1 /*
2  * Copyright (C) 2017 Joe Lawrence <[email protected]>
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-fix2.c - Shadow variables, livepatch demo
20  *
21  * Purpose
22  * -------
23  *
24  * Adds functionality to livepatch-shadow-mod's in-flight data
25  * structures through a shadow variable.  The livepatch patches a
26  * routine that periodically inspects data structures, incrementing a
27  * per-data-structure counter, creating the counter if needed.
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 #define SV_COUNTER	2
47 
48 struct dummy {
49 	struct list_head list;
50 	unsigned long jiffies_expire;
51 };
52 
53 bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
54 {
55 	int *shadow_count;
56 
57 	/*
58 	 * Patch: handle in-flight dummy structures, if they do not
59 	 * already have a SV_COUNTER shadow variable, then attach a
60 	 * new one.
61 	 */
62 	shadow_count = klp_shadow_get_or_alloc(d, SV_COUNTER,
63 				sizeof(*shadow_count), GFP_NOWAIT,
64 				NULL, NULL);
65 	if (shadow_count)
66 		*shadow_count += 1;
67 
68 	return time_after(jiffies, d->jiffies_expire);
69 }
70 
71 void livepatch_fix2_dummy_free(struct dummy *d)
72 {
73 	void **shadow_leak, *leak;
74 	int *shadow_count;
75 
76 	/* Patch: copy the memory leak patch from the fix1 module. */
77 	shadow_leak = klp_shadow_get(d, SV_LEAK);
78 	if (shadow_leak) {
79 		leak = *shadow_leak;
80 		klp_shadow_free(d, SV_LEAK);
81 		kfree(leak);
82 		pr_info("%s: dummy @ %p, prevented leak @ %p\n",
83 			 __func__, d, leak);
84 	} else {
85 		pr_info("%s: dummy @ %p leaked!\n", __func__, d);
86 	}
87 
88 	/*
89 	 * Patch: fetch the SV_COUNTER shadow variable and display
90 	 * the final count.  Detach the shadow variable.
91 	 */
92 	shadow_count = klp_shadow_get(d, SV_COUNTER);
93 	if (shadow_count) {
94 		pr_info("%s: dummy @ %p, check counter = %d\n",
95 			__func__, d, *shadow_count);
96 		klp_shadow_free(d, SV_COUNTER);
97 	}
98 
99 	kfree(d);
100 }
101 
102 static struct klp_func funcs[] = {
103 	{
104 		.old_name = "dummy_check",
105 		.new_func = livepatch_fix2_dummy_check,
106 	},
107 	{
108 		.old_name = "dummy_free",
109 		.new_func = livepatch_fix2_dummy_free,
110 	}, { }
111 };
112 
113 static struct klp_object objs[] = {
114 	{
115 		.name = "livepatch_shadow_mod",
116 		.funcs = funcs,
117 	}, { }
118 };
119 
120 static struct klp_patch patch = {
121 	.mod = THIS_MODULE,
122 	.objs = objs,
123 };
124 
125 static int livepatch_shadow_fix2_init(void)
126 {
127 	int ret;
128 
129 	ret = klp_register_patch(&patch);
130 	if (ret)
131 		return ret;
132 	ret = klp_enable_patch(&patch);
133 	if (ret) {
134 		WARN_ON(klp_unregister_patch(&patch));
135 		return ret;
136 	}
137 	return 0;
138 }
139 
140 static void livepatch_shadow_fix2_exit(void)
141 {
142 	/* Cleanup any existing SV_COUNTER shadow variables */
143 	klp_shadow_free_all(SV_COUNTER);
144 
145 	WARN_ON(klp_unregister_patch(&patch));
146 }
147 
148 module_init(livepatch_shadow_fix2_init);
149 module_exit(livepatch_shadow_fix2_exit);
150 MODULE_LICENSE("GPL");
151 MODULE_INFO(livepatch, "Y");
152