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-mod.c - Shadow variables, buggy module demo 8 * 9 * Purpose 10 * ------- 11 * 12 * As a demonstration of livepatch shadow variable API, this module 13 * introduces memory leak behavior that livepatch modules 14 * livepatch-shadow-fix1.ko and livepatch-shadow-fix2.ko correct and 15 * enhance. 16 * 17 * WARNING - even though the livepatch-shadow-fix modules patch the 18 * memory leak, please load these modules at your own risk -- some 19 * amount of memory may leaked before the bug is patched. 20 * 21 * 22 * Usage 23 * ----- 24 * 25 * Step 1 - Load the buggy demonstration module: 26 * 27 * insmod samples/livepatch/livepatch-shadow-mod.ko 28 * 29 * Watch dmesg output for a few moments to see new dummy being allocated 30 * and a periodic cleanup check. (Note: a small amount of memory is 31 * being leaked.) 32 * 33 * 34 * Step 2 - Load livepatch fix1: 35 * 36 * insmod samples/livepatch/livepatch-shadow-fix1.ko 37 * 38 * Continue watching dmesg and note that now livepatch_fix1_dummy_free() 39 * and livepatch_fix1_dummy_alloc() are logging messages about leaked 40 * memory and eventually leaks prevented. 41 * 42 * 43 * Step 3 - Load livepatch fix2 (on top of fix1): 44 * 45 * insmod samples/livepatch/livepatch-shadow-fix2.ko 46 * 47 * This module extends functionality through shadow variables, as a new 48 * "check" counter is added to the dummy structure. Periodic dmesg 49 * messages will log these as dummies are cleaned up. 50 * 51 * 52 * Step 4 - Cleanup 53 * 54 * Unwind the demonstration by disabling the livepatch fix modules, then 55 * removing them and the demo module: 56 * 57 * echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled 58 * echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled 59 * rmmod livepatch-shadow-fix2 60 * rmmod livepatch-shadow-fix1 61 * rmmod livepatch-shadow-mod 62 */ 63 64 65 #include <linux/kernel.h> 66 #include <linux/module.h> 67 #include <linux/sched.h> 68 #include <linux/slab.h> 69 #include <linux/stat.h> 70 #include <linux/workqueue.h> 71 72 MODULE_LICENSE("GPL"); 73 MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>"); 74 MODULE_DESCRIPTION("Buggy module for shadow variable demo"); 75 76 /* Allocate new dummies every second */ 77 #define ALLOC_PERIOD 1 78 /* Check for expired dummies after a few new ones have been allocated */ 79 #define CLEANUP_PERIOD (3 * ALLOC_PERIOD) 80 /* Dummies expire after a few cleanup instances */ 81 #define EXPIRE_PERIOD (4 * CLEANUP_PERIOD) 82 83 /* 84 * Keep a list of all the dummies so we can clean up any residual ones 85 * on module exit 86 */ 87 static LIST_HEAD(dummy_list); 88 static DEFINE_MUTEX(dummy_list_mutex); 89 90 struct dummy { 91 struct list_head list; 92 unsigned long jiffies_expire; 93 }; 94 95 static __used noinline struct dummy *dummy_alloc(void) 96 { 97 struct dummy *d; 98 int *leak; 99 100 d = kzalloc(sizeof(*d), GFP_KERNEL); 101 if (!d) 102 return NULL; 103 104 d->jiffies_expire = jiffies + secs_to_jiffies(EXPIRE_PERIOD); 105 106 /* Oops, forgot to save leak! */ 107 leak = kzalloc(sizeof(*leak), GFP_KERNEL); 108 if (!leak) { 109 kfree(d); 110 return NULL; 111 } 112 113 pr_info("%s: dummy @ %p, expires @ %lx\n", 114 __func__, d, d->jiffies_expire); 115 116 return d; 117 } 118 119 static __used noinline void dummy_free(struct dummy *d) 120 { 121 pr_info("%s: dummy @ %p, expired = %lx\n", 122 __func__, d, d->jiffies_expire); 123 124 kfree(d); 125 } 126 127 static __used noinline bool dummy_check(struct dummy *d, 128 unsigned long jiffies) 129 { 130 return time_after(jiffies, d->jiffies_expire); 131 } 132 133 /* 134 * alloc_work_func: allocates new dummy structures, allocates additional 135 * memory, aptly named "leak", but doesn't keep 136 * permanent record of it. 137 */ 138 139 static void alloc_work_func(struct work_struct *work); 140 static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func); 141 142 static void alloc_work_func(struct work_struct *work) 143 { 144 struct dummy *d; 145 146 d = dummy_alloc(); 147 if (!d) 148 return; 149 150 mutex_lock(&dummy_list_mutex); 151 list_add(&d->list, &dummy_list); 152 mutex_unlock(&dummy_list_mutex); 153 154 schedule_delayed_work(&alloc_dwork, secs_to_jiffies(ALLOC_PERIOD)); 155 } 156 157 /* 158 * cleanup_work_func: frees dummy structures. Without knownledge of 159 * "leak", it leaks the additional memory that 160 * alloc_work_func created. 161 */ 162 163 static void cleanup_work_func(struct work_struct *work); 164 static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func); 165 166 static void cleanup_work_func(struct work_struct *work) 167 { 168 struct dummy *d, *tmp; 169 unsigned long j; 170 171 j = jiffies; 172 pr_info("%s: jiffies = %lx\n", __func__, j); 173 174 mutex_lock(&dummy_list_mutex); 175 list_for_each_entry_safe(d, tmp, &dummy_list, list) { 176 177 /* Kick out and free any expired dummies */ 178 if (dummy_check(d, j)) { 179 list_del(&d->list); 180 dummy_free(d); 181 } 182 } 183 mutex_unlock(&dummy_list_mutex); 184 185 schedule_delayed_work(&cleanup_dwork, secs_to_jiffies(CLEANUP_PERIOD)); 186 } 187 188 static int livepatch_shadow_mod_init(void) 189 { 190 schedule_delayed_work(&alloc_dwork, secs_to_jiffies(ALLOC_PERIOD)); 191 schedule_delayed_work(&cleanup_dwork, secs_to_jiffies(CLEANUP_PERIOD)); 192 193 return 0; 194 } 195 196 static void livepatch_shadow_mod_exit(void) 197 { 198 struct dummy *d, *tmp; 199 200 /* Wait for any dummies at work */ 201 cancel_delayed_work_sync(&alloc_dwork); 202 cancel_delayed_work_sync(&cleanup_dwork); 203 204 /* Cleanup residual dummies */ 205 list_for_each_entry_safe(d, tmp, &dummy_list, list) { 206 list_del(&d->list); 207 dummy_free(d); 208 } 209 } 210 211 module_init(livepatch_shadow_mod_init); 212 module_exit(livepatch_shadow_mod_exit); 213