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_alloc_meta *alloc_meta = kasan_get_alloc_meta(cache, object); 147 struct kasan_free_meta *free_meta = kasan_get_free_meta(cache, object); 148 unsigned long flags; 149 150 if (alloc_meta) { 151 stack_depot_put(alloc_meta->alloc_track.stack); 152 stack_depot_put(alloc_meta->aux_stack[0]); 153 stack_depot_put(alloc_meta->aux_stack[1]); 154 __memset(alloc_meta, 0, sizeof(*alloc_meta)); 155 } 156 157 if (free_meta && 158 *(u8 *)kasan_mem_to_shadow(object) == KASAN_SLAB_FREETRACK) { 159 stack_depot_put(free_meta->free_track.stack); 160 free_meta->free_track.stack = 0; 161 } 162 163 /* 164 * If init_on_free is enabled and KASAN's free metadata is stored in 165 * the object, zero the metadata. Otherwise, the object's memory will 166 * not be properly zeroed, as KASAN saves the metadata after the slab 167 * allocator zeroes the object. 168 */ 169 if (slab_want_init_on_free(cache) && 170 cache->kasan_info.free_meta_offset == 0) 171 memzero_explicit(free_meta, sizeof(*free_meta)); 172 173 /* 174 * As the object now gets freed from the quarantine, 175 * take note that its free track is no longer exists. 176 */ 177 *(u8 *)kasan_mem_to_shadow(object) = KASAN_SLAB_FREE; 178 179 if (IS_ENABLED(CONFIG_SLAB)) 180 local_irq_save(flags); 181 182 ___cache_free(cache, object, _THIS_IP_); 183 184 if (IS_ENABLED(CONFIG_SLAB)) 185 local_irq_restore(flags); 186 } 187 188 static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache) 189 { 190 struct qlist_node *qlink; 191 192 if (unlikely(qlist_empty(q))) 193 return; 194 195 qlink = q->head; 196 while (qlink) { 197 struct kmem_cache *obj_cache = 198 cache ? cache : qlink_to_cache(qlink); 199 struct qlist_node *next = qlink->next; 200 201 qlink_free(qlink, obj_cache); 202 qlink = next; 203 } 204 qlist_init(q); 205 } 206 207 bool kasan_quarantine_put(struct kmem_cache *cache, void *object) 208 { 209 unsigned long flags; 210 struct qlist_head *q; 211 struct qlist_head temp = QLIST_INIT; 212 struct kasan_free_meta *meta = kasan_get_free_meta(cache, object); 213 214 /* 215 * If there's no metadata for this object, don't put it into 216 * quarantine. 217 */ 218 if (!meta) 219 return false; 220 221 /* 222 * Note: irq must be disabled until after we move the batch to the 223 * global quarantine. Otherwise kasan_quarantine_remove_cache() can 224 * miss some objects belonging to the cache if they are in our local 225 * temp list. kasan_quarantine_remove_cache() executes on_each_cpu() 226 * at the beginning which ensures that it either sees the objects in 227 * per-cpu lists or in the global quarantine. 228 */ 229 local_irq_save(flags); 230 231 q = this_cpu_ptr(&cpu_quarantine); 232 if (q->offline) { 233 local_irq_restore(flags); 234 return false; 235 } 236 qlist_put(q, &meta->quarantine_link, cache->size); 237 if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) { 238 qlist_move_all(q, &temp); 239 240 raw_spin_lock(&quarantine_lock); 241 WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes); 242 qlist_move_all(&temp, &global_quarantine[quarantine_tail]); 243 if (global_quarantine[quarantine_tail].bytes >= 244 READ_ONCE(quarantine_batch_size)) { 245 int new_tail; 246 247 new_tail = quarantine_tail + 1; 248 if (new_tail == QUARANTINE_BATCHES) 249 new_tail = 0; 250 if (new_tail != quarantine_head) 251 quarantine_tail = new_tail; 252 } 253 raw_spin_unlock(&quarantine_lock); 254 } 255 256 local_irq_restore(flags); 257 258 return true; 259 } 260 261 void kasan_quarantine_reduce(void) 262 { 263 size_t total_size, new_quarantine_size, percpu_quarantines; 264 unsigned long flags; 265 int srcu_idx; 266 struct qlist_head to_free = QLIST_INIT; 267 268 if (likely(READ_ONCE(quarantine_size) <= 269 READ_ONCE(quarantine_max_size))) 270 return; 271 272 /* 273 * srcu critical section ensures that kasan_quarantine_remove_cache() 274 * will not miss objects belonging to the cache while they are in our 275 * local to_free list. srcu is chosen because (1) it gives us private 276 * grace period domain that does not interfere with anything else, 277 * and (2) it allows synchronize_srcu() to return without waiting 278 * if there are no pending read critical sections (which is the 279 * expected case). 280 */ 281 srcu_idx = srcu_read_lock(&remove_cache_srcu); 282 raw_spin_lock_irqsave(&quarantine_lock, flags); 283 284 /* 285 * Update quarantine size in case of hotplug. Allocate a fraction of 286 * the installed memory to quarantine minus per-cpu queue limits. 287 */ 288 total_size = (totalram_pages() << PAGE_SHIFT) / 289 QUARANTINE_FRACTION; 290 percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus(); 291 new_quarantine_size = (total_size < percpu_quarantines) ? 292 0 : total_size - percpu_quarantines; 293 WRITE_ONCE(quarantine_max_size, new_quarantine_size); 294 /* Aim at consuming at most 1/2 of slots in quarantine. */ 295 WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE, 296 2 * total_size / QUARANTINE_BATCHES)); 297 298 if (likely(quarantine_size > quarantine_max_size)) { 299 qlist_move_all(&global_quarantine[quarantine_head], &to_free); 300 WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes); 301 quarantine_head++; 302 if (quarantine_head == QUARANTINE_BATCHES) 303 quarantine_head = 0; 304 } 305 306 raw_spin_unlock_irqrestore(&quarantine_lock, flags); 307 308 qlist_free_all(&to_free, NULL); 309 srcu_read_unlock(&remove_cache_srcu, srcu_idx); 310 } 311 312 static void qlist_move_cache(struct qlist_head *from, 313 struct qlist_head *to, 314 struct kmem_cache *cache) 315 { 316 struct qlist_node *curr; 317 318 if (unlikely(qlist_empty(from))) 319 return; 320 321 curr = from->head; 322 qlist_init(from); 323 while (curr) { 324 struct qlist_node *next = curr->next; 325 struct kmem_cache *obj_cache = qlink_to_cache(curr); 326 327 if (obj_cache == cache) 328 qlist_put(to, curr, obj_cache->size); 329 else 330 qlist_put(from, curr, obj_cache->size); 331 332 curr = next; 333 } 334 } 335 336 static void __per_cpu_remove_cache(struct qlist_head *q, void *arg) 337 { 338 struct kmem_cache *cache = arg; 339 unsigned long flags; 340 struct cpu_shrink_qlist *sq; 341 342 sq = this_cpu_ptr(&shrink_qlist); 343 raw_spin_lock_irqsave(&sq->lock, flags); 344 qlist_move_cache(q, &sq->qlist, cache); 345 raw_spin_unlock_irqrestore(&sq->lock, flags); 346 } 347 348 static void per_cpu_remove_cache(void *arg) 349 { 350 struct qlist_head *q; 351 352 q = this_cpu_ptr(&cpu_quarantine); 353 /* 354 * Ensure the ordering between the writing to q->offline and 355 * per_cpu_remove_cache. Prevent cpu_quarantine from being corrupted 356 * by interrupt. 357 */ 358 if (READ_ONCE(q->offline)) 359 return; 360 __per_cpu_remove_cache(q, arg); 361 } 362 363 /* Free all quarantined objects belonging to cache. */ 364 void kasan_quarantine_remove_cache(struct kmem_cache *cache) 365 { 366 unsigned long flags, i; 367 struct qlist_head to_free = QLIST_INIT; 368 int cpu; 369 struct cpu_shrink_qlist *sq; 370 371 /* 372 * Must be careful to not miss any objects that are being moved from 373 * per-cpu list to the global quarantine in kasan_quarantine_put(), 374 * nor objects being freed in kasan_quarantine_reduce(). on_each_cpu() 375 * achieves the first goal, while synchronize_srcu() achieves the 376 * second. 377 */ 378 on_each_cpu(per_cpu_remove_cache, cache, 1); 379 380 for_each_online_cpu(cpu) { 381 sq = per_cpu_ptr(&shrink_qlist, cpu); 382 raw_spin_lock_irqsave(&sq->lock, flags); 383 qlist_move_cache(&sq->qlist, &to_free, cache); 384 raw_spin_unlock_irqrestore(&sq->lock, flags); 385 } 386 qlist_free_all(&to_free, cache); 387 388 raw_spin_lock_irqsave(&quarantine_lock, flags); 389 for (i = 0; i < QUARANTINE_BATCHES; i++) { 390 if (qlist_empty(&global_quarantine[i])) 391 continue; 392 qlist_move_cache(&global_quarantine[i], &to_free, cache); 393 /* Scanning whole quarantine can take a while. */ 394 raw_spin_unlock_irqrestore(&quarantine_lock, flags); 395 cond_resched(); 396 raw_spin_lock_irqsave(&quarantine_lock, flags); 397 } 398 raw_spin_unlock_irqrestore(&quarantine_lock, flags); 399 400 qlist_free_all(&to_free, cache); 401 402 synchronize_srcu(&remove_cache_srcu); 403 } 404 405 static int kasan_cpu_online(unsigned int cpu) 406 { 407 this_cpu_ptr(&cpu_quarantine)->offline = false; 408 return 0; 409 } 410 411 static int kasan_cpu_offline(unsigned int cpu) 412 { 413 struct qlist_head *q; 414 415 q = this_cpu_ptr(&cpu_quarantine); 416 /* Ensure the ordering between the writing to q->offline and 417 * qlist_free_all. Otherwise, cpu_quarantine may be corrupted 418 * by interrupt. 419 */ 420 WRITE_ONCE(q->offline, true); 421 barrier(); 422 qlist_free_all(q, NULL); 423 return 0; 424 } 425 426 static int __init kasan_cpu_quarantine_init(void) 427 { 428 int ret = 0; 429 430 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online", 431 kasan_cpu_online, kasan_cpu_offline); 432 if (ret < 0) 433 pr_err("cpu quarantine register failed [%d]\n", ret); 434 return ret; 435 } 436 late_initcall(kasan_cpu_quarantine_init); 437