1 /*
2 * KASAN quarantine.
3 *
4 * Author: Alexander Potapenko <glider@google.com>
5 * Copyright (C) 2016 Google, Inc.
6 *
7 * Based on code by Dmitry Chernenkov.
8 *
9 * This program is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU General Public License
11 * version 2 as published by the Free Software Foundation.
12 *
13 * This program is distributed in the hope that it will be useful, but
14 * WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * General Public License for more details.
17 *
18 */
19
20 #include <linux/gfp.h>
21 #include <linux/hash.h>
22 #include <linux/kernel.h>
23 #include <linux/mm.h>
24 #include <linux/percpu.h>
25 #include <linux/printk.h>
26 #include <linux/shrinker.h>
27 #include <linux/slab.h>
28 #include <linux/srcu.h>
29 #include <linux/string.h>
30 #include <linux/types.h>
31
32 #include "../slab.h"
33 #include "kasan.h"
34
35 /* Data structure and operations for quarantine queues. */
36
37 /*
38 * Each queue is a signle-linked list, which also stores the total size of
39 * objects inside of it.
40 */
41 struct qlist_head {
42 struct qlist_node *head;
43 struct qlist_node *tail;
44 size_t bytes;
45 };
46
47 #define QLIST_INIT { NULL, NULL, 0 }
48
qlist_empty(struct qlist_head * q)49 static bool qlist_empty(struct qlist_head *q)
50 {
51 return !q->head;
52 }
53
qlist_init(struct qlist_head * q)54 static void qlist_init(struct qlist_head *q)
55 {
56 q->head = q->tail = NULL;
57 q->bytes = 0;
58 }
59
qlist_put(struct qlist_head * q,struct qlist_node * qlink,size_t size)60 static void qlist_put(struct qlist_head *q, struct qlist_node *qlink,
61 size_t size)
62 {
63 if (unlikely(qlist_empty(q)))
64 q->head = qlink;
65 else
66 q->tail->next = qlink;
67 q->tail = qlink;
68 qlink->next = NULL;
69 q->bytes += size;
70 }
71
qlist_move_all(struct qlist_head * from,struct qlist_head * to)72 static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
73 {
74 if (unlikely(qlist_empty(from)))
75 return;
76
77 if (qlist_empty(to)) {
78 *to = *from;
79 qlist_init(from);
80 return;
81 }
82
83 to->tail->next = from->head;
84 to->tail = from->tail;
85 to->bytes += from->bytes;
86
87 qlist_init(from);
88 }
89
90 #define QUARANTINE_PERCPU_SIZE (1 << 20)
91 #define QUARANTINE_BATCHES \
92 (1024 > 4 * CONFIG_NR_CPUS ? 1024 : 4 * CONFIG_NR_CPUS)
93
94 /*
95 * The object quarantine consists of per-cpu queues and a global queue,
96 * guarded by quarantine_lock.
97 */
98 static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);
99
100 /* Round-robin FIFO array of batches. */
101 static struct qlist_head global_quarantine[QUARANTINE_BATCHES];
102 static int quarantine_head;
103 static int quarantine_tail;
104 /* Total size of all objects in global_quarantine across all batches. */
105 static unsigned long quarantine_size;
106 static DEFINE_SPINLOCK(quarantine_lock);
107 DEFINE_STATIC_SRCU(remove_cache_srcu);
108
109 /* Maximum size of the global queue. */
110 static unsigned long quarantine_max_size;
111
112 /*
113 * Target size of a batch in global_quarantine.
114 * Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM.
115 */
116 static unsigned long quarantine_batch_size;
117
118 /*
119 * The fraction of physical memory the quarantine is allowed to occupy.
120 * Quarantine doesn't support memory shrinker with SLAB allocator, so we keep
121 * the ratio low to avoid OOM.
122 */
123 #define QUARANTINE_FRACTION 32
124
qlink_to_cache(struct qlist_node * qlink)125 static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
126 {
127 return virt_to_head_page(qlink)->slab_cache;
128 }
129
qlink_to_object(struct qlist_node * qlink,struct kmem_cache * cache)130 static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
131 {
132 struct kasan_free_meta *free_info =
133 container_of(qlink, struct kasan_free_meta,
134 quarantine_link);
135
136 return ((void *)free_info) - cache->kasan_info.free_meta_offset;
137 }
138
qlink_free(struct qlist_node * qlink,struct kmem_cache * cache)139 static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
140 {
141 void *object = qlink_to_object(qlink, cache);
142 unsigned long flags;
143
144 if (IS_ENABLED(CONFIG_SLAB))
145 local_irq_save(flags);
146
147 ___cache_free(cache, object, _THIS_IP_);
148
149 if (IS_ENABLED(CONFIG_SLAB))
150 local_irq_restore(flags);
151 }
152
qlist_free_all(struct qlist_head * q,struct kmem_cache * cache)153 static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
154 {
155 struct qlist_node *qlink;
156
157 if (unlikely(qlist_empty(q)))
158 return;
159
160 qlink = q->head;
161 while (qlink) {
162 struct kmem_cache *obj_cache =
163 cache ? cache : qlink_to_cache(qlink);
164 struct qlist_node *next = qlink->next;
165
166 qlink_free(qlink, obj_cache);
167 qlink = next;
168 }
169 qlist_init(q);
170 }
171
quarantine_put(struct kasan_free_meta * info,struct kmem_cache * cache)172 void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
173 {
174 unsigned long flags;
175 struct qlist_head *q;
176 struct qlist_head temp = QLIST_INIT;
177
178 /*
179 * Note: irq must be disabled until after we move the batch to the
180 * global quarantine. Otherwise quarantine_remove_cache() can miss
181 * some objects belonging to the cache if they are in our local temp
182 * list. quarantine_remove_cache() executes on_each_cpu() at the
183 * beginning which ensures that it either sees the objects in per-cpu
184 * lists or in the global quarantine.
185 */
186 local_irq_save(flags);
187
188 q = this_cpu_ptr(&cpu_quarantine);
189 qlist_put(q, &info->quarantine_link, cache->size);
190 if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {
191 qlist_move_all(q, &temp);
192
193 spin_lock(&quarantine_lock);
194 WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
195 qlist_move_all(&temp, &global_quarantine[quarantine_tail]);
196 if (global_quarantine[quarantine_tail].bytes >=
197 READ_ONCE(quarantine_batch_size)) {
198 int new_tail;
199
200 new_tail = quarantine_tail + 1;
201 if (new_tail == QUARANTINE_BATCHES)
202 new_tail = 0;
203 if (new_tail != quarantine_head)
204 quarantine_tail = new_tail;
205 }
206 spin_unlock(&quarantine_lock);
207 }
208
209 local_irq_restore(flags);
210 }
211
quarantine_reduce(void)212 void quarantine_reduce(void)
213 {
214 size_t total_size, new_quarantine_size, percpu_quarantines;
215 unsigned long flags;
216 int srcu_idx;
217 struct qlist_head to_free = QLIST_INIT;
218
219 if (likely(READ_ONCE(quarantine_size) <=
220 READ_ONCE(quarantine_max_size)))
221 return;
222
223 /*
224 * srcu critical section ensures that quarantine_remove_cache()
225 * will not miss objects belonging to the cache while they are in our
226 * local to_free list. srcu is chosen because (1) it gives us private
227 * grace period domain that does not interfere with anything else,
228 * and (2) it allows synchronize_srcu() to return without waiting
229 * if there are no pending read critical sections (which is the
230 * expected case).
231 */
232 srcu_idx = srcu_read_lock(&remove_cache_srcu);
233 spin_lock_irqsave(&quarantine_lock, flags);
234
235 /*
236 * Update quarantine size in case of hotplug. Allocate a fraction of
237 * the installed memory to quarantine minus per-cpu queue limits.
238 */
239 total_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) /
240 QUARANTINE_FRACTION;
241 percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
242 new_quarantine_size = (total_size < percpu_quarantines) ?
243 0 : total_size - percpu_quarantines;
244 WRITE_ONCE(quarantine_max_size, new_quarantine_size);
245 /* Aim at consuming at most 1/2 of slots in quarantine. */
246 WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE,
247 2 * total_size / QUARANTINE_BATCHES));
248
249 if (likely(quarantine_size > quarantine_max_size)) {
250 qlist_move_all(&global_quarantine[quarantine_head], &to_free);
251 WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes);
252 quarantine_head++;
253 if (quarantine_head == QUARANTINE_BATCHES)
254 quarantine_head = 0;
255 }
256
257 spin_unlock_irqrestore(&quarantine_lock, flags);
258
259 qlist_free_all(&to_free, NULL);
260 srcu_read_unlock(&remove_cache_srcu, srcu_idx);
261 }
262
qlist_move_cache(struct qlist_head * from,struct qlist_head * to,struct kmem_cache * cache)263 static void qlist_move_cache(struct qlist_head *from,
264 struct qlist_head *to,
265 struct kmem_cache *cache)
266 {
267 struct qlist_node *curr;
268
269 if (unlikely(qlist_empty(from)))
270 return;
271
272 curr = from->head;
273 qlist_init(from);
274 while (curr) {
275 struct qlist_node *next = curr->next;
276 struct kmem_cache *obj_cache = qlink_to_cache(curr);
277
278 if (obj_cache == cache)
279 qlist_put(to, curr, obj_cache->size);
280 else
281 qlist_put(from, curr, obj_cache->size);
282
283 curr = next;
284 }
285 }
286
per_cpu_remove_cache(void * arg)287 static void per_cpu_remove_cache(void *arg)
288 {
289 struct kmem_cache *cache = arg;
290 struct qlist_head to_free = QLIST_INIT;
291 struct qlist_head *q;
292
293 q = this_cpu_ptr(&cpu_quarantine);
294 qlist_move_cache(q, &to_free, cache);
295 qlist_free_all(&to_free, cache);
296 }
297
298 /* Free all quarantined objects belonging to cache. */
quarantine_remove_cache(struct kmem_cache * cache)299 void quarantine_remove_cache(struct kmem_cache *cache)
300 {
301 unsigned long flags, i;
302 struct qlist_head to_free = QLIST_INIT;
303
304 /*
305 * Must be careful to not miss any objects that are being moved from
306 * per-cpu list to the global quarantine in quarantine_put(),
307 * nor objects being freed in quarantine_reduce(). on_each_cpu()
308 * achieves the first goal, while synchronize_srcu() achieves the
309 * second.
310 */
311 on_each_cpu(per_cpu_remove_cache, cache, 1);
312
313 spin_lock_irqsave(&quarantine_lock, flags);
314 for (i = 0; i < QUARANTINE_BATCHES; i++) {
315 if (qlist_empty(&global_quarantine[i]))
316 continue;
317 qlist_move_cache(&global_quarantine[i], &to_free, cache);
318 /* Scanning whole quarantine can take a while. */
319 spin_unlock_irqrestore(&quarantine_lock, flags);
320 cond_resched();
321 spin_lock_irqsave(&quarantine_lock, flags);
322 }
323 spin_unlock_irqrestore(&quarantine_lock, flags);
324
325 qlist_free_all(&to_free, cache);
326
327 synchronize_srcu(&remove_cache_srcu);
328 }
329