// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
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*/
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/*
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* livepatch-shadow-mod.c - Shadow variables, buggy module demo
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*
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* Purpose
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* -------
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*
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* As a demonstration of livepatch shadow variable API, this module
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* introduces memory leak behavior that livepatch modules
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* livepatch-shadow-fix1.ko and livepatch-shadow-fix2.ko correct and
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* enhance.
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*
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* WARNING - even though the livepatch-shadow-fix modules patch the
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* memory leak, please load these modules at your own risk -- some
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* amount of memory may leaked before the bug is patched.
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*
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*
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* Usage
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* -----
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*
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* Step 1 - Load the buggy demonstration module:
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*
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* insmod samples/livepatch/livepatch-shadow-mod.ko
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*
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* Watch dmesg output for a few moments to see new dummy being allocated
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* and a periodic cleanup check. (Note: a small amount of memory is
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* being leaked.)
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*
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*
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* Step 2 - Load livepatch fix1:
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*
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* insmod samples/livepatch/livepatch-shadow-fix1.ko
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*
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* Continue watching dmesg and note that now livepatch_fix1_dummy_free()
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* and livepatch_fix1_dummy_alloc() are logging messages about leaked
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* memory and eventually leaks prevented.
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*
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*
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* Step 3 - Load livepatch fix2 (on top of fix1):
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*
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* insmod samples/livepatch/livepatch-shadow-fix2.ko
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*
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* This module extends functionality through shadow variables, as a new
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* "check" counter is added to the dummy structure. Periodic dmesg
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* messages will log these as dummies are cleaned up.
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*
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*
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* Step 4 - Cleanup
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*
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* Unwind the demonstration by disabling the livepatch fix modules, then
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* removing them and the demo module:
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*
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* echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled
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* echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled
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* rmmod livepatch-shadow-fix2
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* rmmod livepatch-shadow-fix1
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* rmmod livepatch-shadow-mod
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/stat.h>
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#include <linux/workqueue.h>
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");
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MODULE_DESCRIPTION("Buggy module for shadow variable demo");
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/* Allocate new dummies every second */
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#define ALLOC_PERIOD 1
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/* Check for expired dummies after a few new ones have been allocated */
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#define CLEANUP_PERIOD (3 * ALLOC_PERIOD)
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/* Dummies expire after a few cleanup instances */
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#define EXPIRE_PERIOD (4 * CLEANUP_PERIOD)
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/*
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* Keep a list of all the dummies so we can clean up any residual ones
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* on module exit
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*/
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static LIST_HEAD(dummy_list);
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static DEFINE_MUTEX(dummy_list_mutex);
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struct dummy {
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struct list_head list;
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unsigned long jiffies_expire;
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};
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static __used noinline struct dummy *dummy_alloc(void)
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{
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struct dummy *d;
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int *leak;
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d = kzalloc(sizeof(*d), GFP_KERNEL);
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if (!d)
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return NULL;
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d->jiffies_expire = jiffies +
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msecs_to_jiffies(1000 * EXPIRE_PERIOD);
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/* Oops, forgot to save leak! */
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leak = kzalloc(sizeof(*leak), GFP_KERNEL);
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if (!leak) {
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kfree(d);
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return NULL;
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}
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pr_info("%s: dummy @ %p, expires @ %lx\n",
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__func__, d, d->jiffies_expire);
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return d;
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}
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static __used noinline void dummy_free(struct dummy *d)
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{
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pr_info("%s: dummy @ %p, expired = %lx\n",
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__func__, d, d->jiffies_expire);
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kfree(d);
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}
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static __used noinline bool dummy_check(struct dummy *d,
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unsigned long jiffies)
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{
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return time_after(jiffies, d->jiffies_expire);
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}
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/*
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* alloc_work_func: allocates new dummy structures, allocates additional
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* memory, aptly named "leak", but doesn't keep
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* permanent record of it.
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*/
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static void alloc_work_func(struct work_struct *work);
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static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func);
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static void alloc_work_func(struct work_struct *work)
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{
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struct dummy *d;
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d = dummy_alloc();
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if (!d)
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return;
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mutex_lock(&dummy_list_mutex);
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list_add(&d->list, &dummy_list);
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mutex_unlock(&dummy_list_mutex);
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schedule_delayed_work(&alloc_dwork,
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msecs_to_jiffies(1000 * ALLOC_PERIOD));
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}
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/*
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* cleanup_work_func: frees dummy structures. Without knownledge of
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* "leak", it leaks the additional memory that
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* alloc_work_func created.
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*/
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static void cleanup_work_func(struct work_struct *work);
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static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func);
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static void cleanup_work_func(struct work_struct *work)
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{
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struct dummy *d, *tmp;
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unsigned long j;
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j = jiffies;
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pr_info("%s: jiffies = %lx\n", __func__, j);
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mutex_lock(&dummy_list_mutex);
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list_for_each_entry_safe(d, tmp, &dummy_list, list) {
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/* Kick out and free any expired dummies */
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if (dummy_check(d, j)) {
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list_del(&d->list);
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dummy_free(d);
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}
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}
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mutex_unlock(&dummy_list_mutex);
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schedule_delayed_work(&cleanup_dwork,
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msecs_to_jiffies(1000 * CLEANUP_PERIOD));
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}
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static int livepatch_shadow_mod_init(void)
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{
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schedule_delayed_work(&alloc_dwork,
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msecs_to_jiffies(1000 * ALLOC_PERIOD));
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schedule_delayed_work(&cleanup_dwork,
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msecs_to_jiffies(1000 * CLEANUP_PERIOD));
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return 0;
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}
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static void livepatch_shadow_mod_exit(void)
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{
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struct dummy *d, *tmp;
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/* Wait for any dummies at work */
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cancel_delayed_work_sync(&alloc_dwork);
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cancel_delayed_work_sync(&cleanup_dwork);
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/* Cleanup residual dummies */
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list_for_each_entry_safe(d, tmp, &dummy_list, list) {
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list_del(&d->list);
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dummy_free(d);
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}
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}
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module_init(livepatch_shadow_mod_init);
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module_exit(livepatch_shadow_mod_exit);
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