LXR linux/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>
  43static 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
  49static struct klp_func funcs[] = {
  50        {
  51                .old_name = "cmdline_proc_show",
  52                .new_func = livepatch_cmdline_proc_show,
  53        }, { }
  54};
  55
  56static struct klp_object objs[] = {
  57        {
  58                /* name being NULL means vmlinux */
  59                .funcs = funcs,
  60        }, { }
  61};
  62
  63static struct klp_patch patch = {
  64        .mod = THIS_MODULE,
  65        .objs = objs,
  66};
  67
  68static 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
  83static void livepatch_exit(void)
  84{
  85        WARN_ON(klp_disable_patch(&patch));
  86        WARN_ON(klp_unregister_patch(&patch));
  87}
  88
  89module_init(livepatch_init);
  90module_exit(livepatch_exit);
  91MODULE_LICENSE("GPL");
  92