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-fix1.c - Shadow variables, livepatch demo
8 *
9 * Purpose
10 * -------
11 *
12 * Fixes the memory leak introduced in livepatch-shadow-mod through the
13 * use of a shadow variable. This fix demonstrates the "extending" of
14 * short-lived data structures by patching its allocation and release
15 * functions.
16 *
17 *
18 * Usage
19 * -----
20 *
21 * This module is not intended to be standalone. See the "Usage"
22 * section of livepatch-shadow-mod.c.
23 */
24
25 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
26
27 #include <linux/module.h>
28 #include <linux/kernel.h>
29 #include <linux/livepatch.h>
30 #include <linux/slab.h>
31
32 /* Shadow variable enums */
33 #define SV_LEAK 1
34
35 /* Allocate new dummies every second */
36 #define ALLOC_PERIOD 1
37 /* Check for expired dummies after a few new ones have been allocated */
38 #define CLEANUP_PERIOD (3 * ALLOC_PERIOD)
39 /* Dummies expire after a few cleanup instances */
40 #define EXPIRE_PERIOD (4 * CLEANUP_PERIOD)
41
42 struct dummy {
43 struct list_head list;
44 unsigned long jiffies_expire;
45 };
46
47 /*
48 * The constructor makes more sense together with klp_shadow_get_or_alloc().
49 * In this example, it would be safe to assign the pointer also to the shadow
50 * variable returned by klp_shadow_alloc(). But we wanted to show the more
51 * complicated use of the API.
52 */
shadow_leak_ctor(void * obj,void * shadow_data,void * ctor_data)53 static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
54 {
55 void **shadow_leak = shadow_data;
56 void *leak = ctor_data;
57
58 *shadow_leak = leak;
59 return 0;
60 }
61
livepatch_fix1_dummy_alloc(void)62 static struct dummy *livepatch_fix1_dummy_alloc(void)
63 {
64 struct dummy *d;
65 void *leak;
66
67 d = kzalloc(sizeof(*d), GFP_KERNEL);
68 if (!d)
69 return NULL;
70
71 d->jiffies_expire = jiffies +
72 msecs_to_jiffies(1000 * EXPIRE_PERIOD);
73
74 /*
75 * Patch: save the extra memory location into a SV_LEAK shadow
76 * variable. A patched dummy_free routine can later fetch this
77 * pointer to handle resource release.
78 */
79 leak = kzalloc(sizeof(int), GFP_KERNEL);
80 if (!leak) {
81 kfree(d);
82 return NULL;
83 }
84
85 klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
86 shadow_leak_ctor, leak);
87
88 pr_info("%s: dummy @ %p, expires @ %lx\n",
89 __func__, d, d->jiffies_expire);
90
91 return d;
92 }
93
livepatch_fix1_dummy_leak_dtor(void * obj,void * shadow_data)94 static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
95 {
96 void *d = obj;
97 void **shadow_leak = shadow_data;
98
99 kfree(*shadow_leak);
100 pr_info("%s: dummy @ %p, prevented leak @ %p\n",
101 __func__, d, *shadow_leak);
102 }
103
livepatch_fix1_dummy_free(struct dummy * d)104 static void livepatch_fix1_dummy_free(struct dummy *d)
105 {
106 void **shadow_leak;
107
108 /*
109 * Patch: fetch the saved SV_LEAK shadow variable, detach and
110 * free it. Note: handle cases where this shadow variable does
111 * not exist (ie, dummy structures allocated before this livepatch
112 * was loaded.)
113 */
114 shadow_leak = klp_shadow_get(d, SV_LEAK);
115 if (shadow_leak)
116 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
117 else
118 pr_info("%s: dummy @ %p leaked!\n", __func__, d);
119
120 kfree(d);
121 }
122
123 static struct klp_func funcs[] = {
124 {
125 .old_name = "dummy_alloc",
126 .new_func = livepatch_fix1_dummy_alloc,
127 },
128 {
129 .old_name = "dummy_free",
130 .new_func = livepatch_fix1_dummy_free,
131 }, { }
132 };
133
134 static struct klp_object objs[] = {
135 {
136 .name = "livepatch_shadow_mod",
137 .funcs = funcs,
138 }, { }
139 };
140
141 static struct klp_patch patch = {
142 .mod = THIS_MODULE,
143 .objs = objs,
144 };
145
livepatch_shadow_fix1_init(void)146 static int livepatch_shadow_fix1_init(void)
147 {
148 return klp_enable_patch(&patch);
149 }
150
livepatch_shadow_fix1_exit(void)151 static void livepatch_shadow_fix1_exit(void)
152 {
153 /* Cleanup any existing SV_LEAK shadow variables */
154 klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
155 }
156
157 module_init(livepatch_shadow_fix1_init);
158 module_exit(livepatch_shadow_fix1_exit);
159 MODULE_LICENSE("GPL");
160 MODULE_INFO(livepatch, "Y");
161