projects/linux·blob v5.0 · refs

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1/*
2 * Copyright (C) 2017 Joe Lawrence <[email protected]>
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 <[email protected]>");
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 if (!leak) {
122 kfree(d);
123 return NULL;
124 }
125
126 pr_info("%s: dummy @ %p, expires @ %lx\n",
127 __func__, d, d->jiffies_expire);
128
129 return d;
130}
131
132noinline void dummy_free(struct dummy *d)
133{
134 pr_info("%s: dummy @ %p, expired = %lx\n",
135 __func__, d, d->jiffies_expire);
136
137 kfree(d);
138}
139
140noinline bool dummy_check(struct dummy *d, unsigned long jiffies)
141{
142 return time_after(jiffies, d->jiffies_expire);
143}
144
145/*
146 * alloc_work_func: allocates new dummy structures, allocates additional
147 * memory, aptly named "leak", but doesn't keep
148 * permanent record of it.
149 */
150
151static void alloc_work_func(struct work_struct *work);
152static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func);
153
154static void alloc_work_func(struct work_struct *work)
155{
156 struct dummy *d;
157
158 d = dummy_alloc();
159 if (!d)
160 return;
161
162 mutex_lock(&dummy_list_mutex);
163 list_add(&d->list, &dummy_list);
164 mutex_unlock(&dummy_list_mutex);
165
166 schedule_delayed_work(&alloc_dwork,
167 msecs_to_jiffies(1000 * ALLOC_PERIOD));
168}
169
170/*
171 * cleanup_work_func: frees dummy structures. Without knownledge of
172 * "leak", it leaks the additional memory that
173 * alloc_work_func created.
174 */
175
176static void cleanup_work_func(struct work_struct *work);
177static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func);
178
179static void cleanup_work_func(struct work_struct *work)
180{
181 struct dummy *d, *tmp;
182 unsigned long j;
183
184 j = jiffies;
185 pr_info("%s: jiffies = %lx\n", __func__, j);
186
187 mutex_lock(&dummy_list_mutex);
188 list_for_each_entry_safe(d, tmp, &dummy_list, list) {
189
190 /* Kick out and free any expired dummies */
191 if (dummy_check(d, j)) {
192 list_del(&d->list);
193 dummy_free(d);
194 }
195 }
196 mutex_unlock(&dummy_list_mutex);
197
198 schedule_delayed_work(&cleanup_dwork,
199 msecs_to_jiffies(1000 * CLEANUP_PERIOD));
200}
201
202static int livepatch_shadow_mod_init(void)
203{
204 schedule_delayed_work(&alloc_dwork,
205 msecs_to_jiffies(1000 * ALLOC_PERIOD));
206 schedule_delayed_work(&cleanup_dwork,
207 msecs_to_jiffies(1000 * CLEANUP_PERIOD));
208
209 return 0;
210}
211
212static void livepatch_shadow_mod_exit(void)
213{
214 struct dummy *d, *tmp;
215
216 /* Wait for any dummies at work */
217 cancel_delayed_work_sync(&alloc_dwork);
218 cancel_delayed_work_sync(&cleanup_dwork);
219
220 /* Cleanup residual dummies */
221 list_for_each_entry_safe(d, tmp, &dummy_list, list) {
222 list_del(&d->list);
223 dummy_free(d);
224 }
225}
226
227module_init(livepatch_shadow_mod_init);
228module_exit(livepatch_shadow_mod_exit);