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 #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
  42 static bool qlist_empty(struct qlist_head *q)
  43 {
  44         return !q->head;
  45 }
  46
  47 static void qlist_init(struct qlist_head *q)
  48 {
  49         q->head = q->tail = NULL;
  50         q->bytes = 0;
  51 }
  52
  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
  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
 127 static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
 128 {
 129         return virt_to_slab(qlink)->slab_cache;
 130 }
 131
 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
 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
 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
 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
 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
 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
 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
 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. */
 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
 389 static int kasan_cpu_online(unsigned int cpu)
 390 {
 391         this_cpu_ptr(&cpu_quarantine)->offline = false;
 392         return 0;
 393 }
 394
 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
 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);