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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
21 
22 #include <linux/module.h>
23 #include <linux/kernel.h>
24 #include <linux/livepatch.h>
25 
26 /*
27  * This (dumb) live patch overrides the function that prints the
28  * kernel boot cmdline when /proc/cmdline is read.
29  *
30  * Example:
31  *
32  * $ cat /proc/cmdline
33  * <your cmdline>
34  *
35  * $ insmod livepatch-sample.ko
36  * $ cat /proc/cmdline
37  * this has been live patched
38  *
39  * $ echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
40  * $ cat /proc/cmdline
41  * <your cmdline>
42  */
43 
44 #include <linux/seq_file.h>
45 static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
46 {
47 	seq_printf(m, "%s\n", "this has been live patched");
48 	return 0;
49 }
50 
51 static struct klp_func funcs[] = {
52 	{
53 		.old_name = "cmdline_proc_show",
54 		.new_func = livepatch_cmdline_proc_show,
55 	}, { }
56 };
57 
58 static struct klp_object objs[] = {
59 	{
60 		/* name being NULL means vmlinux */
61 		.funcs = funcs,
62 	}, { }
63 };
64 
65 static struct klp_patch patch = {
66 	.mod = THIS_MODULE,
67 	.objs = objs,
68 };
69 
70 static int livepatch_init(void)
71 {
72 	int ret;
73 
74 	ret = klp_register_patch(&patch);
75 	if (ret)
76 		return ret;
77 	ret = klp_enable_patch(&patch);
78 	if (ret) {
79 		WARN_ON(klp_unregister_patch(&patch));
80 		return ret;
81 	}
82 	return 0;
83 }
84 
85 static void livepatch_exit(void)
86 {
87 	WARN_ON(klp_unregister_patch(&patch));
88 }
89 
90 module_init(livepatch_init);
91 module_exit(livepatch_exit);
92 MODULE_LICENSE("GPL");
93 MODULE_INFO(livepatch, "Y");
94