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439e7271 JL |
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 | ||
54 | struct dummy { | |
55 | struct list_head list; | |
56 | unsigned long jiffies_expire; | |
57 | }; | |
58 | ||
59 | struct dummy *livepatch_fix1_dummy_alloc(void) | |
60 | { | |
61 | struct dummy *d; | |
62 | void *leak; | |
63 | ||
64 | d = kzalloc(sizeof(*d), GFP_KERNEL); | |
65 | if (!d) | |
66 | return NULL; | |
67 | ||
68 | d->jiffies_expire = jiffies + | |
69 | msecs_to_jiffies(1000 * EXPIRE_PERIOD); | |
70 | ||
71 | /* | |
72 | * Patch: save the extra memory location into a SV_LEAK shadow | |
73 | * variable. A patched dummy_free routine can later fetch this | |
74 | * pointer to handle resource release. | |
75 | */ | |
76 | leak = kzalloc(sizeof(int), GFP_KERNEL); | |
77 | klp_shadow_alloc(d, SV_LEAK, &leak, sizeof(leak), GFP_KERNEL); | |
78 | ||
79 | pr_info("%s: dummy @ %p, expires @ %lx\n", | |
80 | __func__, d, d->jiffies_expire); | |
81 | ||
82 | return d; | |
83 | } | |
84 | ||
85 | void livepatch_fix1_dummy_free(struct dummy *d) | |
86 | { | |
87 | void **shadow_leak, *leak; | |
88 | ||
89 | /* | |
90 | * Patch: fetch the saved SV_LEAK shadow variable, detach and | |
91 | * free it. Note: handle cases where this shadow variable does | |
92 | * not exist (ie, dummy structures allocated before this livepatch | |
93 | * was loaded.) | |
94 | */ | |
95 | shadow_leak = klp_shadow_get(d, SV_LEAK); | |
96 | if (shadow_leak) { | |
97 | leak = *shadow_leak; | |
98 | klp_shadow_free(d, SV_LEAK); | |
99 | kfree(leak); | |
100 | pr_info("%s: dummy @ %p, prevented leak @ %p\n", | |
101 | __func__, d, leak); | |
102 | } else { | |
103 | pr_info("%s: dummy @ %p leaked!\n", __func__, d); | |
104 | } | |
105 | ||
106 | kfree(d); | |
107 | } | |
108 | ||
109 | static struct klp_func funcs[] = { | |
110 | { | |
111 | .old_name = "dummy_alloc", | |
112 | .new_func = livepatch_fix1_dummy_alloc, | |
113 | }, | |
114 | { | |
115 | .old_name = "dummy_free", | |
116 | .new_func = livepatch_fix1_dummy_free, | |
117 | }, { } | |
118 | }; | |
119 | ||
120 | static struct klp_object objs[] = { | |
121 | { | |
122 | .name = "livepatch_shadow_mod", | |
123 | .funcs = funcs, | |
124 | }, { } | |
125 | }; | |
126 | ||
127 | static struct klp_patch patch = { | |
128 | .mod = THIS_MODULE, | |
129 | .objs = objs, | |
130 | }; | |
131 | ||
132 | static int livepatch_shadow_fix1_init(void) | |
133 | { | |
134 | int ret; | |
135 | ||
439e7271 JL |
136 | ret = klp_register_patch(&patch); |
137 | if (ret) | |
138 | return ret; | |
139 | ret = klp_enable_patch(&patch); | |
140 | if (ret) { | |
141 | WARN_ON(klp_unregister_patch(&patch)); | |
142 | return ret; | |
143 | } | |
144 | return 0; | |
145 | } | |
146 | ||
147 | static void livepatch_shadow_fix1_exit(void) | |
148 | { | |
149 | /* Cleanup any existing SV_LEAK shadow variables */ | |
150 | klp_shadow_free_all(SV_LEAK); | |
151 | ||
152 | WARN_ON(klp_unregister_patch(&patch)); | |
153 | } | |
154 | ||
155 | module_init(livepatch_shadow_fix1_init); | |
156 | module_exit(livepatch_shadow_fix1_exit); | |
157 | MODULE_LICENSE("GPL"); | |
158 | MODULE_INFO(livepatch, "Y"); |