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sizeof(*meta)); 161 162 /* 163 * As the object now gets freed from the quarantine, assume that its 164 * free track is no longer valid. 165 */ 166 *(u8 *)kasan_mem_to_shadow(object) = KASAN_SLAB_FREE; 167 168 ___cache_free(cache, object, _THIS_IP_); 169 170 if (IS_ENABLED(CONFIG_SLAB)) 171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