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 struct dummy *livepatch_fix1_dummy_alloc(void)
  60 {
  61         struct dummy *d;
  62         void *leak;
  63
  64         d = kzalloc(sizeof(*d), GFP_KERNEL);
  65         if (!d)
  66                 return NULL;
  67
  68         d->jiffies_expire = jiffies +
  69                 msecs_to_jiffies(1000 * EXPIRE_PERIOD);
  70
  71         /*
  72          * Patch: save the extra memory location into a SV_LEAK shadow
  73          * variable.  A patched dummy_free routine can later fetch this
  74          * pointer to handle resource release.
  75          */
  76         leak = kzalloc(sizeof(int), GFP_KERNEL);
  77         klp_shadow_alloc(d, SV_LEAK, &leak, sizeof(leak), GFP_KERNEL);
  78
  79         pr_info("%s: dummy @ %p, expires @ %lx\n",
  80                 __func__, d, d->jiffies_expire);
  81
  82         return d;
  83 }
  84
  85 void livepatch_fix1_dummy_free(struct dummy *d)
  86 {
  87         void **shadow_leak, *leak;
  88
  89         /*
  90          * Patch: fetch the saved SV_LEAK shadow variable, detach and
  91          * free it.  Note: handle cases where this shadow variable does
  92          * not exist (ie, dummy structures allocated before this livepatch
  93          * was loaded.)
  94          */
  95         shadow_leak = klp_shadow_get(d, SV_LEAK);
  96         if (shadow_leak) {
  97                 leak = *shadow_leak;
  98                 klp_shadow_free(d, SV_LEAK);
  99                 kfree(leak);
 100                 pr_info("%s: dummy @ %p, prevented leak @ %p\n",
 101                          __func__, d, leak);
 102         } else {
 103                 pr_info("%s: dummy @ %p leaked!\n", __func__, d);
 104         }
 105
 106         kfree(d);
 107 }
 108
 109 static struct klp_func funcs[] = {
 110         {
 111                 .old_name = "dummy_alloc",
 112                 .new_func = livepatch_fix1_dummy_alloc,
 113         },
 114         {
 115                 .old_name = "dummy_free",
 116                 .new_func = livepatch_fix1_dummy_free,
 117         }, { }
 118 };
 119
 120 static struct klp_object objs[] = {
 121         {
 122                 .name = "livepatch_shadow_mod",
 123                 .funcs = funcs,
 124         }, { }
 125 };
 126
 127 static struct klp_patch patch = {
 128         .mod = THIS_MODULE,
 129         .objs = objs,
 130 };
 131
 132 static int livepatch_shadow_fix1_init(void)
 133 {
 134         int ret;
 135
 136         ret = klp_register_patch(&patch);
 137         if (ret)
 138                 return ret;
 139         ret = klp_enable_patch(&patch);
 140         if (ret) {
 141                 WARN_ON(klp_unregister_patch(&patch));
 142                 return ret;
 143         }
 144         return 0;
 145 }
 146
 147 static void livepatch_shadow_fix1_exit(void)
 148 {
 149         /* Cleanup any existing SV_LEAK shadow variables */
 150         klp_shadow_free_all(SV_LEAK);
 151
 152         WARN_ON(klp_unregister_patch(&patch));
 153 }
 154
 155 module_init(livepatch_shadow_fix1_init);
 156 module_exit(livepatch_shadow_fix1_exit);
 157 MODULE_LICENSE("GPL");
 158 MODULE_INFO(livepatch, "Y");