/* * livepatch-sample.c - Kernel Live Patching Sample Module * * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, see <http://www.gnu.org/licenses/>. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/module.h>#include <linux/kernel.h>#include <linux/livepatch.h> /* * This (dumb) live patch overrides the function that prints the * kernel boot cmdline when /proc/cmdline is read. * * Example: * * $ cat /proc/cmdline * <your cmdline> * * $ insmod livepatch-sample.ko * $ cat /proc/cmdline * this has been live patched * * $ echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled * $ cat /proc/cmdline * <your cmdline> */ #include <linux/seq_file.h>static int livepatch_cmdline_proc_show(struct seq_file *m, void *v){	seq_printf(m, "%s\n", "this has been live patched");	return 0;} static struct klp_func funcs[] = {	{		.old_name = "cmdline_proc_show",		.new_func = livepatch_cmdline_proc_show,	}, { }}; static struct klp_object objs[] = {	{		/* name being NULL means vmlinux */		.funcs = funcs,	}, { }}; static struct klp_patch patch = {	.mod = THIS_MODULE,	.objs = objs,}; static int livepatch_init(void){	int ret; 	if (!klp_have_reliable_stack() && !patch.immediate) {		/*		 * WARNING: Be very careful when using 'patch.immediate' in		 * your patches.  It's ok to use it for simple patches like		 * this, but for more complex patches which change function		 * semantics, locking semantics, or data structures, it may not		 * be safe.  Use of this option will also prevent removal of		 * the patch.		 *		 * See Documentation/livepatch/livepatch.txt for more details.		 */		patch.immediate = true;		pr_notice("The consistency model isn't supported for your architecture.  Bypassing safety mechanisms and applying the patch immediately.\n");	} 	ret = klp_register_patch(&patch);	if (ret)		return ret;	ret = klp_enable_patch(&patch);	if (ret) {		WARN_ON(klp_unregister_patch(&patch));		return ret;	}	return 0;} static void livepatch_exit(void){	WARN_ON(klp_unregister_patch(&patch));} module_init(livepatch_init);module_exit(livepatch_exit);MODULE_LICENSE("GPL");MODULE_INFO(livepatch, "Y");