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#define pr_fmt(fmt) "kasan: " fmt
12
13#include <linux/gfp.h>
14#include <linux/hash.h>
15#include <linux/kernel.h>
16#include <linux/mm.h>
17#include <linux/percpu.h>
18#include <linux/printk.h>
19#include <linux/shrinker.h>
20#include <linux/slab.h>
21#include <linux/srcu.h>
22#include <linux/string.h>
23#include <linux/types.h>
24#include <linux/cpuhotplug.h>
25
26#include "../slab.h"
27#include "kasan.h"
28
29/* Data structure and operations for quarantine queues. */
30
31/*
32 * Each queue is a single-linked list, which also stores the total size of
33 * objects inside of it.
34 */
35struct qlist_head {
36 struct qlist_node *head;
37 struct qlist_node *tail;
38 size_t bytes;
39 bool offline;
40};
41
42#define QLIST_INIT { NULL, NULL, 0 }
43
44static bool qlist_empty(struct qlist_head *q)
45{
46 return !q->head;
47}
48
49static void qlist_init(struct qlist_head *q)
50{
51 q->head = q->tail = NULL;
52 q->bytes = 0;
53}
54
55static void qlist_put(struct qlist_head *q, struct qlist_node *qlink,
56 size_t size)
57{
58 if (unlikely(qlist_empty(q)))
59 q->head = qlink;
60 else
61 q->tail->next = qlink;
62 q->tail = qlink;
63 qlink->next = NULL;
64 q->bytes += size;
65}
66
67static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
68{
69 if (unlikely(qlist_empty(from)))
70 return;
71
72 if (qlist_empty(q: to)) {
73 *to = *from;
74 qlist_init(q: from);
75 return;
76 }
77
78 to->tail->next = from->head;
79 to->tail = from->tail;
80 to->bytes += from->bytes;
81
82 qlist_init(q: from);
83}
84
85#define QUARANTINE_PERCPU_SIZE (1 << 20)
86#define QUARANTINE_BATCHES \
87 (1024 > 4 * CONFIG_NR_CPUS ? 1024 : 4 * CONFIG_NR_CPUS)
88
89/*
90 * The object quarantine consists of per-cpu queues and a global queue,
91 * guarded by quarantine_lock.
92 */
93static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);
94
95/* Round-robin FIFO array of batches. */
96static struct qlist_head global_quarantine[QUARANTINE_BATCHES];
97static int quarantine_head;
98static int quarantine_tail;
99/* Total size of all objects in global_quarantine across all batches. */
100static unsigned long quarantine_size;
101static DEFINE_RAW_SPINLOCK(quarantine_lock);
102DEFINE_STATIC_SRCU(remove_cache_srcu);
103
104struct cpu_shrink_qlist {
105 raw_spinlock_t lock;
106 struct qlist_head qlist;
107};
108
109static DEFINE_PER_CPU(struct cpu_shrink_qlist, shrink_qlist) = {
110 .lock = __RAW_SPIN_LOCK_UNLOCKED(shrink_qlist.lock),
111};
112
113/* Maximum size of the global queue. */
114static unsigned long quarantine_max_size;
115
116/*
117 * Target size of a batch in global_quarantine.
118 * Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM.
119 */
120static unsigned long quarantine_batch_size;
121
122/*
123 * The fraction of physical memory the quarantine is allowed to occupy.
124 * Quarantine doesn't support memory shrinker with SLAB allocator, so we keep
125 * the ratio low to avoid OOM.
126 */
127#define QUARANTINE_FRACTION 32
128
129static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
130{
131 return virt_to_slab(addr: qlink)->slab_cache;
132}
133
134static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
135{
136 struct kasan_free_meta *free_info =
137 container_of(qlink, struct kasan_free_meta,
138 quarantine_link);
139
140 return ((void *)free_info) - cache->kasan_info.free_meta_offset;
141}
142
143static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
144{
145 void *object = qlink_to_object(qlink, cache);
146 struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
147 unsigned long flags;
148
149 if (IS_ENABLED(CONFIG_SLAB))
150 local_irq_save(flags);
151
152 /*
153 * If init_on_free is enabled and KASAN's free metadata is stored in
154 * the object, zero the metadata. Otherwise, the object's memory will
155 * not be properly zeroed, as KASAN saves the metadata after the slab
156 * allocator zeroes the object.
157 */
158 if (slab_want_init_on_free(cache) &&
159 cache->kasan_info.free_meta_offset == 0)
160 memzero_explicit(meta, sizeof(*meta));
161
162 /*
163 * As the object now gets freed from the quarantine, assume that its
164 * free track is no longer valid.
165 */
166 *(u8 *)kasan_mem_to_shadow(object) = KASAN_SLAB_FREE;
167
168 ___cache_free(cache, x: object, _THIS_IP_);
169
170 if (IS_ENABLED(CONFIG_SLAB))
171 local_irq_restore(flags);
172}
173
174static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
175{
176 struct qlist_node *qlink;
177
178 if (unlikely(qlist_empty(q)))
179 return;
180
181 qlink = q->head;
182 while (qlink) {
183 struct kmem_cache *obj_cache =
184 cache ? cache : qlink_to_cache(qlink);
185 struct qlist_node *next = qlink->next;
186
187 qlink_free(qlink, cache: obj_cache);
188 qlink = next;
189 }
190 qlist_init(q);
191}
192
193bool kasan_quarantine_put(struct kmem_cache *cache, void *object)
194{
195 unsigned long flags;
196 struct qlist_head *q;
197 struct qlist_head temp = QLIST_INIT;
198 struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
199
200 /*
201 * If there's no metadata for this object, don't put it into
202 * quarantine.
203 */
204 if (!meta)
205 return false;
206
207 /*
208 * Note: irq must be disabled until after we move the batch to the
209 * global quarantine. Otherwise kasan_quarantine_remove_cache() can
210 * miss some objects belonging to the cache if they are in our local
211 * temp list. kasan_quarantine_remove_cache() executes on_each_cpu()
212 * at the beginning which ensures that it either sees the objects in
213 * per-cpu lists or in the global quarantine.
214 */
215 local_irq_save(flags);
216
217 q = this_cpu_ptr(&cpu_quarantine);
218 if (q->offline) {
219 local_irq_restore(flags);
220 return false;
221 }
222 qlist_put(q, qlink: &meta->quarantine_link, size: cache->size);
223 if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {
224 qlist_move_all(from: q, to: &temp);
225
226 raw_spin_lock(&quarantine_lock);
227 WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
228 qlist_move_all(from: &temp, to: &global_quarantine[quarantine_tail]);
229 if (global_quarantine[quarantine_tail].bytes >=
230 READ_ONCE(quarantine_batch_size)) {
231 int new_tail;
232
233 new_tail = quarantine_tail + 1;
234 if (new_tail == QUARANTINE_BATCHES)
235 new_tail = 0;
236 if (new_tail != quarantine_head)
237 quarantine_tail = new_tail;
238 }
239 raw_spin_unlock(&quarantine_lock);
240 }
241
242 local_irq_restore(flags);
243
244 return true;
245}
246
247void kasan_quarantine_reduce(void)
248{
249 size_t total_size, new_quarantine_size, percpu_quarantines;
250 unsigned long flags;
251 int srcu_idx;
252 struct qlist_head to_free = QLIST_INIT;
253
254 if (likely(READ_ONCE(quarantine_size) <=
255 READ_ONCE(quarantine_max_size)))
256 return;
257
258 /*
259 * srcu critical section ensures that kasan_quarantine_remove_cache()
260 * will not miss objects belonging to the cache while they are in our
261 * local to_free list. srcu is chosen because (1) it gives us private
262 * grace period domain that does not interfere with anything else,
263 * and (2) it allows synchronize_srcu() to return without waiting
264 * if there are no pending read critical sections (which is the
265 * expected case).
266 */
267 srcu_idx = srcu_read_lock(ssp: &remove_cache_srcu);
268 raw_spin_lock_irqsave(&quarantine_lock, flags);
269
270 /*
271 * Update quarantine size in case of hotplug. Allocate a fraction of
272 * the installed memory to quarantine minus per-cpu queue limits.
273 */
274 total_size = (totalram_pages() << PAGE_SHIFT) /
275 QUARANTINE_FRACTION;
276 percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
277 new_quarantine_size = (total_size < percpu_quarantines) ?
278 0 : total_size - percpu_quarantines;
279 WRITE_ONCE(quarantine_max_size, new_quarantine_size);
280 /* Aim at consuming at most 1/2 of slots in quarantine. */
281 WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE,
282 2 * total_size / QUARANTINE_BATCHES));
283
284 if (likely(quarantine_size > quarantine_max_size)) {
285 qlist_move_all(from: &global_quarantine[quarantine_head], to: &to_free);
286 WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes);
287 quarantine_head++;
288 if (quarantine_head == QUARANTINE_BATCHES)
289 quarantine_head = 0;
290 }
291
292 raw_spin_unlock_irqrestore(&quarantine_lock, flags);
293
294 qlist_free_all(q: &to_free, NULL);
295 srcu_read_unlock(ssp: &remove_cache_srcu, idx: srcu_idx);
296}
297
298static void qlist_move_cache(struct qlist_head *from,
299 struct qlist_head *to,
300 struct kmem_cache *cache)
301{
302 struct qlist_node *curr;
303
304 if (unlikely(qlist_empty(from)))
305 return;
306
307 curr = from->head;
308 qlist_init(q: from);
309 while (curr) {
310 struct qlist_node *next = curr->next;
311 struct kmem_cache *obj_cache = qlink_to_cache(qlink: curr);
312
313 if (obj_cache == cache)
314 qlist_put(q: to, qlink: curr, size: obj_cache->size);
315 else
316 qlist_put(q: from, qlink: curr, size: obj_cache->size);
317
318 curr = next;
319 }
320}
321
322static void __per_cpu_remove_cache(struct qlist_head *q, void *arg)
323{
324 struct kmem_cache *cache = arg;
325 unsigned long flags;
326 struct cpu_shrink_qlist *sq;
327
328 sq = this_cpu_ptr(&shrink_qlist);
329 raw_spin_lock_irqsave(&sq->lock, flags);
330 qlist_move_cache(from: q, to: &sq->qlist, cache);
331 raw_spin_unlock_irqrestore(&sq->lock, flags);
332}
333
334static void per_cpu_remove_cache(void *arg)
335{
336 struct qlist_head *q;
337
338 q = this_cpu_ptr(&cpu_quarantine);
339 /*
340 * Ensure the ordering between the writing to q->offline and
341 * per_cpu_remove_cache. Prevent cpu_quarantine from being corrupted
342 * by interrupt.
343 */
344 if (READ_ONCE(q->offline))
345 return;
346 __per_cpu_remove_cache(q, arg);
347}
348
349/* Free all quarantined objects belonging to cache. */
350void kasan_quarantine_remove_cache(struct kmem_cache *cache)
351{
352 unsigned long flags, i;
353 struct qlist_head to_free = QLIST_INIT;
354 int cpu;
355 struct cpu_shrink_qlist *sq;
356
357 /*
358 * Must be careful to not miss any objects that are being moved from
359 * per-cpu list to the global quarantine in kasan_quarantine_put(),
360 * nor objects being freed in kasan_quarantine_reduce(). on_each_cpu()
361 * achieves the first goal, while synchronize_srcu() achieves the
362 * second.
363 */
364 on_each_cpu(func: per_cpu_remove_cache, info: cache, wait: 1);
365
366 for_each_online_cpu(cpu) {
367 sq = per_cpu_ptr(&shrink_qlist, cpu);
368 raw_spin_lock_irqsave(&sq->lock, flags);
369 qlist_move_cache(from: &sq->qlist, to: &to_free, cache);
370 raw_spin_unlock_irqrestore(&sq->lock, flags);
371 }
372 qlist_free_all(q: &to_free, cache);
373
374 raw_spin_lock_irqsave(&quarantine_lock, flags);
375 for (i = 0; i < QUARANTINE_BATCHES; i++) {
376 if (qlist_empty(q: &global_quarantine[i]))
377 continue;
378 qlist_move_cache(from: &global_quarantine[i], to: &to_free, cache);
379 /* Scanning whole quarantine can take a while. */
380 raw_spin_unlock_irqrestore(&quarantine_lock, flags);
381 cond_resched();
382 raw_spin_lock_irqsave(&quarantine_lock, flags);
383 }
384 raw_spin_unlock_irqrestore(&quarantine_lock, flags);
385
386 qlist_free_all(q: &to_free, cache);
387
388 synchronize_srcu(ssp: &remove_cache_srcu);
389}
390
391static int kasan_cpu_online(unsigned int cpu)
392{
393 this_cpu_ptr(&cpu_quarantine)->offline = false;
394 return 0;
395}
396
397static int kasan_cpu_offline(unsigned int cpu)
398{
399 struct qlist_head *q;
400
401 q = this_cpu_ptr(&cpu_quarantine);
402 /* Ensure the ordering between the writing to q->offline and
403 * qlist_free_all. Otherwise, cpu_quarantine may be corrupted
404 * by interrupt.
405 */
406 WRITE_ONCE(q->offline, true);
407 barrier();
408 qlist_free_all(q, NULL);
409 return 0;
410}
411
412static int __init kasan_cpu_quarantine_init(void)
413{
414 int ret = 0;
415
416 ret = cpuhp_setup_state(state: CPUHP_AP_ONLINE_DYN, name: "mm/kasan:online",
417 startup: kasan_cpu_online, teardown: kasan_cpu_offline);
418 if (ret < 0)
419 pr_err("cpu quarantine register failed [%d]\n", ret);
420 return ret;
421}
422late_initcall(kasan_cpu_quarantine_init);
423

source code of linux/mm/kasan/quarantine.c