1/*
  2 * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
  3 *
  4 * This program is free software; you can redistribute it and/or
  5 * modify it under the terms of the GNU General Public License
  6 * as published by the Free Software Foundation; either version 2
  7 * of the License, or (at your option) any later version.
  8 *
  9 * This program is distributed in the hope that it will be useful,
 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 12 * GNU General Public License for more details.
 13 *
 14 * You should have received a copy of the GNU General Public License
 15 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 16 */
 17
 18/*
 19 * livepatch-shadow-mod.c - Shadow variables, buggy module demo
 20 *
 21 * Purpose
 22 * -------
 23 *
 24 * As a demonstration of livepatch shadow variable API, this module
 25 * introduces memory leak behavior that livepatch modules
 26 * livepatch-shadow-fix1.ko and livepatch-shadow-fix2.ko correct and
 27 * enhance.
 28 *
 29 * WARNING - even though the livepatch-shadow-fix modules patch the
 30 * memory leak, please load these modules at your own risk -- some
 31 * amount of memory may leaked before the bug is patched.
 32 *
 33 *
 34 * Usage
 35 * -----
 36 *
 37 * Step 1 - Load the buggy demonstration module:
 38 *
 39 *   insmod samples/livepatch/livepatch-shadow-mod.ko
 40 *
 41 * Watch dmesg output for a few moments to see new dummy being allocated
 42 * and a periodic cleanup check.  (Note: a small amount of memory is
 43 * being leaked.)
 44 *
 45 *
 46 * Step 2 - Load livepatch fix1:
 47 *
 48 *   insmod samples/livepatch/livepatch-shadow-fix1.ko
 49 *
 50 * Continue watching dmesg and note that now livepatch_fix1_dummy_free()
 51 * and livepatch_fix1_dummy_alloc() are logging messages about leaked
 52 * memory and eventually leaks prevented.
 53 *
 54 *
 55 * Step 3 - Load livepatch fix2 (on top of fix1):
 56 *
 57 *   insmod samples/livepatch/livepatch-shadow-fix2.ko
 58 *
 59 * This module extends functionality through shadow variables, as a new
 60 * "check" counter is added to the dummy structure.  Periodic dmesg
 61 * messages will log these as dummies are cleaned up.
 62 *
 63 *
 64 * Step 4 - Cleanup
 65 *
 66 * Unwind the demonstration by disabling the livepatch fix modules, then
 67 * removing them and the demo module:
 68 *
 69 *   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled
 70 *   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled
 71 *   rmmod livepatch-shadow-fix2
 72 *   rmmod livepatch-shadow-fix1
 73 *   rmmod livepatch-shadow-mod
 74 */
 75
 76
 77#include <linux/kernel.h>
 78#include <linux/module.h>
 79#include <linux/sched.h>
 80#include <linux/slab.h>
 81#include <linux/stat.h>
 82#include <linux/workqueue.h>
 83
 84MODULE_LICENSE("GPL");
 85MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");
 86MODULE_DESCRIPTION("Buggy module for shadow variable demo");
 87
 88/* Allocate new dummies every second */
 89#define ALLOC_PERIOD	1
 90/* Check for expired dummies after a few new ones have been allocated */
 91#define CLEANUP_PERIOD	(3 * ALLOC_PERIOD)
 92/* Dummies expire after a few cleanup instances */
 93#define EXPIRE_PERIOD	(4 * CLEANUP_PERIOD)
 94
 95/*
 96 * Keep a list of all the dummies so we can clean up any residual ones
 97 * on module exit
 98 */
 99LIST_HEAD(dummy_list);
100DEFINE_MUTEX(dummy_list_mutex);
101
102struct dummy {
103	struct list_head list;
104	unsigned long jiffies_expire;
105};
106
107noinline struct dummy *dummy_alloc(void)
108{
109	struct dummy *d;
110	void *leak;
111
112	d = kzalloc(sizeof(*d), GFP_KERNEL);
113	if (!d)
114		return NULL;
115
116	d->jiffies_expire = jiffies +
117		msecs_to_jiffies(1000 * EXPIRE_PERIOD);
118
119	/* Oops, forgot to save leak! */
120	leak = kzalloc(sizeof(int), GFP_KERNEL);
121
122	pr_info("%s: dummy @ %p, expires @ %lx\n",
123		__func__, d, d->jiffies_expire);
124
125	return d;
126}
127
128noinline void dummy_free(struct dummy *d)
129{
130	pr_info("%s: dummy @ %p, expired = %lx\n",
131		__func__, d, d->jiffies_expire);
132
133	kfree(d);
134}
135
136noinline bool dummy_check(struct dummy *d, unsigned long jiffies)
137{
138	return time_after(jiffies, d->jiffies_expire);
139}
140
141/*
142 * alloc_work_func: allocates new dummy structures, allocates additional
143 *                  memory, aptly named "leak", but doesn't keep
144 *                  permanent record of it.
145 */
146
147static void alloc_work_func(struct work_struct *work);
148static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func);
149
150static void alloc_work_func(struct work_struct *work)
151{
152	struct dummy *d;
153
154	d = dummy_alloc();
155	if (!d)
156		return;
157
158	mutex_lock(&dummy_list_mutex);
159	list_add(&d->list, &dummy_list);
160	mutex_unlock(&dummy_list_mutex);
161
162	schedule_delayed_work(&alloc_dwork,
163		msecs_to_jiffies(1000 * ALLOC_PERIOD));
164}
165
166/*
167 * cleanup_work_func: frees dummy structures.  Without knownledge of
168 *                    "leak", it leaks the additional memory that
169 *                    alloc_work_func created.
170 */
171
172static void cleanup_work_func(struct work_struct *work);
173static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func);
174
175static void cleanup_work_func(struct work_struct *work)
176{
177	struct dummy *d, *tmp;
178	unsigned long j;
179
180	j = jiffies;
181	pr_info("%s: jiffies = %lx\n", __func__, j);
182
183	mutex_lock(&dummy_list_mutex);
184	list_for_each_entry_safe(d, tmp, &dummy_list, list) {
185
186		/* Kick out and free any expired dummies */
187		if (dummy_check(d, j)) {
188			list_del(&d->list);
189			dummy_free(d);
190		}
191	}
192	mutex_unlock(&dummy_list_mutex);
193
194	schedule_delayed_work(&cleanup_dwork,
195		msecs_to_jiffies(1000 * CLEANUP_PERIOD));
196}
197
198static int livepatch_shadow_mod_init(void)
199{
200	schedule_delayed_work(&alloc_dwork,
201		msecs_to_jiffies(1000 * ALLOC_PERIOD));
202	schedule_delayed_work(&cleanup_dwork,
203		msecs_to_jiffies(1000 * CLEANUP_PERIOD));
204
205	return 0;
206}
207
208static void livepatch_shadow_mod_exit(void)
209{
210	struct dummy *d, *tmp;
211
212	/* Wait for any dummies at work */
213	cancel_delayed_work_sync(&alloc_dwork);
214	cancel_delayed_work_sync(&cleanup_dwork);
215
216	/* Cleanup residual dummies */
217	list_for_each_entry_safe(d, tmp, &dummy_list, list) {
218		list_del(&d->list);
219		dummy_free(d);
220	}
221}
222
223module_init(livepatch_shadow_mod_init);
224module_exit(livepatch_shadow_mod_exit);