samples/livepatch/livepatch-shadow-fix1.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-fix1.c - Shadow variables, livepatch demo
  20  *
  21  * Purpose
  22  * -------
  23  *
  24  * Fixes the memory leak introduced in livepatch-shadow-mod through the
  25  * use of a shadow variable.  This fix demonstrates the "extending" of
  26  * short-lived data structures by patching its allocation and release
  27  * functions.
  28  *
  29  *
  30  * Usage
  31  * -----
  32  *
  33  * This module is not intended to be standalone.  See the "Usage"
  34  * section of livepatch-shadow-mod.c.
  35  */
  36
  37 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  38
  39 #include <linux/module.h>
  40 #include <linux/kernel.h>
  41 #include <linux/livepatch.h>
  42 #include <linux/slab.h>
  43
  44 /* Shadow variable enums */
  45 #define SV_LEAK         1
  46
  47 /* Allocate new dummies every second */
  48 #define ALLOC_PERIOD    1
  49 /* Check for expired dummies after a few new ones have been allocated */
  50 #define CLEANUP_PERIOD  (3 * ALLOC_PERIOD)
  51 /* Dummies expire after a few cleanup instances */
  52 #define EXPIRE_PERIOD   (4 * CLEANUP_PERIOD)
  53
  54 struct dummy {
  55         struct list_head list;
  56         unsigned long jiffies_expire;
  57 };
  58
  59 /*
  60  * The constructor makes more sense together with klp_shadow_get_or_alloc().
  61  * In this example, it would be safe to assign the pointer also to the shadow
  62  * variable returned by klp_shadow_alloc().  But we wanted to show the more
  63  * complicated use of the API.
  64  */
  65 static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
  66 {
  67         void **shadow_leak = shadow_data;
  68         void *leak = ctor_data;
  69
  70         *shadow_leak = leak;
  71         return 0;
  72 }
  73
  74 struct dummy *livepatch_fix1_dummy_alloc(void)
  75 {
  76         struct dummy *d;
  77         void *leak;
  78
  79         d = kzalloc(sizeof(*d), GFP_KERNEL);
  80         if (!d)
  81                 return NULL;
  82
  83         d->jiffies_expire = jiffies +
  84                 msecs_to_jiffies(1000 * EXPIRE_PERIOD);
  85
  86         /*
  87          * Patch: save the extra memory location into a SV_LEAK shadow
  88          * variable.  A patched dummy_free routine can later fetch this
  89          * pointer to handle resource release.
  90          */
  91         leak = kzalloc(sizeof(int), GFP_KERNEL);
  92         klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
  93                          shadow_leak_ctor, leak);
  94
  95         pr_info("%s: dummy @ %p, expires @ %lx\n",
  96                 __func__, d, d->jiffies_expire);
  97
  98         return d;
  99 }
 100
 101 static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
 102 {
 103         void *d = obj;
 104         void **shadow_leak = shadow_data;
 105
 106         kfree(*shadow_leak);
 107         pr_info("%s: dummy @ %p, prevented leak @ %p\n",
 108                          __func__, d, *shadow_leak);
 109 }
 110
 111 void livepatch_fix1_dummy_free(struct dummy *d)
 112 {
 113         void **shadow_leak;
 114
 115         /*
 116          * Patch: fetch the saved SV_LEAK shadow variable, detach and
 117          * free it.  Note: handle cases where this shadow variable does
 118          * not exist (ie, dummy structures allocated before this livepatch
 119          * was loaded.)
 120          */
 121         shadow_leak = klp_shadow_get(d, SV_LEAK);
 122         if (shadow_leak)
 123                 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
 124         else
 125                 pr_info("%s: dummy @ %p leaked!\n", __func__, d);
 126
 127         kfree(d);
 128 }
 129
 130 static struct klp_func funcs[] = {
 131         {
 132                 .old_name = "dummy_alloc",
 133                 .new_func = livepatch_fix1_dummy_alloc,
 134         },
 135         {
 136                 .old_name = "dummy_free",
 137                 .new_func = livepatch_fix1_dummy_free,
 138         }, { }
 139 };
 140
 141 static struct klp_object objs[] = {
 142         {
 143                 .name = "livepatch_shadow_mod",
 144                 .funcs = funcs,
 145         }, { }
 146 };
 147
 148 static struct klp_patch patch = {
 149         .mod = THIS_MODULE,
 150         .objs = objs,
 151 };
 152
 153 static int livepatch_shadow_fix1_init(void)
 154 {
 155         int ret;
 156
 157         ret = klp_register_patch(&patch);
 158         if (ret)
 159                 return ret;
 160         ret = klp_enable_patch(&patch);
 161         if (ret) {
 162                 WARN_ON(klp_unregister_patch(&patch));
 163                 return ret;
 164         }
 165         return 0;
 166 }
 167
 168 static void livepatch_shadow_fix1_exit(void)
 169 {
 170         /* Cleanup any existing SV_LEAK shadow variables */
 171         klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
 172
 173         WARN_ON(klp_unregister_patch(&patch));
 174 }
 175
 176 module_init(livepatch_shadow_fix1_init);
 177 module_exit(livepatch_shadow_fix1_exit);
 178 MODULE_LICENSE("GPL");
 179 MODULE_INFO(livepatch, "Y");