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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>4 */5 6/*7 * livepatch-shadow-mod.c - Shadow variables, buggy module demo8 *9 * Purpose10 * -------11 *12 * As a demonstration of livepatch shadow variable API, this module13 * introduces memory leak behavior that livepatch modules14 * livepatch-shadow-fix1.ko and livepatch-shadow-fix2.ko correct and15 * enhance.16 *17 * WARNING - even though the livepatch-shadow-fix modules patch the18 * memory leak, please load these modules at your own risk -- some19 * amount of memory may leaked before the bug is patched.20 *21 *22 * Usage23 * -----24 *25 * Step 1 - Load the buggy demonstration module:26 *27 * insmod samples/livepatch/livepatch-shadow-mod.ko28 *29 * Watch dmesg output for a few moments to see new dummy being allocated30 * and a periodic cleanup check. (Note: a small amount of memory is31 * being leaked.)32 *33 *34 * Step 2 - Load livepatch fix1:35 *36 * insmod samples/livepatch/livepatch-shadow-fix1.ko37 *38 * Continue watching dmesg and note that now livepatch_fix1_dummy_free()39 * and livepatch_fix1_dummy_alloc() are logging messages about leaked40 * 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.ko46 *47 * This module extends functionality through shadow variables, as a new48 * "check" counter is added to the dummy structure. Periodic dmesg49 * messages will log these as dummies are cleaned up.50 *51 *52 * Step 4 - Cleanup53 *54 * Unwind the demonstration by disabling the livepatch fix modules, then55 * removing them and the demo module:56 *57 * echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled58 * echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled59 * rmmod livepatch-shadow-fix260 * rmmod livepatch-shadow-fix161 * rmmod livepatch-shadow-mod62 */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 72MODULE_LICENSE("GPL");73MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");74MODULE_DESCRIPTION("Buggy module for shadow variable demo");75 76/* Allocate new dummies every second */77#define ALLOC_PERIOD 178/* 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 ones85 * on module exit86 */87static LIST_HEAD(dummy_list);88static DEFINE_MUTEX(dummy_list_mutex);89 90struct dummy {91 struct list_head list;92 unsigned long jiffies_expire;93};94 95static __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 120static __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 128static __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 additional136 * memory, aptly named "leak", but doesn't keep137 * permanent record of it.138 */139 140static void alloc_work_func(struct work_struct *work);141static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func);142 143static 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 of161 * "leak", it leaks the additional memory that162 * alloc_work_func created.163 */164 165static void cleanup_work_func(struct work_struct *work);166static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func);167 168static 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 191static 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 201static 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 216module_init(livepatch_shadow_mod_init);217module_exit(livepatch_shadow_mod_exit);218