1 /*
2  * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
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 static void livepatch_fix2_dummy_leak_dtor(void *obj, void *shadow_data)
72 {
73 	void *d = obj;
74 	void **shadow_leak = shadow_data;
75 
76 	kfree(*shadow_leak);
77 	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
78 			 __func__, d, *shadow_leak);
79 }
80 
81 void livepatch_fix2_dummy_free(struct dummy *d)
82 {
83 	void **shadow_leak;
84 	int *shadow_count;
85 
86 	/* Patch: copy the memory leak patch from the fix1 module. */
87 	shadow_leak = klp_shadow_get(d, SV_LEAK);
88 	if (shadow_leak)
89 		klp_shadow_free(d, SV_LEAK, livepatch_fix2_dummy_leak_dtor);
90 	else
91 		pr_info("%s: dummy @ %p leaked!\n", __func__, d);
92 
93 	/*
94 	 * Patch: fetch the SV_COUNTER shadow variable and display
95 	 * the final count.  Detach the shadow variable.
96 	 */
97 	shadow_count = klp_shadow_get(d, SV_COUNTER);
98 	if (shadow_count) {
99 		pr_info("%s: dummy @ %p, check counter = %d\n",
100 			__func__, d, *shadow_count);
101 		klp_shadow_free(d, SV_COUNTER, NULL);
102 	}
103 
104 	kfree(d);
105 }
106 
107 static struct klp_func funcs[] = {
108 	{
109 		.old_name = "dummy_check",
110 		.new_func = livepatch_fix2_dummy_check,
111 	},
112 	{
113 		.old_name = "dummy_free",
114 		.new_func = livepatch_fix2_dummy_free,
115 	}, { }
116 };
117 
118 static struct klp_object objs[] = {
119 	{
120 		.name = "livepatch_shadow_mod",
121 		.funcs = funcs,
122 	}, { }
123 };
124 
125 static struct klp_patch patch = {
126 	.mod = THIS_MODULE,
127 	.objs = objs,
128 };
129 
130 static int livepatch_shadow_fix2_init(void)
131 {
132 	int ret;
133 
134 	ret = klp_register_patch(&patch);
135 	if (ret)
136 		return ret;
137 	ret = klp_enable_patch(&patch);
138 	if (ret) {
139 		WARN_ON(klp_unregister_patch(&patch));
140 		return ret;
141 	}
142 	return 0;
143 }
144 
145 static void livepatch_shadow_fix2_exit(void)
146 {
147 	/* Cleanup any existing SV_COUNTER shadow variables */
148 	klp_shadow_free_all(SV_COUNTER, NULL);
149 
150 	WARN_ON(klp_unregister_patch(&patch));
151 }
152 
153 module_init(livepatch_shadow_fix2_init);
154 module_exit(livepatch_shadow_fix2_exit);
155 MODULE_LICENSE("GPL");
156 MODULE_INFO(livepatch, "Y");
157