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#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>
  45static 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
  51static struct klp_func funcs[] = {
  52        {
  53                .old_name = "cmdline_proc_show",
  54                .new_func = livepatch_cmdline_proc_show,
  55        }, { }
  56};
  57
  58static struct klp_object objs[] = {
  59        {
  60                /* name being NULL means vmlinux */
  61                .funcs = funcs,
  62        }, { }
  63};
  64
  65static struct klp_patch patch = {
  66        .mod = THIS_MODULE,
  67        .objs = objs,
  68};
  69
  70static 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
 100static void livepatch_exit(void)
 101{
 102        WARN_ON(klp_unregister_patch(&patch));
 103}
 104
 105module_init(livepatch_init);
 106module_exit(livepatch_exit);
 107MODULE_LICENSE("GPL");
 108MODULE_INFO(livepatch, "Y");
 109