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-fix2.c - Shadow variables, livepatch demo
8 *
9 * Purpose
10 * -------
11 *
12 * Adds functionality to livepatch-shadow-mod's in-flight data
13 * structures through a shadow variable. The livepatch patches a
14 * routine that periodically inspects data structures, incrementing a
15 * per-data-structure counter, creating the counter if needed.
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 #define SV_COUNTER 2
35
36 struct dummy {
37 struct list_head list;
38 unsigned long jiffies_expire;
39 };
40
41 static bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
42 {
43 int *shadow_count;
44
45 /*
46 * Patch: handle in-flight dummy structures, if they do not
47 * already have a SV_COUNTER shadow variable, then attach a
48 * new one.
49 */
50 shadow_count = klp_shadow_get_or_alloc(d, SV_COUNTER,
51 sizeof(*shadow_count), GFP_NOWAIT,
52 NULL, NULL);
53 if (shadow_count)
54 *shadow_count += 1;
55
56 return time_after(jiffies, d->jiffies_expire);
57 }
58
59 static void livepatch_fix2_dummy_leak_dtor(void *obj, void *shadow_data)
60 {
61 void *d = obj;
62 int **shadow_leak = shadow_data;
63
64 pr_info("%s: dummy @ %p, prevented leak @ %p\n",
65 __func__, d, *shadow_leak);
66 kfree(*shadow_leak);
67 }
68
69 static void livepatch_fix2_dummy_free(struct dummy *d)
70 {
71 int **shadow_leak;
72 int *shadow_count;
73
74 /* Patch: copy the memory leak patch from the fix1 module. */
75 shadow_leak = klp_shadow_get(d, SV_LEAK);
76 if (shadow_leak)
77 klp_shadow_free(d, SV_LEAK, livepatch_fix2_dummy_leak_dtor);
78 else
79 pr_info("%s: dummy @ %p leaked!\n", __func__, d);
80
81 /*
82 * Patch: fetch the SV_COUNTER shadow variable and display
83 * the final count. Detach the shadow variable.
84 */
85 shadow_count = klp_shadow_get(d, SV_COUNTER);
86 if (shadow_count) {
87 pr_info("%s: dummy @ %p, check counter = %d\n",
88 __func__, d, *shadow_count);
89 klp_shadow_free(d, SV_COUNTER, NULL);
90 }
91
92 kfree(d);
93 }
94
95 static struct klp_func funcs[] = {
96 {
97 .old_name = "dummy_check",
98 .new_func = livepatch_fix2_dummy_check,
99 },
100 {
101 .old_name = "dummy_free",
102 .new_func = livepatch_fix2_dummy_free,
103 }, { }
104 };
105
106 static struct klp_object objs[] = {
107 {
108 .name = "livepatch_shadow_mod",
109 .funcs = funcs,
110 }, { }
111 };
112
113 static struct klp_patch patch = {
114 .mod = THIS_MODULE,
115 .objs = objs,
116 };
117
118 static int livepatch_shadow_fix2_init(void)
119 {
120 return klp_enable_patch(&patch);
121 }
122
123 static void livepatch_shadow_fix2_exit(void)
124 {
125 /* Cleanup any existing SV_COUNTER shadow variables */
126 klp_shadow_free_all(SV_COUNTER, NULL);
127 }
128
129 module_init(livepatch_shadow_fix2_init);
130 module_exit(livepatch_shadow_fix2_exit);
131 MODULE_LICENSE("GPL");
132 MODULE_INFO(livepatch, "Y");
133
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