1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
|
// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
*/
/*
* livepatch-shadow-fix1.c - Shadow variables, livepatch demo
*
* Purpose
* -------
*
* Fixes the memory leak introduced in livepatch-shadow-mod through the
* use of a shadow variable. This fix demonstrates the "extending" of
* short-lived data structures by patching its allocation and release
* functions.
*
*
* Usage
* -----
*
* This module is not intended to be standalone. See the "Usage"
* section of livepatch-shadow-mod.c.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/livepatch.h>
#include <linux/slab.h>
/* Shadow variable enums */
#define SV_LEAK 1
/* Allocate new dummies every second */
#define ALLOC_PERIOD 1
/* Check for expired dummies after a few new ones have been allocated */
#define CLEANUP_PERIOD (3 * ALLOC_PERIOD)
/* Dummies expire after a few cleanup instances */
#define EXPIRE_PERIOD (4 * CLEANUP_PERIOD)
struct dummy {
struct list_head list;
unsigned long jiffies_expire;
};
/*
* The constructor makes more sense together with klp_shadow_get_or_alloc().
* In this example, it would be safe to assign the pointer also to the shadow
* variable returned by klp_shadow_alloc(). But we wanted to show the more
* complicated use of the API.
*/
static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
{
int **shadow_leak = shadow_data;
int **leak = ctor_data;
if (!ctor_data)
return -EINVAL;
*shadow_leak = *leak;
return 0;
}
static struct dummy *livepatch_fix1_dummy_alloc(void)
{
struct dummy *d;
int *leak;
d = kzalloc(sizeof(*d), GFP_KERNEL);
if (!d)
return NULL;
d->jiffies_expire = jiffies +
msecs_to_jiffies(1000 * EXPIRE_PERIOD);
/*
* Patch: save the extra memory location into a SV_LEAK shadow
* variable. A patched dummy_free routine can later fetch this
* pointer to handle resource release.
*/
leak = kzalloc(sizeof(*leak), GFP_KERNEL);
if (!leak) {
kfree(d);
return NULL;
}
klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
shadow_leak_ctor, &leak);
pr_info("%s: dummy @ %p, expires @ %lx\n",
__func__, d, d->jiffies_expire);
return d;
}
static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
{
void *d = obj;
int **shadow_leak = shadow_data;
kfree(*shadow_leak);
pr_info("%s: dummy @ %p, prevented leak @ %p\n",
__func__, d, *shadow_leak);
}
static void livepatch_fix1_dummy_free(struct dummy *d)
{
int **shadow_leak;
/*
* Patch: fetch the saved SV_LEAK shadow variable, detach and
* free it. Note: handle cases where this shadow variable does
* not exist (ie, dummy structures allocated before this livepatch
* was loaded.)
*/
shadow_leak = klp_shadow_get(d, SV_LEAK);
if (shadow_leak)
klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
else
pr_info("%s: dummy @ %p leaked!\n", __func__, d);
kfree(d);
}
static struct klp_func funcs[] = {
{
.old_name = "dummy_alloc",
.new_func = livepatch_fix1_dummy_alloc,
},
{
.old_name = "dummy_free",
.new_func = livepatch_fix1_dummy_free,
}, { }
};
static struct klp_object objs[] = {
{
.name = "livepatch_shadow_mod",
.funcs = funcs,
}, { }
};
static struct klp_patch patch = {
.mod = THIS_MODULE,
.objs = objs,
};
static int livepatch_shadow_fix1_init(void)
{
return klp_enable_patch(&patch);
}
static void livepatch_shadow_fix1_exit(void)
{
/* Cleanup any existing SV_LEAK shadow variables */
klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
}
module_init(livepatch_shadow_fix1_init);
module_exit(livepatch_shadow_fix1_exit);
MODULE_LICENSE("GPL");
MODULE_INFO(livepatch, "Y");
|
