summaryrefslogtreecommitdiff
path: root/mm/kasan/quarantine.c
blob: 57334ef2d7efbcb9564bca02afd9d58a59589147 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
// SPDX-License-Identifier: GPL-2.0
/*
 * KASAN quarantine.
 *
 * Author: Alexander Potapenko <glider@google.com>
 * Copyright (C) 2016 Google, Inc.
 *
 * Based on code by Dmitry Chernenkov.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 * 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.
 *
 */

#include <linux/gfp.h>
#include <linux/hash.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/percpu.h>
#include <linux/printk.h>
#include <linux/shrinker.h>
#include <linux/slab.h>
#include <linux/srcu.h>
#include <linux/string.h>
#include <linux/types.h>

#include "../slab.h"
#include "kasan.h"

/* Data structure and operations for quarantine queues. */

/*
 * Each queue is a signle-linked list, which also stores the total size of
 * objects inside of it.
 */
struct qlist_head {
	struct qlist_node *head;
	struct qlist_node *tail;
	size_t bytes;
};

#define QLIST_INIT { NULL, NULL, 0 }

static bool qlist_empty(struct qlist_head *q)
{
	return !q->head;
}

static void qlist_init(struct qlist_head *q)
{
	q->head = q->tail = NULL;
	q->bytes = 0;
}

static void qlist_put(struct qlist_head *q, struct qlist_node *qlink,
		size_t size)
{
	if (unlikely(qlist_empty(q)))
		q->head = qlink;
	else
		q->tail->next = qlink;
	q->tail = qlink;
	qlink->next = NULL;
	q->bytes += size;
}

static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
{
	if (unlikely(qlist_empty(from)))
		return;

	if (qlist_empty(to)) {
		*to = *from;
		qlist_init(from);
		return;
	}

	to->tail->next = from->head;
	to->tail = from->tail;
	to->bytes += from->bytes;

	qlist_init(from);
}

#define QUARANTINE_PERCPU_SIZE (1 << 20)
#define QUARANTINE_BATCHES \
	(1024 > 4 * CONFIG_NR_CPUS ? 1024 : 4 * CONFIG_NR_CPUS)

/*
 * The object quarantine consists of per-cpu queues and a global queue,
 * guarded by quarantine_lock.
 */
static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);

/* Round-robin FIFO array of batches. */
static struct qlist_head global_quarantine[QUARANTINE_BATCHES];
static int quarantine_head;
static int quarantine_tail;
/* Total size of all objects in global_quarantine across all batches. */
static unsigned long quarantine_size;
static DEFINE_RAW_SPINLOCK(quarantine_lock);
DEFINE_STATIC_SRCU(remove_cache_srcu);

/* Maximum size of the global queue. */
static unsigned long quarantine_max_size;

/*
 * Target size of a batch in global_quarantine.
 * Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM.
 */
static unsigned long quarantine_batch_size;

/*
 * The fraction of physical memory the quarantine is allowed to occupy.
 * Quarantine doesn't support memory shrinker with SLAB allocator, so we keep
 * the ratio low to avoid OOM.
 */
#define QUARANTINE_FRACTION 32

static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
{
	return virt_to_head_page(qlink)->slab_cache;
}

static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
{
	struct kasan_free_meta *free_info =
		container_of(qlink, struct kasan_free_meta,
			     quarantine_link);

	return ((void *)free_info) - cache->kasan_info.free_meta_offset;
}

static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
{
	void *object = qlink_to_object(qlink, cache);
	unsigned long flags;

	if (IS_ENABLED(CONFIG_SLAB))
		local_irq_save(flags);

	___cache_free(cache, object, _THIS_IP_);

	if (IS_ENABLED(CONFIG_SLAB))
		local_irq_restore(flags);
}

static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
{
	struct qlist_node *qlink;

	if (unlikely(qlist_empty(q)))
		return;

	qlink = q->head;
	while (qlink) {
		struct kmem_cache *obj_cache =
			cache ? cache :	qlink_to_cache(qlink);
		struct qlist_node *next = qlink->next;

		qlink_free(qlink, obj_cache);
		qlink = next;
	}
	qlist_init(q);
}

void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
{
	unsigned long flags;
	struct qlist_head *q;
	struct qlist_head temp = QLIST_INIT;

	/*
	 * Note: irq must be disabled until after we move the batch to the
	 * global quarantine. Otherwise quarantine_remove_cache() can miss
	 * some objects belonging to the cache if they are in our local temp
	 * list. quarantine_remove_cache() executes on_each_cpu() at the
	 * beginning which ensures that it either sees the objects in per-cpu
	 * lists or in the global quarantine.
	 */
	local_irq_save(flags);

	q = this_cpu_ptr(&cpu_quarantine);
	qlist_put(q, &info->quarantine_link, cache->size);
	if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {
		qlist_move_all(q, &temp);

		raw_spin_lock(&quarantine_lock);
		WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
		qlist_move_all(&temp, &global_quarantine[quarantine_tail]);
		if (global_quarantine[quarantine_tail].bytes >=
				READ_ONCE(quarantine_batch_size)) {
			int new_tail;

			new_tail = quarantine_tail + 1;
			if (new_tail == QUARANTINE_BATCHES)
				new_tail = 0;
			if (new_tail != quarantine_head)
				quarantine_tail = new_tail;
		}
		raw_spin_unlock(&quarantine_lock);
	}

	local_irq_restore(flags);
}

void quarantine_reduce(void)
{
	size_t total_size, new_quarantine_size, percpu_quarantines;
	unsigned long flags;
	int srcu_idx;
	struct qlist_head to_free = QLIST_INIT;

	if (likely(READ_ONCE(quarantine_size) <=
		   READ_ONCE(quarantine_max_size)))
		return;

	/*
	 * srcu critical section ensures that quarantine_remove_cache()
	 * will not miss objects belonging to the cache while they are in our
	 * local to_free list. srcu is chosen because (1) it gives us private
	 * grace period domain that does not interfere with anything else,
	 * and (2) it allows synchronize_srcu() to return without waiting
	 * if there are no pending read critical sections (which is the
	 * expected case).
	 */
	srcu_idx = srcu_read_lock(&remove_cache_srcu);
	raw_spin_lock_irqsave(&quarantine_lock, flags);

	/*
	 * Update quarantine size in case of hotplug. Allocate a fraction of
	 * the installed memory to quarantine minus per-cpu queue limits.
	 */
	total_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) /
		QUARANTINE_FRACTION;
	percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
	new_quarantine_size = (total_size < percpu_quarantines) ?
		0 : total_size - percpu_quarantines;
	WRITE_ONCE(quarantine_max_size, new_quarantine_size);
	/* Aim at consuming at most 1/2 of slots in quarantine. */
	WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE,
		2 * total_size / QUARANTINE_BATCHES));

	if (likely(quarantine_size > quarantine_max_size)) {
		qlist_move_all(&global_quarantine[quarantine_head], &to_free);
		WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes);
		quarantine_head++;
		if (quarantine_head == QUARANTINE_BATCHES)
			quarantine_head = 0;
	}

	raw_spin_unlock_irqrestore(&quarantine_lock, flags);

	qlist_free_all(&to_free, NULL);
	srcu_read_unlock(&remove_cache_srcu, srcu_idx);
}

static void qlist_move_cache(struct qlist_head *from,
				   struct qlist_head *to,
				   struct kmem_cache *cache)
{
	struct qlist_node *curr;

	if (unlikely(qlist_empty(from)))
		return;

	curr = from->head;
	qlist_init(from);
	while (curr) {
		struct qlist_node *next = curr->next;
		struct kmem_cache *obj_cache = qlink_to_cache(curr);

		if (obj_cache == cache)
			qlist_put(to, curr, obj_cache->size);
		else
			qlist_put(from, curr, obj_cache->size);

		curr = next;
	}
}

static void per_cpu_remove_cache(void *arg)
{
	struct kmem_cache *cache = arg;
	struct qlist_head to_free = QLIST_INIT;
	struct qlist_head *q;

	q = this_cpu_ptr(&cpu_quarantine);
	qlist_move_cache(q, &to_free, cache);
	qlist_free_all(&to_free, cache);
}

/* Free all quarantined objects belonging to cache. */
void quarantine_remove_cache(struct kmem_cache *cache)
{
	unsigned long flags, i;
	struct qlist_head to_free = QLIST_INIT;

	/*
	 * Must be careful to not miss any objects that are being moved from
	 * per-cpu list to the global quarantine in quarantine_put(),
	 * nor objects being freed in quarantine_reduce(). on_each_cpu()
	 * achieves the first goal, while synchronize_srcu() achieves the
	 * second.
	 */
	on_each_cpu(per_cpu_remove_cache, cache, 1);

	raw_spin_lock_irqsave(&quarantine_lock, flags);
	for (i = 0; i < QUARANTINE_BATCHES; i++) {
		if (qlist_empty(&global_quarantine[i]))
			continue;
		qlist_move_cache(&global_quarantine[i], &to_free, cache);
		/* Scanning whole quarantine can take a while. */
		raw_spin_unlock_irqrestore(&quarantine_lock, flags);
		cond_resched();
		raw_spin_lock_irqsave(&quarantine_lock, flags);
	}
	raw_spin_unlock_irqrestore(&quarantine_lock, flags);

	qlist_free_all(&to_free, cache);

	synchronize_srcu(&remove_cache_srcu);
}