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 if (!klp_have_reliable_stack() && !patch.immediate) { 137 /* 138 * WARNING: Be very careful when using 'patch.immediate' in 139 * your patches. It's ok to use it for simple patches like 140 * this, but for more complex patches which change function 141 * semantics, locking semantics, or data structures, it may not 142 * be safe. Use of this option will also prevent removal of 143 * the patch. 144 * 145 * See Documentation/livepatch/livepatch.txt for more details. 146 */ 147 patch.immediate = true; 148 pr_notice("The consistency model isn't supported for your architecture. Bypassing safety mechanisms and applying the patch immediately.\n"); 149 } 150 151 ret = klp_register_patch(&patch); 152 if (ret) 153 return ret; 154 ret = klp_enable_patch(&patch); 155 if (ret) { 156 WARN_ON(klp_unregister_patch(&patch)); 157 return ret; 158 } 159 return 0; 160 } 161 162 static void livepatch_shadow_fix1_exit(void) 163 { 164 /* Cleanup any existing SV_LEAK shadow variables */ 165 klp_shadow_free_all(SV_LEAK); 166 167 WARN_ON(klp_unregister_patch(&patch)); 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"); 174