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 * This program is free software; you can redistribute it and/or 11 * modify it under the terms of the GNU General Public License 12 * version 2 as published by the Free Software Foundation. 13 * 14 * This program is distributed in the hope that it will be useful, but 15 * WITHOUT ANY WARRANTY; without even the implied warranty of 16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 17 * General Public License for more details. 18 * 19 */ 20 21 #include <linux/gfp.h> 22 #include <linux/hash.h> 23 #include <linux/kernel.h> 24 #include <linux/mm.h> 25 #include <linux/percpu.h> 26 #include <linux/printk.h> 27 #include <linux/shrinker.h> 28 #include <linux/slab.h> 29 #include <linux/srcu.h> 30 #include <linux/string.h> 31 #include <linux/types.h> 32 33 #include "../slab.h" 34 #include "kasan.h" 35 36 /* Data structure and operations for quarantine queues. */ 37 38 /* 39 * Each queue is a signle-linked list, which also stores the total size of 40 * objects inside of it. 41 */ 42 struct qlist_head { 43 struct qlist_node *head; 44 struct qlist_node *tail; 45 size_t bytes; 46 }; 47 48 #define QLIST_INIT { NULL, NULL, 0 } 49 50 static bool qlist_empty(struct qlist_head *q) 51 { 52 return !q->head; 53 } 54 55 static void qlist_init(struct qlist_head *q) 56 { 57 q->head = q->tail = NULL; 58 q->bytes = 0; 59 } 60 61 static void qlist_put(struct qlist_head *q, struct qlist_node *qlink, 62 size_t size) 63 { 64 if (unlikely(qlist_empty(q))) 65 q->head = qlink; 66 else 67 q->tail->next = qlink; 68 q->tail = qlink; 69 qlink->next = NULL; 70 q->bytes += size; 71 } 72 73 static void qlist_move_all(struct qlist_head *from, struct qlist_head *to) 74 { 75 if (unlikely(qlist_empty(from))) 76 return; 77 78 if (qlist_empty(to)) { 79 *to = *from; 80 qlist_init(from); 81 return; 82 } 83 84 to->tail->next = from->head; 85 to->tail = from->tail; 86 to->bytes += from->bytes; 87 88 qlist_init(from); 89 } 90 91 #define QUARANTINE_PERCPU_SIZE (1 << 20) 92 #define QUARANTINE_BATCHES \ 93 (1024 > 4 * CONFIG_NR_CPUS ? 1024 : 4 * CONFIG_NR_CPUS) 94 95 /* 96 * The object quarantine consists of per-cpu queues and a global queue, 97 * guarded by quarantine_lock. 98 */ 99 static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine); 100 101 /* Round-robin FIFO array of batches. */ 102 static struct qlist_head global_quarantine[QUARANTINE_BATCHES]; 103 static int quarantine_head; 104 static int quarantine_tail; 105 /* Total size of all objects in global_quarantine across all batches. */ 106 static unsigned long quarantine_size; 107 static DEFINE_RAW_SPINLOCK(quarantine_lock); 108 DEFINE_STATIC_SRCU(remove_cache_srcu); 109 110 /* Maximum size of the global queue. */ 111 static unsigned long quarantine_max_size; 112 113 /* 114 * Target size of a batch in global_quarantine. 115 * Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM. 116 */ 117 static unsigned long quarantine_batch_size; 118 119 /* 120 * The fraction of physical memory the quarantine is allowed to occupy. 121 * Quarantine doesn't support memory shrinker with SLAB allocator, so we keep 122 * the ratio low to avoid OOM. 123 */ 124 #define QUARANTINE_FRACTION 32 125 126 static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink) 127 { 128 return virt_to_head_page(qlink)->slab_cache; 129 } 130 131 static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache) 132 { 133 struct kasan_free_meta *free_info = 134 container_of(qlink, struct kasan_free_meta, 135 quarantine_link); 136 137 return ((void *)free_info) - cache->kasan_info.free_meta_offset; 138 } 139 140 static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache) 141 { 142 void *object = qlink_to_object(qlink, cache); 143 unsigned long flags; 144 145 if (IS_ENABLED(CONFIG_SLAB)) 146 local_irq_save(flags); 147 148 *(u8 *)kasan_mem_to_shadow(object) = KASAN_KMALLOC_FREE; 149 ___cache_free(cache, object, _THIS_IP_); 150 151 if (IS_ENABLED(CONFIG_SLAB)) 152 local_irq_restore(flags); 153 } 154 155 static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache) 156 { 157 struct qlist_node *qlink; 158 159 if (unlikely(qlist_empty(q))) 160 return; 161 162 qlink = q->head; 163 while (qlink) { 164 struct kmem_cache *obj_cache = 165 cache ? cache : qlink_to_cache(qlink); 166 struct qlist_node *next = qlink->next; 167 168 qlink_free(qlink, obj_cache); 169 qlink = next; 170 } 171 qlist_init(q); 172 } 173 174 void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache) 175 { 176 unsigned long flags; 177 struct qlist_head *q; 178 struct qlist_head temp = QLIST_INIT; 179 180 /* 181 * Note: irq must be disabled until after we move the batch to the 182 * global quarantine. Otherwise quarantine_remove_cache() can miss 183 * some objects belonging to the cache if they are in our local temp 184 * list. quarantine_remove_cache() executes on_each_cpu() at the 185 * beginning which ensures that it either sees the objects in per-cpu 186 * lists or in the global quarantine. 187 */ 188 local_irq_save(flags); 189 190 q = this_cpu_ptr(&cpu_quarantine); 191 qlist_put(q, &info->quarantine_link, cache->size); 192 if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) { 193 qlist_move_all(q, &temp); 194 195 raw_spin_lock(&quarantine_lock); 196 WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes); 197 qlist_move_all(&temp, &global_quarantine[quarantine_tail]); 198 if (global_quarantine[quarantine_tail].bytes >= 199 READ_ONCE(quarantine_batch_size)) { 200 int new_tail; 201 202 new_tail = quarantine_tail + 1; 203 if (new_tail == QUARANTINE_BATCHES) 204 new_tail = 0; 205 if (new_tail != quarantine_head) 206 quarantine_tail = new_tail; 207 } 208 raw_spin_unlock(&quarantine_lock); 209 } 210 211 local_irq_restore(flags); 212 } 213 214 void quarantine_reduce(void) 215 { 216 size_t total_size, new_quarantine_size, percpu_quarantines; 217 unsigned long flags; 218 int srcu_idx; 219 struct qlist_head to_free = QLIST_INIT; 220 221 if (likely(READ_ONCE(quarantine_size) <= 222 READ_ONCE(quarantine_max_size))) 223 return; 224 225 /* 226 * srcu critical section ensures that quarantine_remove_cache() 227 * will not miss objects belonging to the cache while they are in our 228 * local to_free list. srcu is chosen because (1) it gives us private 229 * grace period domain that does not interfere with anything else, 230 * and (2) it allows synchronize_srcu() to return without waiting 231 * if there are no pending read critical sections (which is the 232 * expected case). 233 */ 234 srcu_idx = srcu_read_lock(&remove_cache_srcu); 235 raw_spin_lock_irqsave(&quarantine_lock, flags); 236 237 /* 238 * Update quarantine size in case of hotplug. Allocate a fraction of 239 * the installed memory to quarantine minus per-cpu queue limits. 240 */ 241 total_size = (totalram_pages() << PAGE_SHIFT) / 242 QUARANTINE_FRACTION; 243 percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus(); 244 new_quarantine_size = (total_size < percpu_quarantines) ? 245 0 : total_size - percpu_quarantines; 246 WRITE_ONCE(quarantine_max_size, new_quarantine_size); 247 /* Aim at consuming at most 1/2 of slots in quarantine. */ 248 WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE, 249 2 * total_size / QUARANTINE_BATCHES)); 250 251 if (likely(quarantine_size > quarantine_max_size)) { 252 qlist_move_all(&global_quarantine[quarantine_head], &to_free); 253 WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes); 254 quarantine_head++; 255 if (quarantine_head == QUARANTINE_BATCHES) 256 quarantine_head = 0; 257 } 258 259 raw_spin_unlock_irqrestore(&quarantine_lock, flags); 260 261 qlist_free_all(&to_free, NULL); 262 srcu_read_unlock(&remove_cache_srcu, srcu_idx); 263 } 264 265 static void qlist_move_cache(struct qlist_head *from, 266 struct qlist_head *to, 267 struct kmem_cache *cache) 268 { 269 struct qlist_node *curr; 270 271 if (unlikely(qlist_empty(from))) 272 return; 273 274 curr = from->head; 275 qlist_init(from); 276 while (curr) { 277 struct qlist_node *next = curr->next; 278 struct kmem_cache *obj_cache = qlink_to_cache(curr); 279 280 if (obj_cache == cache) 281 qlist_put(to, curr, obj_cache->size); 282 else 283 qlist_put(from, curr, obj_cache->size); 284 285 curr = next; 286 } 287 } 288 289 static void per_cpu_remove_cache(void *arg) 290 { 291 struct kmem_cache *cache = arg; 292 struct qlist_head to_free = QLIST_INIT; 293 struct qlist_head *q; 294 295 q = this_cpu_ptr(&cpu_quarantine); 296 qlist_move_cache(q, &to_free, cache); 297 qlist_free_all(&to_free, cache); 298 } 299 300 /* Free all quarantined objects belonging to cache. */ 301 void quarantine_remove_cache(struct kmem_cache *cache) 302 { 303 unsigned long flags, i; 304 struct qlist_head to_free = QLIST_INIT; 305 306 /* 307 * Must be careful to not miss any objects that are being moved from 308 * per-cpu list to the global quarantine in quarantine_put(), 309 * nor objects being freed in quarantine_reduce(). on_each_cpu() 310 * achieves the first goal, while synchronize_srcu() achieves the 311 * second. 312 */ 313 on_each_cpu(per_cpu_remove_cache, cache, 1); 314 315 raw_spin_lock_irqsave(&quarantine_lock, flags); 316 for (i = 0; i < QUARANTINE_BATCHES; i++) { 317 if (qlist_empty(&global_quarantine[i])) 318 continue; 319 qlist_move_cache(&global_quarantine[i], &to_free, cache); 320 /* Scanning whole quarantine can take a while. */ 321 raw_spin_unlock_irqrestore(&quarantine_lock, flags); 322 cond_resched(); 323 raw_spin_lock_irqsave(&quarantine_lock, flags); 324 } 325 raw_spin_unlock_irqrestore(&quarantine_lock, flags); 326 327 qlist_free_all(&to_free, cache); 328 329 synchronize_srcu(&remove_cache_srcu); 330 } 331