1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com> 4 */ 5 6 /* 7 * livepatch-shadow-fix1.c - Shadow variables, livepatch demo 8 * 9 * Purpose 10 * ------- 11 * 12 * Fixes the memory leak introduced in livepatch-shadow-mod through the 13 * use of a shadow variable. This fix demonstrates the "extending" of 14 * short-lived data structures by patching its allocation and release 15 * functions. 16 * 17 * 18 * Usage 19 * ----- 20 * 21 * This module is not intended to be standalone. See the "Usage" 22 * section of livepatch-shadow-mod.c. 23 */ 24 25 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 26 27 #include <linux/module.h> 28 #include <linux/kernel.h> 29 #include <linux/livepatch.h> 30 #include <linux/slab.h> 31 32 /* Shadow variable enums */ 33 #define SV_LEAK 1 34 35 /* Allocate new dummies every second */ 36 #define ALLOC_PERIOD 1 37 /* Check for expired dummies after a few new ones have been allocated */ 38 #define CLEANUP_PERIOD (3 * ALLOC_PERIOD) 39 /* Dummies expire after a few cleanup instances */ 40 #define EXPIRE_PERIOD (4 * CLEANUP_PERIOD) 41 42 struct dummy { 43 struct list_head list; 44 unsigned long jiffies_expire; 45 }; 46 47 /* 48 * The constructor makes more sense together with klp_shadow_get_or_alloc(). 49 * In this example, it would be safe to assign the pointer also to the shadow 50 * variable returned by klp_shadow_alloc(). But we wanted to show the more 51 * complicated use of the API. 52 */ 53 static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data) 54 { 55 int **shadow_leak = shadow_data; 56 int **leak = ctor_data; 57 58 if (!ctor_data) 59 return -EINVAL; 60 61 *shadow_leak = *leak; 62 return 0; 63 } 64 65 static struct dummy *livepatch_fix1_dummy_alloc(void) 66 { 67 struct dummy *d; 68 int *leak; 69 int **shadow_leak; 70 71 d = kzalloc(sizeof(*d), GFP_KERNEL); 72 if (!d) 73 return NULL; 74 75 d->jiffies_expire = jiffies + 76 msecs_to_jiffies(1000 * EXPIRE_PERIOD); 77 78 /* 79 * Patch: save the extra memory location into a SV_LEAK shadow 80 * variable. A patched dummy_free routine can later fetch this 81 * pointer to handle resource release. 82 */ 83 leak = kzalloc(sizeof(*leak), GFP_KERNEL); 84 if (!leak) 85 goto err_leak; 86 87 shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL, 88 shadow_leak_ctor, &leak); 89 if (!shadow_leak) { 90 pr_err("%s: failed to allocate shadow variable for the leaking pointer: dummy @ %p, leak @ %p\n", 91 __func__, d, leak); 92 goto err_shadow; 93 } 94 95 pr_info("%s: dummy @ %p, expires @ %lx\n", 96 __func__, d, d->jiffies_expire); 97 98 return d; 99 100 err_shadow: 101 kfree(leak); 102 err_leak: 103 kfree(d); 104 return NULL; 105 } 106 107 static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data) 108 { 109 void *d = obj; 110 int **shadow_leak = shadow_data; 111 112 pr_info("%s: dummy @ %p, prevented leak @ %p\n", 113 __func__, d, *shadow_leak); 114 kfree(*shadow_leak); 115 } 116 117 static void livepatch_fix1_dummy_free(struct dummy *d) 118 { 119 int **shadow_leak; 120 121 /* 122 * Patch: fetch the saved SV_LEAK shadow variable, detach and 123 * free it. Note: handle cases where this shadow variable does 124 * not exist (ie, dummy structures allocated before this livepatch 125 * was loaded.) 126 */ 127 shadow_leak = klp_shadow_get(d, SV_LEAK); 128 if (shadow_leak) 129 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor); 130 else 131 pr_info("%s: dummy @ %p leaked!\n", __func__, d); 132 133 kfree(d); 134 } 135 136 static struct klp_func funcs[] = { 137 { 138 .old_name = "dummy_alloc", 139 .new_func = livepatch_fix1_dummy_alloc, 140 }, 141 { 142 .old_name = "dummy_free", 143 .new_func = livepatch_fix1_dummy_free, 144 }, { } 145 }; 146 147 static struct klp_object objs[] = { 148 { 149 .name = "livepatch_shadow_mod", 150 .funcs = funcs, 151 }, { } 152 }; 153 154 static struct klp_patch patch = { 155 .mod = THIS_MODULE, 156 .objs = objs, 157 }; 158 159 static int livepatch_shadow_fix1_init(void) 160 { 161 return klp_enable_patch(&patch); 162 } 163 164 static void livepatch_shadow_fix1_exit(void) 165 { 166 /* Cleanup any existing SV_LEAK shadow variables */ 167 klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor); 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