1 /* 2 * Copyright (C) 2017 Joe Lawrence <[email protected]> 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 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 klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL, 93 shadow_leak_ctor, leak); 94 95 pr_info("%s: dummy @ %p, expires @ %lx\n", 96 __func__, d, d->jiffies_expire); 97 98 return d; 99 } 100 101 void livepatch_fix1_dummy_free(struct dummy *d) 102 { 103 void **shadow_leak, *leak; 104 105 /* 106 * Patch: fetch the saved SV_LEAK shadow variable, detach and 107 * free it. Note: handle cases where this shadow variable does 108 * not exist (ie, dummy structures allocated before this livepatch 109 * was loaded.) 110 */ 111 shadow_leak = klp_shadow_get(d, SV_LEAK); 112 if (shadow_leak) { 113 leak = *shadow_leak; 114 klp_shadow_free(d, SV_LEAK); 115 kfree(leak); 116 pr_info("%s: dummy @ %p, prevented leak @ %p\n", 117 __func__, d, leak); 118 } else { 119 pr_info("%s: dummy @ %p leaked!\n", __func__, d); 120 } 121 122 kfree(d); 123 } 124 125 static struct klp_func funcs[] = { 126 { 127 .old_name = "dummy_alloc", 128 .new_func = livepatch_fix1_dummy_alloc, 129 }, 130 { 131 .old_name = "dummy_free", 132 .new_func = livepatch_fix1_dummy_free, 133 }, { } 134 }; 135 136 static struct klp_object objs[] = { 137 { 138 .name = "livepatch_shadow_mod", 139 .funcs = funcs, 140 }, { } 141 }; 142 143 static struct klp_patch patch = { 144 .mod = THIS_MODULE, 145 .objs = objs, 146 }; 147 148 static int livepatch_shadow_fix1_init(void) 149 { 150 int ret; 151 152 ret = klp_register_patch(&patch); 153 if (ret) 154 return ret; 155 ret = klp_enable_patch(&patch); 156 if (ret) { 157 WARN_ON(klp_unregister_patch(&patch)); 158 return ret; 159 } 160 return 0; 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); 167 168 WARN_ON(klp_unregister_patch(&patch)); 169 } 170 171 module_init(livepatch_shadow_fix1_init); 172 module_exit(livepatch_shadow_fix1_exit); 173 MODULE_LICENSE("GPL"); 174 MODULE_INFO(livepatch, "Y"); 175