samples/livepatch/livepatch-callbacks-demo.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
   4  */
   5
   6 /*
   7  * livepatch-callbacks-demo.c - (un)patching callbacks livepatch demo
   8  *
   9  *
  10  * Purpose
  11  * -------
  12  *
  13  * Demonstration of registering livepatch (un)patching callbacks.
  14  *
  15  *
  16  * Usage
  17  * -----
  18  *
  19  * Step 1 - load the simple module
  20  *
  21  *   insmod samples/livepatch/livepatch-callbacks-mod.ko
  22  *
  23  *
  24  * Step 2 - load the demonstration livepatch (with callbacks)
  25  *
  26  *   insmod samples/livepatch/livepatch-callbacks-demo.ko
  27  *
  28  *
  29  * Step 3 - cleanup
  30  *
  31  *   echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
  32  *   rmmod livepatch_callbacks_demo
  33  *   rmmod livepatch_callbacks_mod
  34  *
  35  * Watch dmesg output to see livepatch enablement, callback execution
  36  * and patching operations for both vmlinux and module targets.
  37  *
  38  * NOTE: swap the insmod order of livepatch-callbacks-mod.ko and
  39  *       livepatch-callbacks-demo.ko to observe what happens when a
  40  *       target module is loaded after a livepatch with callbacks.
  41  *
  42  * NOTE: 'pre_patch_ret' is a module parameter that sets the pre-patch
  43  *       callback return status.  Try setting up a non-zero status
  44  *       such as -19 (-ENODEV):
  45  *
  46  *       # Load demo livepatch, vmlinux is patched
  47  *       insmod samples/livepatch/livepatch-callbacks-demo.ko
  48  *
  49  *       # Setup next pre-patch callback to return -ENODEV
  50  *       echo -19 > /sys/module/livepatch_callbacks_demo/parameters/pre_patch_ret
  51  *
  52  *       # Module loader refuses to load the target module
  53  *       insmod samples/livepatch/livepatch-callbacks-mod.ko
  54  *       insmod: ERROR: could not insert module samples/livepatch/livepatch-callbacks-mod.ko: No such device
  55  *
  56  * NOTE: There is a second target module,
  57  *       livepatch-callbacks-busymod.ko, available for experimenting
  58  *       with livepatch (un)patch callbacks.  This module contains
  59  *       a 'sleep_secs' parameter that parks the module on one of the
  60  *       functions that the livepatch demo module wants to patch.
  61  *       Modifying this value and tweaking the order of module loads can
  62  *       effectively demonstrate stalled patch transitions:
  63  *
  64  *       # Load a target module, let it park on 'busymod_work_func' for
  65  *       # thirty seconds
  66  *       insmod samples/livepatch/livepatch-callbacks-busymod.ko sleep_secs=30
  67  *
  68  *       # Meanwhile load the livepatch
  69  *       insmod samples/livepatch/livepatch-callbacks-demo.ko
  70  *
  71  *       # ... then load and unload another target module while the
  72  *       # transition is in progress
  73  *       insmod samples/livepatch/livepatch-callbacks-mod.ko
  74  *       rmmod samples/livepatch/livepatch-callbacks-mod.ko
  75  *
  76  *       # Finally cleanup
  77  *       echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
  78  *       rmmod samples/livepatch/livepatch-callbacks-demo.ko
  79  */
  80
  81 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  82
  83 #include <linux/module.h>
  84 #include <linux/kernel.h>
  85 #include <linux/livepatch.h>
  86
  87 static int pre_patch_ret;
  88 module_param(pre_patch_ret, int, 0644);
  89 MODULE_PARM_DESC(pre_patch_ret, "pre_patch_ret (default=0)");
  90
  91 static const char *const module_state[] = {
  92         [MODULE_STATE_LIVE]     = "[MODULE_STATE_LIVE] Normal state",
  93         [MODULE_STATE_COMING]   = "[MODULE_STATE_COMING] Full formed, running module_init",
  94         [MODULE_STATE_GOING]    = "[MODULE_STATE_GOING] Going away",
  95         [MODULE_STATE_UNFORMED] = "[MODULE_STATE_UNFORMED] Still setting it up",
  96 };
  97
  98 static void callback_info(const char *callback, struct klp_object *obj)
  99 {
 100         if (obj->mod)
 101                 pr_info("%s: %s -> %s\n", callback, obj->mod->name,
 102                         module_state[obj->mod->state]);
 103         else
 104                 pr_info("%s: vmlinux\n", callback);
 105 }
 106
 107 /* Executed on object patching (ie, patch enablement) */
 108 static int pre_patch_callback(struct klp_object *obj)
 109 {
 110         callback_info(__func__, obj);
 111         return pre_patch_ret;
 112 }
 113
 114 /* Executed on object unpatching (ie, patch disablement) */
 115 static void post_patch_callback(struct klp_object *obj)
 116 {
 117         callback_info(__func__, obj);
 118 }
 119
 120 /* Executed on object unpatching (ie, patch disablement) */
 121 static void pre_unpatch_callback(struct klp_object *obj)
 122 {
 123         callback_info(__func__, obj);
 124 }
 125
 126 /* Executed on object unpatching (ie, patch disablement) */
 127 static void post_unpatch_callback(struct klp_object *obj)
 128 {
 129         callback_info(__func__, obj);
 130 }
 131
 132 static void patched_work_func(struct work_struct *work)
 133 {
 134         pr_info("%s\n", __func__);
 135 }
 136
 137 static struct klp_func no_funcs[] = {
 138         { }
 139 };
 140
 141 static struct klp_func busymod_funcs[] = {
 142         {
 143                 .old_name = "busymod_work_func",
 144                 .new_func = patched_work_func,
 145         }, { }
 146 };
 147
 148 static struct klp_object objs[] = {
 149         {
 150                 .name = NULL,   /* vmlinux */
 151                 .funcs = no_funcs,
 152                 .callbacks = {
 153                         .pre_patch = pre_patch_callback,
 154                         .post_patch = post_patch_callback,
 155                         .pre_unpatch = pre_unpatch_callback,
 156                         .post_unpatch = post_unpatch_callback,
 157                 },
 158         },      {
 159                 .name = "livepatch_callbacks_mod",
 160                 .funcs = no_funcs,
 161                 .callbacks = {
 162                         .pre_patch = pre_patch_callback,
 163                         .post_patch = post_patch_callback,
 164                         .pre_unpatch = pre_unpatch_callback,
 165                         .post_unpatch = post_unpatch_callback,
 166                 },
 167         },      {
 168                 .name = "livepatch_callbacks_busymod",
 169                 .funcs = busymod_funcs,
 170                 .callbacks = {
 171                         .pre_patch = pre_patch_callback,
 172                         .post_patch = post_patch_callback,
 173                         .pre_unpatch = pre_unpatch_callback,
 174                         .post_unpatch = post_unpatch_callback,
 175                 },
 176         }, { }
 177 };
 178
 179 static struct klp_patch patch = {
 180         .mod = THIS_MODULE,
 181         .objs = objs,
 182 };
 183
 184 static int livepatch_callbacks_demo_init(void)
 185 {
 186         return klp_enable_patch(&patch);
 187 }
 188
 189 static void livepatch_callbacks_demo_exit(void)
 190 {
 191 }
 192
 193 module_init(livepatch_callbacks_demo_init);
 194 module_exit(livepatch_callbacks_demo_exit);
 195 MODULE_LICENSE("GPL");
 196 MODULE_INFO(livepatch, "Y");