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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
42struct 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 */
53static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
54{
55 int **shadow_leak = shadow_data;
56 int **leak = ctor_data;
57
58 if (!ctor_data)
59 return -EINVAL;
60
61 *shadow_leak = *leak;
62 return 0;
63}
64
65static struct dummy *livepatch_fix1_dummy_alloc(void)
66{
67 struct dummy *d;
68 int *leak;
69 int **shadow_leak;
70
71 d = kzalloc(sizeof(*d), GFP_KERNEL);
72 if (!d)
73 return NULL;
74
75 d->jiffies_expire = jiffies + secs_to_jiffies(EXPIRE_PERIOD);
76
77 /*
78 * Patch: save the extra memory location into a SV_LEAK shadow
79 * variable. A patched dummy_free routine can later fetch this
80 * pointer to handle resource release.
81 */
82 leak = kzalloc(sizeof(*leak), GFP_KERNEL);
83 if (!leak)
84 goto err_leak;
85
86 shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
87 shadow_leak_ctor, &leak);
88 if (!shadow_leak) {
89 pr_err("%s: failed to allocate shadow variable for the leaking pointer: dummy @ %p, leak @ %p\n",
90 __func__, d, leak);
91 goto err_shadow;
92 }
93
94 pr_info("%s: dummy @ %p, expires @ %lx\n",
95 __func__, d, d->jiffies_expire);
96
97 return d;
98
99err_shadow:
100 kfree(leak);
101err_leak:
102 kfree(d);
103 return NULL;
104}
105
106static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
107{
108 void *d = obj;
109 int **shadow_leak = shadow_data;
110
111 pr_info("%s: dummy @ %p, prevented leak @ %p\n",
112 __func__, d, *shadow_leak);
113 kfree(*shadow_leak);
114}
115
116static void livepatch_fix1_dummy_free(struct dummy *d)
117{
118 int **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 return klp_enable_patch(&patch);
161}
162
163static void livepatch_shadow_fix1_exit(void)
164{
165 /* Cleanup any existing SV_LEAK shadow variables */
166 klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
167}
168
169module_init(livepatch_shadow_fix1_init);
170module_exit(livepatch_shadow_fix1_exit);
171MODULE_DESCRIPTION("Live patching demo for shadow variables");
172MODULE_LICENSE("GPL");
173MODULE_INFO(livepatch, "Y");