[linux-2.6-block.git] / samples / livepatch / livepatch-shadow-fix1.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;
};

/*
 * The constructor makes more sense together with klp_shadow_get_or_alloc().
 * In this example, it would be safe to assign the pointer also to the shadow
 * variable returned by klp_shadow_alloc().  But we wanted to show the more
 * complicated use of the API.
 */
static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
{
	void **shadow_leak = shadow_data;
	void *leak = ctor_data;

	*shadow_leak = leak;
	return 0;
}

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, sizeof(leak), GFP_KERNEL,
			 shadow_leak_ctor, leak);

	pr_info("%s: dummy @ %p, expires @ %lx\n",
		__func__, d, d->jiffies_expire);

	return d;
}

static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
{
	void *d = obj;
	void **shadow_leak = shadow_data;

	kfree(*shadow_leak);
	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
			 __func__, d, *shadow_leak);
}

void livepatch_fix1_dummy_free(struct dummy *d)
{
	void **shadow_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)
		klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
	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, livepatch_fix1_dummy_leak_dtor);

	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");
Commit	Line	Data
439e7271 JL	1	/*
	2	* Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
	3	*
	4	* This program is free software; you can redistribute it and/or
	5	* modify it under the terms of the GNU General Public License
	6	* as published by the Free Software Foundation; either version 2
	7	* of the License, or (at your option) any later version.
	8	*
	9	* This program is distributed in the hope that it will be useful,
	10	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	11	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	12	* GNU General Public License for more details.
	13	*
	14	* You should have received a copy of the GNU General Public License
	15	* along with this program; if not, see <http://www.gnu.org/licenses/>.
	16	*/
	17
	18	/*
	19	* livepatch-shadow-fix1.c - Shadow variables, livepatch demo
	20	*
	21	* Purpose
	22	* -------
	23	*
	24	* Fixes the memory leak introduced in livepatch-shadow-mod through the
	25	* use of a shadow variable. This fix demonstrates the "extending" of
	26	* short-lived data structures by patching its allocation and release
	27	* functions.
	28	*
	29	*
	30	* Usage
	31	* -----
	32	*
	33	* This module is not intended to be standalone. See the "Usage"
	34	* section of livepatch-shadow-mod.c.
	35	*/
	36
	37	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
	38
	39	#include <linux/module.h>
	40	#include <linux/kernel.h>
	41	#include <linux/livepatch.h>
	42	#include <linux/slab.h>
	43
	44	/* Shadow variable enums */
	45	#define SV_LEAK 1
	46
	47	/* Allocate new dummies every second */
	48	#define ALLOC_PERIOD 1
	49	/* Check for expired dummies after a few new ones have been allocated */
	50	#define CLEANUP_PERIOD (3 * ALLOC_PERIOD)
	51	/* Dummies expire after a few cleanup instances */
	52	#define EXPIRE_PERIOD (4 * CLEANUP_PERIOD)
	53
	54	struct dummy {
	55	struct list_head list;
	56	unsigned long jiffies_expire;
	57	};
	58
e91c2518 PM	59	/*
	60	* The constructor makes more sense together with klp_shadow_get_or_alloc().
	61	* In this example, it would be safe to assign the pointer also to the shadow
	62	* variable returned by klp_shadow_alloc(). But we wanted to show the more
	63	* complicated use of the API.
	64	*/
	65	static int shadow_leak_ctor(void obj, void shadow_data, void *ctor_data)
	66	{
	67	void **shadow_leak = shadow_data;
	68	void *leak = ctor_data;
	69
	70	*shadow_leak = leak;
	71	return 0;
	72	}
	73
439e7271 JL	74	struct dummy *livepatch_fix1_dummy_alloc(void)
	75	{
	76	struct dummy *d;
	77	void *leak;
	78
	79	d = kzalloc(sizeof(*d), GFP_KERNEL);
	80	if (!d)
	81	return NULL;
	82
	83	d->jiffies_expire = jiffies +
	84	msecs_to_jiffies(1000 * EXPIRE_PERIOD);
	85
	86	/*
	87	* Patch: save the extra memory location into a SV_LEAK shadow
	88	* variable. A patched dummy_free routine can later fetch this
	89	* pointer to handle resource release.
	90	*/
	91	leak = kzalloc(sizeof(int), GFP_KERNEL);
e91c2518 PM	92	klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
e91c2518 PM	93	shadow_leak_ctor, leak);
439e7271 JL	94
	95	pr_info("%s: dummy @ %p, expires @ %lx\n",
	96	__func__, d, d->jiffies_expire);
	97
	98	return d;
	99	}
	100
3b2c77d0 PM	101	static void livepatch_fix1_dummy_leak_dtor(void obj, void shadow_data)
	102	{
	103	void *d = obj;
	104	void **shadow_leak = shadow_data;
	105
	106	kfree(*shadow_leak);
	107	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
	108	__func__, d, *shadow_leak);
	109	}
	110
439e7271 JL	111	void livepatch_fix1_dummy_free(struct dummy *d)
439e7271 JL	112	{
3b2c77d0	113	void **shadow_leak;
439e7271 JL	114
	115	/*
	116	* Patch: fetch the saved SV_LEAK shadow variable, detach and
	117	* free it. Note: handle cases where this shadow variable does
	118	* not exist (ie, dummy structures allocated before this livepatch
	119	* was loaded.)
	120	*/
	121	shadow_leak = klp_shadow_get(d, SV_LEAK);
3b2c77d0 PM	122	if (shadow_leak)
	123	klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
	124	else
439e7271	125	pr_info("%s: dummy @ %p leaked!\n", __func__, d);
439e7271 JL	126
	127	kfree(d);
	128	}
	129
	130	static struct klp_func funcs[] = {
	131	{
	132	.old_name = "dummy_alloc",
	133	.new_func = livepatch_fix1_dummy_alloc,
	134	},
	135	{
	136	.old_name = "dummy_free",
	137	.new_func = livepatch_fix1_dummy_free,
	138	}, { }
	139	};
	140
	141	static struct klp_object objs[] = {
	142	{
	143	.name = "livepatch_shadow_mod",
	144	.funcs = funcs,
	145	}, { }
	146	};
	147
	148	static struct klp_patch patch = {
	149	.mod = THIS_MODULE,
	150	.objs = objs,
	151	};
	152
	153	static int livepatch_shadow_fix1_init(void)
	154	{
	155	int ret;
	156
439e7271 JL	157	ret = klp_register_patch(&patch);
	158	if (ret)
	159	return ret;
	160	ret = klp_enable_patch(&patch);
	161	if (ret) {
	162	WARN_ON(klp_unregister_patch(&patch));
	163	return ret;
	164	}
	165	return 0;
	166	}
	167
	168	static void livepatch_shadow_fix1_exit(void)
	169	{
	170	/* Cleanup any existing SV_LEAK shadow variables */
3b2c77d0	171	klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
439e7271 JL	172
	173	WARN_ON(klp_unregister_patch(&patch));
	174	}
	175
	176	module_init(livepatch_shadow_fix1_init);
	177	module_exit(livepatch_shadow_fix1_exit);
	178	MODULE_LICENSE("GPL");
	179	MODULE_INFO(livepatch, "Y");