linux/samples/livepatch/livepatch-shadow-mod.c at master · flexbed/linux · GitHub

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* 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 <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

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);

linux/samples/livepatch/livepatch-shadow-mod.c at master · flexbed/linux · GitHub

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