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 + secs_to_jiffies(EXPIRE_PERIOD); 76 77 /* 78 * Patch: save the extra memory location into a SV_LEAK shadow 79 * variable. A patched dummy_free routine can later fetch this 80 * pointer to handle resource release. 81 */ 82 leak = kzalloc(sizeof(*leak), GFP_KERNEL); 83 if (!leak) 84 goto err_leak; 85 86 shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL, 87 shadow_leak_ctor, &leak); 88 if (!shadow_leak) { 89 pr_err("%s: failed to allocate shadow variable for the leaking pointer: dummy @ %p, leak @ %p\n", 90 __func__, d, leak); 91 goto err_shadow; 92 } 93 94 pr_info("%s: dummy @ %p, expires @ %lx\n", 95 __func__, d, d->jiffies_expire); 96 97 return d; 98 99 err_shadow: 100 kfree(leak); 101 err_leak: 102 kfree(d); 103 return NULL; 104 } 105 106 static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data) 107 { 108 void *d = obj; 109 int **shadow_leak = shadow_data; 110 111 pr_info("%s: dummy @ %p, prevented leak @ %p\n", 112 __func__, d, *shadow_leak); 113 kfree(*shadow_leak); 114 } 115 116 static void livepatch_fix1_dummy_free(struct dummy *d) 117 { 118 int **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