1 /* 2 * KASAN quarantine. 3 * 4 * Author: Alexander Potapenko <glider@google.com> 5 * Copyright (C) 2016 Google, Inc. 6 * 7 * Based on code by Dmitry Chernenkov. 8 * 9 * This program is free software; you can redistribute it and/or 10 * modify it under the terms of the GNU General Public License 11 * version 2 as published by the Free Software Foundation. 12 * 13 * This program is distributed in the hope that it will be useful, but 14 * WITHOUT ANY WARRANTY; without even the implied warranty of 15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 16 * General Public License for more details. 17 * 18 */ 19 20 #include <linux/gfp.h> 21 #include <linux/hash.h> 22 #include <linux/kernel.h> 23 #include <linux/mm.h> 24 #include <linux/percpu.h> 25 #include <linux/printk.h> 26 #include <linux/shrinker.h> 27 #include <linux/slab.h> 28 #include <linux/srcu.h> 29 #include <linux/string.h> 30 #include <linux/types.h> 31 32 #include "../slab.h" 33 #include "kasan.h" 34 35 /* Data structure and operations for quarantine queues. */ 36 37 /* 38 * Each queue is a signle-linked list, which also stores the total size of 39 * objects inside of it. 40 */ 41 struct qlist_head { 42 struct qlist_node *head; 43 struct qlist_node *tail; 44 size_t bytes; 45 }; 46 47 #define QLIST_INIT { NULL, NULL, 0 } 48 49 static bool qlist_empty(struct qlist_head *q) 50 { 51 return !q->head; 52 } 53 54 static void qlist_init(struct qlist_head *q) 55 { 56 q->head = q->tail = NULL; 57 q->bytes = 0; 58 } 59 60 static void qlist_put(struct qlist_head *q, struct qlist_node *qlink, 61 size_t size) 62 { 63 if (unlikely(qlist_empty(q))) 64 q->head = qlink; 65 else 66 q->tail->next = qlink; 67 q->tail = qlink; 68 qlink->next = NULL; 69 q->bytes += size; 70 } 71 72 static void qlist_move_all(struct qlist_head *from, struct qlist_head *to) 73 { 74 if (unlikely(qlist_empty(from))) 75 return; 76 77 if (qlist_empty(to)) { 78 *to = *from; 79 qlist_init(from); 80 return; 81 } 82 83 to->tail->next = from->head; 84 to->tail = from->tail; 85 to->bytes += from->bytes; 86 87 qlist_init(from); 88 } 89 90 #define QUARANTINE_PERCPU_SIZE (1 << 20) 91 #define QUARANTINE_BATCHES \ 92 (1024 > 4 * CONFIG_NR_CPUS ? 1024 : 4 * CONFIG_NR_CPUS) 93 94 /* 95 * The object quarantine consists of per-cpu queues and a global queue, 96 * guarded by quarantine_lock. 97 */ 98 static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine); 99 100 /* Round-robin FIFO array of batches. */ 101 static struct qlist_head global_quarantine[QUARANTINE_BATCHES]; 102 static int quarantine_head; 103 static int quarantine_tail; 104 /* Total size of all objects in global_quarantine across all batches. */ 105 static unsigned long quarantine_size; 106 static DEFINE_SPINLOCK(quarantine_lock); 107 DEFINE_STATIC_SRCU(remove_cache_srcu); 108 109 /* Maximum size of the global queue. */ 110 static unsigned long quarantine_max_size; 111 112 /* 113 * Target size of a batch in global_quarantine. 114 * Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM. 115 */ 116 static unsigned long quarantine_batch_size; 117 118 /* 119 * The fraction of physical memory the quarantine is allowed to occupy. 120 * Quarantine doesn't support memory shrinker with SLAB allocator, so we keep 121 * the ratio low to avoid OOM. 122 */ 123 #define QUARANTINE_FRACTION 32 124 125 static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink) 126 { 127 return virt_to_head_page(qlink)->slab_cache; 128 } 129 130 static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache) 131 { 132 struct kasan_free_meta *free_info = 133 container_of(qlink, struct kasan_free_meta, 134 quarantine_link); 135 136 return ((void *)free_info) - cache->kasan_info.free_meta_offset; 137 } 138 139 static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache) 140 { 141 void *object = qlink_to_object(qlink, cache); 142 unsigned long flags; 143 144 if (IS_ENABLED(CONFIG_SLAB)) 145 local_irq_save(flags); 146 147 ___cache_free(cache, object, _THIS_IP_); 148 149 if (IS_ENABLED(CONFIG_SLAB)) 150 local_irq_restore(flags); 151 } 152 153 static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache) 154 { 155 struct qlist_node *qlink; 156 157 if (unlikely(qlist_empty(q))) 158 return; 159 160 qlink = q->head; 161 while (qlink) { 162 struct kmem_cache *obj_cache = 163 cache ? cache : qlink_to_cache(qlink); 164 struct qlist_node *next = qlink->next; 165 166 qlink_free(qlink, obj_cache); 167 qlink = next; 168 } 169 qlist_init(q); 170 } 171 172 void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache) 173 { 174 unsigned long flags; 175 struct qlist_head *q; 176 struct qlist_head temp = QLIST_INIT; 177 178 /* 179 * Note: irq must be disabled until after we move the batch to the 180 * global quarantine. Otherwise quarantine_remove_cache() can miss 181 * some objects belonging to the cache if they are in our local temp 182 * list. quarantine_remove_cache() executes on_each_cpu() at the 183 * beginning which ensures that it either sees the objects in per-cpu 184 * lists or in the global quarantine. 185 */ 186 local_irq_save(flags); 187 188 q = this_cpu_ptr(&cpu_quarantine); 189 qlist_put(q, &info->quarantine_link, cache->size); 190 if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) { 191 qlist_move_all(q, &temp); 192 193 spin_lock(&quarantine_lock); 194 WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes); 195 qlist_move_all(&temp, &global_quarantine[quarantine_tail]); 196 if (global_quarantine[quarantine_tail].bytes >= 197 READ_ONCE(quarantine_batch_size)) { 198 int new_tail; 199 200 new_tail = quarantine_tail + 1; 201 if (new_tail == QUARANTINE_BATCHES) 202 new_tail = 0; 203 if (new_tail != quarantine_head) 204 quarantine_tail = new_tail; 205 } 206 spin_unlock(&quarantine_lock); 207 } 208 209 local_irq_restore(flags); 210 } 211 212 void quarantine_reduce(void) 213 { 214 size_t total_size, new_quarantine_size, percpu_quarantines; 215 unsigned long flags; 216 int srcu_idx; 217 struct qlist_head to_free = QLIST_INIT; 218 219 if (likely(READ_ONCE(quarantine_size) <= 220 READ_ONCE(quarantine_max_size))) 221 return; 222 223 /* 224 * srcu critical section ensures that quarantine_remove_cache() 225 * will not miss objects belonging to the cache while they are in our 226 * local to_free list. srcu is chosen because (1) it gives us private 227 * grace period domain that does not interfere with anything else, 228 * and (2) it allows synchronize_srcu() to return without waiting 229 * if there are no pending read critical sections (which is the 230 * expected case). 231 */ 232 srcu_idx = srcu_read_lock(&remove_cache_srcu); 233 spin_lock_irqsave(&quarantine_lock, flags); 234 235 /* 236 * Update quarantine size in case of hotplug. Allocate a fraction of 237 * the installed memory to quarantine minus per-cpu queue limits. 238 */ 239 total_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) / 240 QUARANTINE_FRACTION; 241 percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus(); 242 new_quarantine_size = (total_size < percpu_quarantines) ? 243 0 : total_size - percpu_quarantines; 244 WRITE_ONCE(quarantine_max_size, new_quarantine_size); 245 /* Aim at consuming at most 1/2 of slots in quarantine. */ 246 WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE, 247 2 * total_size / QUARANTINE_BATCHES)); 248 249 if (likely(quarantine_size > quarantine_max_size)) { 250 qlist_move_all(&global_quarantine[quarantine_head], &to_free); 251 WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes); 252 quarantine_head++; 253 if (quarantine_head == QUARANTINE_BATCHES) 254 quarantine_head = 0; 255 } 256 257 spin_unlock_irqrestore(&quarantine_lock, flags); 258 259 qlist_free_all(&to_free, NULL); 260 srcu_read_unlock(&remove_cache_srcu, srcu_idx); 261 } 262 263 static void qlist_move_cache(struct qlist_head *from, 264 struct qlist_head *to, 265 struct kmem_cache *cache) 266 { 267 struct qlist_node *curr; 268 269 if (unlikely(qlist_empty(from))) 270 return; 271 272 curr = from->head; 273 qlist_init(from); 274 while (curr) { 275 struct qlist_node *next = curr->next; 276 struct kmem_cache *obj_cache = qlink_to_cache(curr); 277 278 if (obj_cache == cache) 279 qlist_put(to, curr, obj_cache->size); 280 else 281 qlist_put(from, curr, obj_cache->size); 282 283 curr = next; 284 } 285 } 286 287 static void per_cpu_remove_cache(void *arg) 288 { 289 struct kmem_cache *cache = arg; 290 struct qlist_head to_free = QLIST_INIT; 291 struct qlist_head *q; 292 293 q = this_cpu_ptr(&cpu_quarantine); 294 qlist_move_cache(q, &to_free, cache); 295 qlist_free_all(&to_free, cache); 296 } 297 298 /* Free all quarantined objects belonging to cache. */ 299 void quarantine_remove_cache(struct kmem_cache *cache) 300 { 301 unsigned long flags, i; 302 struct qlist_head to_free = QLIST_INIT; 303 304 /* 305 * Must be careful to not miss any objects that are being moved from 306 * per-cpu list to the global quarantine in quarantine_put(), 307 * nor objects being freed in quarantine_reduce(). on_each_cpu() 308 * achieves the first goal, while synchronize_srcu() achieves the 309 * second. 310 */ 311 on_each_cpu(per_cpu_remove_cache, cache, 1); 312 313 spin_lock_irqsave(&quarantine_lock, flags); 314 for (i = 0; i < QUARANTINE_BATCHES; i++) { 315 if (qlist_empty(&global_quarantine[i])) 316 continue; 317 qlist_move_cache(&global_quarantine[i], &to_free, cache); 318 /* Scanning whole quarantine can take a while. */ 319 spin_unlock_irqrestore(&quarantine_lock, flags); 320 cond_resched(); 321 spin_lock_irqsave(&quarantine_lock, flags); 322 } 323 spin_unlock_irqrestore(&quarantine_lock, flags); 324 325 qlist_free_all(&to_free, cache); 326 327 synchronize_srcu(&remove_cache_srcu); 328 } 329