samples/livepatch/livepatch-shadow-mod.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-shadow-mod.c - Shadow variables, buggy module demo
  20  *
  21  * Purpose
  22  * -------
  23  *
  24  * As a demonstration of livepatch shadow variable API, this module
  25  * introduces memory leak behavior that livepatch modules
  26  * livepatch-shadow-fix1.ko and livepatch-shadow-fix2.ko correct and
  27  * enhance.
  28  *
  29  * WARNING - even though the livepatch-shadow-fix modules patch the
  30  * memory leak, please load these modules at your own risk -- some
  31  * amount of memory may leaked before the bug is patched.
  32  *
  33  *
  34  * Usage
  35  * -----
  36  *
  37  * Step 1 - Load the buggy demonstration module:
  38  *
  39  *   insmod samples/livepatch/livepatch-shadow-mod.ko
  40  *
  41  * Watch dmesg output for a few moments to see new dummy being allocated
  42  * and a periodic cleanup check.  (Note: a small amount of memory is
  43  * being leaked.)
  44  *
  45  *
  46  * Step 2 - Load livepatch fix1:
  47  *
  48  *   insmod samples/livepatch/livepatch-shadow-fix1.ko
  49  *
  50  * Continue watching dmesg and note that now livepatch_fix1_dummy_free()
  51  * and livepatch_fix1_dummy_alloc() are logging messages about leaked
  52  * memory and eventually leaks prevented.
  53  *
  54  *
  55  * Step 3 - Load livepatch fix2 (on top of fix1):
  56  *
  57  *   insmod samples/livepatch/livepatch-shadow-fix2.ko
  58  *
  59  * This module extends functionality through shadow variables, as a new
  60  * "check" counter is added to the dummy structure.  Periodic dmesg
  61  * messages will log these as dummies are cleaned up.
  62  *
  63  *
  64  * Step 4 - Cleanup
  65  *
  66  * Unwind the demonstration by disabling the livepatch fix modules, then
  67  * removing them and the demo module:
  68  *
  69  *   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled
  70  *   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled
  71  *   rmmod livepatch-shadow-fix2
  72  *   rmmod livepatch-shadow-fix1
  73  *   rmmod livepatch-shadow-mod
  74  */
  75
  76
  77 #include <linux/kernel.h>
  78 #include <linux/module.h>
  79 #include <linux/sched.h>
  80 #include <linux/slab.h>
  81 #include <linux/stat.h>
  82 #include <linux/workqueue.h>
  83
  84 MODULE_LICENSE("GPL");
  85 MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");
  86 MODULE_DESCRIPTION("Buggy module for shadow variable demo");
  87
  88 /* Allocate new dummies every second */
  89 #define ALLOC_PERIOD    1
  90 /* Check for expired dummies after a few new ones have been allocated */
  91 #define CLEANUP_PERIOD  (3 * ALLOC_PERIOD)
  92 /* Dummies expire after a few cleanup instances */
  93 #define EXPIRE_PERIOD   (4 * CLEANUP_PERIOD)
  94
  95 /*
  96  * Keep a list of all the dummies so we can clean up any residual ones
  97  * on module exit
  98  */
  99 LIST_HEAD(dummy_list);
 100 DEFINE_MUTEX(dummy_list_mutex);
 101
 102 struct dummy {
 103         struct list_head list;
 104         unsigned long jiffies_expire;
 105 };
 106
 107 noinline struct dummy *dummy_alloc(void)
 108 {
 109         struct dummy *d;
 110         void *leak;
 111
 112         d = kzalloc(sizeof(*d), GFP_KERNEL);
 113         if (!d)
 114                 return NULL;
 115
 116         d->jiffies_expire = jiffies +
 117                 msecs_to_jiffies(1000 * EXPIRE_PERIOD);
 118
 119         /* Oops, forgot to save leak! */
 120         leak = kzalloc(sizeof(int), GFP_KERNEL);
 121
 122         pr_info("%s: dummy @ %p, expires @ %lx\n",
 123                 __func__, d, d->jiffies_expire);
 124
 125         return d;
 126 }
 127
 128 noinline void dummy_free(struct dummy *d)
 129 {
 130         pr_info("%s: dummy @ %p, expired = %lx\n",
 131                 __func__, d, d->jiffies_expire);
 132
 133         kfree(d);
 134 }
 135
 136 noinline bool dummy_check(struct dummy *d, unsigned long jiffies)
 137 {
 138         return time_after(jiffies, d->jiffies_expire);
 139 }
 140
 141 /*
 142  * alloc_work_func: allocates new dummy structures, allocates additional
 143  *                  memory, aptly named "leak", but doesn't keep
 144  *                  permanent record of it.
 145  */
 146
 147 static void alloc_work_func(struct work_struct *work);
 148 static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func);
 149
 150 static void alloc_work_func(struct work_struct *work)
 151 {
 152         struct dummy *d;
 153
 154         d = dummy_alloc();
 155         if (!d)
 156                 return;
 157
 158         mutex_lock(&dummy_list_mutex);
 159         list_add(&d->list, &dummy_list);
 160         mutex_unlock(&dummy_list_mutex);
 161
 162         schedule_delayed_work(&alloc_dwork,
 163                 msecs_to_jiffies(1000 * ALLOC_PERIOD));
 164 }
 165
 166 /*
 167  * cleanup_work_func: frees dummy structures.  Without knownledge of
 168  *                    "leak", it leaks the additional memory that
 169  *                    alloc_work_func created.
 170  */
 171
 172 static void cleanup_work_func(struct work_struct *work);
 173 static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func);
 174
 175 static void cleanup_work_func(struct work_struct *work)
 176 {
 177         struct dummy *d, *tmp;
 178         unsigned long j;
 179
 180         j = jiffies;
 181         pr_info("%s: jiffies = %lx\n", __func__, j);
 182
 183         mutex_lock(&dummy_list_mutex);
 184         list_for_each_entry_safe(d, tmp, &dummy_list, list) {
 185
 186                 /* Kick out and free any expired dummies */
 187                 if (dummy_check(d, j)) {
 188                         list_del(&d->list);
 189                         dummy_free(d);
 190                 }
 191         }
 192         mutex_unlock(&dummy_list_mutex);
 193
 194         schedule_delayed_work(&cleanup_dwork,
 195                 msecs_to_jiffies(1000 * CLEANUP_PERIOD));
 196 }
 197
 198 static int livepatch_shadow_mod_init(void)
 199 {
 200         schedule_delayed_work(&alloc_dwork,
 201                 msecs_to_jiffies(1000 * ALLOC_PERIOD));
 202         schedule_delayed_work(&cleanup_dwork,
 203                 msecs_to_jiffies(1000 * CLEANUP_PERIOD));
 204
 205         return 0;
 206 }
 207
 208 static void livepatch_shadow_mod_exit(void)
 209 {
 210         struct dummy *d, *tmp;
 211
 212         /* Wait for any dummies at work */
 213         cancel_delayed_work_sync(&alloc_dwork);
 214         cancel_delayed_work_sync(&cleanup_dwork);
 215
 216         /* Cleanup residual dummies */
 217         list_for_each_entry_safe(d, tmp, &dummy_list, list) {
 218                 list_del(&d->list);
 219                 dummy_free(d);
 220         }
 221 }
 222
 223 module_init(livepatch_shadow_mod_init);
 224 module_exit(livepatch_shadow_mod_exit);