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13d1cf7e SJ |
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 | ||
d83a7cb3 JP |
20 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
21 | ||
13d1cf7e SJ |
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: | |
700a3048 | 31 | * |
13d1cf7e SJ |
32 | * $ cat /proc/cmdline |
33 | * <your cmdline> | |
700a3048 | 34 | * |
13d1cf7e SJ |
35 | * $ insmod livepatch-sample.ko |
36 | * $ cat /proc/cmdline | |
37 | * this has been live patched | |
700a3048 JP |
38 | * |
39 | * $ echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled | |
40 | * $ cat /proc/cmdline | |
13d1cf7e SJ |
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 | ||
d83a7cb3 JP |
74 | if (!klp_have_reliable_stack() && !patch.immediate) { |
75 | /* | |
76 | * WARNING: Be very careful when using 'patch.immediate' in | |
77 | * your patches. It's ok to use it for simple patches like | |
78 | * this, but for more complex patches which change function | |
79 | * semantics, locking semantics, or data structures, it may not | |
80 | * be safe. Use of this option will also prevent removal of | |
81 | * the patch. | |
82 | * | |
83 | * See Documentation/livepatch/livepatch.txt for more details. | |
84 | */ | |
85 | patch.immediate = true; | |
86 | pr_notice("The consistency model isn't supported for your architecture. Bypassing safety mechanisms and applying the patch immediately.\n"); | |
87 | } | |
88 | ||
13d1cf7e SJ |
89 | ret = klp_register_patch(&patch); |
90 | if (ret) | |
91 | return ret; | |
92 | ret = klp_enable_patch(&patch); | |
93 | if (ret) { | |
94 | WARN_ON(klp_unregister_patch(&patch)); | |
95 | return ret; | |
96 | } | |
97 | return 0; | |
98 | } | |
99 | ||
100 | static void livepatch_exit(void) | |
101 | { | |
13d1cf7e SJ |
102 | WARN_ON(klp_unregister_patch(&patch)); |
103 | } | |
104 | ||
105 | module_init(livepatch_init); | |
106 | module_exit(livepatch_exit); | |
107 | MODULE_LICENSE("GPL"); | |
425595a7 | 108 | MODULE_INFO(livepatch, "Y"); |