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livepatch-shadow-mod.c
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224 lines (189 loc) · 5.81 KB
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/*
* Copyright (C) 2017 Joe Lawrence <[email protected]>
*
* 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-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 <[email protected]>");
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
*/
LIST_HEAD(dummy_list);
DEFINE_MUTEX(dummy_list_mutex);
struct dummy {
struct list_head list;
unsigned long jiffies_expire;
};
noinline struct dummy *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);
/* Oops, forgot to save leak! */
leak = kzalloc(sizeof(int), GFP_KERNEL);
pr_info("%s: dummy @ %p, expires @ %lx\n",
__func__, d, d->jiffies_expire);
return d;
}
noinline void dummy_free(struct dummy *d)
{
pr_info("%s: dummy @ %p, expired = %lx\n",
__func__, d, d->jiffies_expire);
kfree(d);
}
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,
msecs_to_jiffies(1000 * 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,
msecs_to_jiffies(1000 * CLEANUP_PERIOD));
}
static int livepatch_shadow_mod_init(void)
{
schedule_delayed_work(&alloc_dwork,
msecs_to_jiffies(1000 * ALLOC_PERIOD));
schedule_delayed_work(&cleanup_dwork,
msecs_to_jiffies(1000 * 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);