root/samples/livepatch/livepatch-shadow-mod.c

DEFINITIONS

1. dummy_alloc
2. dummy_free
3. dummy_check
4. alloc_work_func
5. cleanup_work_func
6. livepatch_shadow_mod_init
7. livepatch_shadow_mod_exit

   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-shadow-mod.c - Shadow variables, buggy module demo
   8  *
   9  * Purpose
  10  * -------
  11  *
  12  * As a demonstration of livepatch shadow variable API, this module
  13  * introduces memory leak behavior that livepatch modules
  14  * livepatch-shadow-fix1.ko and livepatch-shadow-fix2.ko correct and
  15  * enhance.
  16  *
  17  * WARNING - even though the livepatch-shadow-fix modules patch the
  18  * memory leak, please load these modules at your own risk -- some
  19  * amount of memory may leaked before the bug is patched.
  20  *
  21  *
  22  * Usage
  23  * -----
  24  *
  25  * Step 1 - Load the buggy demonstration module:
  26  *
  27  *   insmod samples/livepatch/livepatch-shadow-mod.ko
  28  *
  29  * Watch dmesg output for a few moments to see new dummy being allocated
  30  * and a periodic cleanup check.  (Note: a small amount of memory is
  31  * being leaked.)
  32  *
  33  *
  34  * Step 2 - Load livepatch fix1:
  35  *
  36  *   insmod samples/livepatch/livepatch-shadow-fix1.ko
  37  *
  38  * Continue watching dmesg and note that now livepatch_fix1_dummy_free()
  39  * and livepatch_fix1_dummy_alloc() are logging messages about leaked
  40  * memory and eventually leaks prevented.
  41  *
  42  *
  43  * Step 3 - Load livepatch fix2 (on top of fix1):
  44  *
  45  *   insmod samples/livepatch/livepatch-shadow-fix2.ko
  46  *
  47  * This module extends functionality through shadow variables, as a new
  48  * "check" counter is added to the dummy structure.  Periodic dmesg
  49  * messages will log these as dummies are cleaned up.
  50  *
  51  *
  52  * Step 4 - Cleanup
  53  *
  54  * Unwind the demonstration by disabling the livepatch fix modules, then
  55  * removing them and the demo module:
  56  *
  57  *   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled
  58  *   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled
  59  *   rmmod livepatch-shadow-fix2
  60  *   rmmod livepatch-shadow-fix1
  61  *   rmmod livepatch-shadow-mod
  62  */
  63 
  64 
  65 #include <linux/kernel.h>
  66 #include <linux/module.h>
  67 #include <linux/sched.h>
  68 #include <linux/slab.h>
  69 #include <linux/stat.h>
  70 #include <linux/workqueue.h>
  71 
  72 MODULE_LICENSE("GPL");
  73 MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");
  74 MODULE_DESCRIPTION("Buggy module for shadow variable demo");
  75 
  76 /* Allocate new dummies every second */
  77 #define ALLOC_PERIOD    1
  78 /* Check for expired dummies after a few new ones have been allocated */
  79 #define CLEANUP_PERIOD  (3 * ALLOC_PERIOD)
  80 /* Dummies expire after a few cleanup instances */
  81 #define EXPIRE_PERIOD   (4 * CLEANUP_PERIOD)
  82 
  83 /*
  84  * Keep a list of all the dummies so we can clean up any residual ones
  85  * on module exit
  86  */
  87 static LIST_HEAD(dummy_list);
  88 static DEFINE_MUTEX(dummy_list_mutex);
  89 
  90 struct dummy {
  91         struct list_head list;
  92         unsigned long jiffies_expire;
  93 };
  94 
  95 static __used noinline struct dummy *dummy_alloc(void)
  96 {
  97         struct dummy *d;
  98         void *leak;
  99 
 100         d = kzalloc(sizeof(*d), GFP_KERNEL);
 101         if (!d)
 102                 return NULL;
 103 
 104         d->jiffies_expire = jiffies +
 105                 msecs_to_jiffies(1000 * EXPIRE_PERIOD);
 106 
 107         /* Oops, forgot to save leak! */
 108         leak = kzalloc(sizeof(int), GFP_KERNEL);
 109         if (!leak) {
 110                 kfree(d);
 111                 return NULL;
 112         }
 113 
 114         pr_info("%s: dummy @ %p, expires @ %lx\n",
 115                 __func__, d, d->jiffies_expire);
 116 
 117         return d;
 118 }
 119 
 120 static __used noinline void dummy_free(struct dummy *d)
 121 {
 122         pr_info("%s: dummy @ %p, expired = %lx\n",
 123                 __func__, d, d->jiffies_expire);
 124 
 125         kfree(d);
 126 }
 127 
 128 static __used noinline bool dummy_check(struct dummy *d,
 129                                            unsigned long jiffies)
 130 {
 131         return time_after(jiffies, d->jiffies_expire);
 132 }
 133 
 134 /*
 135  * alloc_work_func: allocates new dummy structures, allocates additional
 136  *                  memory, aptly named "leak", but doesn't keep
 137  *                  permanent record of it.
 138  */
 139 
 140 static void alloc_work_func(struct work_struct *work);
 141 static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func);
 142 
 143 static void alloc_work_func(struct work_struct *work)
 144 {
 145         struct dummy *d;
 146 
 147         d = dummy_alloc();
 148         if (!d)
 149                 return;
 150 
 151         mutex_lock(&dummy_list_mutex);
 152         list_add(&d->list, &dummy_list);
 153         mutex_unlock(&dummy_list_mutex);
 154 
 155         schedule_delayed_work(&alloc_dwork,
 156                 msecs_to_jiffies(1000 * ALLOC_PERIOD));
 157 }
 158 
 159 /*
 160  * cleanup_work_func: frees dummy structures.  Without knownledge of
 161  *                    "leak", it leaks the additional memory that
 162  *                    alloc_work_func created.
 163  */
 164 
 165 static void cleanup_work_func(struct work_struct *work);
 166 static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func);
 167 
 168 static void cleanup_work_func(struct work_struct *work)
 169 {
 170         struct dummy *d, *tmp;
 171         unsigned long j;
 172 
 173         j = jiffies;
 174         pr_info("%s: jiffies = %lx\n", __func__, j);
 175 
 176         mutex_lock(&dummy_list_mutex);
 177         list_for_each_entry_safe(d, tmp, &dummy_list, list) {
 178 
 179                 /* Kick out and free any expired dummies */
 180                 if (dummy_check(d, j)) {
 181                         list_del(&d->list);
 182                         dummy_free(d);
 183                 }
 184         }
 185         mutex_unlock(&dummy_list_mutex);
 186 
 187         schedule_delayed_work(&cleanup_dwork,
 188                 msecs_to_jiffies(1000 * CLEANUP_PERIOD));
 189 }
 190 
 191 static int livepatch_shadow_mod_init(void)
 192 {
 193         schedule_delayed_work(&alloc_dwork,
 194                 msecs_to_jiffies(1000 * ALLOC_PERIOD));
 195         schedule_delayed_work(&cleanup_dwork,
 196                 msecs_to_jiffies(1000 * CLEANUP_PERIOD));
 197 
 198         return 0;
 199 }
 200 
 201 static void livepatch_shadow_mod_exit(void)
 202 {
 203         struct dummy *d, *tmp;
 204 
 205         /* Wait for any dummies at work */
 206         cancel_delayed_work_sync(&alloc_dwork);
 207         cancel_delayed_work_sync(&cleanup_dwork);
 208 
 209         /* Cleanup residual dummies */
 210         list_for_each_entry_safe(d, tmp, &dummy_list, list) {
 211                 list_del(&d->list);
 212                 dummy_free(d);
 213         }
 214 }
 215 
 216 module_init(livepatch_shadow_mod_init);
 217 module_exit(livepatch_shadow_mod_exit);