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 void **shadow_leak = shadow_data; 56 void *leak = ctor_data; 57 58 *shadow_leak = leak; 59 return 0; 60 } 61 62 static struct dummy *livepatch_fix1_dummy_alloc(void) 63 { 64 struct dummy *d; 65 void *leak; 66 67 d = kzalloc(sizeof(*d), GFP_KERNEL); 68 if (!d) 69 return NULL; 70 71 d->jiffies_expire = jiffies + 72 msecs_to_jiffies(1000 * EXPIRE_PERIOD); 73 74 /* 75 * Patch: save the extra memory location into a SV_LEAK shadow 76 * variable. A patched dummy_free routine can later fetch this 77 * pointer to handle resource release. 78 */ 79 leak = kzalloc(sizeof(int), GFP_KERNEL); 80 if (!leak) { 81 kfree(d); 82 return NULL; 83 } 84 85 klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL, 86 shadow_leak_ctor, leak); 87 88 pr_info("%s: dummy @ %p, expires @ %lx\n", 89 __func__, d, d->jiffies_expire); 90 91 return d; 92 } 93 94 static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data) 95 { 96 void *d = obj; 97 void **shadow_leak = shadow_data; 98 99 kfree(*shadow_leak); 100 pr_info("%s: dummy @ %p, prevented leak @ %p\n", 101 __func__, d, *shadow_leak); 102 } 103 104 static void livepatch_fix1_dummy_free(struct dummy *d) 105 { 106 void **shadow_leak; 107 108 /* 109 * Patch: fetch the saved SV_LEAK shadow variable, detach and 110 * free it. Note: handle cases where this shadow variable does 111 * not exist (ie, dummy structures allocated before this livepatch 112 * was loaded.) 113 */ 114 shadow_leak = klp_shadow_get(d, SV_LEAK); 115 if (shadow_leak) 116 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor); 117 else 118 pr_info("%s: dummy @ %p leaked!\n", __func__, d); 119 120 kfree(d); 121 } 122 123 static struct klp_func funcs[] = { 124 { 125 .old_name = "dummy_alloc", 126 .new_func = livepatch_fix1_dummy_alloc, 127 }, 128 { 129 .old_name = "dummy_free", 130 .new_func = livepatch_fix1_dummy_free, 131 }, { } 132 }; 133 134 static struct klp_object objs[] = { 135 { 136 .name = "livepatch_shadow_mod", 137 .funcs = funcs, 138 }, { } 139 }; 140 141 static struct klp_patch patch = { 142 .mod = THIS_MODULE, 143 .objs = objs, 144 }; 145 146 static int livepatch_shadow_fix1_init(void) 147 { 148 return klp_enable_patch(&patch); 149 } 150 151 static void livepatch_shadow_fix1_exit(void) 152 { 153 /* Cleanup any existing SV_LEAK shadow variables */ 154 klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor); 155 } 156 157 module_init(livepatch_shadow_fix1_init); 158 module_exit(livepatch_shadow_fix1_exit); 159 MODULE_LICENSE("GPL"); 160 MODULE_INFO(livepatch, "Y"); 161