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 static 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 if (!leak) { 93 kfree(d); 94 return NULL; 95 } 96 97 klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL, 98 shadow_leak_ctor, leak); 99 100 pr_info("%s: dummy @ %p, expires @ %lx\n", 101 __func__, d, d->jiffies_expire); 102 103 return d; 104 } 105 106 static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data) 107 { 108 void *d = obj; 109 void **shadow_leak = shadow_data; 110 111 kfree(*shadow_leak); 112 pr_info("%s: dummy @ %p, prevented leak @ %p\n", 113 __func__, d, *shadow_leak); 114 } 115 116 static void livepatch_fix1_dummy_free(struct dummy *d) 117 { 118 void **shadow_leak; 119 120 /* 121 * Patch: fetch the saved SV_LEAK shadow variable, detach and 122 * free it. Note: handle cases where this shadow variable does 123 * not exist (ie, dummy structures allocated before this livepatch 124 * was loaded.) 125 */ 126 shadow_leak = klp_shadow_get(d, SV_LEAK); 127 if (shadow_leak) 128 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor); 129 else 130 pr_info("%s: dummy @ %p leaked!\n", __func__, d); 131 132 kfree(d); 133 } 134 135 static struct klp_func funcs[] = { 136 { 137 .old_name = "dummy_alloc", 138 .new_func = livepatch_fix1_dummy_alloc, 139 }, 140 { 141 .old_name = "dummy_free", 142 .new_func = livepatch_fix1_dummy_free, 143 }, { } 144 }; 145 146 static struct klp_object objs[] = { 147 { 148 .name = "livepatch_shadow_mod", 149 .funcs = funcs, 150 }, { } 151 }; 152 153 static struct klp_patch patch = { 154 .mod = THIS_MODULE, 155 .objs = objs, 156 }; 157 158 static int livepatch_shadow_fix1_init(void) 159 { 160 return klp_enable_patch(&patch); 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, livepatch_fix1_dummy_leak_dtor); 167 } 168 169 module_init(livepatch_shadow_fix1_init); 170 module_exit(livepatch_shadow_fix1_exit); 171 MODULE_LICENSE("GPL"); 172 MODULE_INFO(livepatch, "Y"); 173