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-callbacks-demo.c - (un)patching callbacks livepatch demo
 20 *
 21 *
 22 * Purpose
 23 * -------
 24 *
 25 * Demonstration of registering livepatch (un)patching callbacks.
 26 *
 27 *
 28 * Usage
 29 * -----
 30 *
 31 * Step 1 - load the simple module
 32 *
 33 *   insmod samples/livepatch/livepatch-callbacks-mod.ko
 34 *
 35 *
 36 * Step 2 - load the demonstration livepatch (with callbacks)
 37 *
 38 *   insmod samples/livepatch/livepatch-callbacks-demo.ko
 39 *
 40 *
 41 * Step 3 - cleanup
 42 *
 43 *   echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
 44 *   rmmod livepatch_callbacks_demo
 45 *   rmmod livepatch_callbacks_mod
 46 *
 47 * Watch dmesg output to see livepatch enablement, callback execution
 48 * and patching operations for both vmlinux and module targets.
 49 *
 50 * NOTE: swap the insmod order of livepatch-callbacks-mod.ko and
 51 *       livepatch-callbacks-demo.ko to observe what happens when a
 52 *       target module is loaded after a livepatch with callbacks.
 53 *
 54 * NOTE: 'pre_patch_ret' is a module parameter that sets the pre-patch
 55 *       callback return status.  Try setting up a non-zero status
 56 *       such as -19 (-ENODEV):
 57 *
 58 *       # Load demo livepatch, vmlinux is patched
 59 *       insmod samples/livepatch/livepatch-callbacks-demo.ko
 60 *
 61 *       # Setup next pre-patch callback to return -ENODEV
 62 *       echo -19 > /sys/module/livepatch_callbacks_demo/parameters/pre_patch_ret
 63 *
 64 *       # Module loader refuses to load the target module
 65 *       insmod samples/livepatch/livepatch-callbacks-mod.ko
 66 *       insmod: ERROR: could not insert module samples/livepatch/livepatch-callbacks-mod.ko: No such device
 67 *
 68 * NOTE: There is a second target module,
 69 *       livepatch-callbacks-busymod.ko, available for experimenting
 70 *       with livepatch (un)patch callbacks.  This module contains
 71 *       a 'sleep_secs' parameter that parks the module on one of the
 72 *       functions that the livepatch demo module wants to patch.
 73 *       Modifying this value and tweaking the order of module loads can
 74 *       effectively demonstrate stalled patch transitions:
 75 *
 76 *       # Load a target module, let it park on 'busymod_work_func' for
 77 *       # thirty seconds
 78 *       insmod samples/livepatch/livepatch-callbacks-busymod.ko sleep_secs=30
 79 *
 80 *       # Meanwhile load the livepatch
 81 *       insmod samples/livepatch/livepatch-callbacks-demo.ko
 82 *
 83 *       # ... then load and unload another target module while the
 84 *       # transition is in progress
 85 *       insmod samples/livepatch/livepatch-callbacks-mod.ko
 86 *       rmmod samples/livepatch/livepatch-callbacks-mod.ko
 87 *
 88 *       # Finally cleanup
 89 *       echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
 90 *       rmmod samples/livepatch/livepatch-callbacks-demo.ko
 91 */
 92
 93#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 94
 95#include <linux/module.h>
 96#include <linux/kernel.h>
 97#include <linux/livepatch.h>
 98
 99static int pre_patch_ret;
100module_param(pre_patch_ret, int, 0644);
101MODULE_PARM_DESC(pre_patch_ret, "pre_patch_ret (default=0)");
102
103static const char *const module_state[] = {
104	[MODULE_STATE_LIVE]	= "[MODULE_STATE_LIVE] Normal state",
105	[MODULE_STATE_COMING]	= "[MODULE_STATE_COMING] Full formed, running module_init",
106	[MODULE_STATE_GOING]	= "[MODULE_STATE_GOING] Going away",
107	[MODULE_STATE_UNFORMED]	= "[MODULE_STATE_UNFORMED] Still setting it up",
108};
109
110static void callback_info(const char *callback, struct klp_object *obj)
111{
112	if (obj->mod)
113		pr_info("%s: %s -> %s\n", callback, obj->mod->name,
114			module_state[obj->mod->state]);
115	else
116		pr_info("%s: vmlinux\n", callback);
117}
118
119/* Executed on object patching (ie, patch enablement) */
120static int pre_patch_callback(struct klp_object *obj)
121{
122	callback_info(__func__, obj);
123	return pre_patch_ret;
124}
125
126/* Executed on object unpatching (ie, patch disablement) */
127static void post_patch_callback(struct klp_object *obj)
128{
129	callback_info(__func__, obj);
130}
131
132/* Executed on object unpatching (ie, patch disablement) */
133static void pre_unpatch_callback(struct klp_object *obj)
134{
135	callback_info(__func__, obj);
136}
137
138/* Executed on object unpatching (ie, patch disablement) */
139static void post_unpatch_callback(struct klp_object *obj)
140{
141	callback_info(__func__, obj);
142}
143
144static void patched_work_func(struct work_struct *work)
145{
146	pr_info("%s\n", __func__);
147}
148
149static struct klp_func no_funcs[] = {
150	{ }
151};
152
153static struct klp_func busymod_funcs[] = {
154	{
155		.old_name = "busymod_work_func",
156		.new_func = patched_work_func,
157	}, { }
158};
159
160static struct klp_object objs[] = {
161	{
162		.name = NULL,	/* vmlinux */
163		.funcs = no_funcs,
164		.callbacks = {
165			.pre_patch = pre_patch_callback,
166			.post_patch = post_patch_callback,
167			.pre_unpatch = pre_unpatch_callback,
168			.post_unpatch = post_unpatch_callback,
169		},
170	},	{
171		.name = "livepatch_callbacks_mod",
172		.funcs = no_funcs,
173		.callbacks = {
174			.pre_patch = pre_patch_callback,
175			.post_patch = post_patch_callback,
176			.pre_unpatch = pre_unpatch_callback,
177			.post_unpatch = post_unpatch_callback,
178		},
179	},	{
180		.name = "livepatch_callbacks_busymod",
181		.funcs = busymod_funcs,
182		.callbacks = {
183			.pre_patch = pre_patch_callback,
184			.post_patch = post_patch_callback,
185			.pre_unpatch = pre_unpatch_callback,
186			.post_unpatch = post_unpatch_callback,
187		},
188	}, { }
189};
190
191static struct klp_patch patch = {
192	.mod = THIS_MODULE,
193	.objs = objs,
194};
195
196static int livepatch_callbacks_demo_init(void)
197{
198	int ret;
199
200	ret = klp_register_patch(&patch);
201	if (ret)
202		return ret;
203	ret = klp_enable_patch(&patch);
204	if (ret) {
205		WARN_ON(klp_unregister_patch(&patch));
206		return ret;
207	}
208	return 0;
209}
210
211static void livepatch_callbacks_demo_exit(void)
212{
213	WARN_ON(klp_unregister_patch(&patch));
214}
215
216module_init(livepatch_callbacks_demo_init);
217module_exit(livepatch_callbacks_demo_exit);
218MODULE_LICENSE("GPL");
219MODULE_INFO(livepatch, "Y");