	{
58 		/* name being NULL means vmlinux */
59 		.funcs = funcs,
60 	}, { }
61 };
62 
63 static struct klp_patch patch = {
64 	.mod = THIS_MODULE,
65 	.objs = objs,
66 };
67 
68 static int livepatch_init(void)
69 {
70 	int ret;
71 
72 	ret = klp_register_patch(&patch);
73 	if (ret)
74 		return ret;
75 	ret = klp_enable_patch(&patch);
76 	if (ret) {
77 		WARN_ON(klp_unregister_patch(&patch));
78 		return ret;
79 	}
80 	return 0;
81 }
82 
83 static void livepatch_exit(void)
84 {
85 	WARN_ON(klp_disable_patch(&patch));
86 	WARN_ON(klp_unregister_patch(&patch));
87 }
88 
89 module_init(livepatch_init);
90 module_exit(livepatch_exit);
91 MODULE_LICENSE("GPL");
92