1 // SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) 2 /* 3 * Copyright (C) 2017-2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. 4 * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005 5 * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All rights reserved. 6 * 7 * This driver produces cryptographically secure pseudorandom data. It is divided 8 * into roughly six sections, each with a section header: 9 * 10 * - Initialization and readiness waiting. 11 * - Fast key erasure RNG, the "crng". 12 * - Entropy accumulation and extraction routines. 13 * - Entropy collection routines. 14 * - Userspace reader/writer interfaces. 15 * - Sysctl interface. 16 * 17 * The high level overview is that there is one input pool, into which 18 * various pieces of data are hashed. Prior to initialization, some of that 19 * data is then "credited" as having a certain number of bits of entropy. 20 * When enough bits of entropy are available, the hash is finalized and 21 * handed as a key to a stream cipher that expands it indefinitely for 22 * various consumers. This key is periodically refreshed as the various 23 * entropy collectors, described below, add data to the input pool. 24 */ 25 26 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 27 28 #include <linux/utsname.h> 29 #include <linux/module.h> 30 #include <linux/kernel.h> 31 #include <linux/major.h> 32 #include <linux/string.h> 33 #include <linux/fcntl.h> 34 #include <linux/slab.h> 35 #include <linux/random.h> 36 #include <linux/poll.h> 37 #include <linux/init.h> 38 #include <linux/fs.h> 39 #include <linux/blkdev.h> 40 #include <linux/interrupt.h> 41 #include <linux/mm.h> 42 #include <linux/nodemask.h> 43 #include <linux/spinlock.h> 44 #include <linux/kthread.h> 45 #include <linux/percpu.h> 46 #include <linux/ptrace.h> 47 #include <linux/workqueue.h> 48 #include <linux/irq.h> 49 #include <linux/ratelimit.h> 50 #include <linux/syscalls.h> 51 #include <linux/completion.h> 52 #include <linux/uuid.h> 53 #include <linux/uaccess.h> 54 #include <linux/suspend.h> 55 #include <linux/siphash.h> 56 #include <crypto/chacha.h> 57 #include <crypto/blake2s.h> 58 #include <asm/processor.h> 59 #include <asm/irq.h> 60 #include <asm/irq_regs.h> 61 #include <asm/io.h> 62 63 /********************************************************************* 64 * 65 * Initialization and readiness waiting. 66 * 67 * Much of the RNG infrastructure is devoted to various dependencies 68 * being able to wait until the RNG has collected enough entropy and 69 * is ready for safe consumption. 70 * 71 *********************************************************************/ 72 73 /* 74 * crng_init is protected by base_crng->lock, and only increases 75 * its value (from empty->early->ready). 76 */ 77 static enum { 78 CRNG_EMPTY = 0, /* Little to no entropy collected */ 79 CRNG_EARLY = 1, /* At least POOL_EARLY_BITS collected */ 80 CRNG_READY = 2 /* Fully initialized with POOL_READY_BITS collected */ 81 } crng_init __read_mostly = CRNG_EMPTY; 82 static DEFINE_STATIC_KEY_FALSE(crng_is_ready); 83 #define crng_ready() (static_branch_likely(&crng_is_ready) || crng_init >= CRNG_READY) 84 /* Various types of waiters for crng_init->CRNG_READY transition. */ 85 static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); 86 static struct fasync_struct *fasync; 87 88 /* Control how we warn userspace. */ 89 static struct ratelimit_state urandom_warning = 90 RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE); 91 static int ratelimit_disable __read_mostly = 92 IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM); 93 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644); 94 MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression"); 95 96 /* 97 * Returns whether or not the input pool has been seeded and thus guaranteed 98 * to supply cryptographically secure random numbers. This applies to: the 99 * /dev/urandom device, the get_random_bytes function, and the get_random_{u8, 100 * u16,u32,u64,long} family of functions. 101 * 102 * Returns: true if the input pool has been seeded. 103 * false if the input pool has not been seeded. 104 */ 105 bool rng_is_initialized(void) 106 { 107 return crng_ready(); 108 } 109 EXPORT_SYMBOL(rng_is_initialized); 110 111 static void __cold crng_set_ready(struct work_struct *work) 112 { 113 static_branch_enable(&crng_is_ready); 114 } 115 116 /* Used by wait_for_random_bytes(), and considered an entropy collector, below. */ 117 static void try_to_generate_entropy(void); 118 119 /* 120 * Wait for the input pool to be seeded and thus guaranteed to supply 121 * cryptographically secure random numbers. This applies to: the /dev/urandom 122 * device, the get_random_bytes function, and the get_random_{u8,u16,u32,u64, 123 * int,long} family of functions. Using any of these functions without first 124 * calling this function forfeits the guarantee of security. 125 * 126 * Returns: 0 if the input pool has been seeded. 127 * -ERESTARTSYS if the function was interrupted by a signal. 128 */ 129 int wait_for_random_bytes(void) 130 { 131 while (!crng_ready()) { 132 int ret; 133 134 try_to_generate_entropy(); 135 ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ); 136 if (ret) 137 return ret > 0 ? 0 : ret; 138 } 139 return 0; 140 } 141 EXPORT_SYMBOL(wait_for_random_bytes); 142 143 #define warn_unseeded_randomness() \ 144 if (IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) && !crng_ready()) \ 145 printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", \ 146 __func__, (void *)_RET_IP_, crng_init) 147 148 149 /********************************************************************* 150 * 151 * Fast key erasure RNG, the "crng". 152 * 153 * These functions expand entropy from the entropy extractor into 154 * long streams for external consumption using the "fast key erasure" 155 * RNG described at <https://blog.cr.yp.to/20170723-random.html>. 156 * 157 * There are a few exported interfaces for use by other drivers: 158 * 159 * void get_random_bytes(void *buf, size_t len) 160 * u8 get_random_u8() 161 * u16 get_random_u16() 162 * u32 get_random_u32() 163 * u64 get_random_u64() 164 * unsigned long get_random_long() 165 * 166 * These interfaces will return the requested number of random bytes 167 * into the given buffer or as a return value. This is equivalent to 168 * a read from /dev/urandom. The u8, u16, u32, u64, long family of 169 * functions may be higher performance for one-off random integers, 170 * because they do a bit of buffering and do not invoke reseeding 171 * until the buffer is emptied. 172 * 173 *********************************************************************/ 174 175 enum { 176 CRNG_RESEED_START_INTERVAL = HZ, 177 CRNG_RESEED_INTERVAL = 60 * HZ 178 }; 179 180 static struct { 181 u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long)); 182 unsigned long birth; 183 unsigned long generation; 184 spinlock_t lock; 185 } base_crng = { 186 .lock = __SPIN_LOCK_UNLOCKED(base_crng.lock) 187 }; 188 189 struct crng { 190 u8 key[CHACHA_KEY_SIZE]; 191 unsigned long generation; 192 local_lock_t lock; 193 }; 194 195 static DEFINE_PER_CPU(struct crng, crngs) = { 196 .generation = ULONG_MAX, 197 .lock = INIT_LOCAL_LOCK(crngs.lock), 198 }; 199 200 /* Used by crng_reseed() and crng_make_state() to extract a new seed from the input pool. */ 201 static void extract_entropy(void *buf, size_t len); 202 203 /* This extracts a new crng key from the input pool. */ 204 static void crng_reseed(void) 205 { 206 unsigned long flags; 207 unsigned long next_gen; 208 u8 key[CHACHA_KEY_SIZE]; 209 210 extract_entropy(key, sizeof(key)); 211 212 /* 213 * We copy the new key into the base_crng, overwriting the old one, 214 * and update the generation counter. We avoid hitting ULONG_MAX, 215 * because the per-cpu crngs are initialized to ULONG_MAX, so this 216 * forces new CPUs that come online to always initialize. 217 */ 218 spin_lock_irqsave(&base_crng.lock, flags); 219 memcpy(base_crng.key, key, sizeof(base_crng.key)); 220 next_gen = base_crng.generation + 1; 221 if (next_gen == ULONG_MAX) 222 ++next_gen; 223 WRITE_ONCE(base_crng.generation, next_gen); 224 WRITE_ONCE(base_crng.birth, jiffies); 225 if (!static_branch_likely(&crng_is_ready)) 226 crng_init = CRNG_READY; 227 spin_unlock_irqrestore(&base_crng.lock, flags); 228 memzero_explicit(key, sizeof(key)); 229 } 230 231 /* 232 * This generates a ChaCha block using the provided key, and then 233 * immediately overwrites that key with half the block. It returns 234 * the resultant ChaCha state to the user, along with the second 235 * half of the block containing 32 bytes of random data that may 236 * be used; random_data_len may not be greater than 32. 237 * 238 * The returned ChaCha state contains within it a copy of the old 239 * key value, at index 4, so the state should always be zeroed out 240 * immediately after using in order to maintain forward secrecy. 241 * If the state cannot be erased in a timely manner, then it is 242 * safer to set the random_data parameter to &chacha_state[4] so 243 * that this function overwrites it before returning. 244 */ 245 static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE], 246 u32 chacha_state[CHACHA_STATE_WORDS], 247 u8 *random_data, size_t random_data_len) 248 { 249 u8 first_block[CHACHA_BLOCK_SIZE]; 250 251 BUG_ON(random_data_len > 32); 252 253 chacha_init_consts(chacha_state); 254 memcpy(&chacha_state[4], key, CHACHA_KEY_SIZE); 255 memset(&chacha_state[12], 0, sizeof(u32) * 4); 256 chacha20_block(chacha_state, first_block); 257 258 memcpy(key, first_block, CHACHA_KEY_SIZE); 259 memcpy(random_data, first_block + CHACHA_KEY_SIZE, random_data_len); 260 memzero_explicit(first_block, sizeof(first_block)); 261 } 262 263 /* 264 * Return the interval until the next reseeding, which is normally 265 * CRNG_RESEED_INTERVAL, but during early boot, it is at an interval 266 * proportional to the uptime. 267 */ 268 static unsigned int crng_reseed_interval(void) 269 { 270 static bool early_boot = true; 271 272 if (unlikely(READ_ONCE(early_boot))) { 273 time64_t uptime = ktime_get_seconds(); 274 if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2) 275 WRITE_ONCE(early_boot, false); 276 else 277 return max_t(unsigned int, CRNG_RESEED_START_INTERVAL, 278 (unsigned int)uptime / 2 * HZ); 279 } 280 return CRNG_RESEED_INTERVAL; 281 } 282 283 /* 284 * This function returns a ChaCha state that you may use for generating 285 * random data. It also returns up to 32 bytes on its own of random data 286 * that may be used; random_data_len may not be greater than 32. 287 */ 288 static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], 289 u8 *random_data, size_t random_data_len) 290 { 291 unsigned long flags; 292 struct crng *crng; 293 294 BUG_ON(random_data_len > 32); 295 296 /* 297 * For the fast path, we check whether we're ready, unlocked first, and 298 * then re-check once locked later. In the case where we're really not 299 * ready, we do fast key erasure with the base_crng directly, extracting 300 * when crng_init is CRNG_EMPTY. 301 */ 302 if (!crng_ready()) { 303 bool ready; 304 305 spin_lock_irqsave(&base_crng.lock, flags); 306 ready = crng_ready(); 307 if (!ready) { 308 if (crng_init == CRNG_EMPTY) 309 extract_entropy(base_crng.key, sizeof(base_crng.key)); 310 crng_fast_key_erasure(base_crng.key, chacha_state, 311 random_data, random_data_len); 312 } 313 spin_unlock_irqrestore(&base_crng.lock, flags); 314 if (!ready) 315 return; 316 } 317 318 /* 319 * If the base_crng is old enough, we reseed, which in turn bumps the 320 * generation counter that we check below. 321 */ 322 if (unlikely(time_is_before_jiffies(READ_ONCE(base_crng.birth) + crng_reseed_interval()))) 323 crng_reseed(); 324 325 local_lock_irqsave(&crngs.lock, flags); 326 crng = raw_cpu_ptr(&crngs); 327 328 /* 329 * If our per-cpu crng is older than the base_crng, then it means 330 * somebody reseeded the base_crng. In that case, we do fast key 331 * erasure on the base_crng, and use its output as the new key 332 * for our per-cpu crng. This brings us up to date with base_crng. 333 */ 334 if (unlikely(crng->generation != READ_ONCE(base_crng.generation))) { 335 spin_lock(&base_crng.lock); 336 crng_fast_key_erasure(base_crng.key, chacha_state, 337 crng->key, sizeof(crng->key)); 338 crng->generation = base_crng.generation; 339 spin_unlock(&base_crng.lock); 340 } 341 342 /* 343 * Finally, when we've made it this far, our per-cpu crng has an up 344 * to date key, and we can do fast key erasure with it to produce 345 * some random data and a ChaCha state for the caller. All other 346 * branches of this function are "unlikely", so most of the time we 347 * should wind up here immediately. 348 */ 349 crng_fast_key_erasure(crng->key, chacha_state, random_data, random_data_len); 350 local_unlock_irqrestore(&crngs.lock, flags); 351 } 352 353 static void _get_random_bytes(void *buf, size_t len) 354 { 355 u32 chacha_state[CHACHA_STATE_WORDS]; 356 u8 tmp[CHACHA_BLOCK_SIZE]; 357 size_t first_block_len; 358 359 if (!len) 360 return; 361 362 first_block_len = min_t(size_t, 32, len); 363 crng_make_state(chacha_state, buf, first_block_len); 364 len -= first_block_len; 365 buf += first_block_len; 366 367 while (len) { 368 if (len < CHACHA_BLOCK_SIZE) { 369 chacha20_block(chacha_state, tmp); 370 memcpy(buf, tmp, len); 371 memzero_explicit(tmp, sizeof(tmp)); 372 break; 373 } 374 375 chacha20_block(chacha_state, buf); 376 if (unlikely(chacha_state[12] == 0)) 377 ++chacha_state[13]; 378 len -= CHACHA_BLOCK_SIZE; 379 buf += CHACHA_BLOCK_SIZE; 380 } 381 382 memzero_explicit(chacha_state, sizeof(chacha_state)); 383 } 384 385 /* 386 * This function is the exported kernel interface. It returns some number of 387 * good random numbers, suitable for key generation, seeding TCP sequence 388 * numbers, etc. In order to ensure that the randomness returned by this 389 * function is okay, the function wait_for_random_bytes() should be called and 390 * return 0 at least once at any point prior. 391 */ 392 void get_random_bytes(void *buf, size_t len) 393 { 394 warn_unseeded_randomness(); 395 _get_random_bytes(buf, len); 396 } 397 EXPORT_SYMBOL(get_random_bytes); 398 399 static ssize_t get_random_bytes_user(struct iov_iter *iter) 400 { 401 u32 chacha_state[CHACHA_STATE_WORDS]; 402 u8 block[CHACHA_BLOCK_SIZE]; 403 size_t ret = 0, copied; 404 405 if (unlikely(!iov_iter_count(iter))) 406 return 0; 407 408 /* 409 * Immediately overwrite the ChaCha key at index 4 with random 410 * bytes, in case userspace causes copy_to_iter() below to sleep 411 * forever, so that we still retain forward secrecy in that case. 412 */ 413 crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA_KEY_SIZE); 414 /* 415 * However, if we're doing a read of len <= 32, we don't need to 416 * use chacha_state after, so we can simply return those bytes to 417 * the user directly. 418 */ 419 if (iov_iter_count(iter) <= CHACHA_KEY_SIZE) { 420 ret = copy_to_iter(&chacha_state[4], CHACHA_KEY_SIZE, iter); 421 goto out_zero_chacha; 422 } 423 424 for (;;) { 425 chacha20_block(chacha_state, block); 426 if (unlikely(chacha_state[12] == 0)) 427 ++chacha_state[13]; 428 429 copied = copy_to_iter(block, sizeof(block), iter); 430 ret += copied; 431 if (!iov_iter_count(iter) || copied != sizeof(block)) 432 break; 433 434 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0); 435 if (ret % PAGE_SIZE == 0) { 436 if (signal_pending(current)) 437 break; 438 cond_resched(); 439 } 440 } 441 442 memzero_explicit(block, sizeof(block)); 443 out_zero_chacha: 444 memzero_explicit(chacha_state, sizeof(chacha_state)); 445 return ret ? ret : -EFAULT; 446 } 447 448 /* 449 * Batched entropy returns random integers. The quality of the random 450 * number is good as /dev/urandom. In order to ensure that the randomness 451 * provided by this function is okay, the function wait_for_random_bytes() 452 * should be called and return 0 at least once at any point prior. 453 */ 454 455 #define DEFINE_BATCHED_ENTROPY(type) \ 456 struct batch_ ##type { \ 457 /* \ 458 * We make this 1.5x a ChaCha block, so that we get the \ 459 * remaining 32 bytes from fast key erasure, plus one full \ 460 * block from the detached ChaCha state. We can increase \ 461 * the size of this later if needed so long as we keep the \ 462 * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE. \ 463 */ \ 464 type entropy[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(type))]; \ 465 local_lock_t lock; \ 466 unsigned long generation; \ 467 unsigned int position; \ 468 }; \ 469 \ 470 static DEFINE_PER_CPU(struct batch_ ##type, batched_entropy_ ##type) = { \ 471 .lock = INIT_LOCAL_LOCK(batched_entropy_ ##type.lock), \ 472 .position = UINT_MAX \ 473 }; \ 474 \ 475 type get_random_ ##type(void) \ 476 { \ 477 type ret; \ 478 unsigned long flags; \ 479 struct batch_ ##type *batch; \ 480 unsigned long next_gen; \ 481 \ 482 warn_unseeded_randomness(); \ 483 \ 484 if (!crng_ready()) { \ 485 _get_random_bytes(&ret, sizeof(ret)); \ 486 return ret; \ 487 } \ 488 \ 489 local_lock_irqsave(&batched_entropy_ ##type.lock, flags); \ 490 batch = raw_cpu_ptr(&batched_entropy_##type); \ 491 \ 492 next_gen = READ_ONCE(base_crng.generation); \ 493 if (batch->position >= ARRAY_SIZE(batch->entropy) || \ 494 next_gen != batch->generation) { \ 495 _get_random_bytes(batch->entropy, sizeof(batch->entropy)); \ 496 batch->position = 0; \ 497 batch->generation = next_gen; \ 498 } \ 499 \ 500 ret = batch->entropy[batch->position]; \ 501 batch->entropy[batch->position] = 0; \ 502 ++batch->position; \ 503 local_unlock_irqrestore(&batched_entropy_ ##type.lock, flags); \ 504 return ret; \ 505 } \ 506 EXPORT_SYMBOL(get_random_ ##type); 507 508 DEFINE_BATCHED_ENTROPY(u8) 509 DEFINE_BATCHED_ENTROPY(u16) 510 DEFINE_BATCHED_ENTROPY(u32) 511 DEFINE_BATCHED_ENTROPY(u64) 512 513 #ifdef CONFIG_SMP 514 /* 515 * This function is called when the CPU is coming up, with entry 516 * CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP. 517 */ 518 int __cold random_prepare_cpu(unsigned int cpu) 519 { 520 /* 521 * When the cpu comes back online, immediately invalidate both 522 * the per-cpu crng and all batches, so that we serve fresh 523 * randomness. 524 */ 525 per_cpu_ptr(&crngs, cpu)->generation = ULONG_MAX; 526 per_cpu_ptr(&batched_entropy_u8, cpu)->position = UINT_MAX; 527 per_cpu_ptr(&batched_entropy_u16, cpu)->position = UINT_MAX; 528 per_cpu_ptr(&batched_entropy_u32, cpu)->position = UINT_MAX; 529 per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX; 530 return 0; 531 } 532 #endif 533 534 535 /********************************************************************** 536 * 537 * Entropy accumulation and extraction routines. 538 * 539 * Callers may add entropy via: 540 * 541 * static void mix_pool_bytes(const void *buf, size_t len) 542 * 543 * After which, if added entropy should be credited: 544 * 545 * static void credit_init_bits(size_t bits) 546 * 547 * Finally, extract entropy via: 548 * 549 * static void extract_entropy(void *buf, size_t len) 550 * 551 **********************************************************************/ 552 553 enum { 554 POOL_BITS = BLAKE2S_HASH_SIZE * 8, 555 POOL_READY_BITS = POOL_BITS, /* When crng_init->CRNG_READY */ 556 POOL_EARLY_BITS = POOL_READY_BITS / 2 /* When crng_init->CRNG_EARLY */ 557 }; 558 559 static struct { 560 struct blake2s_state hash; 561 spinlock_t lock; 562 unsigned int init_bits; 563 } input_pool = { 564 .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE), 565 BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4, 566 BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 }, 567 .hash.outlen = BLAKE2S_HASH_SIZE, 568 .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock), 569 }; 570 571 static void _mix_pool_bytes(const void *buf, size_t len) 572 { 573 blake2s_update(&input_pool.hash, buf, len); 574 } 575 576 /* 577 * This function adds bytes into the input pool. It does not 578 * update the initialization bit counter; the caller should call 579 * credit_init_bits if this is appropriate. 580 */ 581 static void mix_pool_bytes(const void *buf, size_t len) 582 { 583 unsigned long flags; 584 585 spin_lock_irqsave(&input_pool.lock, flags); 586 _mix_pool_bytes(buf, len); 587 spin_unlock_irqrestore(&input_pool.lock, flags); 588 } 589 590 /* 591 * This is an HKDF-like construction for using the hashed collected entropy 592 * as a PRF key, that's then expanded block-by-block. 593 */ 594 static void extract_entropy(void *buf, size_t len) 595 { 596 unsigned long flags; 597 u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE]; 598 struct { 599 unsigned long rdseed[32 / sizeof(long)]; 600 size_t counter; 601 } block; 602 size_t i, longs; 603 604 for (i = 0; i < ARRAY_SIZE(block.rdseed);) { 605 longs = arch_get_random_seed_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i); 606 if (longs) { 607 i += longs; 608 continue; 609 } 610 longs = arch_get_random_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i); 611 if (longs) { 612 i += longs; 613 continue; 614 } 615 block.rdseed[i++] = random_get_entropy(); 616 } 617 618 spin_lock_irqsave(&input_pool.lock, flags); 619 620 /* seed = HASHPRF(last_key, entropy_input) */ 621 blake2s_final(&input_pool.hash, seed); 622 623 /* next_key = HASHPRF(seed, RDSEED || 0) */ 624 block.counter = 0; 625 blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed)); 626 blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key)); 627 628 spin_unlock_irqrestore(&input_pool.lock, flags); 629 memzero_explicit(next_key, sizeof(next_key)); 630 631 while (len) { 632 i = min_t(size_t, len, BLAKE2S_HASH_SIZE); 633 /* output = HASHPRF(seed, RDSEED || ++counter) */ 634 ++block.counter; 635 blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed)); 636 len -= i; 637 buf += i; 638 } 639 640 memzero_explicit(seed, sizeof(seed)); 641 memzero_explicit(&block, sizeof(block)); 642 } 643 644 #define credit_init_bits(bits) if (!crng_ready()) _credit_init_bits(bits) 645 646 static void __cold _credit_init_bits(size_t bits) 647 { 648 static struct execute_work set_ready; 649 unsigned int new, orig, add; 650 unsigned long flags; 651 652 if (!bits) 653 return; 654 655 add = min_t(size_t, bits, POOL_BITS); 656 657 orig = READ_ONCE(input_pool.init_bits); 658 do { 659 new = min_t(unsigned int, POOL_BITS, orig + add); 660 } while (!try_cmpxchg(&input_pool.init_bits, &orig, new)); 661 662 if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) { 663 crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */ 664 if (static_key_initialized) 665 execute_in_process_context(crng_set_ready, &set_ready); 666 wake_up_interruptible(&crng_init_wait); 667 kill_fasync(&fasync, SIGIO, POLL_IN); 668 pr_notice("crng init done\n"); 669 if (urandom_warning.missed) 670 pr_notice("%d urandom warning(s) missed due to ratelimiting\n", 671 urandom_warning.missed); 672 } else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) { 673 spin_lock_irqsave(&base_crng.lock, flags); 674 /* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */ 675 if (crng_init == CRNG_EMPTY) { 676 extract_entropy(base_crng.key, sizeof(base_crng.key)); 677 crng_init = CRNG_EARLY; 678 } 679 spin_unlock_irqrestore(&base_crng.lock, flags); 680 } 681 } 682 683 684 /********************************************************************** 685 * 686 * Entropy collection routines. 687 * 688 * The following exported functions are used for pushing entropy into 689 * the above entropy accumulation routines: 690 * 691 * void add_device_randomness(const void *buf, size_t len); 692 * void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy); 693 * void add_bootloader_randomness(const void *buf, size_t len); 694 * void add_vmfork_randomness(const void *unique_vm_id, size_t len); 695 * void add_interrupt_randomness(int irq); 696 * void add_input_randomness(unsigned int type, unsigned int code, unsigned int value); 697 * void add_disk_randomness(struct gendisk *disk); 698 * 699 * add_device_randomness() adds data to the input pool that 700 * is likely to differ between two devices (or possibly even per boot). 701 * This would be things like MAC addresses or serial numbers, or the 702 * read-out of the RTC. This does *not* credit any actual entropy to 703 * the pool, but it initializes the pool to different values for devices 704 * that might otherwise be identical and have very little entropy 705 * available to them (particularly common in the embedded world). 706 * 707 * add_hwgenerator_randomness() is for true hardware RNGs, and will credit 708 * entropy as specified by the caller. If the entropy pool is full it will 709 * block until more entropy is needed. 710 * 711 * add_bootloader_randomness() is called by bootloader drivers, such as EFI 712 * and device tree, and credits its input depending on whether or not the 713 * configuration option CONFIG_RANDOM_TRUST_BOOTLOADER is set. 714 * 715 * add_vmfork_randomness() adds a unique (but not necessarily secret) ID 716 * representing the current instance of a VM to the pool, without crediting, 717 * and then force-reseeds the crng so that it takes effect immediately. 718 * 719 * add_interrupt_randomness() uses the interrupt timing as random 720 * inputs to the entropy pool. Using the cycle counters and the irq source 721 * as inputs, it feeds the input pool roughly once a second or after 64 722 * interrupts, crediting 1 bit of entropy for whichever comes first. 723 * 724 * add_input_randomness() uses the input layer interrupt timing, as well 725 * as the event type information from the hardware. 726 * 727 * add_disk_randomness() uses what amounts to the seek time of block 728 * layer request events, on a per-disk_devt basis, as input to the 729 * entropy pool. Note that high-speed solid state drives with very low 730 * seek times do not make for good sources of entropy, as their seek 731 * times are usually fairly consistent. 732 * 733 * The last two routines try to estimate how many bits of entropy 734 * to credit. They do this by keeping track of the first and second 735 * order deltas of the event timings. 736 * 737 **********************************************************************/ 738 739 static bool trust_cpu __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); 740 static bool trust_bootloader __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER); 741 static int __init parse_trust_cpu(char *arg) 742 { 743 return kstrtobool(arg, &trust_cpu); 744 } 745 static int __init parse_trust_bootloader(char *arg) 746 { 747 return kstrtobool(arg, &trust_bootloader); 748 } 749 early_param("random.trust_cpu", parse_trust_cpu); 750 early_param("random.trust_bootloader", parse_trust_bootloader); 751 752 static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data) 753 { 754 unsigned long flags, entropy = random_get_entropy(); 755 756 /* 757 * Encode a representation of how long the system has been suspended, 758 * in a way that is distinct from prior system suspends. 759 */ 760 ktime_t stamps[] = { ktime_get(), ktime_get_boottime(), ktime_get_real() }; 761 762 spin_lock_irqsave(&input_pool.lock, flags); 763 _mix_pool_bytes(&action, sizeof(action)); 764 _mix_pool_bytes(stamps, sizeof(stamps)); 765 _mix_pool_bytes(&entropy, sizeof(entropy)); 766 spin_unlock_irqrestore(&input_pool.lock, flags); 767 768 if (crng_ready() && (action == PM_RESTORE_PREPARE || 769 (action == PM_POST_SUSPEND && !IS_ENABLED(CONFIG_PM_AUTOSLEEP) && 770 !IS_ENABLED(CONFIG_PM_USERSPACE_AUTOSLEEP)))) { 771 crng_reseed(); 772 pr_notice("crng reseeded on system resumption\n"); 773 } 774 return 0; 775 } 776 777 static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification }; 778 779 /* 780 * This is called extremely early, before time keeping functionality is 781 * available, but arch randomness is. Interrupts are not yet enabled. 782 */ 783 void __init random_init_early(const char *command_line) 784 { 785 unsigned long entropy[BLAKE2S_BLOCK_SIZE / sizeof(long)]; 786 size_t i, longs, arch_bits; 787 788 #if defined(LATENT_ENTROPY_PLUGIN) 789 static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy; 790 _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed)); 791 #endif 792 793 for (i = 0, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) { 794 longs = arch_get_random_seed_longs(entropy, ARRAY_SIZE(entropy) - i); 795 if (longs) { 796 _mix_pool_bytes(entropy, sizeof(*entropy) * longs); 797 i += longs; 798 continue; 799 } 800 longs = arch_get_random_longs(entropy, ARRAY_SIZE(entropy) - i); 801 if (longs) { 802 _mix_pool_bytes(entropy, sizeof(*entropy) * longs); 803 i += longs; 804 continue; 805 } 806 arch_bits -= sizeof(*entropy) * 8; 807 ++i; 808 } 809 810 _mix_pool_bytes(init_utsname(), sizeof(*(init_utsname()))); 811 _mix_pool_bytes(command_line, strlen(command_line)); 812 813 /* Reseed if already seeded by earlier phases. */ 814 if (crng_ready()) 815 crng_reseed(); 816 else if (trust_cpu) 817 _credit_init_bits(arch_bits); 818 } 819 820 /* 821 * This is called a little bit after the prior function, and now there is 822 * access to timestamps counters. Interrupts are not yet enabled. 823 */ 824 void __init random_init(void) 825 { 826 unsigned long entropy = random_get_entropy(); 827 ktime_t now = ktime_get_real(); 828 829 _mix_pool_bytes(&now, sizeof(now)); 830 _mix_pool_bytes(&entropy, sizeof(entropy)); 831 add_latent_entropy(); 832 833 /* 834 * If we were initialized by the cpu or bootloader before jump labels 835 * are initialized, then we should enable the static branch here, where 836 * it's guaranteed that jump labels have been initialized. 837 */ 838 if (!static_branch_likely(&crng_is_ready) && crng_init >= CRNG_READY) 839 crng_set_ready(NULL); 840 841 /* Reseed if already seeded by earlier phases. */ 842 if (crng_ready()) 843 crng_reseed(); 844 845 WARN_ON(register_pm_notifier(&pm_notifier)); 846 847 WARN(!entropy, "Missing cycle counter and fallback timer; RNG " 848 "entropy collection will consequently suffer."); 849 } 850 851 /* 852 * Add device- or boot-specific data to the input pool to help 853 * initialize it. 854 * 855 * None of this adds any entropy; it is meant to avoid the problem of 856 * the entropy pool having similar initial state across largely 857 * identical devices. 858 */ 859 void add_device_randomness(const void *buf, size_t len) 860 { 861 unsigned long entropy = random_get_entropy(); 862 unsigned long flags; 863 864 spin_lock_irqsave(&input_pool.lock, flags); 865 _mix_pool_bytes(&entropy, sizeof(entropy)); 866 _mix_pool_bytes(buf, len); 867 spin_unlock_irqrestore(&input_pool.lock, flags); 868 } 869 EXPORT_SYMBOL(add_device_randomness); 870 871 /* 872 * Interface for in-kernel drivers of true hardware RNGs. 873 * Those devices may produce endless random bits and will be throttled 874 * when our pool is full. 875 */ 876 void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy) 877 { 878 mix_pool_bytes(buf, len); 879 credit_init_bits(entropy); 880 881 /* 882 * Throttle writing to once every reseed interval, unless we're not yet 883 * initialized or no entropy is credited. 884 */ 885 if (!kthread_should_stop() && (crng_ready() || !entropy)) 886 schedule_timeout_interruptible(crng_reseed_interval()); 887 } 888 EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); 889 890 /* 891 * Handle random seed passed by bootloader, and credit it if 892 * CONFIG_RANDOM_TRUST_BOOTLOADER is set. 893 */ 894 void __init add_bootloader_randomness(const void *buf, size_t len) 895 { 896 mix_pool_bytes(buf, len); 897 if (trust_bootloader) 898 credit_init_bits(len * 8); 899 } 900 901 #if IS_ENABLED(CONFIG_VMGENID) 902 static BLOCKING_NOTIFIER_HEAD(vmfork_chain); 903 904 /* 905 * Handle a new unique VM ID, which is unique, not secret, so we 906 * don't credit it, but we do immediately force a reseed after so 907 * that it's used by the crng posthaste. 908 */ 909 void __cold add_vmfork_randomness(const void *unique_vm_id, size_t len) 910 { 911 add_device_randomness(unique_vm_id, len); 912 if (crng_ready()) { 913 crng_reseed(); 914 pr_notice("crng reseeded due to virtual machine fork\n"); 915 } 916 blocking_notifier_call_chain(&vmfork_chain, 0, NULL); 917 } 918 #if IS_MODULE(CONFIG_VMGENID) 919 EXPORT_SYMBOL_GPL(add_vmfork_randomness); 920 #endif 921 922 int __cold register_random_vmfork_notifier(struct notifier_block *nb) 923 { 924 return blocking_notifier_chain_register(&vmfork_chain, nb); 925 } 926 EXPORT_SYMBOL_GPL(register_random_vmfork_notifier); 927 928 int __cold unregister_random_vmfork_notifier(struct notifier_block *nb) 929 { 930 return blocking_notifier_chain_unregister(&vmfork_chain, nb); 931 } 932 EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier); 933 #endif 934 935 struct fast_pool { 936 unsigned long pool[4]; 937 unsigned long last; 938 unsigned int count; 939 struct timer_list mix; 940 }; 941 942 static void mix_interrupt_randomness(struct timer_list *work); 943 944 static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = { 945 #ifdef CONFIG_64BIT 946 #define FASTMIX_PERM SIPHASH_PERMUTATION 947 .pool = { SIPHASH_CONST_0, SIPHASH_CONST_1, SIPHASH_CONST_2, SIPHASH_CONST_3 }, 948 #else 949 #define FASTMIX_PERM HSIPHASH_PERMUTATION 950 .pool = { HSIPHASH_CONST_0, HSIPHASH_CONST_1, HSIPHASH_CONST_2, HSIPHASH_CONST_3 }, 951 #endif 952 .mix = __TIMER_INITIALIZER(mix_interrupt_randomness, 0) 953 }; 954 955 /* 956 * This is [Half]SipHash-1-x, starting from an empty key. Because 957 * the key is fixed, it assumes that its inputs are non-malicious, 958 * and therefore this has no security on its own. s represents the 959 * four-word SipHash state, while v represents a two-word input. 960 */ 961 static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long v2) 962 { 963 s[3] ^= v1; 964 FASTMIX_PERM(s[0], s[1], s[2], s[3]); 965 s[0] ^= v1; 966 s[3] ^= v2; 967 FASTMIX_PERM(s[0], s[1], s[2], s[3]); 968 s[0] ^= v2; 969 } 970 971 #ifdef CONFIG_SMP 972 /* 973 * This function is called when the CPU has just come online, with 974 * entry CPUHP_AP_RANDOM_ONLINE, just after CPUHP_AP_WORKQUEUE_ONLINE. 975 */ 976 int __cold random_online_cpu(unsigned int cpu) 977 { 978 /* 979 * During CPU shutdown and before CPU onlining, add_interrupt_ 980 * randomness() may schedule mix_interrupt_randomness(), and 981 * set the MIX_INFLIGHT flag. However, because the worker can 982 * be scheduled on a different CPU during this period, that 983 * flag will never be cleared. For that reason, we zero out 984 * the flag here, which runs just after workqueues are onlined 985 * for the CPU again. This also has the effect of setting the 986 * irq randomness count to zero so that new accumulated irqs 987 * are fresh. 988 */ 989 per_cpu_ptr(&irq_randomness, cpu)->count = 0; 990 return 0; 991 } 992 #endif 993 994 static void mix_interrupt_randomness(struct timer_list *work) 995 { 996 struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix); 997 /* 998 * The size of the copied stack pool is explicitly 2 longs so that we 999 * only ever ingest half of the siphash output each time, retaining 1000 * the other half as the next "key" that carries over. The entropy is 1001 * supposed to be sufficiently dispersed between bits so on average 1002 * we don't wind up "losing" some. 1003 */ 1004 unsigned long pool[2]; 1005 unsigned int count; 1006 1007 /* Check to see if we're running on the wrong CPU due to hotplug. */ 1008 local_irq_disable(); 1009 if (fast_pool != this_cpu_ptr(&irq_randomness)) { 1010 local_irq_enable(); 1011 return; 1012 } 1013 1014 /* 1015 * Copy the pool to the stack so that the mixer always has a 1016 * consistent view, before we reenable irqs again. 1017 */ 1018 memcpy(pool, fast_pool->pool, sizeof(pool)); 1019 count = fast_pool->count; 1020 fast_pool->count = 0; 1021 fast_pool->last = jiffies; 1022 local_irq_enable(); 1023 1024 mix_pool_bytes(pool, sizeof(pool)); 1025 credit_init_bits(clamp_t(unsigned int, (count & U16_MAX) / 64, 1, sizeof(pool) * 8)); 1026 1027 memzero_explicit(pool, sizeof(pool)); 1028 } 1029 1030 void add_interrupt_randomness(int irq) 1031 { 1032 enum { MIX_INFLIGHT = 1U << 31 }; 1033 unsigned long entropy = random_get_entropy(); 1034 struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness); 1035 struct pt_regs *regs = get_irq_regs(); 1036 unsigned int new_count; 1037 1038 fast_mix(fast_pool->pool, entropy, 1039 (regs ? instruction_pointer(regs) : _RET_IP_) ^ swab(irq)); 1040 new_count = ++fast_pool->count; 1041 1042 if (new_count & MIX_INFLIGHT) 1043 return; 1044 1045 if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ)) 1046 return; 1047 1048 fast_pool->count |= MIX_INFLIGHT; 1049 if (!timer_pending(&fast_pool->mix)) { 1050 fast_pool->mix.expires = jiffies; 1051 add_timer_on(&fast_pool->mix, raw_smp_processor_id()); 1052 } 1053 } 1054 EXPORT_SYMBOL_GPL(add_interrupt_randomness); 1055 1056 /* There is one of these per entropy source */ 1057 struct timer_rand_state { 1058 unsigned long last_time; 1059 long last_delta, last_delta2; 1060 }; 1061 1062 /* 1063 * This function adds entropy to the entropy "pool" by using timing 1064 * delays. It uses the timer_rand_state structure to make an estimate 1065 * of how many bits of entropy this call has added to the pool. The 1066 * value "num" is also added to the pool; it should somehow describe 1067 * the type of event that just happened. 1068 */ 1069 static void add_timer_randomness(struct timer_rand_state *state, unsigned int num) 1070 { 1071 unsigned long entropy = random_get_entropy(), now = jiffies, flags; 1072 long delta, delta2, delta3; 1073 unsigned int bits; 1074 1075 /* 1076 * If we're in a hard IRQ, add_interrupt_randomness() will be called 1077 * sometime after, so mix into the fast pool. 1078 */ 1079 if (in_hardirq()) { 1080 fast_mix(this_cpu_ptr(&irq_randomness)->pool, entropy, num); 1081 } else { 1082 spin_lock_irqsave(&input_pool.lock, flags); 1083 _mix_pool_bytes(&entropy, sizeof(entropy)); 1084 _mix_pool_bytes(&num, sizeof(num)); 1085 spin_unlock_irqrestore(&input_pool.lock, flags); 1086 } 1087 1088 if (crng_ready()) 1089 return; 1090 1091 /* 1092 * Calculate number of bits of randomness we probably added. 1093 * We take into account the first, second and third-order deltas 1094 * in order to make our estimate. 1095 */ 1096 delta = now - READ_ONCE(state->last_time); 1097 WRITE_ONCE(state->last_time, now); 1098 1099 delta2 = delta - READ_ONCE(state->last_delta); 1100 WRITE_ONCE(state->last_delta, delta); 1101 1102 delta3 = delta2 - READ_ONCE(state->last_delta2); 1103 WRITE_ONCE(state->last_delta2, delta2); 1104 1105 if (delta < 0) 1106 delta = -delta; 1107 if (delta2 < 0) 1108 delta2 = -delta2; 1109 if (delta3 < 0) 1110 delta3 = -delta3; 1111 if (delta > delta2) 1112 delta = delta2; 1113 if (delta > delta3) 1114 delta = delta3; 1115 1116 /* 1117 * delta is now minimum absolute delta. Round down by 1 bit 1118 * on general principles, and limit entropy estimate to 11 bits. 1119 */ 1120 bits = min(fls(delta >> 1), 11); 1121 1122 /* 1123 * As mentioned above, if we're in a hard IRQ, add_interrupt_randomness() 1124 * will run after this, which uses a different crediting scheme of 1 bit 1125 * per every 64 interrupts. In order to let that function do accounting 1126 * close to the one in this function, we credit a full 64/64 bit per bit, 1127 * and then subtract one to account for the extra one added. 1128 */ 1129 if (in_hardirq()) 1130 this_cpu_ptr(&irq_randomness)->count += max(1u, bits * 64) - 1; 1131 else 1132 _credit_init_bits(bits); 1133 } 1134 1135 void add_input_randomness(unsigned int type, unsigned int code, unsigned int value) 1136 { 1137 static unsigned char last_value; 1138 static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES }; 1139 1140 /* Ignore autorepeat and the like. */ 1141 if (value == last_value) 1142 return; 1143 1144 last_value = value; 1145 add_timer_randomness(&input_timer_state, 1146 (type << 4) ^ code ^ (code >> 4) ^ value); 1147 } 1148 EXPORT_SYMBOL_GPL(add_input_randomness); 1149 1150 #ifdef CONFIG_BLOCK 1151 void add_disk_randomness(struct gendisk *disk) 1152 { 1153 if (!disk || !disk->random) 1154 return; 1155 /* First major is 1, so we get >= 0x200 here. */ 1156 add_timer_randomness(disk->random, 0x100 + disk_devt(disk)); 1157 } 1158 EXPORT_SYMBOL_GPL(add_disk_randomness); 1159 1160 void __cold rand_initialize_disk(struct gendisk *disk) 1161 { 1162 struct timer_rand_state *state; 1163 1164 /* 1165 * If kzalloc returns null, we just won't use that entropy 1166 * source. 1167 */ 1168 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL); 1169 if (state) { 1170 state->last_time = INITIAL_JIFFIES; 1171 disk->random = state; 1172 } 1173 } 1174 #endif 1175 1176 struct entropy_timer_state { 1177 unsigned long entropy; 1178 struct timer_list timer; 1179 unsigned int samples, samples_per_bit; 1180 }; 1181 1182 /* 1183 * Each time the timer fires, we expect that we got an unpredictable 1184 * jump in the cycle counter. Even if the timer is running on another 1185 * CPU, the timer activity will be touching the stack of the CPU that is 1186 * generating entropy.. 1187 * 1188 * Note that we don't re-arm the timer in the timer itself - we are 1189 * happy to be scheduled away, since that just makes the load more 1190 * complex, but we do not want the timer to keep ticking unless the 1191 * entropy loop is running. 1192 * 1193 * So the re-arming always happens in the entropy loop itself. 1194 */ 1195 static void __cold entropy_timer(struct timer_list *timer) 1196 { 1197 struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer); 1198 1199 if (++state->samples == state->samples_per_bit) { 1200 credit_init_bits(1); 1201 state->samples = 0; 1202 } 1203 } 1204 1205 /* 1206 * If we have an actual cycle counter, see if we can 1207 * generate enough entropy with timing noise 1208 */ 1209 static void __cold try_to_generate_entropy(void) 1210 { 1211 enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = HZ / 15 }; 1212 struct entropy_timer_state stack; 1213 unsigned int i, num_different = 0; 1214 unsigned long last = random_get_entropy(); 1215 1216 for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) { 1217 stack.entropy = random_get_entropy(); 1218 if (stack.entropy != last) 1219 ++num_different; 1220 last = stack.entropy; 1221 } 1222 stack.samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1); 1223 if (stack.samples_per_bit > MAX_SAMPLES_PER_BIT) 1224 return; 1225 1226 stack.samples = 0; 1227 timer_setup_on_stack(&stack.timer, entropy_timer, 0); 1228 while (!crng_ready() && !signal_pending(current)) { 1229 if (!timer_pending(&stack.timer)) 1230 mod_timer(&stack.timer, jiffies); 1231 mix_pool_bytes(&stack.entropy, sizeof(stack.entropy)); 1232 schedule(); 1233 stack.entropy = random_get_entropy(); 1234 } 1235 1236 del_timer_sync(&stack.timer); 1237 destroy_timer_on_stack(&stack.timer); 1238 mix_pool_bytes(&stack.entropy, sizeof(stack.entropy)); 1239 } 1240 1241 1242 /********************************************************************** 1243 * 1244 * Userspace reader/writer interfaces. 1245 * 1246 * getrandom(2) is the primary modern interface into the RNG and should 1247 * be used in preference to anything else. 1248 * 1249 * Reading from /dev/random has the same functionality as calling 1250 * getrandom(2) with flags=0. In earlier versions, however, it had 1251 * vastly different semantics and should therefore be avoided, to 1252 * prevent backwards compatibility issues. 1253 * 1254 * Reading from /dev/urandom has the same functionality as calling 1255 * getrandom(2) with flags=GRND_INSECURE. Because it does not block 1256 * waiting for the RNG to be ready, it should not be used. 1257 * 1258 * Writing to either /dev/random or /dev/urandom adds entropy to 1259 * the input pool but does not credit it. 1260 * 1261 * Polling on /dev/random indicates when the RNG is initialized, on 1262 * the read side, and when it wants new entropy, on the write side. 1263 * 1264 * Both /dev/random and /dev/urandom have the same set of ioctls for 1265 * adding entropy, getting the entropy count, zeroing the count, and 1266 * reseeding the crng. 1267 * 1268 **********************************************************************/ 1269 1270 SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags) 1271 { 1272 struct iov_iter iter; 1273 struct iovec iov; 1274 int ret; 1275 1276 if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE)) 1277 return -EINVAL; 1278 1279 /* 1280 * Requesting insecure and blocking randomness at the same time makes 1281 * no sense. 1282 */ 1283 if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM)) 1284 return -EINVAL; 1285 1286 if (!crng_ready() && !(flags & GRND_INSECURE)) { 1287 if (flags & GRND_NONBLOCK) 1288 return -EAGAIN; 1289 ret = wait_for_random_bytes(); 1290 if (unlikely(ret)) 1291 return ret; 1292 } 1293 1294 ret = import_single_range(READ, ubuf, len, &iov, &iter); 1295 if (unlikely(ret)) 1296 return ret; 1297 return get_random_bytes_user(&iter); 1298 } 1299 1300 static __poll_t random_poll(struct file *file, poll_table *wait) 1301 { 1302 poll_wait(file, &crng_init_wait, wait); 1303 return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM; 1304 } 1305 1306 static ssize_t write_pool_user(struct iov_iter *iter) 1307 { 1308 u8 block[BLAKE2S_BLOCK_SIZE]; 1309 ssize_t ret = 0; 1310 size_t copied; 1311 1312 if (unlikely(!iov_iter_count(iter))) 1313 return 0; 1314 1315 for (;;) { 1316 copied = copy_from_iter(block, sizeof(block), iter); 1317 ret += copied; 1318 mix_pool_bytes(block, copied); 1319 if (!iov_iter_count(iter) || copied != sizeof(block)) 1320 break; 1321 1322 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0); 1323 if (ret % PAGE_SIZE == 0) { 1324 if (signal_pending(current)) 1325 break; 1326 cond_resched(); 1327 } 1328 } 1329 1330 memzero_explicit(block, sizeof(block)); 1331 return ret ? ret : -EFAULT; 1332 } 1333 1334 static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter) 1335 { 1336 return write_pool_user(iter); 1337 } 1338 1339 static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter) 1340 { 1341 static int maxwarn = 10; 1342 1343 /* 1344 * Opportunistically attempt to initialize the RNG on platforms that 1345 * have fast cycle counters, but don't (for now) require it to succeed. 1346 */ 1347 if (!crng_ready()) 1348 try_to_generate_entropy(); 1349 1350 if (!crng_ready()) { 1351 if (!ratelimit_disable && maxwarn <= 0) 1352 ++urandom_warning.missed; 1353 else if (ratelimit_disable || __ratelimit(&urandom_warning)) { 1354 --maxwarn; 1355 pr_notice("%s: uninitialized urandom read (%zu bytes read)\n", 1356 current->comm, iov_iter_count(iter)); 1357 } 1358 } 1359 1360 return get_random_bytes_user(iter); 1361 } 1362 1363 static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter) 1364 { 1365 int ret; 1366 1367 if (!crng_ready() && 1368 ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) || 1369 (kiocb->ki_filp->f_flags & O_NONBLOCK))) 1370 return -EAGAIN; 1371 1372 ret = wait_for_random_bytes(); 1373 if (ret != 0) 1374 return ret; 1375 return get_random_bytes_user(iter); 1376 } 1377 1378 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) 1379 { 1380 int __user *p = (int __user *)arg; 1381 int ent_count; 1382 1383 switch (cmd) { 1384 case RNDGETENTCNT: 1385 /* Inherently racy, no point locking. */ 1386 if (put_user(input_pool.init_bits, p)) 1387 return -EFAULT; 1388 return 0; 1389 case RNDADDTOENTCNT: 1390 if (!capable(CAP_SYS_ADMIN)) 1391 return -EPERM; 1392 if (get_user(ent_count, p)) 1393 return -EFAULT; 1394 if (ent_count < 0) 1395 return -EINVAL; 1396 credit_init_bits(ent_count); 1397 return 0; 1398 case RNDADDENTROPY: { 1399 struct iov_iter iter; 1400 struct iovec iov; 1401 ssize_t ret; 1402 int len; 1403 1404 if (!capable(CAP_SYS_ADMIN)) 1405 return -EPERM; 1406 if (get_user(ent_count, p++)) 1407 return -EFAULT; 1408 if (ent_count < 0) 1409 return -EINVAL; 1410 if (get_user(len, p++)) 1411 return -EFAULT; 1412 ret = import_single_range(WRITE, p, len, &iov, &iter); 1413 if (unlikely(ret)) 1414 return ret; 1415 ret = write_pool_user(&iter); 1416 if (unlikely(ret < 0)) 1417 return ret; 1418 /* Since we're crediting, enforce that it was all written into the pool. */ 1419 if (unlikely(ret != len)) 1420 return -EFAULT; 1421 credit_init_bits(ent_count); 1422 return 0; 1423 } 1424 case RNDZAPENTCNT: 1425 case RNDCLEARPOOL: 1426 /* No longer has any effect. */ 1427 if (!capable(CAP_SYS_ADMIN)) 1428 return -EPERM; 1429 return 0; 1430 case RNDRESEEDCRNG: 1431 if (!capable(CAP_SYS_ADMIN)) 1432 return -EPERM; 1433 if (!crng_ready()) 1434 return -ENODATA; 1435 crng_reseed(); 1436 return 0; 1437 default: 1438 return -EINVAL; 1439 } 1440 } 1441 1442 static int random_fasync(int fd, struct file *filp, int on) 1443 { 1444 return fasync_helper(fd, filp, on, &fasync); 1445 } 1446 1447 const struct file_operations random_fops = { 1448 .read_iter = random_read_iter, 1449 .write_iter = random_write_iter, 1450 .poll = random_poll, 1451 .unlocked_ioctl = random_ioctl, 1452 .compat_ioctl = compat_ptr_ioctl, 1453 .fasync = random_fasync, 1454 .llseek = noop_llseek, 1455 .splice_read = generic_file_splice_read, 1456 .splice_write = iter_file_splice_write, 1457 }; 1458 1459 const struct file_operations urandom_fops = { 1460 .read_iter = urandom_read_iter, 1461 .write_iter = random_write_iter, 1462 .unlocked_ioctl = random_ioctl, 1463 .compat_ioctl = compat_ptr_ioctl, 1464 .fasync = random_fasync, 1465 .llseek = noop_llseek, 1466 .splice_read = generic_file_splice_read, 1467 .splice_write = iter_file_splice_write, 1468 }; 1469 1470 1471 /******************************************************************** 1472 * 1473 * Sysctl interface. 1474 * 1475 * These are partly unused legacy knobs with dummy values to not break 1476 * userspace and partly still useful things. They are usually accessible 1477 * in /proc/sys/kernel/random/ and are as follows: 1478 * 1479 * - boot_id - a UUID representing the current boot. 1480 * 1481 * - uuid - a random UUID, different each time the file is read. 1482 * 1483 * - poolsize - the number of bits of entropy that the input pool can 1484 * hold, tied to the POOL_BITS constant. 1485 * 1486 * - entropy_avail - the number of bits of entropy currently in the 1487 * input pool. Always <= poolsize. 1488 * 1489 * - write_wakeup_threshold - the amount of entropy in the input pool 1490 * below which write polls to /dev/random will unblock, requesting 1491 * more entropy, tied to the POOL_READY_BITS constant. It is writable 1492 * to avoid breaking old userspaces, but writing to it does not 1493 * change any behavior of the RNG. 1494 * 1495 * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL. 1496 * It is writable to avoid breaking old userspaces, but writing 1497 * to it does not change any behavior of the RNG. 1498 * 1499 ********************************************************************/ 1500 1501 #ifdef CONFIG_SYSCTL 1502 1503 #include <linux/sysctl.h> 1504 1505 static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ; 1506 static int sysctl_random_write_wakeup_bits = POOL_READY_BITS; 1507 static int sysctl_poolsize = POOL_BITS; 1508 static u8 sysctl_bootid[UUID_SIZE]; 1509 1510 /* 1511 * This function is used to return both the bootid UUID, and random 1512 * UUID. The difference is in whether table->data is NULL; if it is, 1513 * then a new UUID is generated and returned to the user. 1514 */ 1515 static int proc_do_uuid(struct ctl_table *table, int write, void *buf, 1516 size_t *lenp, loff_t *ppos) 1517 { 1518 u8 tmp_uuid[UUID_SIZE], *uuid; 1519 char uuid_string[UUID_STRING_LEN + 1]; 1520 struct ctl_table fake_table = { 1521 .data = uuid_string, 1522 .maxlen = UUID_STRING_LEN 1523 }; 1524 1525 if (write) 1526 return -EPERM; 1527 1528 uuid = table->data; 1529 if (!uuid) { 1530 uuid = tmp_uuid; 1531 generate_random_uuid(uuid); 1532 } else { 1533 static DEFINE_SPINLOCK(bootid_spinlock); 1534 1535 spin_lock(&bootid_spinlock); 1536 if (!uuid[8]) 1537 generate_random_uuid(uuid); 1538 spin_unlock(&bootid_spinlock); 1539 } 1540 1541 snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid); 1542 return proc_dostring(&fake_table, 0, buf, lenp, ppos); 1543 } 1544 1545 /* The same as proc_dointvec, but writes don't change anything. */ 1546 static int proc_do_rointvec(struct ctl_table *table, int write, void *buf, 1547 size_t *lenp, loff_t *ppos) 1548 { 1549 return write ? 0 : proc_dointvec(table, 0, buf, lenp, ppos); 1550 } 1551 1552 static struct ctl_table random_table[] = { 1553 { 1554 .procname = "poolsize", 1555 .data = &sysctl_poolsize, 1556 .maxlen = sizeof(int), 1557 .mode = 0444, 1558 .proc_handler = proc_dointvec, 1559 }, 1560 { 1561 .procname = "entropy_avail", 1562 .data = &input_pool.init_bits, 1563 .maxlen = sizeof(int), 1564 .mode = 0444, 1565 .proc_handler = proc_dointvec, 1566 }, 1567 { 1568 .procname = "write_wakeup_threshold", 1569 .data = &sysctl_random_write_wakeup_bits, 1570 .maxlen = sizeof(int), 1571 .mode = 0644, 1572 .proc_handler = proc_do_rointvec, 1573 }, 1574 { 1575 .procname = "urandom_min_reseed_secs", 1576 .data = &sysctl_random_min_urandom_seed, 1577 .maxlen = sizeof(int), 1578 .mode = 0644, 1579 .proc_handler = proc_do_rointvec, 1580 }, 1581 { 1582 .procname = "boot_id", 1583 .data = &sysctl_bootid, 1584 .mode = 0444, 1585 .proc_handler = proc_do_uuid, 1586 }, 1587 { 1588 .procname = "uuid", 1589 .mode = 0444, 1590 .proc_handler = proc_do_uuid, 1591 }, 1592 { } 1593 }; 1594 1595 /* 1596 * random_init() is called before sysctl_init(), 1597 * so we cannot call register_sysctl_init() in random_init() 1598 */ 1599 static int __init random_sysctls_init(void) 1600 { 1601 register_sysctl_init("kernel/random", random_table); 1602 return 0; 1603 } 1604 device_initcall(random_sysctls_init); 1605 #endif 1606