xref: /openbmc/linux/mm/kasan/quarantine.c (revision be41d814)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * KASAN quarantine.
4  *
5  * Author: Alexander Potapenko <glider@google.com>
6  * Copyright (C) 2016 Google, Inc.
7  *
8  * Based on code by Dmitry Chernenkov.
9  */
10 
11 #include <linux/gfp.h>
12 #include <linux/hash.h>
13 #include <linux/kernel.h>
14 #include <linux/mm.h>
15 #include <linux/percpu.h>
16 #include <linux/printk.h>
17 #include <linux/shrinker.h>
18 #include <linux/slab.h>
19 #include <linux/srcu.h>
20 #include <linux/string.h>
21 #include <linux/types.h>
22 #include <linux/cpuhotplug.h>
23 
24 #include "../slab.h"
25 #include "kasan.h"
26 
27 /* Data structure and operations for quarantine queues. */
28 
29 /*
30  * Each queue is a single-linked list, which also stores the total size of
31  * objects inside of it.
32  */
33 struct qlist_head {
34 	struct qlist_node *head;
35 	struct qlist_node *tail;
36 	size_t bytes;
37 	bool offline;
38 };
39 
40 #define QLIST_INIT { NULL, NULL, 0 }
41 
qlist_empty(struct qlist_head * q)42 static bool qlist_empty(struct qlist_head *q)
43 {
44 	return !q->head;
45 }
46 
qlist_init(struct qlist_head * q)47 static void qlist_init(struct qlist_head *q)
48 {
49 	q->head = q->tail = NULL;
50 	q->bytes = 0;
51 }
52 
qlist_put(struct qlist_head * q,struct qlist_node * qlink,size_t size)53 static void qlist_put(struct qlist_head *q, struct qlist_node *qlink,
54 		size_t size)
55 {
56 	if (unlikely(qlist_empty(q)))
57 		q->head = qlink;
58 	else
59 		q->tail->next = qlink;
60 	q->tail = qlink;
61 	qlink->next = NULL;
62 	q->bytes += size;
63 }
64 
qlist_move_all(struct qlist_head * from,struct qlist_head * to)65 static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
66 {
67 	if (unlikely(qlist_empty(from)))
68 		return;
69 
70 	if (qlist_empty(to)) {
71 		*to = *from;
72 		qlist_init(from);
73 		return;
74 	}
75 
76 	to->tail->next = from->head;
77 	to->tail = from->tail;
78 	to->bytes += from->bytes;
79 
80 	qlist_init(from);
81 }
82 
83 #define QUARANTINE_PERCPU_SIZE (1 << 20)
84 #define QUARANTINE_BATCHES \
85 	(1024 > 4 * CONFIG_NR_CPUS ? 1024 : 4 * CONFIG_NR_CPUS)
86 
87 /*
88  * The object quarantine consists of per-cpu queues and a global queue,
89  * guarded by quarantine_lock.
90  */
91 static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);
92 
93 /* Round-robin FIFO array of batches. */
94 static struct qlist_head global_quarantine[QUARANTINE_BATCHES];
95 static int quarantine_head;
96 static int quarantine_tail;
97 /* Total size of all objects in global_quarantine across all batches. */
98 static unsigned long quarantine_size;
99 static DEFINE_RAW_SPINLOCK(quarantine_lock);
100 DEFINE_STATIC_SRCU(remove_cache_srcu);
101 
102 struct cpu_shrink_qlist {
103 	raw_spinlock_t lock;
104 	struct qlist_head qlist;
105 };
106 
107 static DEFINE_PER_CPU(struct cpu_shrink_qlist, shrink_qlist) = {
108 	.lock = __RAW_SPIN_LOCK_UNLOCKED(shrink_qlist.lock),
109 };
110 
111 /* Maximum size of the global queue. */
112 static unsigned long quarantine_max_size;
113 
114 /*
115  * Target size of a batch in global_quarantine.
116  * Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM.
117  */
118 static unsigned long quarantine_batch_size;
119 
120 /*
121  * The fraction of physical memory the quarantine is allowed to occupy.
122  * Quarantine doesn't support memory shrinker with SLAB allocator, so we keep
123  * the ratio low to avoid OOM.
124  */
125 #define QUARANTINE_FRACTION 32
126 
qlink_to_cache(struct qlist_node * qlink)127 static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
128 {
129 	return virt_to_slab(qlink)->slab_cache;
130 }
131 
qlink_to_object(struct qlist_node * qlink,struct kmem_cache * cache)132 static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
133 {
134 	struct kasan_free_meta *free_info =
135 		container_of(qlink, struct kasan_free_meta,
136 			     quarantine_link);
137 
138 	return ((void *)free_info) - cache->kasan_info.free_meta_offset;
139 }
140 
qlink_free(struct qlist_node * qlink,struct kmem_cache * cache)141 static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
142 {
143 	void *object = qlink_to_object(qlink, cache);
144 	struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
145 	unsigned long flags;
146 
147 	if (IS_ENABLED(CONFIG_SLAB))
148 		local_irq_save(flags);
149 
150 	/*
151 	 * If init_on_free is enabled and KASAN's free metadata is stored in
152 	 * the object, zero the metadata. Otherwise, the object's memory will
153 	 * not be properly zeroed, as KASAN saves the metadata after the slab
154 	 * allocator zeroes the object.
155 	 */
156 	if (slab_want_init_on_free(cache) &&
157 	    cache->kasan_info.free_meta_offset == 0)
158 		memzero_explicit(meta, sizeof(*meta));
159 
160 	/*
161 	 * As the object now gets freed from the quarantine, assume that its
162 	 * free track is no longer valid.
163 	 */
164 	*(u8 *)kasan_mem_to_shadow(object) = KASAN_SLAB_FREE;
165 
166 	___cache_free(cache, object, _THIS_IP_);
167 
168 	if (IS_ENABLED(CONFIG_SLAB))
169 		local_irq_restore(flags);
170 }
171 
qlist_free_all(struct qlist_head * q,struct kmem_cache * cache)172 static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
173 {
174 	struct qlist_node *qlink;
175 
176 	if (unlikely(qlist_empty(q)))
177 		return;
178 
179 	qlink = q->head;
180 	while (qlink) {
181 		struct kmem_cache *obj_cache =
182 			cache ? cache :	qlink_to_cache(qlink);
183 		struct qlist_node *next = qlink->next;
184 
185 		qlink_free(qlink, obj_cache);
186 		qlink = next;
187 	}
188 	qlist_init(q);
189 }
190 
kasan_quarantine_put(struct kmem_cache * cache,void * object)191 bool kasan_quarantine_put(struct kmem_cache *cache, void *object)
192 {
193 	unsigned long flags;
194 	struct qlist_head *q;
195 	struct qlist_head temp = QLIST_INIT;
196 	struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
197 
198 	/*
199 	 * If there's no metadata for this object, don't put it into
200 	 * quarantine.
201 	 */
202 	if (!meta)
203 		return false;
204 
205 	/*
206 	 * Note: irq must be disabled until after we move the batch to the
207 	 * global quarantine. Otherwise kasan_quarantine_remove_cache() can
208 	 * miss some objects belonging to the cache if they are in our local
209 	 * temp list. kasan_quarantine_remove_cache() executes on_each_cpu()
210 	 * at the beginning which ensures that it either sees the objects in
211 	 * per-cpu lists or in the global quarantine.
212 	 */
213 	local_irq_save(flags);
214 
215 	q = this_cpu_ptr(&cpu_quarantine);
216 	if (q->offline) {
217 		local_irq_restore(flags);
218 		return false;
219 	}
220 	qlist_put(q, &meta->quarantine_link, cache->size);
221 	if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {
222 		qlist_move_all(q, &temp);
223 
224 		raw_spin_lock(&quarantine_lock);
225 		WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
226 		qlist_move_all(&temp, &global_quarantine[quarantine_tail]);
227 		if (global_quarantine[quarantine_tail].bytes >=
228 				READ_ONCE(quarantine_batch_size)) {
229 			int new_tail;
230 
231 			new_tail = quarantine_tail + 1;
232 			if (new_tail == QUARANTINE_BATCHES)
233 				new_tail = 0;
234 			if (new_tail != quarantine_head)
235 				quarantine_tail = new_tail;
236 		}
237 		raw_spin_unlock(&quarantine_lock);
238 	}
239 
240 	local_irq_restore(flags);
241 
242 	return true;
243 }
244 
kasan_quarantine_reduce(void)245 void kasan_quarantine_reduce(void)
246 {
247 	size_t total_size, new_quarantine_size, percpu_quarantines;
248 	unsigned long flags;
249 	int srcu_idx;
250 	struct qlist_head to_free = QLIST_INIT;
251 
252 	if (likely(READ_ONCE(quarantine_size) <=
253 		   READ_ONCE(quarantine_max_size)))
254 		return;
255 
256 	/*
257 	 * srcu critical section ensures that kasan_quarantine_remove_cache()
258 	 * will not miss objects belonging to the cache while they are in our
259 	 * local to_free list. srcu is chosen because (1) it gives us private
260 	 * grace period domain that does not interfere with anything else,
261 	 * and (2) it allows synchronize_srcu() to return without waiting
262 	 * if there are no pending read critical sections (which is the
263 	 * expected case).
264 	 */
265 	srcu_idx = srcu_read_lock(&remove_cache_srcu);
266 	raw_spin_lock_irqsave(&quarantine_lock, flags);
267 
268 	/*
269 	 * Update quarantine size in case of hotplug. Allocate a fraction of
270 	 * the installed memory to quarantine minus per-cpu queue limits.
271 	 */
272 	total_size = (totalram_pages() << PAGE_SHIFT) /
273 		QUARANTINE_FRACTION;
274 	percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
275 	new_quarantine_size = (total_size < percpu_quarantines) ?
276 		0 : total_size - percpu_quarantines;
277 	WRITE_ONCE(quarantine_max_size, new_quarantine_size);
278 	/* Aim at consuming at most 1/2 of slots in quarantine. */
279 	WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE,
280 		2 * total_size / QUARANTINE_BATCHES));
281 
282 	if (likely(quarantine_size > quarantine_max_size)) {
283 		qlist_move_all(&global_quarantine[quarantine_head], &to_free);
284 		WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes);
285 		quarantine_head++;
286 		if (quarantine_head == QUARANTINE_BATCHES)
287 			quarantine_head = 0;
288 	}
289 
290 	raw_spin_unlock_irqrestore(&quarantine_lock, flags);
291 
292 	qlist_free_all(&to_free, NULL);
293 	srcu_read_unlock(&remove_cache_srcu, srcu_idx);
294 }
295 
qlist_move_cache(struct qlist_head * from,struct qlist_head * to,struct kmem_cache * cache)296 static void qlist_move_cache(struct qlist_head *from,
297 				   struct qlist_head *to,
298 				   struct kmem_cache *cache)
299 {
300 	struct qlist_node *curr;
301 
302 	if (unlikely(qlist_empty(from)))
303 		return;
304 
305 	curr = from->head;
306 	qlist_init(from);
307 	while (curr) {
308 		struct qlist_node *next = curr->next;
309 		struct kmem_cache *obj_cache = qlink_to_cache(curr);
310 
311 		if (obj_cache == cache)
312 			qlist_put(to, curr, obj_cache->size);
313 		else
314 			qlist_put(from, curr, obj_cache->size);
315 
316 		curr = next;
317 	}
318 }
319 
__per_cpu_remove_cache(struct qlist_head * q,void * arg)320 static void __per_cpu_remove_cache(struct qlist_head *q, void *arg)
321 {
322 	struct kmem_cache *cache = arg;
323 	unsigned long flags;
324 	struct cpu_shrink_qlist *sq;
325 
326 	sq = this_cpu_ptr(&shrink_qlist);
327 	raw_spin_lock_irqsave(&sq->lock, flags);
328 	qlist_move_cache(q, &sq->qlist, cache);
329 	raw_spin_unlock_irqrestore(&sq->lock, flags);
330 }
331 
per_cpu_remove_cache(void * arg)332 static void per_cpu_remove_cache(void *arg)
333 {
334 	struct qlist_head *q;
335 
336 	q = this_cpu_ptr(&cpu_quarantine);
337 	/*
338 	 * Ensure the ordering between the writing to q->offline and
339 	 * per_cpu_remove_cache.  Prevent cpu_quarantine from being corrupted
340 	 * by interrupt.
341 	 */
342 	if (READ_ONCE(q->offline))
343 		return;
344 	__per_cpu_remove_cache(q, arg);
345 }
346 
347 /* Free all quarantined objects belonging to cache. */
kasan_quarantine_remove_cache(struct kmem_cache * cache)348 void kasan_quarantine_remove_cache(struct kmem_cache *cache)
349 {
350 	unsigned long flags, i;
351 	struct qlist_head to_free = QLIST_INIT;
352 	int cpu;
353 	struct cpu_shrink_qlist *sq;
354 
355 	/*
356 	 * Must be careful to not miss any objects that are being moved from
357 	 * per-cpu list to the global quarantine in kasan_quarantine_put(),
358 	 * nor objects being freed in kasan_quarantine_reduce(). on_each_cpu()
359 	 * achieves the first goal, while synchronize_srcu() achieves the
360 	 * second.
361 	 */
362 	on_each_cpu(per_cpu_remove_cache, cache, 1);
363 
364 	for_each_online_cpu(cpu) {
365 		sq = per_cpu_ptr(&shrink_qlist, cpu);
366 		raw_spin_lock_irqsave(&sq->lock, flags);
367 		qlist_move_cache(&sq->qlist, &to_free, cache);
368 		raw_spin_unlock_irqrestore(&sq->lock, flags);
369 	}
370 	qlist_free_all(&to_free, cache);
371 
372 	raw_spin_lock_irqsave(&quarantine_lock, flags);
373 	for (i = 0; i < QUARANTINE_BATCHES; i++) {
374 		if (qlist_empty(&global_quarantine[i]))
375 			continue;
376 		qlist_move_cache(&global_quarantine[i], &to_free, cache);
377 		/* Scanning whole quarantine can take a while. */
378 		raw_spin_unlock_irqrestore(&quarantine_lock, flags);
379 		cond_resched();
380 		raw_spin_lock_irqsave(&quarantine_lock, flags);
381 	}
382 	raw_spin_unlock_irqrestore(&quarantine_lock, flags);
383 
384 	qlist_free_all(&to_free, cache);
385 
386 	synchronize_srcu(&remove_cache_srcu);
387 }
388 
kasan_cpu_online(unsigned int cpu)389 static int kasan_cpu_online(unsigned int cpu)
390 {
391 	this_cpu_ptr(&cpu_quarantine)->offline = false;
392 	return 0;
393 }
394 
kasan_cpu_offline(unsigned int cpu)395 static int kasan_cpu_offline(unsigned int cpu)
396 {
397 	struct qlist_head *q;
398 
399 	q = this_cpu_ptr(&cpu_quarantine);
400 	/* Ensure the ordering between the writing to q->offline and
401 	 * qlist_free_all. Otherwise, cpu_quarantine may be corrupted
402 	 * by interrupt.
403 	 */
404 	WRITE_ONCE(q->offline, true);
405 	barrier();
406 	qlist_free_all(q, NULL);
407 	return 0;
408 }
409 
kasan_cpu_quarantine_init(void)410 static int __init kasan_cpu_quarantine_init(void)
411 {
412 	int ret = 0;
413 
414 	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online",
415 				kasan_cpu_online, kasan_cpu_offline);
416 	if (ret < 0)
417 		pr_err("kasan cpu quarantine register failed [%d]\n", ret);
418 	return ret;
419 }
420 late_initcall(kasan_cpu_quarantine_init);
421