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 __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;
88 /* Control how we warn userspace. */
89 static struct ratelimit_state urandom_warning =
90 RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE);
91 static int ratelimit_disable __read_mostly =
92 IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
93 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
94 MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
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.
102 * Returns: true if the input pool has been seeded.
103 * false if the input pool has not been seeded.
105 bool rng_is_initialized(void)
109 EXPORT_SYMBOL(rng_is_initialized);
111 static void __cold crng_set_ready(struct work_struct *work)
113 static_branch_enable(&crng_is_ready);
116 /* Used by wait_for_random_bytes(), and considered an entropy collector, below. */
117 static void try_to_generate_entropy(void);
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.
126 * Returns: 0 if the input pool has been seeded.
127 * -ERESTARTSYS if the function was interrupted by a signal.
129 int wait_for_random_bytes(void)
131 while (!crng_ready()) {
134 try_to_generate_entropy();
135 ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
137 return ret > 0 ? 0 : ret;
141 EXPORT_SYMBOL(wait_for_random_bytes);
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)
149 /*********************************************************************
151 * Fast key erasure RNG, the "crng".
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>.
157 * There are a few exported interfaces for use by other drivers:
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()
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.
172 *********************************************************************/
175 CRNG_RESEED_START_INTERVAL = HZ,
176 CRNG_RESEED_INTERVAL = 60 * HZ
180 u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long));
182 unsigned long generation;
185 .lock = __SPIN_LOCK_UNLOCKED(base_crng.lock)
189 u8 key[CHACHA_KEY_SIZE];
190 unsigned long generation;
194 static DEFINE_PER_CPU(struct crng, crngs) = {
195 .generation = ULONG_MAX,
196 .lock = INIT_LOCAL_LOCK(crngs.lock),
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);
202 /* This extracts a new crng key from the input pool. */
203 static void crng_reseed(void)
206 unsigned long next_gen;
207 u8 key[CHACHA_KEY_SIZE];
209 extract_entropy(key, sizeof(key));
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.
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)
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));
231 * This generates a ChaCha block using the provided key, and then
232 * immediately overwrites 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.
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.
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)
248 u8 first_block[CHACHA_BLOCK_SIZE];
250 BUG_ON(random_data_len > 32);
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);
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));
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.
268 static bool crng_has_old_seed(void)
270 static bool early_boot = true;
271 unsigned long interval = CRNG_RESEED_INTERVAL;
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);
278 interval = max_t(unsigned int, CRNG_RESEED_START_INTERVAL,
279 (unsigned int)uptime / 2 * HZ);
281 return time_is_before_jiffies(READ_ONCE(base_crng.birth) + interval);
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.
289 static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
290 u8 *random_data, size_t random_data_len)
295 BUG_ON(random_data_len > 32);
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.
306 spin_lock_irqsave(&base_crng.lock, flags);
307 ready = crng_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);
314 spin_unlock_irqrestore(&base_crng.lock, flags);
320 * If the base_crng is old enough, we reseed, which in turn bumps the
321 * generation counter that we check below.
323 if (unlikely(crng_has_old_seed()))
326 local_lock_irqsave(&crngs.lock, flags);
327 crng = raw_cpu_ptr(&crngs);
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.
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);
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.
350 crng_fast_key_erasure(crng->key, chacha_state, random_data, random_data_len);
351 local_unlock_irqrestore(&crngs.lock, flags);
354 static void _get_random_bytes(void *buf, size_t len)
356 u32 chacha_state[CHACHA_STATE_WORDS];
357 u8 tmp[CHACHA_BLOCK_SIZE];
358 size_t first_block_len;
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;
369 if (len < CHACHA_BLOCK_SIZE) {
370 chacha20_block(chacha_state, tmp);
371 memcpy(buf, tmp, len);
372 memzero_explicit(tmp, sizeof(tmp));
376 chacha20_block(chacha_state, buf);
377 if (unlikely(chacha_state[12] == 0))
379 len -= CHACHA_BLOCK_SIZE;
380 buf += CHACHA_BLOCK_SIZE;
383 memzero_explicit(chacha_state, sizeof(chacha_state));
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.
393 void get_random_bytes(void *buf, size_t len)
395 warn_unseeded_randomness();
396 _get_random_bytes(buf, len);
398 EXPORT_SYMBOL(get_random_bytes);
400 static ssize_t get_random_bytes_user(struct iov_iter *iter)
402 u32 chacha_state[CHACHA_STATE_WORDS];
403 u8 block[CHACHA_BLOCK_SIZE];
404 size_t ret = 0, copied;
406 if (unlikely(!iov_iter_count(iter)))
410 * Immediately overwrite the ChaCha key at index 4 with random
411 * bytes, in case userspace causes copy_to_iter() below to sleep
412 * forever, so that we still retain forward secrecy in that case.
414 crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA_KEY_SIZE);
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
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;
426 chacha20_block(chacha_state, block);
427 if (unlikely(chacha_state[12] == 0))
430 copied = copy_to_iter(block, sizeof(block), iter);
432 if (!iov_iter_count(iter) || copied != sizeof(block))
435 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
436 if (ret % PAGE_SIZE == 0) {
437 if (signal_pending(current))
443 memzero_explicit(block, sizeof(block));
445 memzero_explicit(chacha_state, sizeof(chacha_state));
446 return ret ? ret : -EFAULT;
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.
456 #define DEFINE_BATCHED_ENTROPY(type) \
457 struct batch_ ##type { \
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. \
465 type entropy[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(type))]; \
467 unsigned long generation; \
468 unsigned int position; \
471 static DEFINE_PER_CPU(struct batch_ ##type, batched_entropy_ ##type) = { \
472 .lock = INIT_LOCAL_LOCK(batched_entropy_ ##type.lock), \
473 .position = UINT_MAX \
476 type get_random_ ##type(void) \
479 unsigned long flags; \
480 struct batch_ ##type *batch; \
481 unsigned long next_gen; \
483 warn_unseeded_randomness(); \
485 if (!crng_ready()) { \
486 _get_random_bytes(&ret, sizeof(ret)); \
490 local_lock_irqsave(&batched_entropy_ ##type.lock, flags); \
491 batch = raw_cpu_ptr(&batched_entropy_##type); \
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; \
501 ret = batch->entropy[batch->position]; \
502 batch->entropy[batch->position] = 0; \
504 local_unlock_irqrestore(&batched_entropy_ ##type.lock, flags); \
507 EXPORT_SYMBOL(get_random_ ##type);
509 DEFINE_BATCHED_ENTROPY(u64)
510 DEFINE_BATCHED_ENTROPY(u32)
514 * This function is called when the CPU is coming up, with entry
515 * CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP.
517 int __cold random_prepare_cpu(unsigned int cpu)
520 * When the cpu comes back online, immediately invalidate both
521 * the per-cpu crng and all batches, so that we serve fresh
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;
532 /**********************************************************************
534 * Entropy accumulation and extraction routines.
536 * Callers may add entropy via:
538 * static void mix_pool_bytes(const void *buf, size_t len)
540 * After which, if added entropy should be credited:
542 * static void credit_init_bits(size_t bits)
544 * Finally, extract entropy via:
546 * static void extract_entropy(void *buf, size_t len)
548 **********************************************************************/
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 */
557 struct blake2s_state hash;
559 unsigned int init_bits;
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),
568 static void _mix_pool_bytes(const void *buf, size_t len)
570 blake2s_update(&input_pool.hash, buf, len);
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.
578 static void mix_pool_bytes(const void *buf, size_t len)
582 spin_lock_irqsave(&input_pool.lock, flags);
583 _mix_pool_bytes(buf, len);
584 spin_unlock_irqrestore(&input_pool.lock, flags);
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.
591 static void extract_entropy(void *buf, size_t len)
594 u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
596 unsigned long rdseed[32 / sizeof(long)];
601 for (i = 0; i < ARRAY_SIZE(block.rdseed);) {
602 longs = arch_get_random_seed_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
607 longs = arch_get_random_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
612 block.rdseed[i++] = random_get_entropy();
615 spin_lock_irqsave(&input_pool.lock, flags);
617 /* seed = HASHPRF(last_key, entropy_input) */
618 blake2s_final(&input_pool.hash, seed);
620 /* next_key = HASHPRF(seed, RDSEED || 0) */
622 blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
623 blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
625 spin_unlock_irqrestore(&input_pool.lock, flags);
626 memzero_explicit(next_key, sizeof(next_key));
629 i = min_t(size_t, len, BLAKE2S_HASH_SIZE);
630 /* output = HASHPRF(seed, RDSEED || ++counter) */
632 blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
637 memzero_explicit(seed, sizeof(seed));
638 memzero_explicit(&block, sizeof(block));
641 #define credit_init_bits(bits) if (!crng_ready()) _credit_init_bits(bits)
643 static void __cold _credit_init_bits(size_t bits)
645 static struct execute_work set_ready;
646 unsigned int new, orig, add;
652 add = min_t(size_t, bits, POOL_BITS);
654 orig = READ_ONCE(input_pool.init_bits);
656 new = min_t(unsigned int, POOL_BITS, orig + add);
657 } while (!try_cmpxchg(&input_pool.init_bits, &orig, new));
659 if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
660 crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */
661 if (static_key_initialized)
662 execute_in_process_context(crng_set_ready, &set_ready);
663 wake_up_interruptible(&crng_init_wait);
664 kill_fasync(&fasync, SIGIO, POLL_IN);
665 pr_notice("crng init done\n");
666 if (urandom_warning.missed)
667 pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
668 urandom_warning.missed);
669 } else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
670 spin_lock_irqsave(&base_crng.lock, flags);
671 /* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */
672 if (crng_init == CRNG_EMPTY) {
673 extract_entropy(base_crng.key, sizeof(base_crng.key));
674 crng_init = CRNG_EARLY;
676 spin_unlock_irqrestore(&base_crng.lock, flags);
681 /**********************************************************************
683 * Entropy collection routines.
685 * The following exported functions are used for pushing entropy into
686 * the above entropy accumulation routines:
688 * void add_device_randomness(const void *buf, size_t len);
689 * void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy);
690 * void add_bootloader_randomness(const void *buf, size_t len);
691 * void add_vmfork_randomness(const void *unique_vm_id, size_t len);
692 * void add_interrupt_randomness(int irq);
693 * void add_input_randomness(unsigned int type, unsigned int code, unsigned int value);
694 * void add_disk_randomness(struct gendisk *disk);
696 * add_device_randomness() adds data to the input pool that
697 * is likely to differ between two devices (or possibly even per boot).
698 * This would be things like MAC addresses or serial numbers, or the
699 * read-out of the RTC. This does *not* credit any actual entropy to
700 * the pool, but it initializes the pool to different values for devices
701 * that might otherwise be identical and have very little entropy
702 * available to them (particularly common in the embedded world).
704 * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
705 * entropy as specified by the caller. If the entropy pool is full it will
706 * block until more entropy is needed.
708 * add_bootloader_randomness() is called by bootloader drivers, such as EFI
709 * and device tree, and credits its input depending on whether or not the
710 * configuration option CONFIG_RANDOM_TRUST_BOOTLOADER is set.
712 * add_vmfork_randomness() adds a unique (but not necessarily secret) ID
713 * representing the current instance of a VM to the pool, without crediting,
714 * and then force-reseeds the crng so that it takes effect immediately.
716 * add_interrupt_randomness() uses the interrupt timing as random
717 * inputs to the entropy pool. Using the cycle counters and the irq source
718 * as inputs, it feeds the input pool roughly once a second or after 64
719 * interrupts, crediting 1 bit of entropy for whichever comes first.
721 * add_input_randomness() uses the input layer interrupt timing, as well
722 * as the event type information from the hardware.
724 * add_disk_randomness() uses what amounts to the seek time of block
725 * layer request events, on a per-disk_devt basis, as input to the
726 * entropy pool. Note that high-speed solid state drives with very low
727 * seek times do not make for good sources of entropy, as their seek
728 * times are usually fairly consistent.
730 * The last two routines try to estimate how many bits of entropy
731 * to credit. They do this by keeping track of the first and second
732 * order deltas of the event timings.
734 **********************************************************************/
736 static bool trust_cpu __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
737 static bool trust_bootloader __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER);
738 static int __init parse_trust_cpu(char *arg)
740 return kstrtobool(arg, &trust_cpu);
742 static int __init parse_trust_bootloader(char *arg)
744 return kstrtobool(arg, &trust_bootloader);
746 early_param("random.trust_cpu", parse_trust_cpu);
747 early_param("random.trust_bootloader", parse_trust_bootloader);
749 static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data)
751 unsigned long flags, entropy = random_get_entropy();
754 * Encode a representation of how long the system has been suspended,
755 * in a way that is distinct from prior system suspends.
757 ktime_t stamps[] = { ktime_get(), ktime_get_boottime(), ktime_get_real() };
759 spin_lock_irqsave(&input_pool.lock, flags);
760 _mix_pool_bytes(&action, sizeof(action));
761 _mix_pool_bytes(stamps, sizeof(stamps));
762 _mix_pool_bytes(&entropy, sizeof(entropy));
763 spin_unlock_irqrestore(&input_pool.lock, flags);
765 if (crng_ready() && (action == PM_RESTORE_PREPARE ||
766 (action == PM_POST_SUSPEND && !IS_ENABLED(CONFIG_PM_AUTOSLEEP) &&
767 !IS_ENABLED(CONFIG_PM_USERSPACE_AUTOSLEEP)))) {
769 pr_notice("crng reseeded on system resumption\n");
774 static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification };
777 * The first collection of entropy occurs at system boot while interrupts
778 * are still turned off. Here we push in latent entropy, RDSEED, a timestamp,
779 * utsname(), and the command line. Depending on the above configuration knob,
780 * RDSEED may be considered sufficient for initialization. Note that much
781 * earlier setup may already have pushed entropy into the input pool by the
784 int __init random_init(const char *command_line)
786 ktime_t now = ktime_get_real();
787 size_t i, longs, arch_bits;
788 unsigned long entropy[BLAKE2S_BLOCK_SIZE / sizeof(long)];
790 #if defined(LATENT_ENTROPY_PLUGIN)
791 static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
792 _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
795 for (i = 0, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) {
796 longs = arch_get_random_seed_longs(entropy, ARRAY_SIZE(entropy) - i);
798 _mix_pool_bytes(entropy, sizeof(*entropy) * longs);
802 longs = arch_get_random_longs(entropy, ARRAY_SIZE(entropy) - i);
804 _mix_pool_bytes(entropy, sizeof(*entropy) * longs);
808 entropy[0] = random_get_entropy();
809 _mix_pool_bytes(entropy, sizeof(*entropy));
810 arch_bits -= sizeof(*entropy) * 8;
813 _mix_pool_bytes(&now, sizeof(now));
814 _mix_pool_bytes(utsname(), sizeof(*(utsname())));
815 _mix_pool_bytes(command_line, strlen(command_line));
816 add_latent_entropy();
819 * If we were initialized by the bootloader before jump labels are
820 * initialized, then we should enable the static branch here, where
821 * it's guaranteed that jump labels have been initialized.
823 if (!static_branch_likely(&crng_is_ready) && crng_init >= CRNG_READY)
824 crng_set_ready(NULL);
829 _credit_init_bits(arch_bits);
831 WARN_ON(register_pm_notifier(&pm_notifier));
833 WARN(!random_get_entropy(), "Missing cycle counter and fallback timer; RNG "
834 "entropy collection will consequently suffer.");
839 * Add device- or boot-specific data to the input pool to help
842 * None of this adds any entropy; it is meant to avoid the problem of
843 * the entropy pool having similar initial state across largely
846 void add_device_randomness(const void *buf, size_t len)
848 unsigned long entropy = random_get_entropy();
851 spin_lock_irqsave(&input_pool.lock, flags);
852 _mix_pool_bytes(&entropy, sizeof(entropy));
853 _mix_pool_bytes(buf, len);
854 spin_unlock_irqrestore(&input_pool.lock, flags);
856 EXPORT_SYMBOL(add_device_randomness);
859 * Interface for in-kernel drivers of true hardware RNGs.
860 * Those devices may produce endless random bits and will be throttled
861 * when our pool is full.
863 void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy)
865 mix_pool_bytes(buf, len);
866 credit_init_bits(entropy);
869 * Throttle writing to once every CRNG_RESEED_INTERVAL, unless
870 * we're not yet initialized.
872 if (!kthread_should_stop() && crng_ready())
873 schedule_timeout_interruptible(CRNG_RESEED_INTERVAL);
875 EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
878 * Handle random seed passed by bootloader, and credit it if
879 * CONFIG_RANDOM_TRUST_BOOTLOADER is set.
881 void __init add_bootloader_randomness(const void *buf, size_t len)
883 mix_pool_bytes(buf, len);
884 if (trust_bootloader)
885 credit_init_bits(len * 8);
888 #if IS_ENABLED(CONFIG_VMGENID)
889 static BLOCKING_NOTIFIER_HEAD(vmfork_chain);
892 * Handle a new unique VM ID, which is unique, not secret, so we
893 * don't credit it, but we do immediately force a reseed after so
894 * that it's used by the crng posthaste.
896 void __cold add_vmfork_randomness(const void *unique_vm_id, size_t len)
898 add_device_randomness(unique_vm_id, len);
901 pr_notice("crng reseeded due to virtual machine fork\n");
903 blocking_notifier_call_chain(&vmfork_chain, 0, NULL);
905 #if IS_MODULE(CONFIG_VMGENID)
906 EXPORT_SYMBOL_GPL(add_vmfork_randomness);
909 int __cold register_random_vmfork_notifier(struct notifier_block *nb)
911 return blocking_notifier_chain_register(&vmfork_chain, nb);
913 EXPORT_SYMBOL_GPL(register_random_vmfork_notifier);
915 int __cold unregister_random_vmfork_notifier(struct notifier_block *nb)
917 return blocking_notifier_chain_unregister(&vmfork_chain, nb);
919 EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier);
923 struct work_struct mix;
924 unsigned long pool[4];
929 static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = {
931 #define FASTMIX_PERM SIPHASH_PERMUTATION
932 .pool = { SIPHASH_CONST_0, SIPHASH_CONST_1, SIPHASH_CONST_2, SIPHASH_CONST_3 }
934 #define FASTMIX_PERM HSIPHASH_PERMUTATION
935 .pool = { HSIPHASH_CONST_0, HSIPHASH_CONST_1, HSIPHASH_CONST_2, HSIPHASH_CONST_3 }
940 * This is [Half]SipHash-1-x, starting from an empty key. Because
941 * the key is fixed, it assumes that its inputs are non-malicious,
942 * and therefore this has no security on its own. s represents the
943 * four-word SipHash state, while v represents a two-word input.
945 static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long v2)
948 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
951 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
957 * This function is called when the CPU has just come online, with
958 * entry CPUHP_AP_RANDOM_ONLINE, just after CPUHP_AP_WORKQUEUE_ONLINE.
960 int __cold random_online_cpu(unsigned int cpu)
963 * During CPU shutdown and before CPU onlining, add_interrupt_
964 * randomness() may schedule mix_interrupt_randomness(), and
965 * set the MIX_INFLIGHT flag. However, because the worker can
966 * be scheduled on a different CPU during this period, that
967 * flag will never be cleared. For that reason, we zero out
968 * the flag here, which runs just after workqueues are onlined
969 * for the CPU again. This also has the effect of setting the
970 * irq randomness count to zero so that new accumulated irqs
973 per_cpu_ptr(&irq_randomness, cpu)->count = 0;
978 static void mix_interrupt_randomness(struct work_struct *work)
980 struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix);
982 * The size of the copied stack pool is explicitly 2 longs so that we
983 * only ever ingest half of the siphash output each time, retaining
984 * the other half as the next "key" that carries over. The entropy is
985 * supposed to be sufficiently dispersed between bits so on average
986 * we don't wind up "losing" some.
988 unsigned long pool[2];
991 /* Check to see if we're running on the wrong CPU due to hotplug. */
993 if (fast_pool != this_cpu_ptr(&irq_randomness)) {
999 * Copy the pool to the stack so that the mixer always has a
1000 * consistent view, before we reenable irqs again.
1002 memcpy(pool, fast_pool->pool, sizeof(pool));
1003 count = fast_pool->count;
1004 fast_pool->count = 0;
1005 fast_pool->last = jiffies;
1008 mix_pool_bytes(pool, sizeof(pool));
1009 credit_init_bits(max(1u, (count & U16_MAX) / 64));
1011 memzero_explicit(pool, sizeof(pool));
1014 void add_interrupt_randomness(int irq)
1016 enum { MIX_INFLIGHT = 1U << 31 };
1017 unsigned long entropy = random_get_entropy();
1018 struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
1019 struct pt_regs *regs = get_irq_regs();
1020 unsigned int new_count;
1022 fast_mix(fast_pool->pool, entropy,
1023 (regs ? instruction_pointer(regs) : _RET_IP_) ^ swab(irq));
1024 new_count = ++fast_pool->count;
1026 if (new_count & MIX_INFLIGHT)
1029 if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ))
1032 if (unlikely(!fast_pool->mix.func))
1033 INIT_WORK(&fast_pool->mix, mix_interrupt_randomness);
1034 fast_pool->count |= MIX_INFLIGHT;
1035 queue_work_on(raw_smp_processor_id(), system_highpri_wq, &fast_pool->mix);
1037 EXPORT_SYMBOL_GPL(add_interrupt_randomness);
1039 /* There is one of these per entropy source */
1040 struct timer_rand_state {
1041 unsigned long last_time;
1042 long last_delta, last_delta2;
1046 * This function adds entropy to the entropy "pool" by using timing
1047 * delays. It uses the timer_rand_state structure to make an estimate
1048 * of how many bits of entropy this call has added to the pool. The
1049 * value "num" is also added to the pool; it should somehow describe
1050 * the type of event that just happened.
1052 static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
1054 unsigned long entropy = random_get_entropy(), now = jiffies, flags;
1055 long delta, delta2, delta3;
1059 * If we're in a hard IRQ, add_interrupt_randomness() will be called
1060 * sometime after, so mix into the fast pool.
1063 fast_mix(this_cpu_ptr(&irq_randomness)->pool, entropy, num);
1065 spin_lock_irqsave(&input_pool.lock, flags);
1066 _mix_pool_bytes(&entropy, sizeof(entropy));
1067 _mix_pool_bytes(&num, sizeof(num));
1068 spin_unlock_irqrestore(&input_pool.lock, flags);
1075 * Calculate number of bits of randomness we probably added.
1076 * We take into account the first, second and third-order deltas
1077 * in order to make our estimate.
1079 delta = now - READ_ONCE(state->last_time);
1080 WRITE_ONCE(state->last_time, now);
1082 delta2 = delta - READ_ONCE(state->last_delta);
1083 WRITE_ONCE(state->last_delta, delta);
1085 delta3 = delta2 - READ_ONCE(state->last_delta2);
1086 WRITE_ONCE(state->last_delta2, delta2);
1100 * delta is now minimum absolute delta. Round down by 1 bit
1101 * on general principles, and limit entropy estimate to 11 bits.
1103 bits = min(fls(delta >> 1), 11);
1106 * As mentioned above, if we're in a hard IRQ, add_interrupt_randomness()
1107 * will run after this, which uses a different crediting scheme of 1 bit
1108 * per every 64 interrupts. In order to let that function do accounting
1109 * close to the one in this function, we credit a full 64/64 bit per bit,
1110 * and then subtract one to account for the extra one added.
1113 this_cpu_ptr(&irq_randomness)->count += max(1u, bits * 64) - 1;
1115 _credit_init_bits(bits);
1118 void add_input_randomness(unsigned int type, unsigned int code, unsigned int value)
1120 static unsigned char last_value;
1121 static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES };
1123 /* Ignore autorepeat and the like. */
1124 if (value == last_value)
1128 add_timer_randomness(&input_timer_state,
1129 (type << 4) ^ code ^ (code >> 4) ^ value);
1131 EXPORT_SYMBOL_GPL(add_input_randomness);
1134 void add_disk_randomness(struct gendisk *disk)
1136 if (!disk || !disk->random)
1138 /* First major is 1, so we get >= 0x200 here. */
1139 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
1141 EXPORT_SYMBOL_GPL(add_disk_randomness);
1143 void __cold rand_initialize_disk(struct gendisk *disk)
1145 struct timer_rand_state *state;
1148 * If kzalloc returns null, we just won't use that entropy
1151 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1153 state->last_time = INITIAL_JIFFIES;
1154 disk->random = state;
1159 struct entropy_timer_state {
1160 unsigned long entropy;
1161 struct timer_list timer;
1162 unsigned int samples, samples_per_bit;
1166 * Each time the timer fires, we expect that we got an unpredictable
1167 * jump in the cycle counter. Even if the timer is running on another
1168 * CPU, the timer activity will be touching the stack of the CPU that is
1169 * generating entropy..
1171 * Note that we don't re-arm the timer in the timer itself - we are
1172 * happy to be scheduled away, since that just makes the load more
1173 * complex, but we do not want the timer to keep ticking unless the
1174 * entropy loop is running.
1176 * So the re-arming always happens in the entropy loop itself.
1178 static void __cold entropy_timer(struct timer_list *timer)
1180 struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer);
1182 if (++state->samples == state->samples_per_bit) {
1183 credit_init_bits(1);
1189 * If we have an actual cycle counter, see if we can
1190 * generate enough entropy with timing noise
1192 static void __cold try_to_generate_entropy(void)
1194 enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = HZ / 30 };
1195 struct entropy_timer_state stack;
1196 unsigned int i, num_different = 0;
1197 unsigned long last = random_get_entropy();
1199 for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
1200 stack.entropy = random_get_entropy();
1201 if (stack.entropy != last)
1203 last = stack.entropy;
1205 stack.samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1);
1206 if (stack.samples_per_bit > MAX_SAMPLES_PER_BIT)
1210 timer_setup_on_stack(&stack.timer, entropy_timer, 0);
1211 while (!crng_ready() && !signal_pending(current)) {
1212 if (!timer_pending(&stack.timer))
1213 mod_timer(&stack.timer, jiffies + 1);
1214 mix_pool_bytes(&stack.entropy, sizeof(stack.entropy));
1216 stack.entropy = random_get_entropy();
1219 del_timer_sync(&stack.timer);
1220 destroy_timer_on_stack(&stack.timer);
1221 mix_pool_bytes(&stack.entropy, sizeof(stack.entropy));
1225 /**********************************************************************
1227 * Userspace reader/writer interfaces.
1229 * getrandom(2) is the primary modern interface into the RNG and should
1230 * be used in preference to anything else.
1232 * Reading from /dev/random has the same functionality as calling
1233 * getrandom(2) with flags=0. In earlier versions, however, it had
1234 * vastly different semantics and should therefore be avoided, to
1235 * prevent backwards compatibility issues.
1237 * Reading from /dev/urandom has the same functionality as calling
1238 * getrandom(2) with flags=GRND_INSECURE. Because it does not block
1239 * waiting for the RNG to be ready, it should not be used.
1241 * Writing to either /dev/random or /dev/urandom adds entropy to
1242 * the input pool but does not credit it.
1244 * Polling on /dev/random indicates when the RNG is initialized, on
1245 * the read side, and when it wants new entropy, on the write side.
1247 * Both /dev/random and /dev/urandom have the same set of ioctls for
1248 * adding entropy, getting the entropy count, zeroing the count, and
1249 * reseeding the crng.
1251 **********************************************************************/
1253 SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
1255 struct iov_iter iter;
1259 if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
1263 * Requesting insecure and blocking randomness at the same time makes
1266 if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
1269 if (!crng_ready() && !(flags & GRND_INSECURE)) {
1270 if (flags & GRND_NONBLOCK)
1272 ret = wait_for_random_bytes();
1277 ret = import_single_range(READ, ubuf, len, &iov, &iter);
1280 return get_random_bytes_user(&iter);
1283 static __poll_t random_poll(struct file *file, poll_table *wait)
1285 poll_wait(file, &crng_init_wait, wait);
1286 return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
1289 static ssize_t write_pool_user(struct iov_iter *iter)
1291 u8 block[BLAKE2S_BLOCK_SIZE];
1295 if (unlikely(!iov_iter_count(iter)))
1299 copied = copy_from_iter(block, sizeof(block), iter);
1301 mix_pool_bytes(block, copied);
1302 if (!iov_iter_count(iter) || copied != sizeof(block))
1305 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
1306 if (ret % PAGE_SIZE == 0) {
1307 if (signal_pending(current))
1313 memzero_explicit(block, sizeof(block));
1314 return ret ? ret : -EFAULT;
1317 static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter)
1319 return write_pool_user(iter);
1322 static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1324 static int maxwarn = 10;
1327 * Opportunistically attempt to initialize the RNG on platforms that
1328 * have fast cycle counters, but don't (for now) require it to succeed.
1331 try_to_generate_entropy();
1333 if (!crng_ready()) {
1334 if (!ratelimit_disable && maxwarn <= 0)
1335 ++urandom_warning.missed;
1336 else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
1338 pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
1339 current->comm, iov_iter_count(iter));
1343 return get_random_bytes_user(iter);
1346 static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1350 ret = wait_for_random_bytes();
1353 return get_random_bytes_user(iter);
1356 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1358 int __user *p = (int __user *)arg;
1363 /* Inherently racy, no point locking. */
1364 if (put_user(input_pool.init_bits, p))
1367 case RNDADDTOENTCNT:
1368 if (!capable(CAP_SYS_ADMIN))
1370 if (get_user(ent_count, p))
1374 credit_init_bits(ent_count);
1376 case RNDADDENTROPY: {
1377 struct iov_iter iter;
1382 if (!capable(CAP_SYS_ADMIN))
1384 if (get_user(ent_count, p++))
1388 if (get_user(len, p++))
1390 ret = import_single_range(WRITE, p, len, &iov, &iter);
1393 ret = write_pool_user(&iter);
1394 if (unlikely(ret < 0))
1396 /* Since we're crediting, enforce that it was all written into the pool. */
1397 if (unlikely(ret != len))
1399 credit_init_bits(ent_count);
1404 /* No longer has any effect. */
1405 if (!capable(CAP_SYS_ADMIN))
1409 if (!capable(CAP_SYS_ADMIN))
1420 static int random_fasync(int fd, struct file *filp, int on)
1422 return fasync_helper(fd, filp, on, &fasync);
1425 const struct file_operations random_fops = {
1426 .read_iter = random_read_iter,
1427 .write_iter = random_write_iter,
1428 .poll = random_poll,
1429 .unlocked_ioctl = random_ioctl,
1430 .compat_ioctl = compat_ptr_ioctl,
1431 .fasync = random_fasync,
1432 .llseek = noop_llseek,
1433 .splice_read = generic_file_splice_read,
1434 .splice_write = iter_file_splice_write,
1437 const struct file_operations urandom_fops = {
1438 .read_iter = urandom_read_iter,
1439 .write_iter = random_write_iter,
1440 .unlocked_ioctl = random_ioctl,
1441 .compat_ioctl = compat_ptr_ioctl,
1442 .fasync = random_fasync,
1443 .llseek = noop_llseek,
1444 .splice_read = generic_file_splice_read,
1445 .splice_write = iter_file_splice_write,
1449 /********************************************************************
1453 * These are partly unused legacy knobs with dummy values to not break
1454 * userspace and partly still useful things. They are usually accessible
1455 * in /proc/sys/kernel/random/ and are as follows:
1457 * - boot_id - a UUID representing the current boot.
1459 * - uuid - a random UUID, different each time the file is read.
1461 * - poolsize - the number of bits of entropy that the input pool can
1462 * hold, tied to the POOL_BITS constant.
1464 * - entropy_avail - the number of bits of entropy currently in the
1465 * input pool. Always <= poolsize.
1467 * - write_wakeup_threshold - the amount of entropy in the input pool
1468 * below which write polls to /dev/random will unblock, requesting
1469 * more entropy, tied to the POOL_READY_BITS constant. It is writable
1470 * to avoid breaking old userspaces, but writing to it does not
1471 * change any behavior of the RNG.
1473 * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL.
1474 * It is writable to avoid breaking old userspaces, but writing
1475 * to it does not change any behavior of the RNG.
1477 ********************************************************************/
1479 #ifdef CONFIG_SYSCTL
1481 #include <linux/sysctl.h>
1483 static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ;
1484 static int sysctl_random_write_wakeup_bits = POOL_READY_BITS;
1485 static int sysctl_poolsize = POOL_BITS;
1486 static u8 sysctl_bootid[UUID_SIZE];
1489 * This function is used to return both the bootid UUID, and random
1490 * UUID. The difference is in whether table->data is NULL; if it is,
1491 * then a new UUID is generated and returned to the user.
1493 static int proc_do_uuid(struct ctl_table *table, int write, void *buf,
1494 size_t *lenp, loff_t *ppos)
1496 u8 tmp_uuid[UUID_SIZE], *uuid;
1497 char uuid_string[UUID_STRING_LEN + 1];
1498 struct ctl_table fake_table = {
1499 .data = uuid_string,
1500 .maxlen = UUID_STRING_LEN
1509 generate_random_uuid(uuid);
1511 static DEFINE_SPINLOCK(bootid_spinlock);
1513 spin_lock(&bootid_spinlock);
1515 generate_random_uuid(uuid);
1516 spin_unlock(&bootid_spinlock);
1519 snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
1520 return proc_dostring(&fake_table, 0, buf, lenp, ppos);
1523 /* The same as proc_dointvec, but writes don't change anything. */
1524 static int proc_do_rointvec(struct ctl_table *table, int write, void *buf,
1525 size_t *lenp, loff_t *ppos)
1527 return write ? 0 : proc_dointvec(table, 0, buf, lenp, ppos);
1530 static struct ctl_table random_table[] = {
1532 .procname = "poolsize",
1533 .data = &sysctl_poolsize,
1534 .maxlen = sizeof(int),
1536 .proc_handler = proc_dointvec,
1539 .procname = "entropy_avail",
1540 .data = &input_pool.init_bits,
1541 .maxlen = sizeof(int),
1543 .proc_handler = proc_dointvec,
1546 .procname = "write_wakeup_threshold",
1547 .data = &sysctl_random_write_wakeup_bits,
1548 .maxlen = sizeof(int),
1550 .proc_handler = proc_do_rointvec,
1553 .procname = "urandom_min_reseed_secs",
1554 .data = &sysctl_random_min_urandom_seed,
1555 .maxlen = sizeof(int),
1557 .proc_handler = proc_do_rointvec,
1560 .procname = "boot_id",
1561 .data = &sysctl_bootid,
1563 .proc_handler = proc_do_uuid,
1568 .proc_handler = proc_do_uuid,
1574 * random_init() is called before sysctl_init(),
1575 * so we cannot call register_sysctl_init() in random_init()
1577 static int __init random_sysctls_init(void)
1579 register_sysctl_init("kernel/random", random_table);
1582 device_initcall(random_sysctls_init);