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