samples/livepatch/livepatch-callbacks-demo.c

   1 /*
   2  * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 /*
  19  * livepatch-callbacks-demo.c - (un)patching callbacks livepatch demo
  20  *
  21  *
  22  * Purpose
  23  * -------
  24  *
  25  * Demonstration of registering livepatch (un)patching callbacks.
  26  *
  27  *
  28  * Usage
  29  * -----
  30  *
  31  * Step 1 - load the simple module
  32  *
  33  *   insmod samples/livepatch/livepatch-callbacks-mod.ko
  34  *
  35  *
  36  * Step 2 - load the demonstration livepatch (with callbacks)
  37  *
  38  *   insmod samples/livepatch/livepatch-callbacks-demo.ko
  39  *
  40  *
  41  * Step 3 - cleanup
  42  *
  43  *   echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
  44  *   rmmod livepatch_callbacks_demo
  45  *   rmmod livepatch_callbacks_mod
  46  *
  47  * Watch dmesg output to see livepatch enablement, callback execution
  48  * and patching operations for both vmlinux and module targets.
  49  *
  50  * NOTE: swap the insmod order of livepatch-callbacks-mod.ko and
  51  *       livepatch-callbacks-demo.ko to observe what happens when a
  52  *       target module is loaded after a livepatch with callbacks.
  53  *
  54  * NOTE: 'pre_patch_ret' is a module parameter that sets the pre-patch
  55  *       callback return status.  Try setting up a non-zero status
  56  *       such as -19 (-ENODEV):
  57  *
  58  *       # Load demo livepatch, vmlinux is patched
  59  *       insmod samples/livepatch/livepatch-callbacks-demo.ko
  60  *
  61  *       # Setup next pre-patch callback to return -ENODEV
  62  *       echo -19 > /sys/module/livepatch_callbacks_demo/parameters/pre_patch_ret
  63  *
  64  *       # Module loader refuses to load the target module
  65  *       insmod samples/livepatch/livepatch-callbacks-mod.ko
  66  *       insmod: ERROR: could not insert module samples/livepatch/livepatch-callbacks-mod.ko: No such device
  67  *
  68  * NOTE: There is a second target module,
  69  *       livepatch-callbacks-busymod.ko, available for experimenting
  70  *       with livepatch (un)patch callbacks.  This module contains
  71  *       a 'sleep_secs' parameter that parks the module on one of the
  72  *       functions that the livepatch demo module wants to patch.
  73  *       Modifying this value and tweaking the order of module loads can
  74  *       effectively demonstrate stalled patch transitions:
  75  *
  76  *       # Load a target module, let it park on 'busymod_work_func' for
  77  *       # thirty seconds
  78  *       insmod samples/livepatch/livepatch-callbacks-busymod.ko sleep_secs=30
  79  *
  80  *       # Meanwhile load the livepatch
  81  *       insmod samples/livepatch/livepatch-callbacks-demo.ko
  82  *
  83  *       # ... then load and unload another target module while the
  84  *       # transition is in progress
  85  *       insmod samples/livepatch/livepatch-callbacks-mod.ko
  86  *       rmmod samples/livepatch/livepatch-callbacks-mod.ko
  87  *
  88  *       # Finally cleanup
  89  *       echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
  90  *       rmmod samples/livepatch/livepatch-callbacks-demo.ko
  91  */
  92
  93 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  94
  95 #include <linux/module.h>
  96 #include <linux/kernel.h>
  97 #include <linux/livepatch.h>
  98
  99 static int pre_patch_ret;
 100 module_param(pre_patch_ret, int, 0644);
 101 MODULE_PARM_DESC(pre_patch_ret, "pre_patch_ret (default=0)");
 102
 103 static const char *const module_state[] = {
 104         [MODULE_STATE_LIVE]     = "[MODULE_STATE_LIVE] Normal state",
 105         [MODULE_STATE_COMING]   = "[MODULE_STATE_COMING] Full formed, running module_init",
 106         [MODULE_STATE_GOING]    = "[MODULE_STATE_GOING] Going away",
 107         [MODULE_STATE_UNFORMED] = "[MODULE_STATE_UNFORMED] Still setting it up",
 108 };
 109
 110 static void callback_info(const char *callback, struct klp_object *obj)
 111 {
 112         if (obj->mod)
 113                 pr_info("%s: %s -> %s\n", callback, obj->mod->name,
 114                         module_state[obj->mod->state]);
 115         else
 116                 pr_info("%s: vmlinux\n", callback);
 117 }
 118
 119 /* Executed on object patching (ie, patch enablement) */
 120 static int pre_patch_callback(struct klp_object *obj)
 121 {
 122         callback_info(__func__, obj);
 123         return pre_patch_ret;
 124 }
 125
 126 /* Executed on object unpatching (ie, patch disablement) */
 127 static void post_patch_callback(struct klp_object *obj)
 128 {
 129         callback_info(__func__, obj);
 130 }
 131
 132 /* Executed on object unpatching (ie, patch disablement) */
 133 static void pre_unpatch_callback(struct klp_object *obj)
 134 {
 135         callback_info(__func__, obj);
 136 }
 137
 138 /* Executed on object unpatching (ie, patch disablement) */
 139 static void post_unpatch_callback(struct klp_object *obj)
 140 {
 141         callback_info(__func__, obj);
 142 }
 143
 144 static void patched_work_func(struct work_struct *work)
 145 {
 146         pr_info("%s\n", __func__);
 147 }
 148
 149 static struct klp_func no_funcs[] = {
 150         { }
 151 };
 152
 153 static struct klp_func busymod_funcs[] = {
 154         {
 155                 .old_name = "busymod_work_func",
 156                 .new_func = patched_work_func,
 157         }, { }
 158 };
 159
 160 static struct klp_object objs[] = {
 161         {
 162                 .name = NULL,   /* vmlinux */
 163                 .funcs = no_funcs,
 164                 .callbacks = {
 165                         .pre_patch = pre_patch_callback,
 166                         .post_patch = post_patch_callback,
 167                         .pre_unpatch = pre_unpatch_callback,
 168                         .post_unpatch = post_unpatch_callback,
 169                 },
 170         },      {
 171                 .name = "livepatch_callbacks_mod",
 172                 .funcs = no_funcs,
 173                 .callbacks = {
 174                         .pre_patch = pre_patch_callback,
 175                         .post_patch = post_patch_callback,
 176                         .pre_unpatch = pre_unpatch_callback,
 177                         .post_unpatch = post_unpatch_callback,
 178                 },
 179         },      {
 180                 .name = "livepatch_callbacks_busymod",
 181                 .funcs = busymod_funcs,
 182                 .callbacks = {
 183                         .pre_patch = pre_patch_callback,
 184                         .post_patch = post_patch_callback,
 185                         .pre_unpatch = pre_unpatch_callback,
 186                         .post_unpatch = post_unpatch_callback,
 187                 },
 188         }, { }
 189 };
 190
 191 static struct klp_patch patch = {
 192         .mod = THIS_MODULE,
 193         .objs = objs,
 194 };
 195
 196 static int livepatch_callbacks_demo_init(void)
 197 {
 198         int ret;
 199
 200         if (!klp_have_reliable_stack() && !patch.immediate) {
 201                 /*
 202                  * WARNING: Be very careful when using 'patch.immediate' in
 203                  * your patches.  It's ok to use it for simple patches like
 204                  * this, but for more complex patches which change function
 205                  * semantics, locking semantics, or data structures, it may not
 206                  * be safe.  Use of this option will also prevent removal of
 207                  * the patch.
 208                  *
 209                  * See Documentation/livepatch/livepatch.txt for more details.
 210                  */
 211                 patch.immediate = true;
 212                 pr_notice("The consistency model isn't supported for your architecture.  Bypassing safety mechanisms and applying the patch immediately.\n");
 213         }
 214
 215         ret = klp_register_patch(&patch);
 216         if (ret)
 217                 return ret;
 218         ret = klp_enable_patch(&patch);
 219         if (ret) {
 220                 WARN_ON(klp_unregister_patch(&patch));
 221                 return ret;
 222         }
 223         return 0;
 224 }
 225
 226 static void livepatch_callbacks_demo_exit(void)
 227 {
 228         WARN_ON(klp_unregister_patch(&patch));
 229 }
 230
 231 module_init(livepatch_callbacks_demo_init);
 232 module_exit(livepatch_callbacks_demo_exit);
 233 MODULE_LICENSE("GPL");
 234 MODULE_INFO(livepatch, "Y");