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 #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         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
  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 {
 102         WARN_ON(klp_unregister_patch(&patch));
 103 }
 104
 105 module_init(livepatch_init);
 106 module_exit(livepatch_exit);
 107 MODULE_LICENSE("GPL");
 108 MODULE_INFO(livepatch, "Y");