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1// SPDX-License-Identifier: GPL-2.02/*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: " fmt12 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 of33 * 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 else61 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(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 */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 keep125 * the ratio low to avoid OOM.126 */127#define QUARANTINE_FRACTION 32128 129static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)130{131 return virt_to_slab(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 *free_meta = kasan_get_free_meta(cache, object);147 148 /*149 * Note: Keep per-object metadata to allow KASAN print stack traces for150 * use-after-free-before-realloc bugs.151 */152 153 /*154 * If init_on_free is enabled and KASAN's free metadata is stored in155 * the object, zero the metadata. Otherwise, the object's memory will156 * not be properly zeroed, as KASAN saves the metadata after the slab157 * 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 166static 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 185bool 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 into194 * quarantine.195 */196 if (!meta)197 return false;198 199 /*200 * Note: irq must be disabled until after we move the batch to the201 * global quarantine. Otherwise kasan_quarantine_remove_cache() can202 * miss some objects belonging to the cache if they are in our local203 * temp list. kasan_quarantine_remove_cache() executes on_each_cpu()204 * at the beginning which ensures that it either sees the objects in205 * 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 239void 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 our253 * local to_free list. srcu is chosen because (1) it gives us private254 * grace period domain that does not interfere with anything else,255 * and (2) it allows synchronize_srcu() to return without waiting256 * if there are no pending read critical sections (which is the257 * 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 of264 * 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 290static 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 else308 qlist_put(from, curr, obj_cache->size);309 310 curr = next;311 }312}313 314static 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 326static 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 and333 * per_cpu_remove_cache. Prevent cpu_quarantine from being corrupted334 * 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. */342void 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 from351 * 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 the354 * 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 383static int kasan_cpu_online(unsigned int cpu)384{385 this_cpu_ptr(&cpu_quarantine)->offline = false;386 return 0;387}388 389static 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 and395 * qlist_free_all. Otherwise, cpu_quarantine may be corrupted396 * by interrupt.397 */398 WRITE_ONCE(q->offline, true);399 barrier();400 qlist_free_all(q, NULL);401 return 0;402}403 404static 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}414late_initcall(kasan_cpu_quarantine_init);415