1 // SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
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.
7 * This driver produces cryptographically secure pseudorandom data. It is divided
8 * into roughly six sections, each with a section header:
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.
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.
26 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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>
39 #include <linux/blkdev.h>
40 #include <linux/interrupt.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>
60 #include <asm/irq_regs.h>
63 /*********************************************************************
65 * Initialization and readiness waiting.
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.
71 *********************************************************************/
74 * crng_init is protected by base_crng->lock, and only increases
75 * its value (from empty->early->ready).
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 = CRNG_EMPTY;
82 #define crng_ready() (likely(crng_init >= CRNG_READY))
83 /* Various types of waiters for crng_init->CRNG_READY transition. */
84 static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
85 static struct fasync_struct *fasync;
86 static DEFINE_SPINLOCK(random_ready_chain_lock);
87 static RAW_NOTIFIER_HEAD(random_ready_chain);
89 /* Control how we warn userspace. */
90 static struct ratelimit_state urandom_warning =
91 RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
92 static int ratelimit_disable __read_mostly =
93 IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
94 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
95 MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
98 * Returns whether or not the input pool has been seeded and thus guaranteed
99 * to supply cryptographically secure random numbers. This applies to: the
100 * /dev/urandom device, the get_random_bytes function, and the get_random_{u32,
101 * ,u64,int,long} family of functions.
103 * Returns: true if the input pool has been seeded.
104 * false if the input pool has not been seeded.
106 bool rng_is_initialized(void)
110 EXPORT_SYMBOL(rng_is_initialized);
112 /* Used by wait_for_random_bytes(), and considered an entropy collector, below. */
113 static void try_to_generate_entropy(void);
116 * Wait for the input pool to be seeded and thus guaranteed to supply
117 * cryptographically secure random numbers. This applies to: the /dev/urandom
118 * device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
119 * family of functions. Using any of these functions without first calling
120 * this function forfeits the guarantee of security.
122 * Returns: 0 if the input pool has been seeded.
123 * -ERESTARTSYS if the function was interrupted by a signal.
125 int wait_for_random_bytes(void)
127 while (!crng_ready()) {
130 try_to_generate_entropy();
131 ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
133 return ret > 0 ? 0 : ret;
137 EXPORT_SYMBOL(wait_for_random_bytes);
140 * Add a callback function that will be invoked when the input
141 * pool is initialised.
143 * returns: 0 if callback is successfully added
144 * -EALREADY if pool is already initialised (callback not called)
146 int register_random_ready_notifier(struct notifier_block *nb)
154 spin_lock_irqsave(&random_ready_chain_lock, flags);
156 ret = raw_notifier_chain_register(&random_ready_chain, nb);
157 spin_unlock_irqrestore(&random_ready_chain_lock, flags);
162 * Delete a previously registered readiness callback function.
164 int unregister_random_ready_notifier(struct notifier_block *nb)
169 spin_lock_irqsave(&random_ready_chain_lock, flags);
170 ret = raw_notifier_chain_unregister(&random_ready_chain, nb);
171 spin_unlock_irqrestore(&random_ready_chain_lock, flags);
175 static void process_random_ready_list(void)
179 spin_lock_irqsave(&random_ready_chain_lock, flags);
180 raw_notifier_call_chain(&random_ready_chain, 0, NULL);
181 spin_unlock_irqrestore(&random_ready_chain_lock, flags);
184 #define warn_unseeded_randomness() \
185 _warn_unseeded_randomness(__func__, (void *)_RET_IP_)
187 static void _warn_unseeded_randomness(const char *func_name, void *caller)
189 if (!IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) || crng_ready())
191 printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n",
192 func_name, caller, crng_init);
196 /*********************************************************************
198 * Fast key erasure RNG, the "crng".
200 * These functions expand entropy from the entropy extractor into
201 * long streams for external consumption using the "fast key erasure"
202 * RNG described at <https://blog.cr.yp.to/20170723-random.html>.
204 * There are a few exported interfaces for use by other drivers:
206 * void get_random_bytes(void *buf, size_t nbytes)
207 * u32 get_random_u32()
208 * u64 get_random_u64()
209 * unsigned int get_random_int()
210 * unsigned long get_random_long()
212 * These interfaces will return the requested number of random bytes
213 * into the given buffer or as a return value. This is equivalent to
214 * a read from /dev/urandom. The u32, u64, int, and long family of
215 * functions may be higher performance for one-off random integers,
216 * because they do a bit of buffering and do not invoke reseeding
217 * until the buffer is emptied.
219 *********************************************************************/
222 CRNG_RESEED_START_INTERVAL = HZ,
223 CRNG_RESEED_INTERVAL = 60 * HZ
227 u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long));
229 unsigned long generation;
232 .lock = __SPIN_LOCK_UNLOCKED(base_crng.lock)
236 u8 key[CHACHA_KEY_SIZE];
237 unsigned long generation;
241 static DEFINE_PER_CPU(struct crng, crngs) = {
242 .generation = ULONG_MAX,
243 .lock = INIT_LOCAL_LOCK(crngs.lock),
246 /* Used by crng_reseed() and crng_make_state() to extract a new seed from the input pool. */
247 static void extract_entropy(void *buf, size_t nbytes);
249 /* This extracts a new crng key from the input pool. */
250 static void crng_reseed(void)
253 unsigned long next_gen;
254 u8 key[CHACHA_KEY_SIZE];
256 extract_entropy(key, sizeof(key));
259 * We copy the new key into the base_crng, overwriting the old one,
260 * and update the generation counter. We avoid hitting ULONG_MAX,
261 * because the per-cpu crngs are initialized to ULONG_MAX, so this
262 * forces new CPUs that come online to always initialize.
264 spin_lock_irqsave(&base_crng.lock, flags);
265 memcpy(base_crng.key, key, sizeof(base_crng.key));
266 next_gen = base_crng.generation + 1;
267 if (next_gen == ULONG_MAX)
269 WRITE_ONCE(base_crng.generation, next_gen);
270 WRITE_ONCE(base_crng.birth, jiffies);
272 crng_init = CRNG_READY;
273 spin_unlock_irqrestore(&base_crng.lock, flags);
274 memzero_explicit(key, sizeof(key));
278 * This generates a ChaCha block using the provided key, and then
279 * immediately overwites that key with half the block. It returns
280 * the resultant ChaCha state to the user, along with the second
281 * half of the block containing 32 bytes of random data that may
282 * be used; random_data_len may not be greater than 32.
284 * The returned ChaCha state contains within it a copy of the old
285 * key value, at index 4, so the state should always be zeroed out
286 * immediately after using in order to maintain forward secrecy.
287 * If the state cannot be erased in a timely manner, then it is
288 * safer to set the random_data parameter to &chacha_state[4] so
289 * that this function overwrites it before returning.
291 static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE],
292 u32 chacha_state[CHACHA_STATE_WORDS],
293 u8 *random_data, size_t random_data_len)
295 u8 first_block[CHACHA_BLOCK_SIZE];
297 BUG_ON(random_data_len > 32);
299 chacha_init_consts(chacha_state);
300 memcpy(&chacha_state[4], key, CHACHA_KEY_SIZE);
301 memset(&chacha_state[12], 0, sizeof(u32) * 4);
302 chacha20_block(chacha_state, first_block);
304 memcpy(key, first_block, CHACHA_KEY_SIZE);
305 memcpy(random_data, first_block + CHACHA_KEY_SIZE, random_data_len);
306 memzero_explicit(first_block, sizeof(first_block));
310 * Return whether the crng seed is considered to be sufficiently old
311 * that a reseeding is needed. This happens if the last reseeding
312 * was CRNG_RESEED_INTERVAL ago, or during early boot, at an interval
313 * proportional to the uptime.
315 static bool crng_has_old_seed(void)
317 static bool early_boot = true;
318 unsigned long interval = CRNG_RESEED_INTERVAL;
320 if (unlikely(READ_ONCE(early_boot))) {
321 time64_t uptime = ktime_get_seconds();
322 if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2)
323 WRITE_ONCE(early_boot, false);
325 interval = max_t(unsigned int, CRNG_RESEED_START_INTERVAL,
326 (unsigned int)uptime / 2 * HZ);
328 return time_is_before_jiffies(READ_ONCE(base_crng.birth) + interval);
332 * This function returns a ChaCha state that you may use for generating
333 * random data. It also returns up to 32 bytes on its own of random data
334 * that may be used; random_data_len may not be greater than 32.
336 static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
337 u8 *random_data, size_t random_data_len)
342 BUG_ON(random_data_len > 32);
345 * For the fast path, we check whether we're ready, unlocked first, and
346 * then re-check once locked later. In the case where we're really not
347 * ready, we do fast key erasure with the base_crng directly, extracting
348 * when crng_init is CRNG_EMPTY.
353 spin_lock_irqsave(&base_crng.lock, flags);
354 ready = crng_ready();
356 if (crng_init == CRNG_EMPTY)
357 extract_entropy(base_crng.key, sizeof(base_crng.key));
358 crng_fast_key_erasure(base_crng.key, chacha_state,
359 random_data, random_data_len);
361 spin_unlock_irqrestore(&base_crng.lock, flags);
367 * If the base_crng is old enough, we reseed, which in turn bumps the
368 * generation counter that we check below.
370 if (unlikely(crng_has_old_seed()))
373 local_lock_irqsave(&crngs.lock, flags);
374 crng = raw_cpu_ptr(&crngs);
377 * If our per-cpu crng is older than the base_crng, then it means
378 * somebody reseeded the base_crng. In that case, we do fast key
379 * erasure on the base_crng, and use its output as the new key
380 * for our per-cpu crng. This brings us up to date with base_crng.
382 if (unlikely(crng->generation != READ_ONCE(base_crng.generation))) {
383 spin_lock(&base_crng.lock);
384 crng_fast_key_erasure(base_crng.key, chacha_state,
385 crng->key, sizeof(crng->key));
386 crng->generation = base_crng.generation;
387 spin_unlock(&base_crng.lock);
391 * Finally, when we've made it this far, our per-cpu crng has an up
392 * to date key, and we can do fast key erasure with it to produce
393 * some random data and a ChaCha state for the caller. All other
394 * branches of this function are "unlikely", so most of the time we
395 * should wind up here immediately.
397 crng_fast_key_erasure(crng->key, chacha_state, random_data, random_data_len);
398 local_unlock_irqrestore(&crngs.lock, flags);
401 static void _get_random_bytes(void *buf, size_t nbytes)
403 u32 chacha_state[CHACHA_STATE_WORDS];
404 u8 tmp[CHACHA_BLOCK_SIZE];
410 len = min_t(size_t, 32, nbytes);
411 crng_make_state(chacha_state, buf, len);
416 if (nbytes < CHACHA_BLOCK_SIZE) {
417 chacha20_block(chacha_state, tmp);
418 memcpy(buf, tmp, nbytes);
419 memzero_explicit(tmp, sizeof(tmp));
423 chacha20_block(chacha_state, buf);
424 if (unlikely(chacha_state[12] == 0))
426 nbytes -= CHACHA_BLOCK_SIZE;
427 buf += CHACHA_BLOCK_SIZE;
430 memzero_explicit(chacha_state, sizeof(chacha_state));
434 * This function is the exported kernel interface. It returns some
435 * number of good random numbers, suitable for key generation, seeding
436 * TCP sequence numbers, etc. It does not rely on the hardware random
437 * number generator. For random bytes direct from the hardware RNG
438 * (when available), use get_random_bytes_arch(). In order to ensure
439 * that the randomness provided by this function is okay, the function
440 * wait_for_random_bytes() should be called and return 0 at least once
441 * at any point prior.
443 void get_random_bytes(void *buf, size_t nbytes)
445 warn_unseeded_randomness();
446 _get_random_bytes(buf, nbytes);
448 EXPORT_SYMBOL(get_random_bytes);
450 static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
452 size_t len, left, ret = 0;
453 u32 chacha_state[CHACHA_STATE_WORDS];
454 u8 output[CHACHA_BLOCK_SIZE];
460 * Immediately overwrite the ChaCha key at index 4 with random
461 * bytes, in case userspace causes copy_to_user() below to sleep
462 * forever, so that we still retain forward secrecy in that case.
464 crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA_KEY_SIZE);
466 * However, if we're doing a read of len <= 32, we don't need to
467 * use chacha_state after, so we can simply return those bytes to
470 if (nbytes <= CHACHA_KEY_SIZE) {
471 ret = nbytes - copy_to_user(buf, &chacha_state[4], nbytes);
472 goto out_zero_chacha;
476 chacha20_block(chacha_state, output);
477 if (unlikely(chacha_state[12] == 0))
480 len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE);
481 left = copy_to_user(buf, output, len);
493 BUILD_BUG_ON(PAGE_SIZE % CHACHA_BLOCK_SIZE != 0);
494 if (ret % PAGE_SIZE == 0) {
495 if (signal_pending(current))
501 memzero_explicit(output, sizeof(output));
503 memzero_explicit(chacha_state, sizeof(chacha_state));
504 return ret ? ret : -EFAULT;
508 * Batched entropy returns random integers. The quality of the random
509 * number is good as /dev/urandom. In order to ensure that the randomness
510 * provided by this function is okay, the function wait_for_random_bytes()
511 * should be called and return 0 at least once at any point prior.
513 struct batched_entropy {
516 * We make this 1.5x a ChaCha block, so that we get the
517 * remaining 32 bytes from fast key erasure, plus one full
518 * block from the detached ChaCha state. We can increase
519 * the size of this later if needed so long as we keep the
520 * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE.
522 u64 entropy_u64[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u64))];
523 u32 entropy_u32[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u32))];
526 unsigned long generation;
527 unsigned int position;
531 static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = {
532 .lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock),
536 u64 get_random_u64(void)
540 struct batched_entropy *batch;
541 unsigned long next_gen;
543 warn_unseeded_randomness();
546 _get_random_bytes(&ret, sizeof(ret));
550 local_lock_irqsave(&batched_entropy_u64.lock, flags);
551 batch = raw_cpu_ptr(&batched_entropy_u64);
553 next_gen = READ_ONCE(base_crng.generation);
554 if (batch->position >= ARRAY_SIZE(batch->entropy_u64) ||
555 next_gen != batch->generation) {
556 _get_random_bytes(batch->entropy_u64, sizeof(batch->entropy_u64));
558 batch->generation = next_gen;
561 ret = batch->entropy_u64[batch->position];
562 batch->entropy_u64[batch->position] = 0;
564 local_unlock_irqrestore(&batched_entropy_u64.lock, flags);
567 EXPORT_SYMBOL(get_random_u64);
569 static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = {
570 .lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock),
574 u32 get_random_u32(void)
578 struct batched_entropy *batch;
579 unsigned long next_gen;
581 warn_unseeded_randomness();
584 _get_random_bytes(&ret, sizeof(ret));
588 local_lock_irqsave(&batched_entropy_u32.lock, flags);
589 batch = raw_cpu_ptr(&batched_entropy_u32);
591 next_gen = READ_ONCE(base_crng.generation);
592 if (batch->position >= ARRAY_SIZE(batch->entropy_u32) ||
593 next_gen != batch->generation) {
594 _get_random_bytes(batch->entropy_u32, sizeof(batch->entropy_u32));
596 batch->generation = next_gen;
599 ret = batch->entropy_u32[batch->position];
600 batch->entropy_u32[batch->position] = 0;
602 local_unlock_irqrestore(&batched_entropy_u32.lock, flags);
605 EXPORT_SYMBOL(get_random_u32);
609 * This function is called when the CPU is coming up, with entry
610 * CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP.
612 int random_prepare_cpu(unsigned int cpu)
615 * When the cpu comes back online, immediately invalidate both
616 * the per-cpu crng and all batches, so that we serve fresh
619 per_cpu_ptr(&crngs, cpu)->generation = ULONG_MAX;
620 per_cpu_ptr(&batched_entropy_u32, cpu)->position = UINT_MAX;
621 per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX;
627 * randomize_page - Generate a random, page aligned address
628 * @start: The smallest acceptable address the caller will take.
629 * @range: The size of the area, starting at @start, within which the
630 * random address must fall.
632 * If @start + @range would overflow, @range is capped.
634 * NOTE: Historical use of randomize_range, which this replaces, presumed that
635 * @start was already page aligned. We now align it regardless.
637 * Return: A page aligned address within [start, start + range). On error,
638 * @start is returned.
640 unsigned long randomize_page(unsigned long start, unsigned long range)
642 if (!PAGE_ALIGNED(start)) {
643 range -= PAGE_ALIGN(start) - start;
644 start = PAGE_ALIGN(start);
647 if (start > ULONG_MAX - range)
648 range = ULONG_MAX - start;
650 range >>= PAGE_SHIFT;
655 return start + (get_random_long() % range << PAGE_SHIFT);
659 * This function will use the architecture-specific hardware random
660 * number generator if it is available. It is not recommended for
661 * use. Use get_random_bytes() instead. It returns the number of
664 size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes)
666 size_t left = nbytes;
671 size_t chunk = min_t(size_t, left, sizeof(unsigned long));
673 if (!arch_get_random_long(&v))
676 memcpy(p, &v, chunk);
681 return nbytes - left;
683 EXPORT_SYMBOL(get_random_bytes_arch);
686 /**********************************************************************
688 * Entropy accumulation and extraction routines.
690 * Callers may add entropy via:
692 * static void mix_pool_bytes(const void *in, size_t nbytes)
694 * After which, if added entropy should be credited:
696 * static void credit_init_bits(size_t nbits)
698 * Finally, extract entropy via:
700 * static void extract_entropy(void *buf, size_t nbytes)
702 **********************************************************************/
705 POOL_BITS = BLAKE2S_HASH_SIZE * 8,
706 POOL_READY_BITS = POOL_BITS, /* When crng_init->CRNG_READY */
707 POOL_EARLY_BITS = POOL_READY_BITS / 2 /* When crng_init->CRNG_EARLY */
711 struct blake2s_state hash;
713 unsigned int init_bits;
715 .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE),
716 BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4,
717 BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 },
718 .hash.outlen = BLAKE2S_HASH_SIZE,
719 .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
722 static void _mix_pool_bytes(const void *in, size_t nbytes)
724 blake2s_update(&input_pool.hash, in, nbytes);
728 * This function adds bytes into the input pool. It does not
729 * update the initialization bit counter; the caller should call
730 * credit_init_bits if this is appropriate.
732 static void mix_pool_bytes(const void *in, size_t nbytes)
736 spin_lock_irqsave(&input_pool.lock, flags);
737 _mix_pool_bytes(in, nbytes);
738 spin_unlock_irqrestore(&input_pool.lock, flags);
742 * This is an HKDF-like construction for using the hashed collected entropy
743 * as a PRF key, that's then expanded block-by-block.
745 static void extract_entropy(void *buf, size_t nbytes)
748 u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
750 unsigned long rdseed[32 / sizeof(long)];
755 for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) {
756 if (!arch_get_random_seed_long(&block.rdseed[i]) &&
757 !arch_get_random_long(&block.rdseed[i]))
758 block.rdseed[i] = random_get_entropy();
761 spin_lock_irqsave(&input_pool.lock, flags);
763 /* seed = HASHPRF(last_key, entropy_input) */
764 blake2s_final(&input_pool.hash, seed);
766 /* next_key = HASHPRF(seed, RDSEED || 0) */
768 blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
769 blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
771 spin_unlock_irqrestore(&input_pool.lock, flags);
772 memzero_explicit(next_key, sizeof(next_key));
775 i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE);
776 /* output = HASHPRF(seed, RDSEED || ++counter) */
778 blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
783 memzero_explicit(seed, sizeof(seed));
784 memzero_explicit(&block, sizeof(block));
787 static void credit_init_bits(size_t nbits)
789 unsigned int new, orig, add;
792 if (crng_ready() || !nbits)
795 add = min_t(size_t, nbits, POOL_BITS);
798 orig = READ_ONCE(input_pool.init_bits);
799 new = min_t(unsigned int, POOL_BITS, orig + add);
800 } while (cmpxchg(&input_pool.init_bits, orig, new) != orig);
802 if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
803 crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */
804 process_random_ready_list();
805 wake_up_interruptible(&crng_init_wait);
806 kill_fasync(&fasync, SIGIO, POLL_IN);
807 pr_notice("crng init done\n");
808 if (urandom_warning.missed)
809 pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
810 urandom_warning.missed);
811 } else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
812 spin_lock_irqsave(&base_crng.lock, flags);
813 /* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */
814 if (crng_init == CRNG_EMPTY) {
815 extract_entropy(base_crng.key, sizeof(base_crng.key));
816 crng_init = CRNG_EARLY;
818 spin_unlock_irqrestore(&base_crng.lock, flags);
823 /**********************************************************************
825 * Entropy collection routines.
827 * The following exported functions are used for pushing entropy into
828 * the above entropy accumulation routines:
830 * void add_device_randomness(const void *buf, size_t size);
831 * void add_hwgenerator_randomness(const void *buffer, size_t count,
833 * void add_bootloader_randomness(const void *buf, size_t size);
834 * void add_vmfork_randomness(const void *unique_vm_id, size_t size);
835 * void add_interrupt_randomness(int irq);
836 * void add_input_randomness(unsigned int type, unsigned int code,
837 * unsigned int value);
838 * void add_disk_randomness(struct gendisk *disk);
840 * add_device_randomness() adds data to the input pool that
841 * is likely to differ between two devices (or possibly even per boot).
842 * This would be things like MAC addresses or serial numbers, or the
843 * read-out of the RTC. This does *not* credit any actual entropy to
844 * the pool, but it initializes the pool to different values for devices
845 * that might otherwise be identical and have very little entropy
846 * available to them (particularly common in the embedded world).
848 * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
849 * entropy as specified by the caller. If the entropy pool is full it will
850 * block until more entropy is needed.
852 * add_bootloader_randomness() is called by bootloader drivers, such as EFI
853 * and device tree, and credits its input depending on whether or not the
854 * configuration option CONFIG_RANDOM_TRUST_BOOTLOADER is set.
856 * add_vmfork_randomness() adds a unique (but not necessarily secret) ID
857 * representing the current instance of a VM to the pool, without crediting,
858 * and then force-reseeds the crng so that it takes effect immediately.
860 * add_interrupt_randomness() uses the interrupt timing as random
861 * inputs to the entropy pool. Using the cycle counters and the irq source
862 * as inputs, it feeds the input pool roughly once a second or after 64
863 * interrupts, crediting 1 bit of entropy for whichever comes first.
865 * add_input_randomness() uses the input layer interrupt timing, as well
866 * as the event type information from the hardware.
868 * add_disk_randomness() uses what amounts to the seek time of block
869 * layer request events, on a per-disk_devt basis, as input to the
870 * entropy pool. Note that high-speed solid state drives with very low
871 * seek times do not make for good sources of entropy, as their seek
872 * times are usually fairly consistent.
874 * The last two routines try to estimate how many bits of entropy
875 * to credit. They do this by keeping track of the first and second
876 * order deltas of the event timings.
878 **********************************************************************/
880 static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
881 static bool trust_bootloader __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER);
882 static int __init parse_trust_cpu(char *arg)
884 return kstrtobool(arg, &trust_cpu);
886 static int __init parse_trust_bootloader(char *arg)
888 return kstrtobool(arg, &trust_bootloader);
890 early_param("random.trust_cpu", parse_trust_cpu);
891 early_param("random.trust_bootloader", parse_trust_bootloader);
893 static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data)
895 unsigned long flags, entropy = random_get_entropy();
898 * Encode a representation of how long the system has been suspended,
899 * in a way that is distinct from prior system suspends.
901 ktime_t stamps[] = { ktime_get(), ktime_get_boottime(), ktime_get_real() };
903 spin_lock_irqsave(&input_pool.lock, flags);
904 _mix_pool_bytes(&action, sizeof(action));
905 _mix_pool_bytes(stamps, sizeof(stamps));
906 _mix_pool_bytes(&entropy, sizeof(entropy));
907 spin_unlock_irqrestore(&input_pool.lock, flags);
909 if (crng_ready() && (action == PM_RESTORE_PREPARE ||
910 (action == PM_POST_SUSPEND &&
911 !IS_ENABLED(CONFIG_PM_AUTOSLEEP) && !IS_ENABLED(CONFIG_ANDROID)))) {
913 pr_notice("crng reseeded on system resumption\n");
918 static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification };
921 * The first collection of entropy occurs at system boot while interrupts
922 * are still turned off. Here we push in latent entropy, RDSEED, a timestamp,
923 * utsname(), and the command line. Depending on the above configuration knob,
924 * RDSEED may be considered sufficient for initialization. Note that much
925 * earlier setup may already have pushed entropy into the input pool by the
928 int __init random_init(const char *command_line)
930 ktime_t now = ktime_get_real();
931 unsigned int i, arch_bytes;
934 #if defined(LATENT_ENTROPY_PLUGIN)
935 static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
936 _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
939 for (i = 0, arch_bytes = BLAKE2S_BLOCK_SIZE;
940 i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
941 if (!arch_get_random_seed_long_early(&rv) &&
942 !arch_get_random_long_early(&rv)) {
943 rv = random_get_entropy();
944 arch_bytes -= sizeof(rv);
946 _mix_pool_bytes(&rv, sizeof(rv));
948 _mix_pool_bytes(&now, sizeof(now));
949 _mix_pool_bytes(utsname(), sizeof(*(utsname())));
950 _mix_pool_bytes(command_line, strlen(command_line));
951 add_latent_entropy();
956 credit_init_bits(arch_bytes * 8);
958 WARN_ON(register_pm_notifier(&pm_notifier));
960 WARN(!random_get_entropy(), "Missing cycle counter and fallback timer; RNG "
961 "entropy collection will consequently suffer.");
966 * Add device- or boot-specific data to the input pool to help
969 * None of this adds any entropy; it is meant to avoid the problem of
970 * the entropy pool having similar initial state across largely
973 void add_device_randomness(const void *buf, size_t size)
975 unsigned long entropy = random_get_entropy();
978 spin_lock_irqsave(&input_pool.lock, flags);
979 _mix_pool_bytes(&entropy, sizeof(entropy));
980 _mix_pool_bytes(buf, size);
981 spin_unlock_irqrestore(&input_pool.lock, flags);
983 EXPORT_SYMBOL(add_device_randomness);
986 * Interface for in-kernel drivers of true hardware RNGs.
987 * Those devices may produce endless random bits and will be throttled
988 * when our pool is full.
990 void add_hwgenerator_randomness(const void *buffer, size_t count,
993 mix_pool_bytes(buffer, count);
994 credit_init_bits(entropy);
997 * Throttle writing to once every CRNG_RESEED_INTERVAL, unless
998 * we're not yet initialized.
1000 if (!kthread_should_stop() && crng_ready())
1001 schedule_timeout_interruptible(CRNG_RESEED_INTERVAL);
1003 EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
1006 * Handle random seed passed by bootloader, and credit it if
1007 * CONFIG_RANDOM_TRUST_BOOTLOADER is set.
1009 void add_bootloader_randomness(const void *buf, size_t size)
1011 mix_pool_bytes(buf, size);
1012 if (trust_bootloader)
1013 credit_init_bits(size * 8);
1015 EXPORT_SYMBOL_GPL(add_bootloader_randomness);
1017 #if IS_ENABLED(CONFIG_VMGENID)
1018 static BLOCKING_NOTIFIER_HEAD(vmfork_chain);
1021 * Handle a new unique VM ID, which is unique, not secret, so we
1022 * don't credit it, but we do immediately force a reseed after so
1023 * that it's used by the crng posthaste.
1025 void add_vmfork_randomness(const void *unique_vm_id, size_t size)
1027 add_device_randomness(unique_vm_id, size);
1030 pr_notice("crng reseeded due to virtual machine fork\n");
1032 blocking_notifier_call_chain(&vmfork_chain, 0, NULL);
1034 #if IS_MODULE(CONFIG_VMGENID)
1035 EXPORT_SYMBOL_GPL(add_vmfork_randomness);
1038 int register_random_vmfork_notifier(struct notifier_block *nb)
1040 return blocking_notifier_chain_register(&vmfork_chain, nb);
1042 EXPORT_SYMBOL_GPL(register_random_vmfork_notifier);
1044 int unregister_random_vmfork_notifier(struct notifier_block *nb)
1046 return blocking_notifier_chain_unregister(&vmfork_chain, nb);
1048 EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier);
1052 struct work_struct mix;
1053 unsigned long pool[4];
1058 static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = {
1060 #define FASTMIX_PERM SIPHASH_PERMUTATION
1061 .pool = { SIPHASH_CONST_0, SIPHASH_CONST_1, SIPHASH_CONST_2, SIPHASH_CONST_3 }
1063 #define FASTMIX_PERM HSIPHASH_PERMUTATION
1064 .pool = { HSIPHASH_CONST_0, HSIPHASH_CONST_1, HSIPHASH_CONST_2, HSIPHASH_CONST_3 }
1069 * This is [Half]SipHash-1-x, starting from an empty key. Because
1070 * the key is fixed, it assumes that its inputs are non-malicious,
1071 * and therefore this has no security on its own. s represents the
1072 * four-word SipHash state, while v represents a two-word input.
1074 static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long v2)
1077 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1080 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1086 * This function is called when the CPU has just come online, with
1087 * entry CPUHP_AP_RANDOM_ONLINE, just after CPUHP_AP_WORKQUEUE_ONLINE.
1089 int random_online_cpu(unsigned int cpu)
1092 * During CPU shutdown and before CPU onlining, add_interrupt_
1093 * randomness() may schedule mix_interrupt_randomness(), and
1094 * set the MIX_INFLIGHT flag. However, because the worker can
1095 * be scheduled on a different CPU during this period, that
1096 * flag will never be cleared. For that reason, we zero out
1097 * the flag here, which runs just after workqueues are onlined
1098 * for the CPU again. This also has the effect of setting the
1099 * irq randomness count to zero so that new accumulated irqs
1102 per_cpu_ptr(&irq_randomness, cpu)->count = 0;
1107 static void mix_interrupt_randomness(struct work_struct *work)
1109 struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix);
1111 * The size of the copied stack pool is explicitly 2 longs so that we
1112 * only ever ingest half of the siphash output each time, retaining
1113 * the other half as the next "key" that carries over. The entropy is
1114 * supposed to be sufficiently dispersed between bits so on average
1115 * we don't wind up "losing" some.
1117 unsigned long pool[2];
1120 /* Check to see if we're running on the wrong CPU due to hotplug. */
1121 local_irq_disable();
1122 if (fast_pool != this_cpu_ptr(&irq_randomness)) {
1128 * Copy the pool to the stack so that the mixer always has a
1129 * consistent view, before we reenable irqs again.
1131 memcpy(pool, fast_pool->pool, sizeof(pool));
1132 count = fast_pool->count;
1133 fast_pool->count = 0;
1134 fast_pool->last = jiffies;
1137 mix_pool_bytes(pool, sizeof(pool));
1138 credit_init_bits(max(1u, (count & U16_MAX) / 64));
1140 memzero_explicit(pool, sizeof(pool));
1143 void add_interrupt_randomness(int irq)
1145 enum { MIX_INFLIGHT = 1U << 31 };
1146 unsigned long entropy = random_get_entropy();
1147 struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
1148 struct pt_regs *regs = get_irq_regs();
1149 unsigned int new_count;
1151 fast_mix(fast_pool->pool, entropy,
1152 (regs ? instruction_pointer(regs) : _RET_IP_) ^ swab(irq));
1153 new_count = ++fast_pool->count;
1155 if (new_count & MIX_INFLIGHT)
1158 if (new_count < 64 && !time_is_before_jiffies(fast_pool->last + HZ))
1161 if (unlikely(!fast_pool->mix.func))
1162 INIT_WORK(&fast_pool->mix, mix_interrupt_randomness);
1163 fast_pool->count |= MIX_INFLIGHT;
1164 queue_work_on(raw_smp_processor_id(), system_highpri_wq, &fast_pool->mix);
1166 EXPORT_SYMBOL_GPL(add_interrupt_randomness);
1168 /* There is one of these per entropy source */
1169 struct timer_rand_state {
1170 unsigned long last_time;
1171 long last_delta, last_delta2;
1175 * This function adds entropy to the entropy "pool" by using timing
1176 * delays. It uses the timer_rand_state structure to make an estimate
1177 * of how many bits of entropy this call has added to the pool. The
1178 * value "num" is also added to the pool; it should somehow describe
1179 * the type of event that just happened.
1181 static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
1183 unsigned long entropy = random_get_entropy(), now = jiffies, flags;
1184 long delta, delta2, delta3;
1188 * If we're in a hard IRQ, add_interrupt_randomness() will be called
1189 * sometime after, so mix into the fast pool.
1192 fast_mix(this_cpu_ptr(&irq_randomness)->pool, entropy, num);
1194 spin_lock_irqsave(&input_pool.lock, flags);
1195 _mix_pool_bytes(&entropy, sizeof(entropy));
1196 _mix_pool_bytes(&num, sizeof(num));
1197 spin_unlock_irqrestore(&input_pool.lock, flags);
1204 * Calculate number of bits of randomness we probably added.
1205 * We take into account the first, second and third-order deltas
1206 * in order to make our estimate.
1208 delta = now - READ_ONCE(state->last_time);
1209 WRITE_ONCE(state->last_time, now);
1211 delta2 = delta - READ_ONCE(state->last_delta);
1212 WRITE_ONCE(state->last_delta, delta);
1214 delta3 = delta2 - READ_ONCE(state->last_delta2);
1215 WRITE_ONCE(state->last_delta2, delta2);
1229 * delta is now minimum absolute delta. Round down by 1 bit
1230 * on general principles, and limit entropy estimate to 11 bits.
1232 bits = min(fls(delta >> 1), 11);
1235 * As mentioned above, if we're in a hard IRQ, add_interrupt_randomness()
1236 * will run after this, which uses a different crediting scheme of 1 bit
1237 * per every 64 interrupts. In order to let that function do accounting
1238 * close to the one in this function, we credit a full 64/64 bit per bit,
1239 * and then subtract one to account for the extra one added.
1242 this_cpu_ptr(&irq_randomness)->count += max(1u, bits * 64) - 1;
1244 credit_init_bits(bits);
1247 void add_input_randomness(unsigned int type, unsigned int code,
1250 static unsigned char last_value;
1251 static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES };
1253 /* Ignore autorepeat and the like. */
1254 if (value == last_value)
1258 add_timer_randomness(&input_timer_state,
1259 (type << 4) ^ code ^ (code >> 4) ^ value);
1261 EXPORT_SYMBOL_GPL(add_input_randomness);
1264 void add_disk_randomness(struct gendisk *disk)
1266 if (!disk || !disk->random)
1268 /* First major is 1, so we get >= 0x200 here. */
1269 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
1271 EXPORT_SYMBOL_GPL(add_disk_randomness);
1273 void rand_initialize_disk(struct gendisk *disk)
1275 struct timer_rand_state *state;
1278 * If kzalloc returns null, we just won't use that entropy
1281 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1283 state->last_time = INITIAL_JIFFIES;
1284 disk->random = state;
1289 struct entropy_timer_state {
1290 unsigned long entropy;
1291 struct timer_list timer;
1292 unsigned int samples, samples_per_bit;
1296 * Each time the timer fires, we expect that we got an unpredictable
1297 * jump in the cycle counter. Even if the timer is running on another
1298 * CPU, the timer activity will be touching the stack of the CPU that is
1299 * generating entropy..
1301 * Note that we don't re-arm the timer in the timer itself - we are
1302 * happy to be scheduled away, since that just makes the load more
1303 * complex, but we do not want the timer to keep ticking unless the
1304 * entropy loop is running.
1306 * So the re-arming always happens in the entropy loop itself.
1308 static void entropy_timer(struct timer_list *timer)
1310 struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer);
1312 if (++state->samples == state->samples_per_bit) {
1313 credit_init_bits(1);
1319 * If we have an actual cycle counter, see if we can
1320 * generate enough entropy with timing noise
1322 static void try_to_generate_entropy(void)
1324 enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = 32 };
1325 struct entropy_timer_state stack;
1326 unsigned int i, num_different = 0;
1327 unsigned long last = random_get_entropy();
1329 for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
1330 stack.entropy = random_get_entropy();
1331 if (stack.entropy != last)
1333 last = stack.entropy;
1335 stack.samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1);
1336 if (stack.samples_per_bit > MAX_SAMPLES_PER_BIT)
1340 timer_setup_on_stack(&stack.timer, entropy_timer, 0);
1341 while (!crng_ready() && !signal_pending(current)) {
1342 if (!timer_pending(&stack.timer))
1343 mod_timer(&stack.timer, jiffies + 1);
1344 mix_pool_bytes(&stack.entropy, sizeof(stack.entropy));
1346 stack.entropy = random_get_entropy();
1349 del_timer_sync(&stack.timer);
1350 destroy_timer_on_stack(&stack.timer);
1351 mix_pool_bytes(&stack.entropy, sizeof(stack.entropy));
1355 /**********************************************************************
1357 * Userspace reader/writer interfaces.
1359 * getrandom(2) is the primary modern interface into the RNG and should
1360 * be used in preference to anything else.
1362 * Reading from /dev/random has the same functionality as calling
1363 * getrandom(2) with flags=0. In earlier versions, however, it had
1364 * vastly different semantics and should therefore be avoided, to
1365 * prevent backwards compatibility issues.
1367 * Reading from /dev/urandom has the same functionality as calling
1368 * getrandom(2) with flags=GRND_INSECURE. Because it does not block
1369 * waiting for the RNG to be ready, it should not be used.
1371 * Writing to either /dev/random or /dev/urandom adds entropy to
1372 * the input pool but does not credit it.
1374 * Polling on /dev/random indicates when the RNG is initialized, on
1375 * the read side, and when it wants new entropy, on the write side.
1377 * Both /dev/random and /dev/urandom have the same set of ioctls for
1378 * adding entropy, getting the entropy count, zeroing the count, and
1379 * reseeding the crng.
1381 **********************************************************************/
1383 SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
1386 if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
1390 * Requesting insecure and blocking randomness at the same time makes
1393 if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
1396 if (count > INT_MAX)
1399 if (!(flags & GRND_INSECURE) && !crng_ready()) {
1402 if (flags & GRND_NONBLOCK)
1404 ret = wait_for_random_bytes();
1408 return get_random_bytes_user(buf, count);
1411 static __poll_t random_poll(struct file *file, poll_table *wait)
1413 poll_wait(file, &crng_init_wait, wait);
1414 return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
1417 static int write_pool(const char __user *ubuf, size_t count)
1421 u8 block[BLAKE2S_BLOCK_SIZE];
1424 len = min(count, sizeof(block));
1425 if (copy_from_user(block, ubuf, len)) {
1431 mix_pool_bytes(block, len);
1436 memzero_explicit(block, sizeof(block));
1440 static ssize_t random_write(struct file *file, const char __user *buffer,
1441 size_t count, loff_t *ppos)
1445 ret = write_pool(buffer, count);
1449 return (ssize_t)count;
1452 static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
1455 static int maxwarn = 10;
1458 * Opportunistically attempt to initialize the RNG on platforms that
1459 * have fast cycle counters, but don't (for now) require it to succeed.
1462 try_to_generate_entropy();
1464 if (!crng_ready()) {
1465 if (!ratelimit_disable && maxwarn <= 0)
1466 ++urandom_warning.missed;
1467 else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
1469 pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
1470 current->comm, nbytes);
1474 return get_random_bytes_user(buf, nbytes);
1477 static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes,
1482 ret = wait_for_random_bytes();
1485 return get_random_bytes_user(buf, nbytes);
1488 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1490 int size, ent_count;
1491 int __user *p = (int __user *)arg;
1496 /* Inherently racy, no point locking. */
1497 if (put_user(input_pool.init_bits, p))
1500 case RNDADDTOENTCNT:
1501 if (!capable(CAP_SYS_ADMIN))
1503 if (get_user(ent_count, p))
1507 credit_init_bits(ent_count);
1510 if (!capable(CAP_SYS_ADMIN))
1512 if (get_user(ent_count, p++))
1516 if (get_user(size, p++))
1518 retval = write_pool((const char __user *)p, size);
1521 credit_init_bits(ent_count);
1525 /* No longer has any effect. */
1526 if (!capable(CAP_SYS_ADMIN))
1530 if (!capable(CAP_SYS_ADMIN))
1541 static int random_fasync(int fd, struct file *filp, int on)
1543 return fasync_helper(fd, filp, on, &fasync);
1546 const struct file_operations random_fops = {
1547 .read = random_read,
1548 .write = random_write,
1549 .poll = random_poll,
1550 .unlocked_ioctl = random_ioctl,
1551 .compat_ioctl = compat_ptr_ioctl,
1552 .fasync = random_fasync,
1553 .llseek = noop_llseek,
1556 const struct file_operations urandom_fops = {
1557 .read = urandom_read,
1558 .write = random_write,
1559 .unlocked_ioctl = random_ioctl,
1560 .compat_ioctl = compat_ptr_ioctl,
1561 .fasync = random_fasync,
1562 .llseek = noop_llseek,
1566 /********************************************************************
1570 * These are partly unused legacy knobs with dummy values to not break
1571 * userspace and partly still useful things. They are usually accessible
1572 * in /proc/sys/kernel/random/ and are as follows:
1574 * - boot_id - a UUID representing the current boot.
1576 * - uuid - a random UUID, different each time the file is read.
1578 * - poolsize - the number of bits of entropy that the input pool can
1579 * hold, tied to the POOL_BITS constant.
1581 * - entropy_avail - the number of bits of entropy currently in the
1582 * input pool. Always <= poolsize.
1584 * - write_wakeup_threshold - the amount of entropy in the input pool
1585 * below which write polls to /dev/random will unblock, requesting
1586 * more entropy, tied to the POOL_READY_BITS constant. It is writable
1587 * to avoid breaking old userspaces, but writing to it does not
1588 * change any behavior of the RNG.
1590 * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL.
1591 * It is writable to avoid breaking old userspaces, but writing
1592 * to it does not change any behavior of the RNG.
1594 ********************************************************************/
1596 #ifdef CONFIG_SYSCTL
1598 #include <linux/sysctl.h>
1600 static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ;
1601 static int sysctl_random_write_wakeup_bits = POOL_READY_BITS;
1602 static int sysctl_poolsize = POOL_BITS;
1603 static u8 sysctl_bootid[UUID_SIZE];
1606 * This function is used to return both the bootid UUID, and random
1607 * UUID. The difference is in whether table->data is NULL; if it is,
1608 * then a new UUID is generated and returned to the user.
1610 static int proc_do_uuid(struct ctl_table *table, int write, void *buffer,
1611 size_t *lenp, loff_t *ppos)
1613 u8 tmp_uuid[UUID_SIZE], *uuid;
1614 char uuid_string[UUID_STRING_LEN + 1];
1615 struct ctl_table fake_table = {
1616 .data = uuid_string,
1617 .maxlen = UUID_STRING_LEN
1626 generate_random_uuid(uuid);
1628 static DEFINE_SPINLOCK(bootid_spinlock);
1630 spin_lock(&bootid_spinlock);
1632 generate_random_uuid(uuid);
1633 spin_unlock(&bootid_spinlock);
1636 snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
1637 return proc_dostring(&fake_table, 0, buffer, lenp, ppos);
1640 /* The same as proc_dointvec, but writes don't change anything. */
1641 static int proc_do_rointvec(struct ctl_table *table, int write, void *buffer,
1642 size_t *lenp, loff_t *ppos)
1644 return write ? 0 : proc_dointvec(table, 0, buffer, lenp, ppos);
1647 static struct ctl_table random_table[] = {
1649 .procname = "poolsize",
1650 .data = &sysctl_poolsize,
1651 .maxlen = sizeof(int),
1653 .proc_handler = proc_dointvec,
1656 .procname = "entropy_avail",
1657 .data = &input_pool.init_bits,
1658 .maxlen = sizeof(int),
1660 .proc_handler = proc_dointvec,
1663 .procname = "write_wakeup_threshold",
1664 .data = &sysctl_random_write_wakeup_bits,
1665 .maxlen = sizeof(int),
1667 .proc_handler = proc_do_rointvec,
1670 .procname = "urandom_min_reseed_secs",
1671 .data = &sysctl_random_min_urandom_seed,
1672 .maxlen = sizeof(int),
1674 .proc_handler = proc_do_rointvec,
1677 .procname = "boot_id",
1678 .data = &sysctl_bootid,
1680 .proc_handler = proc_do_uuid,
1685 .proc_handler = proc_do_uuid,
1691 * random_init() is called before sysctl_init(),
1692 * so we cannot call register_sysctl_init() in random_init()
1694 static int __init random_sysctls_init(void)
1696 register_sysctl_init("kernel/random", random_table);
1699 device_initcall(random_sysctls_init);