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
dummy_alloc(void)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
dummy_free(struct dummy * d)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
dummy_check(struct dummy * d,unsigned long jiffies)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
alloc_work_func(struct work_struct * work)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
cleanup_work_func(struct work_struct * work)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
livepatch_shadow_mod_init(void)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
livepatch_shadow_mod_exit(void)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);
218