/* * Copyright (C) 2017 Joe Lawrence <joe.lawrence@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/>. */ /* * livepatch-shadow-fix1.c - Shadow variables, livepatch demo * * Purpose * ------- * * Fixes the memory leak introduced in livepatch-shadow-mod through the * use of a shadow variable.  This fix demonstrates the "extending" of * short-lived data structures by patching its allocation and release * functions. * * * Usage * ----- * * This module is not intended to be standalone.  See the "Usage" * section of livepatch-shadow-mod.c. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/module.h>#include <linux/kernel.h>#include <linux/livepatch.h>#include <linux/slab.h> /* Shadow variable enums */#define SV_LEAK		1 /* Allocate new dummies every second */#define ALLOC_PERIOD	1/* Check for expired dummies after a few new ones have been allocated */#define CLEANUP_PERIOD	(3 * ALLOC_PERIOD)/* Dummies expire after a few cleanup instances */#define EXPIRE_PERIOD	(4 * CLEANUP_PERIOD) struct dummy {	struct list_head list;	unsigned long jiffies_expire;}; struct dummy *livepatch_fix1_dummy_alloc(void){	struct dummy *d;	void *leak; 	d = kzalloc(sizeof(*d), GFP_KERNEL);	if (!d)		return NULL; 	d->jiffies_expire = jiffies +		msecs_to_jiffies(1000 * EXPIRE_PERIOD); 	/*	 * Patch: save the extra memory location into a SV_LEAK shadow	 * variable.  A patched dummy_free routine can later fetch this	 * pointer to handle resource release.	 */	leak = kzalloc(sizeof(int), GFP_KERNEL);	klp_shadow_alloc(d, SV_LEAK, &leak, sizeof(leak), GFP_KERNEL); 	pr_info("%s: dummy @ %p, expires @ %lx\n",		__func__, d, d->jiffies_expire); 	return d;} void livepatch_fix1_dummy_free(struct dummy *d){	void **shadow_leak, *leak; 	/*	 * Patch: fetch the saved SV_LEAK shadow variable, detach and	 * free it.  Note: handle cases where this shadow variable does	 * not exist (ie, dummy structures allocated before this livepatch	 * was loaded.)	 */	shadow_leak = klp_shadow_get(d, SV_LEAK);	if (shadow_leak) {		leak = *shadow_leak;		klp_shadow_free(d, SV_LEAK);		kfree(leak);		pr_info("%s: dummy @ %p, prevented leak @ %p\n",			 __func__, d, leak);	} else {		pr_info("%s: dummy @ %p leaked!\n", __func__, d);	} 	kfree(d);} static struct klp_func funcs[] = {	{		.old_name = "dummy_alloc",		.new_func = livepatch_fix1_dummy_alloc,	},	{		.old_name = "dummy_free",		.new_func = livepatch_fix1_dummy_free,	}, { }}; static struct klp_object objs[] = {	{		.name = "livepatch_shadow_mod",		.funcs = funcs,	}, { }}; static struct klp_patch patch = {	.mod = THIS_MODULE,	.objs = objs,}; static int livepatch_shadow_fix1_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_shadow_fix1_exit(void){	/* Cleanup any existing SV_LEAK shadow variables */	klp_shadow_free_all(SV_LEAK); 	WARN_ON(klp_unregister_patch(&patch));} module_init(livepatch_shadow_fix1_init);module_exit(livepatch_shadow_fix1_exit);MODULE_LICENSE("GPL");MODULE_INFO(livepatch, "Y");