| 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 + |
| 105 | msecs_to_jiffies(1000 * EXPIRE_PERIOD); |
| 106 | |
| 107 | /* Oops, forgot to save leak! */ |
| 108 | leak = kzalloc(sizeof(*leak), GFP_KERNEL); |
| 109 | if (!leak) { |
| 110 | kfree(d); |
| 111 | return NULL; |
| 112 | } |
| 113 | |
| 114 | pr_info("%s: dummy @ %p, expires @ %lx\n", |
| 115 | __func__, d, d->jiffies_expire); |
| 116 | |
| 117 | return d; |
| 118 | } |
| 119 | |
| 120 | static __used noinline void dummy_free(struct dummy *d) |
| 121 | { |
| 122 | pr_info("%s: dummy @ %p, expired = %lx\n", |
| 123 | __func__, d, d->jiffies_expire); |
| 124 | |
| 125 | kfree(d); |
| 126 | } |
| 127 | |
| 128 | static __used noinline bool dummy_check(struct dummy *d, |
| 129 | unsigned long jiffies) |
| 130 | { |
| 131 | return time_after(jiffies, d->jiffies_expire); |
| 132 | } |
| 133 | |
| 134 | /* |
| 135 | * alloc_work_func: allocates new dummy structures, allocates additional |
| 136 | * memory, aptly named "leak", but doesn't keep |
| 137 | * permanent record of it. |
| 138 | */ |
| 139 | |
| 140 | static void alloc_work_func(struct work_struct *work); |
| 141 | static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func); |
| 142 | |
| 143 | static void alloc_work_func(struct work_struct *work) |
| 144 | { |
| 145 | struct dummy *d; |
| 146 | |
| 147 | d = dummy_alloc(); |
| 148 | if (!d) |
| 149 | return; |
| 150 | |
| 151 | mutex_lock(&dummy_list_mutex); |
| 152 | list_add(&d->list, &dummy_list); |
| 153 | mutex_unlock(&dummy_list_mutex); |
| 154 | |
| 155 | schedule_delayed_work(&alloc_dwork, |
| 156 | msecs_to_jiffies(1000 * ALLOC_PERIOD)); |
| 157 | } |
| 158 | |
| 159 | /* |
| 160 | * cleanup_work_func: frees dummy structures. Without knownledge of |
| 161 | * "leak", it leaks the additional memory that |
| 162 | * alloc_work_func created. |
| 163 | */ |
| 164 | |
| 165 | static void cleanup_work_func(struct work_struct *work); |
| 166 | static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func); |
| 167 | |
| 168 | static void cleanup_work_func(struct work_struct *work) |
| 169 | { |
| 170 | struct dummy *d, *tmp; |
| 171 | unsigned long j; |
| 172 | |
| 173 | j = jiffies; |
| 174 | pr_info("%s: jiffies = %lx\n", __func__, j); |
| 175 | |
| 176 | mutex_lock(&dummy_list_mutex); |
| 177 | list_for_each_entry_safe(d, tmp, &dummy_list, list) { |
| 178 | |
| 179 | /* Kick out and free any expired dummies */ |
| 180 | if (dummy_check(d, j)) { |
| 181 | list_del(&d->list); |
| 182 | dummy_free(d); |
| 183 | } |
| 184 | } |
| 185 | mutex_unlock(&dummy_list_mutex); |
| 186 | |
| 187 | schedule_delayed_work(&cleanup_dwork, |
| 188 | msecs_to_jiffies(1000 * CLEANUP_PERIOD)); |
| 189 | } |
| 190 | |
| 191 | static int livepatch_shadow_mod_init(void) |
| 192 | { |
| 193 | schedule_delayed_work(&alloc_dwork, |
| 194 | msecs_to_jiffies(1000 * ALLOC_PERIOD)); |
| 195 | schedule_delayed_work(&cleanup_dwork, |
| 196 | msecs_to_jiffies(1000 * CLEANUP_PERIOD)); |
| 197 | |
| 198 | return 0; |
| 199 | } |
| 200 | |
| 201 | static void livepatch_shadow_mod_exit(void) |
| 202 | { |
| 203 | struct dummy *d, *tmp; |
| 204 | |
| 205 | /* Wait for any dummies at work */ |
| 206 | cancel_delayed_work_sync(&alloc_dwork); |
| 207 | cancel_delayed_work_sync(&cleanup_dwork); |
| 208 | |
| 209 | /* Cleanup residual dummies */ |
| 210 | list_for_each_entry_safe(d, tmp, &dummy_list, list) { |
| 211 | list_del(&d->list); |
| 212 | dummy_free(d); |
| 213 | } |
| 214 | } |
| 215 | |
| 216 | module_init(livepatch_shadow_mod_init); |
| 217 | module_exit(livepatch_shadow_mod_exit); |