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| 3 | * Copyright (C) 2017 Joe Lawrence <[email protected]>
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| 4 |
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| 5 |
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| 6 | |
| 7 | * livepatch-shadow-fix1.c - Shadow variables, livepatch demo
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| 8 | *
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| 9 | * Purpose
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| 10 | * -------
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| 11 | *
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| 12 | * Fixes the memory leak introduced in livepatch-shadow-mod through the
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| 13 | * use of a shadow variable. This fix demonstrates the "extending" of
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| 14 | * short-lived data structures by patching its allocation and release
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| 15 | * functions.
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| 16 | *
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| 17 | *
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| 18 | * Usage
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| 19 | * -----
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| 20 | *
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| 21 | * This module is not intended to be standalone. See the "Usage"
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| 22 | * section of livepatch-shadow-mod.c.
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| 23 |
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| 24 |
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| 25 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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| 26 |
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| 27 | #include <linux/module.h>
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| 28 | #include <linux/kernel.h>
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| 29 | #include <linux/livepatch.h>
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| 30 | #include <linux/slab.h>
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| 31 |
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| 32 |
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| 33 | #define SV_LEAK 1
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| 34 |
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| 35 |
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| 36 | #define ALLOC_PERIOD 1
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| 37 |
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| 38 | #define CLEANUP_PERIOD (3 * ALLOC_PERIOD)
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| 39 |
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| 40 | #define EXPIRE_PERIOD (4 * CLEANUP_PERIOD)
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| 41 |
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| 42 | struct dummy {
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| 43 | struct list_head list;
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| 44 | unsigned long jiffies_expire;
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| 45 | };
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| 46 |
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| 47 | |
| 48 | * The constructor makes more sense together with klp_shadow_get_or_alloc().
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| 49 | * In this example, it would be safe to assign the pointer also to the shadow
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| 50 | * variable returned by klp_shadow_alloc(). But we wanted to show the more
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| 51 | * complicated use of the API.
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| 52 |
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| 53 | static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
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| 54 | {
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| 55 | int **shadow_leak = shadow_data;
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| 56 | int **leak = ctor_data;
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| 57 |
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| 58 | if (!ctor_data)
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| 59 | return -EINVAL;
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| 60 |
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| 61 | *shadow_leak = *leak;
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| 62 | return 0;
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| 63 | }
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| 64 |
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| 65 | static struct dummy *livepatch_fix1_dummy_alloc(void)
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| 66 | {
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| 67 | struct dummy *d;
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| 68 | int *leak;
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| 69 | int **shadow_leak;
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| 70 |
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| 71 | d = kzalloc(sizeof(*d), GFP_KERNEL);
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| 72 | if (!d)
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| 73 | return NULL;
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| 74 |
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| 75 | d->jiffies_expire = jiffies +
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| 76 | msecs_to_jiffies(1000 * EXPIRE_PERIOD);
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| 77 |
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| 78 | |
| 79 | * Patch: save the extra memory location into a SV_LEAK shadow
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| 80 | * variable. A patched dummy_free routine can later fetch this
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| 81 | * pointer to handle resource release.
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| 82 |
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| 83 | leak = kzalloc(sizeof(*leak), GFP_KERNEL);
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| 84 | if (!leak)
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| 85 | goto err_leak;
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| 86 |
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| 87 | shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
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| 88 | shadow_leak_ctor, &leak);
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| 89 | if (!shadow_leak) {
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| 90 | pr_err("%s: failed to allocate shadow variable for the leaking pointer: dummy @ %p, leak @ %p\n",
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| 91 | __func__, d, leak);
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| 92 | goto err_shadow;
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| 93 | }
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| 94 |
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| 95 | pr_info("%s: dummy @ %p, expires @ %lx\n",
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| 96 | __func__, d, d->jiffies_expire);
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| 97 |
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| 98 | return d;
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| 99 |
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| 100 | err_shadow:
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| 101 | kfree(leak);
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| 102 | err_leak:
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| 103 | kfree(d);
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| 104 | return NULL;
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| 105 | }
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| 106 |
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| 107 | static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
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| 108 | {
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| 109 | void *d = obj;
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| 110 | int **shadow_leak = shadow_data;
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| 111 |
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| 112 | pr_info("%s: dummy @ %p, prevented leak @ %p\n",
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| 113 | __func__, d, *shadow_leak);
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| 114 | kfree(*shadow_leak);
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| 115 | }
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| 116 |
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| 117 | static void livepatch_fix1_dummy_free(struct dummy *d)
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| 118 | {
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| 119 | int **shadow_leak;
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| 120 |
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| 121 | |
| 122 | * Patch: fetch the saved SV_LEAK shadow variable, detach and
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| 123 | * free it. Note: handle cases where this shadow variable does
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| 124 | * not exist (ie, dummy structures allocated before this livepatch
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| 125 | * was loaded.)
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| 126 |
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| 127 | shadow_leak = klp_shadow_get(d, SV_LEAK);
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| 128 | if (shadow_leak)
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| 129 | klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
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| 130 | else
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| 131 | pr_info("%s: dummy @ %p leaked!\n", __func__, d);
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| 132 |
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| 133 | kfree(d);
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| 134 | }
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| 135 |
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| 136 | static struct klp_func funcs[] = {
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| 137 | {
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| 138 | .old_name = "dummy_alloc",
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| 139 | .new_func = livepatch_fix1_dummy_alloc,
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| 140 | },
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| 141 | {
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| 142 | .old_name = "dummy_free",
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| 143 | .new_func = livepatch_fix1_dummy_free,
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| 144 | }, { }
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| 145 | };
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| 146 |
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| 147 | static struct klp_object objs[] = {
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| 148 | {
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| 149 | .name = "livepatch_shadow_mod",
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| 150 | .funcs = funcs,
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| 151 | }, { }
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| 152 | };
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| 153 |
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| 154 | static struct klp_patch patch = {
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| 155 | .mod = THIS_MODULE,
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| 156 | .objs = objs,
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| 157 | };
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| 158 |
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| 159 | static int livepatch_shadow_fix1_init(void)
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| 160 | {
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| 161 | return klp_enable_patch(&patch);
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| 162 | }
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| 163 |
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| 164 | static void livepatch_shadow_fix1_exit(void)
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| 165 | {
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| 166 |
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| 167 | klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
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| 168 | }
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| 169 |
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| 170 | module_init(livepatch_shadow_fix1_init);
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| 171 | module_exit(livepatch_shadow_fix1_exit);
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| 172 | MODULE_LICENSE("GPL");
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| 173 | MODULE_INFO(livepatch, "Y");
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