// SPDX-License-Identifier: GPL-2.0-or-later/* * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com> */ /* * livepatch-shadow-mod.c - Shadow variables, buggy module demo * * Purpose * ------- * * As a demonstration of livepatch shadow variable API, this module * introduces memory leak behavior that livepatch modules * livepatch-shadow-fix1.ko and livepatch-shadow-fix2.ko correct and * enhance. * * WARNING - even though the livepatch-shadow-fix modules patch the * memory leak, please load these modules at your own risk -- some * amount of memory may leaked before the bug is patched. * * * Usage * ----- * * Step 1 - Load the buggy demonstration module: * *   insmod samples/livepatch/livepatch-shadow-mod.ko * * Watch dmesg output for a few moments to see new dummy being allocated * and a periodic cleanup check.  (Note: a small amount of memory is * being leaked.) * * * Step 2 - Load livepatch fix1: * *   insmod samples/livepatch/livepatch-shadow-fix1.ko * * Continue watching dmesg and note that now livepatch_fix1_dummy_free() * and livepatch_fix1_dummy_alloc() are logging messages about leaked * memory and eventually leaks prevented. * * * Step 3 - Load livepatch fix2 (on top of fix1): * *   insmod samples/livepatch/livepatch-shadow-fix2.ko * * This module extends functionality through shadow variables, as a new * "check" counter is added to the dummy structure.  Periodic dmesg * messages will log these as dummies are cleaned up. * * * Step 4 - Cleanup * * Unwind the demonstration by disabling the livepatch fix modules, then * removing them and the demo module: * *   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled *   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled *   rmmod livepatch-shadow-fix2 *   rmmod livepatch-shadow-fix1 *   rmmod livepatch-shadow-mod */  #include <linux/kernel.h>#include <linux/module.h>#include <linux/sched.h>#include <linux/slab.h>#include <linux/stat.h>#include <linux/workqueue.h> MODULE_LICENSE("GPL");MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");MODULE_DESCRIPTION("Buggy module for shadow variable demo"); /* 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) /* * Keep a list of all the dummies so we can clean up any residual ones * on module exit */static LIST_HEAD(dummy_list);static DEFINE_MUTEX(dummy_list_mutex); struct dummy {	struct list_head list;	unsigned long jiffies_expire;}; static __used noinline struct dummy *dummy_alloc(void){	struct dummy *d;	int *leak; 	d = kzalloc(sizeof(*d), GFP_KERNEL);	if (!d)		return NULL; 	d->jiffies_expire = jiffies + secs_to_jiffies(EXPIRE_PERIOD); 	/* Oops, forgot to save leak! */	leak = kzalloc(sizeof(*leak), GFP_KERNEL);	if (!leak) {		kfree(d);		return NULL;	} 	pr_info("%s: dummy @ %p, expires @ %lx\n",		__func__, d, d->jiffies_expire); 	return d;} static __used noinline void dummy_free(struct dummy *d){	pr_info("%s: dummy @ %p, expired = %lx\n",		__func__, d, d->jiffies_expire); 	kfree(d);} static __used noinline bool dummy_check(struct dummy *d,					   unsigned long jiffies){	return time_after(jiffies, d->jiffies_expire);} /* * alloc_work_func: allocates new dummy structures, allocates additional *                  memory, aptly named "leak", but doesn't keep *                  permanent record of it. */ static void alloc_work_func(struct work_struct *work);static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func); static void alloc_work_func(struct work_struct *work){	struct dummy *d; 	d = dummy_alloc();	if (!d)		return; 	mutex_lock(&dummy_list_mutex);	list_add(&d->list, &dummy_list);	mutex_unlock(&dummy_list_mutex); 	schedule_delayed_work(&alloc_dwork, secs_to_jiffies(ALLOC_PERIOD));} /* * cleanup_work_func: frees dummy structures.  Without knownledge of *                    "leak", it leaks the additional memory that *                    alloc_work_func created. */ static void cleanup_work_func(struct work_struct *work);static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func); static void cleanup_work_func(struct work_struct *work){	struct dummy *d, *tmp;	unsigned long j; 	j = jiffies;	pr_info("%s: jiffies = %lx\n", __func__, j); 	mutex_lock(&dummy_list_mutex);	list_for_each_entry_safe(d, tmp, &dummy_list, list) { 		/* Kick out and free any expired dummies */		if (dummy_check(d, j)) {			list_del(&d->list);			dummy_free(d);		}	}	mutex_unlock(&dummy_list_mutex); 	schedule_delayed_work(&cleanup_dwork, secs_to_jiffies(CLEANUP_PERIOD));} static int livepatch_shadow_mod_init(void){	schedule_delayed_work(&alloc_dwork, secs_to_jiffies(ALLOC_PERIOD));	schedule_delayed_work(&cleanup_dwork, secs_to_jiffies(CLEANUP_PERIOD)); 	return 0;} static void livepatch_shadow_mod_exit(void){	struct dummy *d, *tmp; 	/* Wait for any dummies at work */	cancel_delayed_work_sync(&alloc_dwork);	cancel_delayed_work_sync(&cleanup_dwork); 	/* Cleanup residual dummies */	list_for_each_entry_safe(d, tmp, &dummy_list, list) {		list_del(&d->list);		dummy_free(d);	}} module_init(livepatch_shadow_mod_init);module_exit(livepatch_shadow_mod_exit);