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
 48struct dummy {
 49	struct list_head list;
 50	unsigned long jiffies_expire;
 51};
 52
 53bool 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
 71static 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
 81void 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
107static 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
118static struct klp_object objs[] = {
119	{
120		.name = "livepatch_shadow_mod",
121		.funcs = funcs,
122	}, { }
123};
124
125static struct klp_patch patch = {
126	.mod = THIS_MODULE,
127	.objs = objs,
128};
129
130static 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
145static 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
153module_init(livepatch_shadow_fix2_init);
154module_exit(livepatch_shadow_fix2_exit);
155MODULE_LICENSE("GPL");
156MODULE_INFO(livepatch, "Y");