mm/kasan/quarantine.c

   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  */
  35 struct 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
  44 static bool qlist_empty(struct qlist_head *q)
  45 {
  46         return !q->head;
  47 }
  48
  49 static void qlist_init(struct qlist_head *q)
  50 {
  51         q->head = q->tail = NULL;
  52         q->bytes = 0;
  53 }
  54
  55 static 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
  67 static 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(to)) {
  73                 *to = *from;
  74                 qlist_init(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(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  */
  93 static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);
  94
  95 /* Round-robin FIFO array of batches. */
  96 static struct qlist_head global_quarantine[QUARANTINE_BATCHES];
  97 static int quarantine_head;
  98 static int quarantine_tail;
  99 /* Total size of all objects in global_quarantine across all batches. */
 100 static unsigned long quarantine_size;
 101 static DEFINE_RAW_SPINLOCK(quarantine_lock);
 102 DEFINE_STATIC_SRCU(remove_cache_srcu);
 103
 104 struct cpu_shrink_qlist {
 105         raw_spinlock_t lock;
 106         struct qlist_head qlist;
 107 };
 108
 109 static 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. */
 114 static 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  */
 120 static 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
 129 static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
 130 {
 131         return virt_to_slab(qlink)->slab_cache;
 132 }
 133
 134 static 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
 143 static 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 *free_meta = kasan_get_free_meta(cache, object);
 147
 148         /*
 149          * Note: Keep per-object metadata to allow KASAN print stack traces for
 150          * use-after-free-before-realloc bugs.
 151          */
 152
 153         /*
 154          * If init_on_free is enabled and KASAN's free metadata is stored in
 155          * the object, zero the metadata. Otherwise, the object's memory will
 156          * not be properly zeroed, as KASAN saves the metadata after the slab
 157          * allocator zeroes the object.
 158          */
 159         if (slab_want_init_on_free(cache) &&
 160             cache->kasan_info.free_meta_offset == 0)
 161                 memzero_explicit(free_meta, sizeof(*free_meta));
 162
 163         ___cache_free(cache, object, _THIS_IP_);
 164 }
 165
 166 static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
 167 {
 168         struct qlist_node *qlink;
 169
 170         if (unlikely(qlist_empty(q)))
 171                 return;
 172
 173         qlink = q->head;
 174         while (qlink) {
 175                 struct kmem_cache *obj_cache =
 176                         cache ? cache : qlink_to_cache(qlink);
 177                 struct qlist_node *next = qlink->next;
 178
 179                 qlink_free(qlink, obj_cache);
 180                 qlink = next;
 181         }
 182         qlist_init(q);
 183 }
 184
 185 bool kasan_quarantine_put(struct kmem_cache *cache, void *object)
 186 {
 187         unsigned long flags;
 188         struct qlist_head *q;
 189         struct qlist_head temp = QLIST_INIT;
 190         struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
 191
 192         /*
 193          * If there's no metadata for this object, don't put it into
 194          * quarantine.
 195          */
 196         if (!meta)
 197                 return false;
 198
 199         /*
 200          * Note: irq must be disabled until after we move the batch to the
 201          * global quarantine. Otherwise kasan_quarantine_remove_cache() can
 202          * miss some objects belonging to the cache if they are in our local
 203          * temp list. kasan_quarantine_remove_cache() executes on_each_cpu()
 204          * at the beginning which ensures that it either sees the objects in
 205          * per-cpu lists or in the global quarantine.
 206          */
 207         local_irq_save(flags);
 208
 209         q = this_cpu_ptr(&cpu_quarantine);
 210         if (q->offline) {
 211                 local_irq_restore(flags);
 212                 return false;
 213         }
 214         qlist_put(q, &meta->quarantine_link, cache->size);
 215         if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {
 216                 qlist_move_all(q, &temp);
 217
 218                 raw_spin_lock(&quarantine_lock);
 219                 WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
 220                 qlist_move_all(&temp, &global_quarantine[quarantine_tail]);
 221                 if (global_quarantine[quarantine_tail].bytes >=
 222                                 READ_ONCE(quarantine_batch_size)) {
 223                         int new_tail;
 224
 225                         new_tail = quarantine_tail + 1;
 226                         if (new_tail == QUARANTINE_BATCHES)
 227                                 new_tail = 0;
 228                         if (new_tail != quarantine_head)
 229                                 quarantine_tail = new_tail;
 230                 }
 231                 raw_spin_unlock(&quarantine_lock);
 232         }
 233
 234         local_irq_restore(flags);
 235
 236         return true;
 237 }
 238
 239 void kasan_quarantine_reduce(void)
 240 {
 241         size_t total_size, new_quarantine_size, percpu_quarantines;
 242         unsigned long flags;
 243         int srcu_idx;
 244         struct qlist_head to_free = QLIST_INIT;
 245
 246         if (likely(READ_ONCE(quarantine_size) <=
 247                    READ_ONCE(quarantine_max_size)))
 248                 return;
 249
 250         /*
 251          * srcu critical section ensures that kasan_quarantine_remove_cache()
 252          * will not miss objects belonging to the cache while they are in our
 253          * local to_free list. srcu is chosen because (1) it gives us private
 254          * grace period domain that does not interfere with anything else,
 255          * and (2) it allows synchronize_srcu() to return without waiting
 256          * if there are no pending read critical sections (which is the
 257          * expected case).
 258          */
 259         srcu_idx = srcu_read_lock(&remove_cache_srcu);
 260         raw_spin_lock_irqsave(&quarantine_lock, flags);
 261
 262         /*
 263          * Update quarantine size in case of hotplug. Allocate a fraction of
 264          * the installed memory to quarantine minus per-cpu queue limits.
 265          */
 266         total_size = (totalram_pages() << PAGE_SHIFT) /
 267                 QUARANTINE_FRACTION;
 268         percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
 269         new_quarantine_size = (total_size < percpu_quarantines) ?
 270                 0 : total_size - percpu_quarantines;
 271         WRITE_ONCE(quarantine_max_size, new_quarantine_size);
 272         /* Aim at consuming at most 1/2 of slots in quarantine. */
 273         WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE,
 274                 2 * total_size / QUARANTINE_BATCHES));
 275
 276         if (likely(quarantine_size > quarantine_max_size)) {
 277                 qlist_move_all(&global_quarantine[quarantine_head], &to_free);
 278                 WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes);
 279                 quarantine_head++;
 280                 if (quarantine_head == QUARANTINE_BATCHES)
 281                         quarantine_head = 0;
 282         }
 283
 284         raw_spin_unlock_irqrestore(&quarantine_lock, flags);
 285
 286         qlist_free_all(&to_free, NULL);
 287         srcu_read_unlock(&remove_cache_srcu, srcu_idx);
 288 }
 289
 290 static void qlist_move_cache(struct qlist_head *from,
 291                                    struct qlist_head *to,
 292                                    struct kmem_cache *cache)
 293 {
 294         struct qlist_node *curr;
 295
 296         if (unlikely(qlist_empty(from)))
 297                 return;
 298
 299         curr = from->head;
 300         qlist_init(from);
 301         while (curr) {
 302                 struct qlist_node *next = curr->next;
 303                 struct kmem_cache *obj_cache = qlink_to_cache(curr);
 304
 305                 if (obj_cache == cache)
 306                         qlist_put(to, curr, obj_cache->size);
 307                 else
 308                         qlist_put(from, curr, obj_cache->size);
 309
 310                 curr = next;
 311         }
 312 }
 313
 314 static void __per_cpu_remove_cache(struct qlist_head *q, void *arg)
 315 {
 316         struct kmem_cache *cache = arg;
 317         unsigned long flags;
 318         struct cpu_shrink_qlist *sq;
 319
 320         sq = this_cpu_ptr(&shrink_qlist);
 321         raw_spin_lock_irqsave(&sq->lock, flags);
 322         qlist_move_cache(q, &sq->qlist, cache);
 323         raw_spin_unlock_irqrestore(&sq->lock, flags);
 324 }
 325
 326 static void per_cpu_remove_cache(void *arg)
 327 {
 328         struct qlist_head *q;
 329
 330         q = this_cpu_ptr(&cpu_quarantine);
 331         /*
 332          * Ensure the ordering between the writing to q->offline and
 333          * per_cpu_remove_cache.  Prevent cpu_quarantine from being corrupted
 334          * by interrupt.
 335          */
 336         if (READ_ONCE(q->offline))
 337                 return;
 338         __per_cpu_remove_cache(q, arg);
 339 }
 340
 341 /* Free all quarantined objects belonging to cache. */
 342 void kasan_quarantine_remove_cache(struct kmem_cache *cache)
 343 {
 344         unsigned long flags, i;
 345         struct qlist_head to_free = QLIST_INIT;
 346         int cpu;
 347         struct cpu_shrink_qlist *sq;
 348
 349         /*
 350          * Must be careful to not miss any objects that are being moved from
 351          * per-cpu list to the global quarantine in kasan_quarantine_put(),
 352          * nor objects being freed in kasan_quarantine_reduce(). on_each_cpu()
 353          * achieves the first goal, while synchronize_srcu() achieves the
 354          * second.
 355          */
 356         on_each_cpu(per_cpu_remove_cache, cache, 1);
 357
 358         for_each_online_cpu(cpu) {
 359                 sq = per_cpu_ptr(&shrink_qlist, cpu);
 360                 raw_spin_lock_irqsave(&sq->lock, flags);
 361                 qlist_move_cache(&sq->qlist, &to_free, cache);
 362                 raw_spin_unlock_irqrestore(&sq->lock, flags);
 363         }
 364         qlist_free_all(&to_free, cache);
 365
 366         raw_spin_lock_irqsave(&quarantine_lock, flags);
 367         for (i = 0; i < QUARANTINE_BATCHES; i++) {
 368                 if (qlist_empty(&global_quarantine[i]))
 369                         continue;
 370                 qlist_move_cache(&global_quarantine[i], &to_free, cache);
 371                 /* Scanning whole quarantine can take a while. */
 372                 raw_spin_unlock_irqrestore(&quarantine_lock, flags);
 373                 cond_resched();
 374                 raw_spin_lock_irqsave(&quarantine_lock, flags);
 375         }
 376         raw_spin_unlock_irqrestore(&quarantine_lock, flags);
 377
 378         qlist_free_all(&to_free, cache);
 379
 380         synchronize_srcu(&remove_cache_srcu);
 381 }
 382
 383 static int kasan_cpu_online(unsigned int cpu)
 384 {
 385         this_cpu_ptr(&cpu_quarantine)->offline = false;
 386         return 0;
 387 }
 388
 389 static int kasan_cpu_offline(unsigned int cpu)
 390 {
 391         struct qlist_head *q;
 392
 393         q = this_cpu_ptr(&cpu_quarantine);
 394         /* Ensure the ordering between the writing to q->offline and
 395          * qlist_free_all. Otherwise, cpu_quarantine may be corrupted
 396          * by interrupt.
 397          */
 398         WRITE_ONCE(q->offline, true);
 399         barrier();
 400         qlist_free_all(q, NULL);
 401         return 0;
 402 }
 403
 404 static int __init kasan_cpu_quarantine_init(void)
 405 {
 406         int ret = 0;
 407
 408         ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online",
 409                                 kasan_cpu_online, kasan_cpu_offline);
 410         if (ret < 0)
 411                 pr_err("cpu quarantine register failed [%d]\n", ret);
 412         return ret;
 413 }
 414 late_initcall(kasan_cpu_quarantine_init);