| 1 | |
| 2 | * Copyright (C) 2017 Joe Lawrence <[email protected]>
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| 3 | *
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| 4 | * This program is free software; you can redistribute it and/or
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| 5 | * modify it under the terms of the GNU General Public License
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| 6 | * as published by the Free Software Foundation; either version 2
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| 7 | * of the License, or (at your option) any later version.
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| 8 | *
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| 9 | * This program is distributed in the hope that it will be useful,
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| 10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 12 | * GNU General Public License for more details.
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| 13 | *
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| 14 | * You should have received a copy of the GNU General Public License
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| 15 | * along with this program; if not, see <http://www.gnu.org/licenses/>.
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| 16 |
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| 17 |
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| 18 | |
| 19 | * livepatch-shadow-fix2.c - Shadow variables, livepatch demo
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| 20 | *
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| 21 | * Purpose
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| 22 | * -------
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| 23 | *
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| 24 | * Adds functionality to livepatch-shadow-mod's in-flight data
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| 25 | * structures through a shadow variable. The livepatch patches a
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| 26 | * routine that periodically inspects data structures, incrementing a
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| 27 | * per-data-structure counter, creating the counter if needed.
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| 28 | *
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| 29 | *
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| 30 | * Usage
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| 31 | * -----
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| 32 | *
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| 33 | * This module is not intended to be standalone. See the "Usage"
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| 34 | * section of livepatch-shadow-mod.c.
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| 35 |
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| 36 |
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| 37 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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| 38 |
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| 39 | #include <linux/module.h>
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| 40 | #include <linux/kernel.h>
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| 41 | #include <linux/livepatch.h>
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| 42 | #include <linux/slab.h>
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| 43 |
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| 44 |
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| 45 | #define SV_LEAK 1
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| 46 | #define SV_COUNTER 2
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| 47 |
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| 48 | struct dummy {
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| 49 | struct list_head list;
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| 50 | unsigned long jiffies_expire;
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| 51 | };
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| 52 |
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| 53 | bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
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| 54 | {
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| 55 | int *shadow_count;
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| 56 | int count;
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| 57 |
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| 58 | |
| 59 | * Patch: handle in-flight dummy structures, if they do not
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| 60 | * already have a SV_COUNTER shadow variable, then attach a
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| 61 | * new one.
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| 62 |
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| 63 | count = 0;
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| 64 | shadow_count = klp_shadow_get_or_alloc(d, SV_COUNTER,
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| 65 | &count, sizeof(count),
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| 66 | GFP_NOWAIT);
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| 67 | if (shadow_count)
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| 68 | *shadow_count += 1;
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| 69 |
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| 70 | return time_after(jiffies, d->jiffies_expire);
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| 71 | }
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| 72 |
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| 73 | void livepatch_fix2_dummy_free(struct dummy *d)
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| 74 | {
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| 75 | void **shadow_leak, *leak;
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| 76 | int *shadow_count;
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| 77 |
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| 78 |
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| 79 | shadow_leak = klp_shadow_get(d, SV_LEAK);
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| 80 | if (shadow_leak) {
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| 81 | leak = *shadow_leak;
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| 82 | klp_shadow_free(d, SV_LEAK);
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| 83 | kfree(leak);
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| 84 | pr_info("%s: dummy @ %p, prevented leak @ %p\n",
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| 85 | __func__, d, leak);
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| 86 | } else {
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| 87 | pr_info("%s: dummy @ %p leaked!\n", __func__, d);
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| 88 | }
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| 89 |
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| 90 | |
| 91 | * Patch: fetch the SV_COUNTER shadow variable and display
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| 92 | * the final count. Detach the shadow variable.
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| 93 |
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| 94 | shadow_count = klp_shadow_get(d, SV_COUNTER);
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| 95 | if (shadow_count) {
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| 96 | pr_info("%s: dummy @ %p, check counter = %d\n",
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| 97 | __func__, d, *shadow_count);
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| 98 | klp_shadow_free(d, SV_COUNTER);
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| 99 | }
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| 100 |
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| 101 | kfree(d);
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| 102 | }
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| 103 |
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| 104 | static struct klp_func funcs[] = {
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| 105 | {
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| 106 | .old_name = "dummy_check",
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| 107 | .new_func = livepatch_fix2_dummy_check,
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| 108 | },
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| 109 | {
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| 110 | .old_name = "dummy_free",
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| 111 | .new_func = livepatch_fix2_dummy_free,
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| 112 | }, { }
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| 113 | };
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| 114 |
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| 115 | static struct klp_object objs[] = {
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| 116 | {
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| 117 | .name = "livepatch_shadow_mod",
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| 118 | .funcs = funcs,
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| 119 | }, { }
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| 120 | };
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| 121 |
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| 122 | static struct klp_patch patch = {
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| 123 | .mod = THIS_MODULE,
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| 124 | .objs = objs,
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| 125 | };
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| 126 |
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| 127 | static int livepatch_shadow_fix2_init(void)
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| 128 | {
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| 129 | int ret;
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| 130 |
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| 131 | if (!klp_have_reliable_stack() && !patch.immediate) {
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| 132 | |
| 133 | * WARNING: Be very careful when using 'patch.immediate' in
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| 134 | * your patches. It's ok to use it for simple patches like
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| 135 | * this, but for more complex patches which change function
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| 136 | * semantics, locking semantics, or data structures, it may not
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| 137 | * be safe. Use of this option will also prevent removal of
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| 138 | * the patch.
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| 139 | *
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| 140 | * See Documentation/livepatch/livepatch.txt for more details.
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| 141 |
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| 142 | patch.immediate = true;
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| 143 | pr_notice("The consistency model isn't supported for your architecture. Bypassing safety mechanisms and applying the patch immediately.\n");
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| 144 | }
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| 145 |
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| 146 | ret = klp_register_patch(&patch);
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| 147 | if (ret)
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| 148 | return ret;
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| 149 | ret = klp_enable_patch(&patch);
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| 150 | if (ret) {
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| 151 | WARN_ON(klp_unregister_patch(&patch));
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| 152 | return ret;
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| 153 | }
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| 154 | return 0;
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| 155 | }
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| 156 |
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| 157 | static void livepatch_shadow_fix2_exit(void)
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| 158 | {
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| 159 |
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| 160 | klp_shadow_free_all(SV_COUNTER);
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| 161 |
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| 162 | WARN_ON(klp_unregister_patch(&patch));
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| 163 | }
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| 164 |
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| 165 | module_init(livepatch_shadow_fix2_init);
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| 166 | module_exit(livepatch_shadow_fix2_exit);
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| 167 | MODULE_LICENSE("GPL");
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| 168 | MODULE_INFO(livepatch, "Y");
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