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