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
36struct dummy {
37	struct list_head list;
38	unsigned long jiffies_expire;
39};
40
41static 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
59static 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
69static 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
95static 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
106static struct klp_object objs[] = {
107	{
108		.name = "livepatch_shadow_mod",
109		.funcs = funcs,
110	}, { }
111};
112
113static struct klp_patch patch = {
114	.mod = THIS_MODULE,
115	.objs = objs,
116};
117
118static int livepatch_shadow_fix2_init(void)
119{
120	return klp_enable_patch(&patch);
121}
122
123static 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
129module_init(livepatch_shadow_fix2_init);
130module_exit(livepatch_shadow_fix2_exit);
131MODULE_LICENSE("GPL");
132MODULE_INFO(livepatch, "Y");
133