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_{u8,
100 * u16,u32,u64,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_{u8,u16,u32,u64,
123 * int,long} family of functions. Using any of these functions without first
124 * calling this function forfeits the guarantee of security.
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)
161 * u16 get_random_u16()
162 * u32 get_random_u32()
163 * u32 get_random_u32_below(u32 ceil)
164 * u32 get_random_u32_above(u32 floor)
165 * u32 get_random_u32_inclusive(u32 floor, u32 ceil)
166 * u64 get_random_u64()
167 * unsigned long get_random_long()
169 * These interfaces will return the requested number of random bytes
170 * into the given buffer or as a return value. This is equivalent to
171 * a read from /dev/urandom. The u8, u16, u32, u64, long family of
172 * functions may be higher performance for one-off random integers,
173 * because they do a bit of buffering and do not invoke reseeding
174 * until the buffer is emptied.
176 *********************************************************************/
179 CRNG_RESEED_START_INTERVAL = HZ,
180 CRNG_RESEED_INTERVAL = 60 * HZ
184 u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long));
186 unsigned long generation;
189 .lock = __SPIN_LOCK_UNLOCKED(base_crng.lock)
193 u8 key[CHACHA_KEY_SIZE];
194 unsigned long generation;
198 static DEFINE_PER_CPU(struct crng, crngs) = {
199 .generation = ULONG_MAX,
200 .lock = INIT_LOCAL_LOCK(crngs.lock),
203 /* Used by crng_reseed() and crng_make_state() to extract a new seed from the input pool. */
204 static void extract_entropy(void *buf, size_t len);
206 /* This extracts a new crng key from the input pool. */
207 static void crng_reseed(void)
210 unsigned long next_gen;
211 u8 key[CHACHA_KEY_SIZE];
213 extract_entropy(key, sizeof(key));
216 * We copy the new key into the base_crng, overwriting the old one,
217 * and update the generation counter. We avoid hitting ULONG_MAX,
218 * because the per-cpu crngs are initialized to ULONG_MAX, so this
219 * forces new CPUs that come online to always initialize.
221 spin_lock_irqsave(&base_crng.lock, flags);
222 memcpy(base_crng.key, key, sizeof(base_crng.key));
223 next_gen = base_crng.generation + 1;
224 if (next_gen == ULONG_MAX)
226 WRITE_ONCE(base_crng.generation, next_gen);
227 WRITE_ONCE(base_crng.birth, jiffies);
228 if (!static_branch_likely(&crng_is_ready))
229 crng_init = CRNG_READY;
230 spin_unlock_irqrestore(&base_crng.lock, flags);
231 memzero_explicit(key, sizeof(key));
235 * This generates a ChaCha block using the provided key, and then
236 * immediately overwrites that key with half the block. It returns
237 * the resultant ChaCha state to the user, along with the second
238 * half of the block containing 32 bytes of random data that may
239 * be used; random_data_len may not be greater than 32.
241 * The returned ChaCha state contains within it a copy of the old
242 * key value, at index 4, so the state should always be zeroed out
243 * immediately after using in order to maintain forward secrecy.
244 * If the state cannot be erased in a timely manner, then it is
245 * safer to set the random_data parameter to &chacha_state[4] so
246 * that this function overwrites it before returning.
248 static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE],
249 u32 chacha_state[CHACHA_STATE_WORDS],
250 u8 *random_data, size_t random_data_len)
252 u8 first_block[CHACHA_BLOCK_SIZE];
254 BUG_ON(random_data_len > 32);
256 chacha_init_consts(chacha_state);
257 memcpy(&chacha_state[4], key, CHACHA_KEY_SIZE);
258 memset(&chacha_state[12], 0, sizeof(u32) * 4);
259 chacha20_block(chacha_state, first_block);
261 memcpy(key, first_block, CHACHA_KEY_SIZE);
262 memcpy(random_data, first_block + CHACHA_KEY_SIZE, random_data_len);
263 memzero_explicit(first_block, sizeof(first_block));
267 * Return the interval until the next reseeding, which is normally
268 * CRNG_RESEED_INTERVAL, but during early boot, it is at an interval
269 * proportional to the uptime.
271 static unsigned int crng_reseed_interval(void)
273 static bool early_boot = true;
275 if (unlikely(READ_ONCE(early_boot))) {
276 time64_t uptime = ktime_get_seconds();
277 if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2)
278 WRITE_ONCE(early_boot, false);
280 return max_t(unsigned int, CRNG_RESEED_START_INTERVAL,
281 (unsigned int)uptime / 2 * HZ);
283 return CRNG_RESEED_INTERVAL;
287 * This function returns a ChaCha state that you may use for generating
288 * random data. It also returns up to 32 bytes on its own of random data
289 * that may be used; random_data_len may not be greater than 32.
291 static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
292 u8 *random_data, size_t random_data_len)
297 BUG_ON(random_data_len > 32);
300 * For the fast path, we check whether we're ready, unlocked first, and
301 * then re-check once locked later. In the case where we're really not
302 * ready, we do fast key erasure with the base_crng directly, extracting
303 * when crng_init is CRNG_EMPTY.
308 spin_lock_irqsave(&base_crng.lock, flags);
309 ready = crng_ready();
311 if (crng_init == CRNG_EMPTY)
312 extract_entropy(base_crng.key, sizeof(base_crng.key));
313 crng_fast_key_erasure(base_crng.key, chacha_state,
314 random_data, random_data_len);
316 spin_unlock_irqrestore(&base_crng.lock, flags);
322 * If the base_crng is old enough, we reseed, which in turn bumps the
323 * generation counter that we check below.
325 if (unlikely(time_is_before_jiffies(READ_ONCE(base_crng.birth) + crng_reseed_interval())))
328 local_lock_irqsave(&crngs.lock, flags);
329 crng = raw_cpu_ptr(&crngs);
332 * If our per-cpu crng is older than the base_crng, then it means
333 * somebody reseeded the base_crng. In that case, we do fast key
334 * erasure on the base_crng, and use its output as the new key
335 * for our per-cpu crng. This brings us up to date with base_crng.
337 if (unlikely(crng->generation != READ_ONCE(base_crng.generation))) {
338 spin_lock(&base_crng.lock);
339 crng_fast_key_erasure(base_crng.key, chacha_state,
340 crng->key, sizeof(crng->key));
341 crng->generation = base_crng.generation;
342 spin_unlock(&base_crng.lock);
346 * Finally, when we've made it this far, our per-cpu crng has an up
347 * to date key, and we can do fast key erasure with it to produce
348 * some random data and a ChaCha state for the caller. All other
349 * branches of this function are "unlikely", so most of the time we
350 * should wind up here immediately.
352 crng_fast_key_erasure(crng->key, chacha_state, random_data, random_data_len);
353 local_unlock_irqrestore(&crngs.lock, flags);
356 static void _get_random_bytes(void *buf, size_t len)
358 u32 chacha_state[CHACHA_STATE_WORDS];
359 u8 tmp[CHACHA_BLOCK_SIZE];
360 size_t first_block_len;
365 first_block_len = min_t(size_t, 32, len);
366 crng_make_state(chacha_state, buf, first_block_len);
367 len -= first_block_len;
368 buf += first_block_len;
371 if (len < CHACHA_BLOCK_SIZE) {
372 chacha20_block(chacha_state, tmp);
373 memcpy(buf, tmp, len);
374 memzero_explicit(tmp, sizeof(tmp));
378 chacha20_block(chacha_state, buf);
379 if (unlikely(chacha_state[12] == 0))
381 len -= CHACHA_BLOCK_SIZE;
382 buf += CHACHA_BLOCK_SIZE;
385 memzero_explicit(chacha_state, sizeof(chacha_state));
389 * This function is the exported kernel interface. It returns some number of
390 * good random numbers, suitable for key generation, seeding TCP sequence
391 * numbers, etc. In order to ensure that the randomness returned by this
392 * function is okay, the function wait_for_random_bytes() should be called and
393 * return 0 at least once at any point prior.
395 void get_random_bytes(void *buf, size_t len)
397 warn_unseeded_randomness();
398 _get_random_bytes(buf, len);
400 EXPORT_SYMBOL(get_random_bytes);
402 static ssize_t get_random_bytes_user(struct iov_iter *iter)
404 u32 chacha_state[CHACHA_STATE_WORDS];
405 u8 block[CHACHA_BLOCK_SIZE];
406 size_t ret = 0, copied;
408 if (unlikely(!iov_iter_count(iter)))
412 * Immediately overwrite the ChaCha key at index 4 with random
413 * bytes, in case userspace causes copy_to_iter() below to sleep
414 * forever, so that we still retain forward secrecy in that case.
416 crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA_KEY_SIZE);
418 * However, if we're doing a read of len <= 32, we don't need to
419 * use chacha_state after, so we can simply return those bytes to
422 if (iov_iter_count(iter) <= CHACHA_KEY_SIZE) {
423 ret = copy_to_iter(&chacha_state[4], CHACHA_KEY_SIZE, iter);
424 goto out_zero_chacha;
428 chacha20_block(chacha_state, block);
429 if (unlikely(chacha_state[12] == 0))
432 copied = copy_to_iter(block, sizeof(block), iter);
434 if (!iov_iter_count(iter) || copied != sizeof(block))
437 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
438 if (ret % PAGE_SIZE == 0) {
439 if (signal_pending(current))
445 memzero_explicit(block, sizeof(block));
447 memzero_explicit(chacha_state, sizeof(chacha_state));
448 return ret ? ret : -EFAULT;
452 * Batched entropy returns random integers. The quality of the random
453 * number is good as /dev/urandom. In order to ensure that the randomness
454 * provided by this function is okay, the function wait_for_random_bytes()
455 * should be called and return 0 at least once at any point prior.
458 #define DEFINE_BATCHED_ENTROPY(type) \
459 struct batch_ ##type { \
461 * We make this 1.5x a ChaCha block, so that we get the \
462 * remaining 32 bytes from fast key erasure, plus one full \
463 * block from the detached ChaCha state. We can increase \
464 * the size of this later if needed so long as we keep the \
465 * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE. \
467 type entropy[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(type))]; \
469 unsigned long generation; \
470 unsigned int position; \
473 static DEFINE_PER_CPU(struct batch_ ##type, batched_entropy_ ##type) = { \
474 .lock = INIT_LOCAL_LOCK(batched_entropy_ ##type.lock), \
475 .position = UINT_MAX \
478 type get_random_ ##type(void) \
481 unsigned long flags; \
482 struct batch_ ##type *batch; \
483 unsigned long next_gen; \
485 warn_unseeded_randomness(); \
487 if (!crng_ready()) { \
488 _get_random_bytes(&ret, sizeof(ret)); \
492 local_lock_irqsave(&batched_entropy_ ##type.lock, flags); \
493 batch = raw_cpu_ptr(&batched_entropy_##type); \
495 next_gen = READ_ONCE(base_crng.generation); \
496 if (batch->position >= ARRAY_SIZE(batch->entropy) || \
497 next_gen != batch->generation) { \
498 _get_random_bytes(batch->entropy, sizeof(batch->entropy)); \
499 batch->position = 0; \
500 batch->generation = next_gen; \
503 ret = batch->entropy[batch->position]; \
504 batch->entropy[batch->position] = 0; \
506 local_unlock_irqrestore(&batched_entropy_ ##type.lock, flags); \
509 EXPORT_SYMBOL(get_random_ ##type);
511 DEFINE_BATCHED_ENTROPY(u8)
512 DEFINE_BATCHED_ENTROPY(u16)
513 DEFINE_BATCHED_ENTROPY(u32)
514 DEFINE_BATCHED_ENTROPY(u64)
516 u32 __get_random_u32_below(u32 ceil)
519 * This is the slow path for variable ceil. It is still fast, most of
520 * the time, by doing traditional reciprocal multiplication and
521 * opportunistically comparing the lower half to ceil itself, before
522 * falling back to computing a larger bound, and then rejecting samples
523 * whose lower half would indicate a range indivisible by ceil. The use
524 * of `-ceil % ceil` is analogous to `2^32 % ceil`, but is computable
527 u32 rand = get_random_u32();
531 * This function is technically undefined for ceil == 0, and in fact
532 * for the non-underscored constant version in the header, we build bug
533 * on that. But for the non-constant case, it's convenient to have that
534 * evaluate to being a straight call to get_random_u32(), so that
535 * get_random_u32_inclusive() can work over its whole range without
536 * undefined behavior.
541 mult = (u64)ceil * rand;
542 if (unlikely((u32)mult < ceil)) {
543 u32 bound = -ceil % ceil;
544 while (unlikely((u32)mult < bound))
545 mult = (u64)ceil * get_random_u32();
549 EXPORT_SYMBOL(__get_random_u32_below);
553 * This function is called when the CPU is coming up, with entry
554 * CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP.
556 int __cold random_prepare_cpu(unsigned int cpu)
559 * When the cpu comes back online, immediately invalidate both
560 * the per-cpu crng and all batches, so that we serve fresh
563 per_cpu_ptr(&crngs, cpu)->generation = ULONG_MAX;
564 per_cpu_ptr(&batched_entropy_u8, cpu)->position = UINT_MAX;
565 per_cpu_ptr(&batched_entropy_u16, cpu)->position = UINT_MAX;
566 per_cpu_ptr(&batched_entropy_u32, cpu)->position = UINT_MAX;
567 per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX;
573 /**********************************************************************
575 * Entropy accumulation and extraction routines.
577 * Callers may add entropy via:
579 * static void mix_pool_bytes(const void *buf, size_t len)
581 * After which, if added entropy should be credited:
583 * static void credit_init_bits(size_t bits)
585 * Finally, extract entropy via:
587 * static void extract_entropy(void *buf, size_t len)
589 **********************************************************************/
592 POOL_BITS = BLAKE2S_HASH_SIZE * 8,
593 POOL_READY_BITS = POOL_BITS, /* When crng_init->CRNG_READY */
594 POOL_EARLY_BITS = POOL_READY_BITS / 2 /* When crng_init->CRNG_EARLY */
598 struct blake2s_state hash;
600 unsigned int init_bits;
602 .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE),
603 BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4,
604 BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 },
605 .hash.outlen = BLAKE2S_HASH_SIZE,
606 .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
609 static void _mix_pool_bytes(const void *buf, size_t len)
611 blake2s_update(&input_pool.hash, buf, len);
615 * This function adds bytes into the input pool. It does not
616 * update the initialization bit counter; the caller should call
617 * credit_init_bits if this is appropriate.
619 static void mix_pool_bytes(const void *buf, size_t len)
623 spin_lock_irqsave(&input_pool.lock, flags);
624 _mix_pool_bytes(buf, len);
625 spin_unlock_irqrestore(&input_pool.lock, flags);
629 * This is an HKDF-like construction for using the hashed collected entropy
630 * as a PRF key, that's then expanded block-by-block.
632 static void extract_entropy(void *buf, size_t len)
635 u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
637 unsigned long rdseed[32 / sizeof(long)];
642 for (i = 0; i < ARRAY_SIZE(block.rdseed);) {
643 longs = arch_get_random_seed_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
648 longs = arch_get_random_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
653 block.rdseed[i++] = random_get_entropy();
656 spin_lock_irqsave(&input_pool.lock, flags);
658 /* seed = HASHPRF(last_key, entropy_input) */
659 blake2s_final(&input_pool.hash, seed);
661 /* next_key = HASHPRF(seed, RDSEED || 0) */
663 blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
664 blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
666 spin_unlock_irqrestore(&input_pool.lock, flags);
667 memzero_explicit(next_key, sizeof(next_key));
670 i = min_t(size_t, len, BLAKE2S_HASH_SIZE);
671 /* output = HASHPRF(seed, RDSEED || ++counter) */
673 blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
678 memzero_explicit(seed, sizeof(seed));
679 memzero_explicit(&block, sizeof(block));
682 #define credit_init_bits(bits) if (!crng_ready()) _credit_init_bits(bits)
684 static void __cold _credit_init_bits(size_t bits)
686 static struct execute_work set_ready;
687 unsigned int new, orig, add;
693 add = min_t(size_t, bits, POOL_BITS);
695 orig = READ_ONCE(input_pool.init_bits);
697 new = min_t(unsigned int, POOL_BITS, orig + add);
698 } while (!try_cmpxchg(&input_pool.init_bits, &orig, new));
700 if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
701 crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */
702 if (static_key_initialized)
703 execute_in_process_context(crng_set_ready, &set_ready);
704 wake_up_interruptible(&crng_init_wait);
705 kill_fasync(&fasync, SIGIO, POLL_IN);
706 pr_notice("crng init done\n");
707 if (urandom_warning.missed)
708 pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
709 urandom_warning.missed);
710 } else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
711 spin_lock_irqsave(&base_crng.lock, flags);
712 /* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */
713 if (crng_init == CRNG_EMPTY) {
714 extract_entropy(base_crng.key, sizeof(base_crng.key));
715 crng_init = CRNG_EARLY;
717 spin_unlock_irqrestore(&base_crng.lock, flags);
722 /**********************************************************************
724 * Entropy collection routines.
726 * The following exported functions are used for pushing entropy into
727 * the above entropy accumulation routines:
729 * void add_device_randomness(const void *buf, size_t len);
730 * void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy);
731 * void add_bootloader_randomness(const void *buf, size_t len);
732 * void add_vmfork_randomness(const void *unique_vm_id, size_t len);
733 * void add_interrupt_randomness(int irq);
734 * void add_input_randomness(unsigned int type, unsigned int code, unsigned int value);
735 * void add_disk_randomness(struct gendisk *disk);
737 * add_device_randomness() adds data to the input pool that
738 * is likely to differ between two devices (or possibly even per boot).
739 * This would be things like MAC addresses or serial numbers, or the
740 * read-out of the RTC. This does *not* credit any actual entropy to
741 * the pool, but it initializes the pool to different values for devices
742 * that might otherwise be identical and have very little entropy
743 * available to them (particularly common in the embedded world).
745 * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
746 * entropy as specified by the caller. If the entropy pool is full it will
747 * block until more entropy is needed.
749 * add_bootloader_randomness() is called by bootloader drivers, such as EFI
750 * and device tree, and credits its input depending on whether or not the
751 * configuration option CONFIG_RANDOM_TRUST_BOOTLOADER is set.
753 * add_vmfork_randomness() adds a unique (but not necessarily secret) ID
754 * representing the current instance of a VM to the pool, without crediting,
755 * and then force-reseeds the crng so that it takes effect immediately.
757 * add_interrupt_randomness() uses the interrupt timing as random
758 * inputs to the entropy pool. Using the cycle counters and the irq source
759 * as inputs, it feeds the input pool roughly once a second or after 64
760 * interrupts, crediting 1 bit of entropy for whichever comes first.
762 * add_input_randomness() uses the input layer interrupt timing, as well
763 * as the event type information from the hardware.
765 * add_disk_randomness() uses what amounts to the seek time of block
766 * layer request events, on a per-disk_devt basis, as input to the
767 * entropy pool. Note that high-speed solid state drives with very low
768 * seek times do not make for good sources of entropy, as their seek
769 * times are usually fairly consistent.
771 * The last two routines try to estimate how many bits of entropy
772 * to credit. They do this by keeping track of the first and second
773 * order deltas of the event timings.
775 **********************************************************************/
777 static bool trust_cpu __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
778 static bool trust_bootloader __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER);
779 static int __init parse_trust_cpu(char *arg)
781 return kstrtobool(arg, &trust_cpu);
783 static int __init parse_trust_bootloader(char *arg)
785 return kstrtobool(arg, &trust_bootloader);
787 early_param("random.trust_cpu", parse_trust_cpu);
788 early_param("random.trust_bootloader", parse_trust_bootloader);
790 static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data)
792 unsigned long flags, entropy = random_get_entropy();
795 * Encode a representation of how long the system has been suspended,
796 * in a way that is distinct from prior system suspends.
798 ktime_t stamps[] = { ktime_get(), ktime_get_boottime(), ktime_get_real() };
800 spin_lock_irqsave(&input_pool.lock, flags);
801 _mix_pool_bytes(&action, sizeof(action));
802 _mix_pool_bytes(stamps, sizeof(stamps));
803 _mix_pool_bytes(&entropy, sizeof(entropy));
804 spin_unlock_irqrestore(&input_pool.lock, flags);
806 if (crng_ready() && (action == PM_RESTORE_PREPARE ||
807 (action == PM_POST_SUSPEND && !IS_ENABLED(CONFIG_PM_AUTOSLEEP) &&
808 !IS_ENABLED(CONFIG_PM_USERSPACE_AUTOSLEEP)))) {
810 pr_notice("crng reseeded on system resumption\n");
815 static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification };
818 * This is called extremely early, before time keeping functionality is
819 * available, but arch randomness is. Interrupts are not yet enabled.
821 void __init random_init_early(const char *command_line)
823 unsigned long entropy[BLAKE2S_BLOCK_SIZE / sizeof(long)];
824 size_t i, longs, arch_bits;
826 #if defined(LATENT_ENTROPY_PLUGIN)
827 static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
828 _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
831 for (i = 0, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) {
832 longs = arch_get_random_seed_longs_early(entropy, ARRAY_SIZE(entropy) - i);
834 _mix_pool_bytes(entropy, sizeof(*entropy) * longs);
838 longs = arch_get_random_longs_early(entropy, ARRAY_SIZE(entropy) - i);
840 _mix_pool_bytes(entropy, sizeof(*entropy) * longs);
844 arch_bits -= sizeof(*entropy) * 8;
848 _mix_pool_bytes(init_utsname(), sizeof(*(init_utsname())));
849 _mix_pool_bytes(command_line, strlen(command_line));
851 /* Reseed if already seeded by earlier phases. */
855 _credit_init_bits(arch_bits);
859 * This is called a little bit after the prior function, and now there is
860 * access to timestamps counters. Interrupts are not yet enabled.
862 void __init random_init(void)
864 unsigned long entropy = random_get_entropy();
865 ktime_t now = ktime_get_real();
867 _mix_pool_bytes(&now, sizeof(now));
868 _mix_pool_bytes(&entropy, sizeof(entropy));
869 add_latent_entropy();
872 * If we were initialized by the cpu or bootloader before jump labels
873 * are initialized, then we should enable the static branch here, where
874 * it's guaranteed that jump labels have been initialized.
876 if (!static_branch_likely(&crng_is_ready) && crng_init >= CRNG_READY)
877 crng_set_ready(NULL);
879 /* Reseed if already seeded by earlier phases. */
883 WARN_ON(register_pm_notifier(&pm_notifier));
885 WARN(!entropy, "Missing cycle counter and fallback timer; RNG "
886 "entropy collection will consequently suffer.");
890 * Add device- or boot-specific data to the input pool to help
893 * None of this adds any entropy; it is meant to avoid the problem of
894 * the entropy pool having similar initial state across largely
897 void add_device_randomness(const void *buf, size_t len)
899 unsigned long entropy = random_get_entropy();
902 spin_lock_irqsave(&input_pool.lock, flags);
903 _mix_pool_bytes(&entropy, sizeof(entropy));
904 _mix_pool_bytes(buf, len);
905 spin_unlock_irqrestore(&input_pool.lock, flags);
907 EXPORT_SYMBOL(add_device_randomness);
910 * Interface for in-kernel drivers of true hardware RNGs.
911 * Those devices may produce endless random bits and will be throttled
912 * when our pool is full.
914 void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy)
916 mix_pool_bytes(buf, len);
917 credit_init_bits(entropy);
920 * Throttle writing to once every reseed interval, unless we're not yet
921 * initialized or no entropy is credited.
923 if (!kthread_should_stop() && (crng_ready() || !entropy))
924 schedule_timeout_interruptible(crng_reseed_interval());
926 EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
929 * Handle random seed passed by bootloader, and credit it if
930 * CONFIG_RANDOM_TRUST_BOOTLOADER is set.
932 void __init add_bootloader_randomness(const void *buf, size_t len)
934 mix_pool_bytes(buf, len);
935 if (trust_bootloader)
936 credit_init_bits(len * 8);
939 #if IS_ENABLED(CONFIG_VMGENID)
940 static BLOCKING_NOTIFIER_HEAD(vmfork_chain);
943 * Handle a new unique VM ID, which is unique, not secret, so we
944 * don't credit it, but we do immediately force a reseed after so
945 * that it's used by the crng posthaste.
947 void __cold add_vmfork_randomness(const void *unique_vm_id, size_t len)
949 add_device_randomness(unique_vm_id, len);
952 pr_notice("crng reseeded due to virtual machine fork\n");
954 blocking_notifier_call_chain(&vmfork_chain, 0, NULL);
956 #if IS_MODULE(CONFIG_VMGENID)
957 EXPORT_SYMBOL_GPL(add_vmfork_randomness);
960 int __cold register_random_vmfork_notifier(struct notifier_block *nb)
962 return blocking_notifier_chain_register(&vmfork_chain, nb);
964 EXPORT_SYMBOL_GPL(register_random_vmfork_notifier);
966 int __cold unregister_random_vmfork_notifier(struct notifier_block *nb)
968 return blocking_notifier_chain_unregister(&vmfork_chain, nb);
970 EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier);
974 unsigned long pool[4];
977 struct timer_list mix;
980 static void mix_interrupt_randomness(struct timer_list *work);
982 static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = {
984 #define FASTMIX_PERM SIPHASH_PERMUTATION
985 .pool = { SIPHASH_CONST_0, SIPHASH_CONST_1, SIPHASH_CONST_2, SIPHASH_CONST_3 },
987 #define FASTMIX_PERM HSIPHASH_PERMUTATION
988 .pool = { HSIPHASH_CONST_0, HSIPHASH_CONST_1, HSIPHASH_CONST_2, HSIPHASH_CONST_3 },
990 .mix = __TIMER_INITIALIZER(mix_interrupt_randomness, 0)
994 * This is [Half]SipHash-1-x, starting from an empty key. Because
995 * the key is fixed, it assumes that its inputs are non-malicious,
996 * and therefore this has no security on its own. s represents the
997 * four-word SipHash state, while v represents a two-word input.
999 static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long v2)
1002 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1005 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1011 * This function is called when the CPU has just come online, with
1012 * entry CPUHP_AP_RANDOM_ONLINE, just after CPUHP_AP_WORKQUEUE_ONLINE.
1014 int __cold random_online_cpu(unsigned int cpu)
1017 * During CPU shutdown and before CPU onlining, add_interrupt_
1018 * randomness() may schedule mix_interrupt_randomness(), and
1019 * set the MIX_INFLIGHT flag. However, because the worker can
1020 * be scheduled on a different CPU during this period, that
1021 * flag will never be cleared. For that reason, we zero out
1022 * the flag here, which runs just after workqueues are onlined
1023 * for the CPU again. This also has the effect of setting the
1024 * irq randomness count to zero so that new accumulated irqs
1027 per_cpu_ptr(&irq_randomness, cpu)->count = 0;
1032 static void mix_interrupt_randomness(struct timer_list *work)
1034 struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix);
1036 * The size of the copied stack pool is explicitly 2 longs so that we
1037 * only ever ingest half of the siphash output each time, retaining
1038 * the other half as the next "key" that carries over. The entropy is
1039 * supposed to be sufficiently dispersed between bits so on average
1040 * we don't wind up "losing" some.
1042 unsigned long pool[2];
1045 /* Check to see if we're running on the wrong CPU due to hotplug. */
1046 local_irq_disable();
1047 if (fast_pool != this_cpu_ptr(&irq_randomness)) {
1053 * Copy the pool to the stack so that the mixer always has a
1054 * consistent view, before we reenable irqs again.
1056 memcpy(pool, fast_pool->pool, sizeof(pool));
1057 count = fast_pool->count;
1058 fast_pool->count = 0;
1059 fast_pool->last = jiffies;
1062 mix_pool_bytes(pool, sizeof(pool));
1063 credit_init_bits(clamp_t(unsigned int, (count & U16_MAX) / 64, 1, sizeof(pool) * 8));
1065 memzero_explicit(pool, sizeof(pool));
1068 void add_interrupt_randomness(int irq)
1070 enum { MIX_INFLIGHT = 1U << 31 };
1071 unsigned long entropy = random_get_entropy();
1072 struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
1073 struct pt_regs *regs = get_irq_regs();
1074 unsigned int new_count;
1076 fast_mix(fast_pool->pool, entropy,
1077 (regs ? instruction_pointer(regs) : _RET_IP_) ^ swab(irq));
1078 new_count = ++fast_pool->count;
1080 if (new_count & MIX_INFLIGHT)
1083 if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ))
1086 fast_pool->count |= MIX_INFLIGHT;
1087 if (!timer_pending(&fast_pool->mix)) {
1088 fast_pool->mix.expires = jiffies;
1089 add_timer_on(&fast_pool->mix, raw_smp_processor_id());
1092 EXPORT_SYMBOL_GPL(add_interrupt_randomness);
1094 /* There is one of these per entropy source */
1095 struct timer_rand_state {
1096 unsigned long last_time;
1097 long last_delta, last_delta2;
1101 * This function adds entropy to the entropy "pool" by using timing
1102 * delays. It uses the timer_rand_state structure to make an estimate
1103 * of how many bits of entropy this call has added to the pool. The
1104 * value "num" is also added to the pool; it should somehow describe
1105 * the type of event that just happened.
1107 static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
1109 unsigned long entropy = random_get_entropy(), now = jiffies, flags;
1110 long delta, delta2, delta3;
1114 * If we're in a hard IRQ, add_interrupt_randomness() will be called
1115 * sometime after, so mix into the fast pool.
1118 fast_mix(this_cpu_ptr(&irq_randomness)->pool, entropy, num);
1120 spin_lock_irqsave(&input_pool.lock, flags);
1121 _mix_pool_bytes(&entropy, sizeof(entropy));
1122 _mix_pool_bytes(&num, sizeof(num));
1123 spin_unlock_irqrestore(&input_pool.lock, flags);
1130 * Calculate number of bits of randomness we probably added.
1131 * We take into account the first, second and third-order deltas
1132 * in order to make our estimate.
1134 delta = now - READ_ONCE(state->last_time);
1135 WRITE_ONCE(state->last_time, now);
1137 delta2 = delta - READ_ONCE(state->last_delta);
1138 WRITE_ONCE(state->last_delta, delta);
1140 delta3 = delta2 - READ_ONCE(state->last_delta2);
1141 WRITE_ONCE(state->last_delta2, delta2);
1155 * delta is now minimum absolute delta. Round down by 1 bit
1156 * on general principles, and limit entropy estimate to 11 bits.
1158 bits = min(fls(delta >> 1), 11);
1161 * As mentioned above, if we're in a hard IRQ, add_interrupt_randomness()
1162 * will run after this, which uses a different crediting scheme of 1 bit
1163 * per every 64 interrupts. In order to let that function do accounting
1164 * close to the one in this function, we credit a full 64/64 bit per bit,
1165 * and then subtract one to account for the extra one added.
1168 this_cpu_ptr(&irq_randomness)->count += max(1u, bits * 64) - 1;
1170 _credit_init_bits(bits);
1173 void add_input_randomness(unsigned int type, unsigned int code, unsigned int value)
1175 static unsigned char last_value;
1176 static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES };
1178 /* Ignore autorepeat and the like. */
1179 if (value == last_value)
1183 add_timer_randomness(&input_timer_state,
1184 (type << 4) ^ code ^ (code >> 4) ^ value);
1186 EXPORT_SYMBOL_GPL(add_input_randomness);
1189 void add_disk_randomness(struct gendisk *disk)
1191 if (!disk || !disk->random)
1193 /* First major is 1, so we get >= 0x200 here. */
1194 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
1196 EXPORT_SYMBOL_GPL(add_disk_randomness);
1198 void __cold rand_initialize_disk(struct gendisk *disk)
1200 struct timer_rand_state *state;
1203 * If kzalloc returns null, we just won't use that entropy
1206 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1208 state->last_time = INITIAL_JIFFIES;
1209 disk->random = state;
1214 struct entropy_timer_state {
1215 unsigned long entropy;
1216 struct timer_list timer;
1217 unsigned int samples, samples_per_bit;
1221 * Each time the timer fires, we expect that we got an unpredictable
1222 * jump in the cycle counter. Even if the timer is running on another
1223 * CPU, the timer activity will be touching the stack of the CPU that is
1224 * generating entropy..
1226 * Note that we don't re-arm the timer in the timer itself - we are
1227 * happy to be scheduled away, since that just makes the load more
1228 * complex, but we do not want the timer to keep ticking unless the
1229 * entropy loop is running.
1231 * So the re-arming always happens in the entropy loop itself.
1233 static void __cold entropy_timer(struct timer_list *timer)
1235 struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer);
1237 if (++state->samples == state->samples_per_bit) {
1238 credit_init_bits(1);
1244 * If we have an actual cycle counter, see if we can
1245 * generate enough entropy with timing noise
1247 static void __cold try_to_generate_entropy(void)
1249 enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = HZ / 15 };
1250 struct entropy_timer_state stack;
1251 unsigned int i, num_different = 0;
1252 unsigned long last = random_get_entropy();
1254 for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
1255 stack.entropy = random_get_entropy();
1256 if (stack.entropy != last)
1258 last = stack.entropy;
1260 stack.samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1);
1261 if (stack.samples_per_bit > MAX_SAMPLES_PER_BIT)
1265 timer_setup_on_stack(&stack.timer, entropy_timer, 0);
1266 while (!crng_ready() && !signal_pending(current)) {
1267 if (!timer_pending(&stack.timer))
1268 mod_timer(&stack.timer, jiffies);
1269 mix_pool_bytes(&stack.entropy, sizeof(stack.entropy));
1271 stack.entropy = random_get_entropy();
1274 del_timer_sync(&stack.timer);
1275 destroy_timer_on_stack(&stack.timer);
1276 mix_pool_bytes(&stack.entropy, sizeof(stack.entropy));
1280 /**********************************************************************
1282 * Userspace reader/writer interfaces.
1284 * getrandom(2) is the primary modern interface into the RNG and should
1285 * be used in preference to anything else.
1287 * Reading from /dev/random has the same functionality as calling
1288 * getrandom(2) with flags=0. In earlier versions, however, it had
1289 * vastly different semantics and should therefore be avoided, to
1290 * prevent backwards compatibility issues.
1292 * Reading from /dev/urandom has the same functionality as calling
1293 * getrandom(2) with flags=GRND_INSECURE. Because it does not block
1294 * waiting for the RNG to be ready, it should not be used.
1296 * Writing to either /dev/random or /dev/urandom adds entropy to
1297 * the input pool but does not credit it.
1299 * Polling on /dev/random indicates when the RNG is initialized, on
1300 * the read side, and when it wants new entropy, on the write side.
1302 * Both /dev/random and /dev/urandom have the same set of ioctls for
1303 * adding entropy, getting the entropy count, zeroing the count, and
1304 * reseeding the crng.
1306 **********************************************************************/
1308 SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
1310 struct iov_iter iter;
1314 if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
1318 * Requesting insecure and blocking randomness at the same time makes
1321 if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
1324 if (!crng_ready() && !(flags & GRND_INSECURE)) {
1325 if (flags & GRND_NONBLOCK)
1327 ret = wait_for_random_bytes();
1332 ret = import_single_range(READ, ubuf, len, &iov, &iter);
1335 return get_random_bytes_user(&iter);
1338 static __poll_t random_poll(struct file *file, poll_table *wait)
1340 poll_wait(file, &crng_init_wait, wait);
1341 return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
1344 static ssize_t write_pool_user(struct iov_iter *iter)
1346 u8 block[BLAKE2S_BLOCK_SIZE];
1350 if (unlikely(!iov_iter_count(iter)))
1354 copied = copy_from_iter(block, sizeof(block), iter);
1356 mix_pool_bytes(block, copied);
1357 if (!iov_iter_count(iter) || copied != sizeof(block))
1360 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
1361 if (ret % PAGE_SIZE == 0) {
1362 if (signal_pending(current))
1368 memzero_explicit(block, sizeof(block));
1369 return ret ? ret : -EFAULT;
1372 static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter)
1374 return write_pool_user(iter);
1377 static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1379 static int maxwarn = 10;
1382 * Opportunistically attempt to initialize the RNG on platforms that
1383 * have fast cycle counters, but don't (for now) require it to succeed.
1386 try_to_generate_entropy();
1388 if (!crng_ready()) {
1389 if (!ratelimit_disable && maxwarn <= 0)
1390 ++urandom_warning.missed;
1391 else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
1393 pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
1394 current->comm, iov_iter_count(iter));
1398 return get_random_bytes_user(iter);
1401 static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1405 if (!crng_ready() &&
1406 ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
1407 (kiocb->ki_filp->f_flags & O_NONBLOCK)))
1410 ret = wait_for_random_bytes();
1413 return get_random_bytes_user(iter);
1416 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1418 int __user *p = (int __user *)arg;
1423 /* Inherently racy, no point locking. */
1424 if (put_user(input_pool.init_bits, p))
1427 case RNDADDTOENTCNT:
1428 if (!capable(CAP_SYS_ADMIN))
1430 if (get_user(ent_count, p))
1434 credit_init_bits(ent_count);
1436 case RNDADDENTROPY: {
1437 struct iov_iter iter;
1442 if (!capable(CAP_SYS_ADMIN))
1444 if (get_user(ent_count, p++))
1448 if (get_user(len, p++))
1450 ret = import_single_range(WRITE, p, len, &iov, &iter);
1453 ret = write_pool_user(&iter);
1454 if (unlikely(ret < 0))
1456 /* Since we're crediting, enforce that it was all written into the pool. */
1457 if (unlikely(ret != len))
1459 credit_init_bits(ent_count);
1464 /* No longer has any effect. */
1465 if (!capable(CAP_SYS_ADMIN))
1469 if (!capable(CAP_SYS_ADMIN))
1480 static int random_fasync(int fd, struct file *filp, int on)
1482 return fasync_helper(fd, filp, on, &fasync);
1485 const struct file_operations random_fops = {
1486 .read_iter = random_read_iter,
1487 .write_iter = random_write_iter,
1488 .poll = random_poll,
1489 .unlocked_ioctl = random_ioctl,
1490 .compat_ioctl = compat_ptr_ioctl,
1491 .fasync = random_fasync,
1492 .llseek = noop_llseek,
1493 .splice_read = generic_file_splice_read,
1494 .splice_write = iter_file_splice_write,
1497 const struct file_operations urandom_fops = {
1498 .read_iter = urandom_read_iter,
1499 .write_iter = random_write_iter,
1500 .unlocked_ioctl = random_ioctl,
1501 .compat_ioctl = compat_ptr_ioctl,
1502 .fasync = random_fasync,
1503 .llseek = noop_llseek,
1504 .splice_read = generic_file_splice_read,
1505 .splice_write = iter_file_splice_write,
1509 /********************************************************************
1513 * These are partly unused legacy knobs with dummy values to not break
1514 * userspace and partly still useful things. They are usually accessible
1515 * in /proc/sys/kernel/random/ and are as follows:
1517 * - boot_id - a UUID representing the current boot.
1519 * - uuid - a random UUID, different each time the file is read.
1521 * - poolsize - the number of bits of entropy that the input pool can
1522 * hold, tied to the POOL_BITS constant.
1524 * - entropy_avail - the number of bits of entropy currently in the
1525 * input pool. Always <= poolsize.
1527 * - write_wakeup_threshold - the amount of entropy in the input pool
1528 * below which write polls to /dev/random will unblock, requesting
1529 * more entropy, tied to the POOL_READY_BITS constant. It is writable
1530 * to avoid breaking old userspaces, but writing to it does not
1531 * change any behavior of the RNG.
1533 * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL.
1534 * It is writable to avoid breaking old userspaces, but writing
1535 * to it does not change any behavior of the RNG.
1537 ********************************************************************/
1539 #ifdef CONFIG_SYSCTL
1541 #include <linux/sysctl.h>
1543 static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ;
1544 static int sysctl_random_write_wakeup_bits = POOL_READY_BITS;
1545 static int sysctl_poolsize = POOL_BITS;
1546 static u8 sysctl_bootid[UUID_SIZE];
1549 * This function is used to return both the bootid UUID, and random
1550 * UUID. The difference is in whether table->data is NULL; if it is,
1551 * then a new UUID is generated and returned to the user.
1553 static int proc_do_uuid(struct ctl_table *table, int write, void *buf,
1554 size_t *lenp, loff_t *ppos)
1556 u8 tmp_uuid[UUID_SIZE], *uuid;
1557 char uuid_string[UUID_STRING_LEN + 1];
1558 struct ctl_table fake_table = {
1559 .data = uuid_string,
1560 .maxlen = UUID_STRING_LEN
1569 generate_random_uuid(uuid);
1571 static DEFINE_SPINLOCK(bootid_spinlock);
1573 spin_lock(&bootid_spinlock);
1575 generate_random_uuid(uuid);
1576 spin_unlock(&bootid_spinlock);
1579 snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
1580 return proc_dostring(&fake_table, 0, buf, lenp, ppos);
1583 /* The same as proc_dointvec, but writes don't change anything. */
1584 static int proc_do_rointvec(struct ctl_table *table, int write, void *buf,
1585 size_t *lenp, loff_t *ppos)
1587 return write ? 0 : proc_dointvec(table, 0, buf, lenp, ppos);
1590 static struct ctl_table random_table[] = {
1592 .procname = "poolsize",
1593 .data = &sysctl_poolsize,
1594 .maxlen = sizeof(int),
1596 .proc_handler = proc_dointvec,
1599 .procname = "entropy_avail",
1600 .data = &input_pool.init_bits,
1601 .maxlen = sizeof(int),
1603 .proc_handler = proc_dointvec,
1606 .procname = "write_wakeup_threshold",
1607 .data = &sysctl_random_write_wakeup_bits,
1608 .maxlen = sizeof(int),
1610 .proc_handler = proc_do_rointvec,
1613 .procname = "urandom_min_reseed_secs",
1614 .data = &sysctl_random_min_urandom_seed,
1615 .maxlen = sizeof(int),
1617 .proc_handler = proc_do_rointvec,
1620 .procname = "boot_id",
1621 .data = &sysctl_bootid,
1623 .proc_handler = proc_do_uuid,
1628 .proc_handler = proc_do_uuid,
1634 * random_init() is called before sysctl_init(),
1635 * so we cannot call register_sysctl_init() in random_init()
1637 static int __init random_sysctls_init(void)
1639 register_sysctl_init("kernel/random", random_table);
1642 device_initcall(random_sysctls_init);