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-fix1.c - Shadow variables, livepatch demo
  8 *
  9 * Purpose
 10 * -------
 11 *
 12 * Fixes the memory leak introduced in livepatch-shadow-mod through the
 13 * use of a shadow variable.  This fix demonstrates the "extending" of
 14 * short-lived data structures by patching its allocation and release
 15 * functions.
 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
 35/* Allocate new dummies every second */
 36#define ALLOC_PERIOD	1
 37/* Check for expired dummies after a few new ones have been allocated */
 38#define CLEANUP_PERIOD	(3 * ALLOC_PERIOD)
 39/* Dummies expire after a few cleanup instances */
 40#define EXPIRE_PERIOD	(4 * CLEANUP_PERIOD)
 41
 42struct dummy {
 43	struct list_head list;
 44	unsigned long jiffies_expire;
 45};
 46
 47/*
 48 * The constructor makes more sense together with klp_shadow_get_or_alloc().
 49 * In this example, it would be safe to assign the pointer also to the shadow
 50 * variable returned by klp_shadow_alloc().  But we wanted to show the more
 51 * complicated use of the API.
 52 */
 53static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
 54{
 55	void **shadow_leak = shadow_data;
 56	void *leak = ctor_data;
 57
 58	*shadow_leak = leak;
 59	return 0;
 60}
 61
 62static struct dummy *livepatch_fix1_dummy_alloc(void)
 63{
 64	struct dummy *d;
 65	void *leak;
 66
 67	d = kzalloc(sizeof(*d), GFP_KERNEL);
 68	if (!d)
 69		return NULL;
 70
 71	d->jiffies_expire = jiffies +
 72		msecs_to_jiffies(1000 * EXPIRE_PERIOD);
 73
 74	/*
 75	 * Patch: save the extra memory location into a SV_LEAK shadow
 76	 * variable.  A patched dummy_free routine can later fetch this
 77	 * pointer to handle resource release.
 78	 */
 79	leak = kzalloc(sizeof(int), GFP_KERNEL);
 80	if (!leak) {
 81		kfree(d);
 82		return NULL;
 83	}
 84
 85	klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
 86			 shadow_leak_ctor, leak);
 87
 88	pr_info("%s: dummy @ %p, expires @ %lx\n",
 89		__func__, d, d->jiffies_expire);
 90
 91	return d;
 92}
 93
 94static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
 95{
 96	void *d = obj;
 97	void **shadow_leak = shadow_data;
 98
 99	kfree(*shadow_leak);
100	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
101			 __func__, d, *shadow_leak);
102}
103
104static void livepatch_fix1_dummy_free(struct dummy *d)
105{
106	void **shadow_leak;
107
108	/*
109	 * Patch: fetch the saved SV_LEAK shadow variable, detach and
110	 * free it.  Note: handle cases where this shadow variable does
111	 * not exist (ie, dummy structures allocated before this livepatch
112	 * was loaded.)
113	 */
114	shadow_leak = klp_shadow_get(d, SV_LEAK);
115	if (shadow_leak)
116		klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
117	else
118		pr_info("%s: dummy @ %p leaked!\n", __func__, d);
119
120	kfree(d);
121}
122
123static struct klp_func funcs[] = {
124	{
125		.old_name = "dummy_alloc",
126		.new_func = livepatch_fix1_dummy_alloc,
127	},
128	{
129		.old_name = "dummy_free",
130		.new_func = livepatch_fix1_dummy_free,
131	}, { }
132};
133
134static struct klp_object objs[] = {
135	{
136		.name = "livepatch_shadow_mod",
137		.funcs = funcs,
138	}, { }
139};
140
141static struct klp_patch patch = {
142	.mod = THIS_MODULE,
143	.objs = objs,
144};
145
146static int livepatch_shadow_fix1_init(void)
147{
148	return klp_enable_patch(&patch);
149}
150
151static void livepatch_shadow_fix1_exit(void)
152{
153	/* Cleanup any existing SV_LEAK shadow variables */
154	klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
155}
156
157module_init(livepatch_shadow_fix1_init);
158module_exit(livepatch_shadow_fix1_exit);
159MODULE_LICENSE("GPL");
160MODULE_INFO(livepatch, "Y");