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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-fix1.c - Shadow variables, livepatch demo
20 *
21 * Purpose
22 * -------
23 *
24 * Fixes the memory leak introduced in livepatch-shadow-mod through the
25 * use of a shadow variable. This fix demonstrates the "extending" of
26 * short-lived data structures by patching its allocation and release
27 * functions.
28 *
29 *
30 * Usage
31 * -----
32 *
33 * This module is not intended to be standalone. See the "Usage"
34 * section of livepatch-shadow-mod.c.
35 */
36
37#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
38
39#include <linux/module.h>
40#include <linux/kernel.h>
41#include <linux/livepatch.h>
42#include <linux/slab.h>
43
44/* Shadow variable enums */
45#define SV_LEAK 1
46
47/* Allocate new dummies every second */
48#define ALLOC_PERIOD 1
49/* Check for expired dummies after a few new ones have been allocated */
50#define CLEANUP_PERIOD (3 * ALLOC_PERIOD)
51/* Dummies expire after a few cleanup instances */
52#define EXPIRE_PERIOD (4 * CLEANUP_PERIOD)
53
54struct dummy {
55 struct list_head list;
56 unsigned long jiffies_expire;
57};
58
59/*
60 * The constructor makes more sense together with klp_shadow_get_or_alloc().
61 * In this example, it would be safe to assign the pointer also to the shadow
62 * variable returned by klp_shadow_alloc(). But we wanted to show the more
63 * complicated use of the API.
64 */
65static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
66{
67 void **shadow_leak = shadow_data;
68 void *leak = ctor_data;
69
70 *shadow_leak = leak;
71 return 0;
72}
73
74struct dummy *livepatch_fix1_dummy_alloc(void)
75{
76 struct dummy *d;
77 void *leak;
78
79 d = kzalloc(sizeof(*d), GFP_KERNEL);
80 if (!d)
81 return NULL;
82
83 d->jiffies_expire = jiffies +
84 msecs_to_jiffies(1000 * EXPIRE_PERIOD);
85
86 /*
87 * Patch: save the extra memory location into a SV_LEAK shadow
88 * variable. A patched dummy_free routine can later fetch this
89 * pointer to handle resource release.
90 */
91 leak = kzalloc(sizeof(int), GFP_KERNEL);
92 if (!leak) {
93 kfree(d);
94 return NULL;
95 }
96
97 klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
98 shadow_leak_ctor, leak);
99
100 pr_info("%s: dummy @ %p, expires @ %lx\n",
101 __func__, d, d->jiffies_expire);
102
103 return d;
104}
105
106static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
107{
108 void *d = obj;
109 void **shadow_leak = shadow_data;
110
111 kfree(*shadow_leak);
112 pr_info("%s: dummy @ %p, prevented leak @ %p\n",
113 __func__, d, *shadow_leak);
114}
115
116void livepatch_fix1_dummy_free(struct dummy *d)
117{
118 void **shadow_leak;
119
120 /*
121 * Patch: fetch the saved SV_LEAK shadow variable, detach and
122 * free it. Note: handle cases where this shadow variable does
123 * not exist (ie, dummy structures allocated before this livepatch
124 * was loaded.)
125 */
126 shadow_leak = klp_shadow_get(d, SV_LEAK);
127 if (shadow_leak)
128 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
129 else
130 pr_info("%s: dummy @ %p leaked!\n", __func__, d);
131
132 kfree(d);
133}
134
135static struct klp_func funcs[] = {
136 {
137 .old_name = "dummy_alloc",
138 .new_func = livepatch_fix1_dummy_alloc,
139 },
140 {
141 .old_name = "dummy_free",
142 .new_func = livepatch_fix1_dummy_free,
143 }, { }
144};
145
146static struct klp_object objs[] = {
147 {
148 .name = "livepatch_shadow_mod",
149 .funcs = funcs,
150 }, { }
151};
152
153static struct klp_patch patch = {
154 .mod = THIS_MODULE,
155 .objs = objs,
156};
157
158static int livepatch_shadow_fix1_init(void)
159{
160 int ret;
161
162 ret = klp_register_patch(&patch);
163 if (ret)
164 return ret;
165 ret = klp_enable_patch(&patch);
166 if (ret) {
167 WARN_ON(klp_unregister_patch(&patch));
168 return ret;
169 }
170 return 0;
171}
172
173static void livepatch_shadow_fix1_exit(void)
174{
175 /* Cleanup any existing SV_LEAK shadow variables */
176 klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
177
178 WARN_ON(klp_unregister_patch(&patch));
179}
180
181module_init(livepatch_shadow_fix1_init);
182module_exit(livepatch_shadow_fix1_exit);
183MODULE_LICENSE("GPL");
184MODULE_INFO(livepatch, "Y");