samples/livepatch/livepatch-shadow-fix1.c

   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-fix1.c - Shadow variables, livepatch demo
   8  *
   9  * Purpose
  10  * -------
  11  *
  12  * Fixes the memory leak introduced in livepatch-shadow-mod through the
  13  * use of a shadow variable.  This fix demonstrates the "extending" of
  14  * short-lived data structures by patching its allocation and release
  15  * functions.
  16  *
  17  *
  18  * Usage
  19  * -----
  20  *
  21  * This module is not intended to be standalone.  See the "Usage"
  22  * section of livepatch-shadow-mod.c.
  23  */
  24
  25 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  26
  27 #include <linux/module.h>
  28 #include <linux/kernel.h>
  29 #include <linux/livepatch.h>
  30 #include <linux/slab.h>
  31
  32 /* Shadow variable enums */
  33 #define SV_LEAK         1
  34
  35 /* Allocate new dummies every second */
  36 #define ALLOC_PERIOD    1
  37 /* Check for expired dummies after a few new ones have been allocated */
  38 #define CLEANUP_PERIOD  (3 * ALLOC_PERIOD)
  39 /* Dummies expire after a few cleanup instances */
  40 #define EXPIRE_PERIOD   (4 * CLEANUP_PERIOD)
  41
  42 struct dummy {
  43         struct list_head list;
  44         unsigned long jiffies_expire;
  45 };
  46
  47 /*
  48  * The constructor makes more sense together with klp_shadow_get_or_alloc().
  49  * In this example, it would be safe to assign the pointer also to the shadow
  50  * variable returned by klp_shadow_alloc().  But we wanted to show the more
  51  * complicated use of the API.
  52  */
  53 static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
  54 {
  55         int **shadow_leak = shadow_data;
  56         int **leak = ctor_data;
  57
  58         if (!ctor_data)
  59                 return -EINVAL;
  60
  61         *shadow_leak = *leak;
  62         return 0;
  63 }
  64
  65 static struct dummy *livepatch_fix1_dummy_alloc(void)
  66 {
  67         struct dummy *d;
  68         int *leak;
  69         int **shadow_leak;
  70
  71         d = kzalloc(sizeof(*d), GFP_KERNEL);
  72         if (!d)
  73                 return NULL;
  74
  75         d->jiffies_expire = jiffies +
  76                 msecs_to_jiffies(1000 * EXPIRE_PERIOD);
  77
  78         /*
  79          * Patch: save the extra memory location into a SV_LEAK shadow
  80          * variable.  A patched dummy_free routine can later fetch this
  81          * pointer to handle resource release.
  82          */
  83         leak = kzalloc(sizeof(*leak), GFP_KERNEL);
  84         if (!leak)
  85                 goto err_leak;
  86
  87         shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
  88                                        shadow_leak_ctor, &leak);
  89         if (!shadow_leak) {
  90                 pr_err("%s: failed to allocate shadow variable for the leaking pointer: dummy @ %p, leak @ %p\n",
  91                        __func__, d, leak);
  92                 goto err_shadow;
  93         }
  94
  95         pr_info("%s: dummy @ %p, expires @ %lx\n",
  96                 __func__, d, d->jiffies_expire);
  97
  98         return d;
  99
 100 err_shadow:
 101         kfree(leak);
 102 err_leak:
 103         kfree(d);
 104         return NULL;
 105 }
 106
 107 static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
 108 {
 109         void *d = obj;
 110         int **shadow_leak = shadow_data;
 111
 112         kfree(*shadow_leak);
 113         pr_info("%s: dummy @ %p, prevented leak @ %p\n",
 114                          __func__, d, *shadow_leak);
 115 }
 116
 117 static void livepatch_fix1_dummy_free(struct dummy *d)
 118 {
 119         int **shadow_leak;
 120
 121         /*
 122          * Patch: fetch the saved SV_LEAK shadow variable, detach and
 123          * free it.  Note: handle cases where this shadow variable does
 124          * not exist (ie, dummy structures allocated before this livepatch
 125          * was loaded.)
 126          */
 127         shadow_leak = klp_shadow_get(d, SV_LEAK);
 128         if (shadow_leak)
 129                 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
 130         else
 131                 pr_info("%s: dummy @ %p leaked!\n", __func__, d);
 132
 133         kfree(d);
 134 }
 135
 136 static struct klp_func funcs[] = {
 137         {
 138                 .old_name = "dummy_alloc",
 139                 .new_func = livepatch_fix1_dummy_alloc,
 140         },
 141         {
 142                 .old_name = "dummy_free",
 143                 .new_func = livepatch_fix1_dummy_free,
 144         }, { }
 145 };
 146
 147 static struct klp_object objs[] = {
 148         {
 149                 .name = "livepatch_shadow_mod",
 150                 .funcs = funcs,
 151         }, { }
 152 };
 153
 154 static struct klp_patch patch = {
 155         .mod = THIS_MODULE,
 156         .objs = objs,
 157 };
 158
 159 static int livepatch_shadow_fix1_init(void)
 160 {
 161         return klp_enable_patch(&patch);
 162 }
 163
 164 static void livepatch_shadow_fix1_exit(void)
 165 {
 166         /* Cleanup any existing SV_LEAK shadow variables */
 167         klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
 168 }
 169
 170 module_init(livepatch_shadow_fix1_init);
 171 module_exit(livepatch_shadow_fix1_exit);
 172 MODULE_LICENSE("GPL");
 173 MODULE_INFO(livepatch, "Y");