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 static 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         if (!leak) {
  93                 kfree(d);
  94                 return NULL;
  95         }
  96
  97         klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
  98                          shadow_leak_ctor, leak);
  99
 100         pr_info("%s: dummy @ %p, expires @ %lx\n",
 101                 __func__, d, d->jiffies_expire);
 102
 103         return d;
 104 }
 105
 106 static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
 107 {
 108         void *d = obj;
 109         void **shadow_leak = shadow_data;
 110
 111         kfree(*shadow_leak);
 112         pr_info("%s: dummy @ %p, prevented leak @ %p\n",
 113                          __func__, d, *shadow_leak);
 114 }
 115
 116 static void livepatch_fix1_dummy_free(struct dummy *d)
 117 {
 118         void **shadow_leak;
 119
 120         /*
 121          * Patch: fetch the saved SV_LEAK shadow variable, detach and
 122          * free it.  Note: handle cases where this shadow variable does
 123          * not exist (ie, dummy structures allocated before this livepatch
 124          * was loaded.)
 125          */
 126         shadow_leak = klp_shadow_get(d, SV_LEAK);
 127         if (shadow_leak)
 128                 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
 129         else
 130                 pr_info("%s: dummy @ %p leaked!\n", __func__, d);
 131
 132         kfree(d);
 133 }
 134
 135 static struct klp_func funcs[] = {
 136         {
 137                 .old_name = "dummy_alloc",
 138                 .new_func = livepatch_fix1_dummy_alloc,
 139         },
 140         {
 141                 .old_name = "dummy_free",
 142                 .new_func = livepatch_fix1_dummy_free,
 143         }, { }
 144 };
 145
 146 static struct klp_object objs[] = {
 147         {
 148                 .name = "livepatch_shadow_mod",
 149                 .funcs = funcs,
 150         }, { }
 151 };
 152
 153 static struct klp_patch patch = {
 154         .mod = THIS_MODULE,
 155         .objs = objs,
 156 };
 157
 158 static int livepatch_shadow_fix1_init(void)
 159 {
 160         return klp_enable_patch(&patch);
 161 }
 162
 163 static void livepatch_shadow_fix1_exit(void)
 164 {
 165         /* Cleanup any existing SV_LEAK shadow variables */
 166         klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
 167 }
 168
 169 module_init(livepatch_shadow_fix1_init);
 170 module_exit(livepatch_shadow_fix1_exit);
 171 MODULE_LICENSE("GPL");
 172 MODULE_INFO(livepatch, "Y");