159 lines
3.7 KiB
C
159 lines
3.7 KiB
C
/*
|
|
* Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
|
|
*
|
|
* 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-fix1.c - Shadow variables, livepatch demo
|
|
*
|
|
* Purpose
|
|
* -------
|
|
*
|
|
* Fixes the memory leak introduced in livepatch-shadow-mod through the
|
|
* use of a shadow variable. This fix demonstrates the "extending" of
|
|
* short-lived data structures by patching its allocation and release
|
|
* functions.
|
|
*
|
|
*
|
|
* Usage
|
|
* -----
|
|
*
|
|
* This module is not intended to be standalone. See the "Usage"
|
|
* section of livepatch-shadow-mod.c.
|
|
*/
|
|
|
|
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
|
|
|
|
#include <linux/module.h>
|
|
#include <linux/kernel.h>
|
|
#include <linux/livepatch.h>
|
|
#include <linux/slab.h>
|
|
|
|
/* Shadow variable enums */
|
|
#define SV_LEAK 1
|
|
|
|
/* 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)
|
|
|
|
struct dummy {
|
|
struct list_head list;
|
|
unsigned long jiffies_expire;
|
|
};
|
|
|
|
struct dummy *livepatch_fix1_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);
|
|
|
|
/*
|
|
* Patch: save the extra memory location into a SV_LEAK shadow
|
|
* variable. A patched dummy_free routine can later fetch this
|
|
* pointer to handle resource release.
|
|
*/
|
|
leak = kzalloc(sizeof(int), GFP_KERNEL);
|
|
klp_shadow_alloc(d, SV_LEAK, &leak, sizeof(leak), GFP_KERNEL);
|
|
|
|
pr_info("%s: dummy @ %p, expires @ %lx\n",
|
|
__func__, d, d->jiffies_expire);
|
|
|
|
return d;
|
|
}
|
|
|
|
void livepatch_fix1_dummy_free(struct dummy *d)
|
|
{
|
|
void **shadow_leak, *leak;
|
|
|
|
/*
|
|
* Patch: fetch the saved SV_LEAK shadow variable, detach and
|
|
* free it. Note: handle cases where this shadow variable does
|
|
* not exist (ie, dummy structures allocated before this livepatch
|
|
* was loaded.)
|
|
*/
|
|
shadow_leak = klp_shadow_get(d, SV_LEAK);
|
|
if (shadow_leak) {
|
|
leak = *shadow_leak;
|
|
klp_shadow_free(d, SV_LEAK);
|
|
kfree(leak);
|
|
pr_info("%s: dummy @ %p, prevented leak @ %p\n",
|
|
__func__, d, leak);
|
|
} else {
|
|
pr_info("%s: dummy @ %p leaked!\n", __func__, d);
|
|
}
|
|
|
|
kfree(d);
|
|
}
|
|
|
|
static struct klp_func funcs[] = {
|
|
{
|
|
.old_name = "dummy_alloc",
|
|
.new_func = livepatch_fix1_dummy_alloc,
|
|
},
|
|
{
|
|
.old_name = "dummy_free",
|
|
.new_func = livepatch_fix1_dummy_free,
|
|
}, { }
|
|
};
|
|
|
|
static struct klp_object objs[] = {
|
|
{
|
|
.name = "livepatch_shadow_mod",
|
|
.funcs = funcs,
|
|
}, { }
|
|
};
|
|
|
|
static struct klp_patch patch = {
|
|
.mod = THIS_MODULE,
|
|
.objs = objs,
|
|
};
|
|
|
|
static int livepatch_shadow_fix1_init(void)
|
|
{
|
|
int ret;
|
|
|
|
ret = klp_register_patch(&patch);
|
|
if (ret)
|
|
return ret;
|
|
ret = klp_enable_patch(&patch);
|
|
if (ret) {
|
|
WARN_ON(klp_unregister_patch(&patch));
|
|
return ret;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
static void livepatch_shadow_fix1_exit(void)
|
|
{
|
|
/* Cleanup any existing SV_LEAK shadow variables */
|
|
klp_shadow_free_all(SV_LEAK);
|
|
|
|
WARN_ON(klp_unregister_patch(&patch));
|
|
}
|
|
|
|
module_init(livepatch_shadow_fix1_init);
|
|
module_exit(livepatch_shadow_fix1_exit);
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_INFO(livepatch, "Y");
|