samples/livepatch/livepatch-sample.c

   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");