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 /* 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 static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data) 102 { 103 void *d = obj; 104 void **shadow_leak = shadow_data; 105 106 kfree(*shadow_leak); 107 pr_info("%s: dummy @ %p, prevented leak @ %p\n", 108 __func__, d, *shadow_leak); 109 } 110 111 void livepatch_fix1_dummy_free(struct dummy *d) 112 { 113 void **shadow_leak; 114 115 /* 116 * Patch: fetch the saved SV_LEAK shadow variable, detach and 117 * free it. Note: handle cases where this shadow variable does 118 * not exist (ie, dummy structures allocated before this livepatch 119 * was loaded.) 120 */ 121 shadow_leak = klp_shadow_get(d, SV_LEAK); 122 if (shadow_leak) 123 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor); 124 else 125 pr_info("%s: dummy @ %p leaked!\n", __func__, d); 126 127 kfree(d); 128 } 129 130 static struct klp_func funcs[] = { 131 { 132 .old_name = "dummy_alloc", 133 .new_func = livepatch_fix1_dummy_alloc, 134 }, 135 { 136 .old_name = "dummy_free", 137 .new_func = livepatch_fix1_dummy_free, 138 }, { } 139 }; 140 141 static struct klp_object objs[] = { 142 { 143 .name = "livepatch_shadow_mod", 144 .funcs = funcs, 145 }, { } 146 }; 147 148 static struct klp_patch patch = { 149 .mod = THIS_MODULE, 150 .objs = objs, 151 }; 152 153 static int livepatch_shadow_fix1_init(void) 154 { 155 int ret; 156 157 ret = klp_register_patch(&patch); 158 if (ret) 159 return ret; 160 ret = klp_enable_patch(&patch); 161 if (ret) { 162 WARN_ON(klp_unregister_patch(&patch)); 163 return ret; 164 } 165 return 0; 166 } 167 168 static void livepatch_shadow_fix1_exit(void) 169 { 170 /* Cleanup any existing SV_LEAK shadow variables */ 171 klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor); 172 173 WARN_ON(klp_unregister_patch(&patch)); 174 } 175 176 module_init(livepatch_shadow_fix1_init); 177 module_exit(livepatch_shadow_fix1_exit); 178 MODULE_LICENSE("GPL"); 179 MODULE_INFO(livepatch, "Y"); 180