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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213// 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);