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 /* Maximum size of the global queue. */ 103 static unsigned long quarantine_max_size; 104 105 /* 106 * Target size of a batch in global_quarantine. 107 * Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM. 108 */ 109 static unsigned long quarantine_batch_size; 110 111 /* 112 * The fraction of physical memory the quarantine is allowed to occupy. 113 * Quarantine doesn't support memory shrinker with SLAB allocator, so we keep 114 * the ratio low to avoid OOM. 115 */ 116 #define QUARANTINE_FRACTION 32 117 118 static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink) 119 { 120 return virt_to_head_page(qlink)->slab_cache; 121 } 122 123 static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache) 124 { 125 struct kasan_free_meta *free_info = 126 container_of(qlink, struct kasan_free_meta, 127 quarantine_link); 128 129 return ((void *)free_info) - cache->kasan_info.free_meta_offset; 130 } 131 132 static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache) 133 { 134 void *object = qlink_to_object(qlink, cache); 135 unsigned long flags; 136 137 if (IS_ENABLED(CONFIG_SLAB)) 138 local_irq_save(flags); 139 140 /* 141 * As the object now gets freed from the quarantine, assume that its 142 * free track is no longer valid. 143 */ 144 *(u8 *)kasan_mem_to_shadow(object) = KASAN_KMALLOC_FREE; 145 146 ___cache_free(cache, object, _THIS_IP_); 147 148 if (IS_ENABLED(CONFIG_SLAB)) 149 local_irq_restore(flags); 150 } 151 152 static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache) 153 { 154 struct qlist_node *qlink; 155 156 if (unlikely(qlist_empty(q))) 157 return; 158 159 qlink = q->head; 160 while (qlink) { 161 struct kmem_cache *obj_cache = 162 cache ? cache : qlink_to_cache(qlink); 163 struct qlist_node *next = qlink->next; 164 165 qlink_free(qlink, obj_cache); 166 qlink = next; 167 } 168 qlist_init(q); 169 } 170 171 bool kasan_quarantine_put(struct kmem_cache *cache, void *object) 172 { 173 unsigned long flags; 174 struct qlist_head *q; 175 struct qlist_head temp = QLIST_INIT; 176 struct kasan_free_meta *meta = kasan_get_free_meta(cache, object); 177 178 /* 179 * If there's no metadata for this object, don't put it into 180 * quarantine. 181 */ 182 if (!meta) 183 return false; 184 185 /* 186 * Note: irq must be disabled until after we move the batch to the 187 * global quarantine. Otherwise kasan_quarantine_remove_cache() can 188 * miss some objects belonging to the cache if they are in our local 189 * temp list. kasan_quarantine_remove_cache() executes on_each_cpu() 190 * at the beginning which ensures that it either sees the objects in 191 * per-cpu lists or in the global quarantine. 192 */ 193 local_irq_save(flags); 194 195 q = this_cpu_ptr(&cpu_quarantine); 196 if (q->offline) { 197 local_irq_restore(flags); 198 return false; 199 } 200 qlist_put(q, &meta->quarantine_link, cache->size); 201 if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) { 202 qlist_move_all(q, &temp); 203 204 raw_spin_lock(&quarantine_lock); 205 WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes); 206 qlist_move_all(&temp, &global_quarantine[quarantine_tail]); 207 if (global_quarantine[quarantine_tail].bytes >= 208 READ_ONCE(quarantine_batch_size)) { 209 int new_tail; 210 211 new_tail = quarantine_tail + 1; 212 if (new_tail == QUARANTINE_BATCHES) 213 new_tail = 0; 214 if (new_tail != quarantine_head) 215 quarantine_tail = new_tail; 216 } 217 raw_spin_unlock(&quarantine_lock); 218 } 219 220 local_irq_restore(flags); 221 222 return true; 223 } 224 225 void kasan_quarantine_reduce(void) 226 { 227 size_t total_size, new_quarantine_size, percpu_quarantines; 228 unsigned long flags; 229 int srcu_idx; 230 struct qlist_head to_free = QLIST_INIT; 231 232 if (likely(READ_ONCE(quarantine_size) <= 233 READ_ONCE(quarantine_max_size))) 234 return; 235 236 /* 237 * srcu critical section ensures that kasan_quarantine_remove_cache() 238 * will not miss objects belonging to the cache while they are in our 239 * local to_free list. srcu is chosen because (1) it gives us private 240 * grace period domain that does not interfere with anything else, 241 * and (2) it allows synchronize_srcu() to return without waiting 242 * if there are no pending read critical sections (which is the 243 * expected case). 244 */ 245 srcu_idx = srcu_read_lock(&remove_cache_srcu); 246 raw_spin_lock_irqsave(&quarantine_lock, flags); 247 248 /* 249 * Update quarantine size in case of hotplug. Allocate a fraction of 250 * the installed memory to quarantine minus per-cpu queue limits. 251 */ 252 total_size = (totalram_pages() << PAGE_SHIFT) / 253 QUARANTINE_FRACTION; 254 percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus(); 255 new_quarantine_size = (total_size < percpu_quarantines) ? 256 0 : total_size - percpu_quarantines; 257 WRITE_ONCE(quarantine_max_size, new_quarantine_size); 258 /* Aim at consuming at most 1/2 of slots in quarantine. */ 259 WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE, 260 2 * total_size / QUARANTINE_BATCHES)); 261 262 if (likely(quarantine_size > quarantine_max_size)) { 263 qlist_move_all(&global_quarantine[quarantine_head], &to_free); 264 WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes); 265 quarantine_head++; 266 if (quarantine_head == QUARANTINE_BATCHES) 267 quarantine_head = 0; 268 } 269 270 raw_spin_unlock_irqrestore(&quarantine_lock, flags); 271 272 qlist_free_all(&to_free, NULL); 273 srcu_read_unlock(&remove_cache_srcu, srcu_idx); 274 } 275 276 static void qlist_move_cache(struct qlist_head *from, 277 struct qlist_head *to, 278 struct kmem_cache *cache) 279 { 280 struct qlist_node *curr; 281 282 if (unlikely(qlist_empty(from))) 283 return; 284 285 curr = from->head; 286 qlist_init(from); 287 while (curr) { 288 struct qlist_node *next = curr->next; 289 struct kmem_cache *obj_cache = qlink_to_cache(curr); 290 291 if (obj_cache == cache) 292 qlist_put(to, curr, obj_cache->size); 293 else 294 qlist_put(from, curr, obj_cache->size); 295 296 curr = next; 297 } 298 } 299 300 static void per_cpu_remove_cache(void *arg) 301 { 302 struct kmem_cache *cache = arg; 303 struct qlist_head to_free = QLIST_INIT; 304 struct qlist_head *q; 305 306 q = this_cpu_ptr(&cpu_quarantine); 307 qlist_move_cache(q, &to_free, cache); 308 qlist_free_all(&to_free, cache); 309 } 310 311 /* Free all quarantined objects belonging to cache. */ 312 void kasan_quarantine_remove_cache(struct kmem_cache *cache) 313 { 314 unsigned long flags, i; 315 struct qlist_head to_free = QLIST_INIT; 316 317 /* 318 * Must be careful to not miss any objects that are being moved from 319 * per-cpu list to the global quarantine in kasan_quarantine_put(), 320 * nor objects being freed in kasan_quarantine_reduce(). on_each_cpu() 321 * achieves the first goal, while synchronize_srcu() achieves the 322 * second. 323 */ 324 on_each_cpu(per_cpu_remove_cache, cache, 1); 325 326 raw_spin_lock_irqsave(&quarantine_lock, flags); 327 for (i = 0; i < QUARANTINE_BATCHES; i++) { 328 if (qlist_empty(&global_quarantine[i])) 329 continue; 330 qlist_move_cache(&global_quarantine[i], &to_free, cache); 331 /* Scanning whole quarantine can take a while. */ 332 raw_spin_unlock_irqrestore(&quarantine_lock, flags); 333 cond_resched(); 334 raw_spin_lock_irqsave(&quarantine_lock, flags); 335 } 336 raw_spin_unlock_irqrestore(&quarantine_lock, flags); 337 338 qlist_free_all(&to_free, cache); 339 340 synchronize_srcu(&remove_cache_srcu); 341 } 342 343 static int kasan_cpu_online(unsigned int cpu) 344 { 345 this_cpu_ptr(&cpu_quarantine)->offline = false; 346 return 0; 347 } 348 349 static int kasan_cpu_offline(unsigned int cpu) 350 { 351 struct qlist_head *q; 352 353 q = this_cpu_ptr(&cpu_quarantine); 354 /* Ensure the ordering between the writing to q->offline and 355 * qlist_free_all. Otherwise, cpu_quarantine may be corrupted 356 * by interrupt. 357 */ 358 WRITE_ONCE(q->offline, true); 359 barrier(); 360 qlist_free_all(q, NULL); 361 return 0; 362 } 363 364 static int __init kasan_cpu_quarantine_init(void) 365 { 366 int ret = 0; 367 368 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online", 369 kasan_cpu_online, kasan_cpu_offline); 370 if (ret < 0) 371 pr_err("kasan cpu quarantine register failed [%d]\n", ret); 372 return ret; 373 } 374 late_initcall(kasan_cpu_quarantine_init); 375