xref: /linux/samples/livepatch/livepatch-shadow-fix2.c (revision 4f2c0a4acffbec01079c28f839422e64ddeff004)
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 
livepatch_fix2_dummy_check(struct dummy * d,unsigned long jiffies)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 
livepatch_fix2_dummy_leak_dtor(void * obj,void * shadow_data)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 
livepatch_fix2_dummy_free(struct dummy * d)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 
livepatch_shadow_fix2_init(void)118 static int livepatch_shadow_fix2_init(void)
119 {
120 	return klp_enable_patch(&patch);
121 }
122 
livepatch_shadow_fix2_exit(void)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