1// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
2/*
3 * Copyright (C) 2017-2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
4 * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
5 * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All rights reserved.
6 *
7 * This driver produces cryptographically secure pseudorandom data. It is divided
8 * into roughly six sections, each with a section header:
9 *
10 * - Initialization and readiness waiting.
11 * - Fast key erasure RNG, the "crng".
12 * - Entropy accumulation and extraction routines.
13 * - Entropy collection routines.
14 * - Userspace reader/writer interfaces.
15 * - Sysctl interface.
16 *
17 * The high level overview is that there is one input pool, into which
18 * various pieces of data are hashed. Prior to initialization, some of that
19 * data is then "credited" as having a certain number of bits of entropy.
20 * When enough bits of entropy are available, the hash is finalized and
21 * handed as a key to a stream cipher that expands it indefinitely for
22 * various consumers. This key is periodically refreshed as the various
23 * entropy collectors, described below, add data to the input pool.
24 */
25
26#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
27
28#include <linux/utsname.h>
29#include <linux/module.h>
30#include <linux/kernel.h>
31#include <linux/major.h>
32#include <linux/string.h>
33#include <linux/fcntl.h>
34#include <linux/slab.h>
35#include <linux/random.h>
36#include <linux/poll.h>
37#include <linux/init.h>
38#include <linux/fs.h>
39#include <linux/blkdev.h>
40#include <linux/interrupt.h>
41#include <linux/mm.h>
42#include <linux/nodemask.h>
43#include <linux/spinlock.h>
44#include <linux/kthread.h>
45#include <linux/percpu.h>
46#include <linux/ptrace.h>
47#include <linux/workqueue.h>
48#include <linux/irq.h>
49#include <linux/ratelimit.h>
50#include <linux/syscalls.h>
51#include <linux/completion.h>
52#include <linux/uuid.h>
53#include <linux/uaccess.h>
54#include <linux/suspend.h>
55#include <linux/siphash.h>
56#include <linux/sched/isolation.h>
57#include <crypto/chacha.h>
58#include <crypto/blake2s.h>
59#ifdef CONFIG_VDSO_GETRANDOM
60#include <vdso/getrandom.h>
61#include <vdso/datapage.h>
62#include <vdso/vsyscall.h>
63#endif
64#include <asm/archrandom.h>
65#include <asm/processor.h>
66#include <asm/irq.h>
67#include <asm/irq_regs.h>
68#include <asm/io.h>
69
70/*********************************************************************
71 *
72 * Initialization and readiness waiting.
73 *
74 * Much of the RNG infrastructure is devoted to various dependencies
75 * being able to wait until the RNG has collected enough entropy and
76 * is ready for safe consumption.
77 *
78 *********************************************************************/
79
80/*
81 * crng_init is protected by base_crng->lock, and only increases
82 * its value (from empty->early->ready).
83 */
84static enum {
85 CRNG_EMPTY = 0, /* Little to no entropy collected */
86 CRNG_EARLY = 1, /* At least POOL_EARLY_BITS collected */
87 CRNG_READY = 2 /* Fully initialized with POOL_READY_BITS collected */
88} crng_init __read_mostly = CRNG_EMPTY;
89static DEFINE_STATIC_KEY_FALSE(crng_is_ready);
90#define crng_ready() (static_branch_likely(&crng_is_ready) || crng_init >= CRNG_READY)
91/* Various types of waiters for crng_init->CRNG_READY transition. */
92static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
93static struct fasync_struct *fasync;
94static ATOMIC_NOTIFIER_HEAD(random_ready_notifier);
95
96/* Control how we warn userspace. */
97static struct ratelimit_state urandom_warning =
98 RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE);
99static int ratelimit_disable __read_mostly =
100 IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
101module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
102MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
103
104/*
105 * Returns whether or not the input pool has been seeded and thus guaranteed
106 * to supply cryptographically secure random numbers. This applies to: the
107 * /dev/urandom device, the get_random_bytes function, and the get_random_{u8,
108 * u16,u32,u64,long} family of functions.
109 *
110 * Returns: true if the input pool has been seeded.
111 * false if the input pool has not been seeded.
112 */
113bool rng_is_initialized(void)
114{
115 return crng_ready();
116}
117EXPORT_SYMBOL(rng_is_initialized);
118
119static void __cold crng_set_ready(struct work_struct *work)
120{
121 static_branch_enable(&crng_is_ready);
122}
123
124/* Used by wait_for_random_bytes(), and considered an entropy collector, below. */
125static void try_to_generate_entropy(void);
126
127/*
128 * Wait for the input pool to be seeded and thus guaranteed to supply
129 * cryptographically secure random numbers. This applies to: the /dev/urandom
130 * device, the get_random_bytes function, and the get_random_{u8,u16,u32,u64,
131 * long} family of functions. Using any of these functions without first
132 * calling this function forfeits the guarantee of security.
133 *
134 * Returns: 0 if the input pool has been seeded.
135 * -ERESTARTSYS if the function was interrupted by a signal.
136 */
137int wait_for_random_bytes(void)
138{
139 while (!crng_ready()) {
140 int ret;
141
142 try_to_generate_entropy();
143 ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
144 if (ret)
145 return ret > 0 ? 0 : ret;
146 }
147 return 0;
148}
149EXPORT_SYMBOL(wait_for_random_bytes);
150
151/*
152 * Add a callback function that will be invoked when the crng is initialised,
153 * or immediately if it already has been. Only use this is you are absolutely
154 * sure it is required. Most users should instead be able to test
155 * `rng_is_initialized()` on demand, or make use of `get_random_bytes_wait()`.
156 */
157int __cold execute_with_initialized_rng(struct notifier_block *nb)
158{
159 unsigned long flags;
160 int ret = 0;
161
162 spin_lock_irqsave(&random_ready_notifier.lock, flags);
163 if (crng_ready())
164 nb->notifier_call(nb, 0, NULL);
165 else
166 ret = raw_notifier_chain_register(nh: (struct raw_notifier_head *)&random_ready_notifier.head, nb);
167 spin_unlock_irqrestore(lock: &random_ready_notifier.lock, flags);
168 return ret;
169}
170
171#define warn_unseeded_randomness() \
172 if (IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) && !crng_ready()) \
173 printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", \
174 __func__, (void *)_RET_IP_, crng_init)
175
176
177/*********************************************************************
178 *
179 * Fast key erasure RNG, the "crng".
180 *
181 * These functions expand entropy from the entropy extractor into
182 * long streams for external consumption using the "fast key erasure"
183 * RNG described at <https://blog.cr.yp.to/20170723-random.html>.
184 *
185 * There are a few exported interfaces for use by other drivers:
186 *
187 * void get_random_bytes(void *buf, size_t len)
188 * u8 get_random_u8()
189 * u16 get_random_u16()
190 * u32 get_random_u32()
191 * u32 get_random_u32_below(u32 ceil)
192 * u32 get_random_u32_above(u32 floor)
193 * u32 get_random_u32_inclusive(u32 floor, u32 ceil)
194 * u64 get_random_u64()
195 * unsigned long get_random_long()
196 *
197 * These interfaces will return the requested number of random bytes
198 * into the given buffer or as a return value. This is equivalent to
199 * a read from /dev/urandom. The u8, u16, u32, u64, long family of
200 * functions may be higher performance for one-off random integers,
201 * because they do a bit of buffering and do not invoke reseeding
202 * until the buffer is emptied.
203 *
204 *********************************************************************/
205
206enum {
207 CRNG_RESEED_START_INTERVAL = HZ,
208 CRNG_RESEED_INTERVAL = 60 * HZ
209};
210
211static struct {
212 u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long));
213 unsigned long generation;
214 spinlock_t lock;
215} base_crng = {
216 .lock = __SPIN_LOCK_UNLOCKED(base_crng.lock)
217};
218
219struct crng {
220 u8 key[CHACHA_KEY_SIZE];
221 unsigned long generation;
222 local_lock_t lock;
223};
224
225static DEFINE_PER_CPU(struct crng, crngs) = {
226 .generation = ULONG_MAX,
227 .lock = INIT_LOCAL_LOCK(crngs.lock),
228};
229
230/*
231 * Return the interval until the next reseeding, which is normally
232 * CRNG_RESEED_INTERVAL, but during early boot, it is at an interval
233 * proportional to the uptime.
234 */
235static unsigned int crng_reseed_interval(void)
236{
237 static bool early_boot = true;
238
239 if (unlikely(READ_ONCE(early_boot))) {
240 time64_t uptime = ktime_get_seconds();
241 if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2)
242 WRITE_ONCE(early_boot, false);
243 else
244 return max_t(unsigned int, CRNG_RESEED_START_INTERVAL,
245 (unsigned int)uptime / 2 * HZ);
246 }
247 return CRNG_RESEED_INTERVAL;
248}
249
250/* Used by crng_reseed() and crng_make_state() to extract a new seed from the input pool. */
251static void extract_entropy(void *buf, size_t len);
252
253/* This extracts a new crng key from the input pool. */
254static void crng_reseed(struct work_struct *work)
255{
256 static DECLARE_DELAYED_WORK(next_reseed, crng_reseed);
257 unsigned long flags;
258 unsigned long next_gen;
259 u8 key[CHACHA_KEY_SIZE];
260
261 /* Immediately schedule the next reseeding, so that it fires sooner rather than later. */
262 if (likely(system_unbound_wq))
263 queue_delayed_work(wq: system_unbound_wq, dwork: &next_reseed, delay: crng_reseed_interval());
264
265 extract_entropy(buf: key, len: sizeof(key));
266
267 /*
268 * We copy the new key into the base_crng, overwriting the old one,
269 * and update the generation counter. We avoid hitting ULONG_MAX,
270 * because the per-cpu crngs are initialized to ULONG_MAX, so this
271 * forces new CPUs that come online to always initialize.
272 */
273 spin_lock_irqsave(&base_crng.lock, flags);
274 memcpy(to: base_crng.key, from: key, len: sizeof(base_crng.key));
275 next_gen = base_crng.generation + 1;
276 if (next_gen == ULONG_MAX)
277 ++next_gen;
278 WRITE_ONCE(base_crng.generation, next_gen);
279#ifdef CONFIG_VDSO_GETRANDOM
280 /* base_crng.generation's invalid value is ULONG_MAX, while
281 * vdso_k_rng_data->generation's invalid value is 0, so add one to the
282 * former to arrive at the latter. Use smp_store_release so that this
283 * is ordered with the write above to base_crng.generation. Pairs with
284 * the smp_rmb() before the syscall in the vDSO code.
285 *
286 * Cast to unsigned long for 32-bit architectures, since atomic 64-bit
287 * operations are not supported on those architectures. This is safe
288 * because base_crng.generation is a 32-bit value. On big-endian
289 * architectures it will be stored in the upper 32 bits, but that's okay
290 * because the vDSO side only checks whether the value changed, without
291 * actually using or interpreting the value.
292 */
293 smp_store_release((unsigned long *)&vdso_k_rng_data->generation, next_gen + 1);
294#endif
295 if (!static_branch_likely(&crng_is_ready))
296 crng_init = CRNG_READY;
297 spin_unlock_irqrestore(lock: &base_crng.lock, flags);
298 memzero_explicit(s: key, count: sizeof(key));
299}
300
301/*
302 * This generates a ChaCha block using the provided key, and then
303 * immediately overwrites that key with half the block. It returns
304 * the resultant ChaCha state to the user, along with the second
305 * half of the block containing 32 bytes of random data that may
306 * be used; random_data_len may not be greater than 32.
307 *
308 * The returned ChaCha state contains within it a copy of the old
309 * key value, at index 4, so the state should always be zeroed out
310 * immediately after using in order to maintain forward secrecy.
311 * If the state cannot be erased in a timely manner, then it is
312 * safer to set the random_data parameter to &chacha_state->x[4]
313 * so that this function overwrites it before returning.
314 */
315static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE],
316 struct chacha_state *chacha_state,
317 u8 *random_data, size_t random_data_len)
318{
319 u8 first_block[CHACHA_BLOCK_SIZE];
320
321 BUG_ON(random_data_len > 32);
322
323 chacha_init_consts(state: chacha_state);
324 memcpy(to: &chacha_state->x[4], from: key, CHACHA_KEY_SIZE);
325 memset(s: &chacha_state->x[12], c: 0, n: sizeof(u32) * 4);
326 chacha20_block(state: chacha_state, out: first_block);
327
328 memcpy(to: key, from: first_block, CHACHA_KEY_SIZE);
329 memcpy(to: random_data, from: first_block + CHACHA_KEY_SIZE, len: random_data_len);
330 memzero_explicit(s: first_block, count: sizeof(first_block));
331}
332
333/*
334 * This function returns a ChaCha state that you may use for generating
335 * random data. It also returns up to 32 bytes on its own of random data
336 * that may be used; random_data_len may not be greater than 32.
337 */
338static void crng_make_state(struct chacha_state *chacha_state,
339 u8 *random_data, size_t random_data_len)
340{
341 unsigned long flags;
342 struct crng *crng;
343
344 BUG_ON(random_data_len > 32);
345
346 /*
347 * For the fast path, we check whether we're ready, unlocked first, and
348 * then re-check once locked later. In the case where we're really not
349 * ready, we do fast key erasure with the base_crng directly, extracting
350 * when crng_init is CRNG_EMPTY.
351 */
352 if (!crng_ready()) {
353 bool ready;
354
355 spin_lock_irqsave(&base_crng.lock, flags);
356 ready = crng_ready();
357 if (!ready) {
358 if (crng_init == CRNG_EMPTY)
359 extract_entropy(buf: base_crng.key, len: sizeof(base_crng.key));
360 crng_fast_key_erasure(key: base_crng.key, chacha_state,
361 random_data, random_data_len);
362 }
363 spin_unlock_irqrestore(lock: &base_crng.lock, flags);
364 if (!ready)
365 return;
366 }
367
368 local_lock_irqsave(&crngs.lock, flags);
369 crng = raw_cpu_ptr(&crngs);
370
371 /*
372 * If our per-cpu crng is older than the base_crng, then it means
373 * somebody reseeded the base_crng. In that case, we do fast key
374 * erasure on the base_crng, and use its output as the new key
375 * for our per-cpu crng. This brings us up to date with base_crng.
376 */
377 if (unlikely(crng->generation != READ_ONCE(base_crng.generation))) {
378 spin_lock(lock: &base_crng.lock);
379 crng_fast_key_erasure(key: base_crng.key, chacha_state,
380 random_data: crng->key, random_data_len: sizeof(crng->key));
381 crng->generation = base_crng.generation;
382 spin_unlock(lock: &base_crng.lock);
383 }
384
385 /*
386 * Finally, when we've made it this far, our per-cpu crng has an up
387 * to date key, and we can do fast key erasure with it to produce
388 * some random data and a ChaCha state for the caller. All other
389 * branches of this function are "unlikely", so most of the time we
390 * should wind up here immediately.
391 */
392 crng_fast_key_erasure(key: crng->key, chacha_state, random_data, random_data_len);
393 local_unlock_irqrestore(&crngs.lock, flags);
394}
395
396static void _get_random_bytes(void *buf, size_t len)
397{
398 struct chacha_state chacha_state;
399 u8 tmp[CHACHA_BLOCK_SIZE];
400 size_t first_block_len;
401
402 if (!len)
403 return;
404
405 first_block_len = min_t(size_t, 32, len);
406 crng_make_state(chacha_state: &chacha_state, random_data: buf, random_data_len: first_block_len);
407 len -= first_block_len;
408 buf += first_block_len;
409
410 while (len) {
411 if (len < CHACHA_BLOCK_SIZE) {
412 chacha20_block(state: &chacha_state, out: tmp);
413 memcpy(to: buf, from: tmp, len);
414 memzero_explicit(s: tmp, count: sizeof(tmp));
415 break;
416 }
417
418 chacha20_block(state: &chacha_state, out: buf);
419 if (unlikely(chacha_state.x[12] == 0))
420 ++chacha_state.x[13];
421 len -= CHACHA_BLOCK_SIZE;
422 buf += CHACHA_BLOCK_SIZE;
423 }
424
425 chacha_zeroize_state(state: &chacha_state);
426}
427
428/*
429 * This returns random bytes in arbitrary quantities. The quality of the
430 * random bytes is good as /dev/urandom. In order to ensure that the
431 * randomness provided by this function is okay, the function
432 * wait_for_random_bytes() should be called and return 0 at least once
433 * at any point prior.
434 */
435void get_random_bytes(void *buf, size_t len)
436{
437 warn_unseeded_randomness();
438 _get_random_bytes(buf, len);
439}
440EXPORT_SYMBOL(get_random_bytes);
441
442static ssize_t get_random_bytes_user(struct iov_iter *iter)
443{
444 struct chacha_state chacha_state;
445 u8 block[CHACHA_BLOCK_SIZE];
446 size_t ret = 0, copied;
447
448 if (unlikely(!iov_iter_count(iter)))
449 return 0;
450
451 /*
452 * Immediately overwrite the ChaCha key at index 4 with random
453 * bytes, in case userspace causes copy_to_iter() below to sleep
454 * forever, so that we still retain forward secrecy in that case.
455 */
456 crng_make_state(chacha_state: &chacha_state, random_data: (u8 *)&chacha_state.x[4],
457 CHACHA_KEY_SIZE);
458 /*
459 * However, if we're doing a read of len <= 32, we don't need to
460 * use chacha_state after, so we can simply return those bytes to
461 * the user directly.
462 */
463 if (iov_iter_count(i: iter) <= CHACHA_KEY_SIZE) {
464 ret = copy_to_iter(addr: &chacha_state.x[4], CHACHA_KEY_SIZE, i: iter);
465 goto out_zero_chacha;
466 }
467
468 for (;;) {
469 chacha20_block(state: &chacha_state, out: block);
470 if (unlikely(chacha_state.x[12] == 0))
471 ++chacha_state.x[13];
472
473 copied = copy_to_iter(addr: block, bytes: sizeof(block), i: iter);
474 ret += copied;
475 if (!iov_iter_count(i: iter) || copied != sizeof(block))
476 break;
477
478 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
479 if (ret % PAGE_SIZE == 0) {
480 if (signal_pending(current))
481 break;
482 cond_resched();
483 }
484 }
485
486 memzero_explicit(s: block, count: sizeof(block));
487out_zero_chacha:
488 chacha_zeroize_state(state: &chacha_state);
489 return ret ? ret : -EFAULT;
490}
491
492/*
493 * Batched entropy returns random integers. The quality of the random
494 * number is good as /dev/urandom. In order to ensure that the randomness
495 * provided by this function is okay, the function wait_for_random_bytes()
496 * should be called and return 0 at least once at any point prior.
497 */
498
499#define DEFINE_BATCHED_ENTROPY(type) \
500struct batch_ ##type { \
501 /* \
502 * We make this 1.5x a ChaCha block, so that we get the \
503 * remaining 32 bytes from fast key erasure, plus one full \
504 * block from the detached ChaCha state. We can increase \
505 * the size of this later if needed so long as we keep the \
506 * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE. \
507 */ \
508 type entropy[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(type))]; \
509 local_lock_t lock; \
510 unsigned long generation; \
511 unsigned int position; \
512}; \
513 \
514static DEFINE_PER_CPU(struct batch_ ##type, batched_entropy_ ##type) = { \
515 .lock = INIT_LOCAL_LOCK(batched_entropy_ ##type.lock), \
516 .position = UINT_MAX \
517}; \
518 \
519type get_random_ ##type(void) \
520{ \
521 type ret; \
522 unsigned long flags; \
523 struct batch_ ##type *batch; \
524 unsigned long next_gen; \
525 \
526 warn_unseeded_randomness(); \
527 \
528 if (!crng_ready()) { \
529 _get_random_bytes(&ret, sizeof(ret)); \
530 return ret; \
531 } \
532 \
533 local_lock_irqsave(&batched_entropy_ ##type.lock, flags); \
534 batch = raw_cpu_ptr(&batched_entropy_##type); \
535 \
536 next_gen = READ_ONCE(base_crng.generation); \
537 if (batch->position >= ARRAY_SIZE(batch->entropy) || \
538 next_gen != batch->generation) { \
539 _get_random_bytes(batch->entropy, sizeof(batch->entropy)); \
540 batch->position = 0; \
541 batch->generation = next_gen; \
542 } \
543 \
544 ret = batch->entropy[batch->position]; \
545 batch->entropy[batch->position] = 0; \
546 ++batch->position; \
547 local_unlock_irqrestore(&batched_entropy_ ##type.lock, flags); \
548 return ret; \
549} \
550EXPORT_SYMBOL(get_random_ ##type);
551
552DEFINE_BATCHED_ENTROPY(u8)
553DEFINE_BATCHED_ENTROPY(u16)
554DEFINE_BATCHED_ENTROPY(u32)
555DEFINE_BATCHED_ENTROPY(u64)
556
557u32 __get_random_u32_below(u32 ceil)
558{
559 /*
560 * This is the slow path for variable ceil. It is still fast, most of
561 * the time, by doing traditional reciprocal multiplication and
562 * opportunistically comparing the lower half to ceil itself, before
563 * falling back to computing a larger bound, and then rejecting samples
564 * whose lower half would indicate a range indivisible by ceil. The use
565 * of `-ceil % ceil` is analogous to `2^32 % ceil`, but is computable
566 * in 32-bits.
567 */
568 u32 rand = get_random_u32();
569 u64 mult;
570
571 /*
572 * This function is technically undefined for ceil == 0, and in fact
573 * for the non-underscored constant version in the header, we build bug
574 * on that. But for the non-constant case, it's convenient to have that
575 * evaluate to being a straight call to get_random_u32(), so that
576 * get_random_u32_inclusive() can work over its whole range without
577 * undefined behavior.
578 */
579 if (unlikely(!ceil))
580 return rand;
581
582 mult = (u64)ceil * rand;
583 if (unlikely((u32)mult < ceil)) {
584 u32 bound = -ceil % ceil;
585 while (unlikely((u32)mult < bound))
586 mult = (u64)ceil * get_random_u32();
587 }
588 return mult >> 32;
589}
590EXPORT_SYMBOL(__get_random_u32_below);
591
592#ifdef CONFIG_SMP
593/*
594 * This function is called when the CPU is coming up, with entry
595 * CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP.
596 */
597int __cold random_prepare_cpu(unsigned int cpu)
598{
599 /*
600 * When the cpu comes back online, immediately invalidate both
601 * the per-cpu crng and all batches, so that we serve fresh
602 * randomness.
603 */
604 per_cpu_ptr(&crngs, cpu)->generation = ULONG_MAX;
605 per_cpu_ptr(&batched_entropy_u8, cpu)->position = UINT_MAX;
606 per_cpu_ptr(&batched_entropy_u16, cpu)->position = UINT_MAX;
607 per_cpu_ptr(&batched_entropy_u32, cpu)->position = UINT_MAX;
608 per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX;
609 return 0;
610}
611#endif
612
613
614/**********************************************************************
615 *
616 * Entropy accumulation and extraction routines.
617 *
618 * Callers may add entropy via:
619 *
620 * static void mix_pool_bytes(const void *buf, size_t len)
621 *
622 * After which, if added entropy should be credited:
623 *
624 * static void credit_init_bits(size_t bits)
625 *
626 * Finally, extract entropy via:
627 *
628 * static void extract_entropy(void *buf, size_t len)
629 *
630 **********************************************************************/
631
632enum {
633 POOL_BITS = BLAKE2S_HASH_SIZE * 8,
634 POOL_READY_BITS = POOL_BITS, /* When crng_init->CRNG_READY */
635 POOL_EARLY_BITS = POOL_READY_BITS / 2 /* When crng_init->CRNG_EARLY */
636};
637
638static struct {
639 struct blake2s_state hash;
640 spinlock_t lock;
641 unsigned int init_bits;
642} input_pool = {
643 .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE),
644 BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4,
645 BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 },
646 .hash.outlen = BLAKE2S_HASH_SIZE,
647 .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
648};
649
650static void _mix_pool_bytes(const void *buf, size_t len)
651{
652 blake2s_update(state: &input_pool.hash, in: buf, inlen: len);
653}
654
655/*
656 * This function adds bytes into the input pool. It does not
657 * update the initialization bit counter; the caller should call
658 * credit_init_bits if this is appropriate.
659 */
660static void mix_pool_bytes(const void *buf, size_t len)
661{
662 unsigned long flags;
663
664 spin_lock_irqsave(&input_pool.lock, flags);
665 _mix_pool_bytes(buf, len);
666 spin_unlock_irqrestore(lock: &input_pool.lock, flags);
667}
668
669/*
670 * This is an HKDF-like construction for using the hashed collected entropy
671 * as a PRF key, that's then expanded block-by-block.
672 */
673static void extract_entropy(void *buf, size_t len)
674{
675 unsigned long flags;
676 u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
677 struct {
678 unsigned long rdseed[32 / sizeof(long)];
679 size_t counter;
680 } block;
681 size_t i, longs;
682
683 for (i = 0; i < ARRAY_SIZE(block.rdseed);) {
684 longs = arch_get_random_seed_longs(v: &block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
685 if (longs) {
686 i += longs;
687 continue;
688 }
689 longs = arch_get_random_longs(v: &block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
690 if (longs) {
691 i += longs;
692 continue;
693 }
694 block.rdseed[i++] = random_get_entropy();
695 }
696
697 spin_lock_irqsave(&input_pool.lock, flags);
698
699 /* seed = HASHPRF(last_key, entropy_input) */
700 blake2s_final(state: &input_pool.hash, out: seed);
701
702 /* next_key = HASHPRF(seed, RDSEED || 0) */
703 block.counter = 0;
704 blake2s(out: next_key, in: (u8 *)&block, key: seed, outlen: sizeof(next_key), inlen: sizeof(block), keylen: sizeof(seed));
705 blake2s_init_key(state: &input_pool.hash, outlen: BLAKE2S_HASH_SIZE, key: next_key, keylen: sizeof(next_key));
706
707 spin_unlock_irqrestore(lock: &input_pool.lock, flags);
708 memzero_explicit(s: next_key, count: sizeof(next_key));
709
710 while (len) {
711 i = min_t(size_t, len, BLAKE2S_HASH_SIZE);
712 /* output = HASHPRF(seed, RDSEED || ++counter) */
713 ++block.counter;
714 blake2s(out: buf, in: (u8 *)&block, key: seed, outlen: i, inlen: sizeof(block), keylen: sizeof(seed));
715 len -= i;
716 buf += i;
717 }
718
719 memzero_explicit(s: seed, count: sizeof(seed));
720 memzero_explicit(s: &block, count: sizeof(block));
721}
722
723#define credit_init_bits(bits) if (!crng_ready()) _credit_init_bits(bits)
724
725static void __cold _credit_init_bits(size_t bits)
726{
727 static DECLARE_WORK(set_ready, crng_set_ready);
728 unsigned int new, orig, add;
729 unsigned long flags;
730 int m;
731
732 if (!bits)
733 return;
734
735 add = min_t(size_t, bits, POOL_BITS);
736
737 orig = READ_ONCE(input_pool.init_bits);
738 do {
739 new = min_t(unsigned int, POOL_BITS, orig + add);
740 } while (!try_cmpxchg(&input_pool.init_bits, &orig, new));
741
742 if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
743 crng_reseed(NULL); /* Sets crng_init to CRNG_READY under base_crng.lock. */
744 if (static_key_initialized && system_unbound_wq)
745 queue_work(wq: system_unbound_wq, work: &set_ready);
746 atomic_notifier_call_chain(nh: &random_ready_notifier, val: 0, NULL);
747#ifdef CONFIG_VDSO_GETRANDOM
748 WRITE_ONCE(vdso_k_rng_data->is_ready, true);
749#endif
750 wake_up_interruptible(&crng_init_wait);
751 kill_fasync(&fasync, SIGIO, POLL_IN);
752 pr_notice("crng init done\n");
753 m = ratelimit_state_get_miss(rs: &urandom_warning);
754 if (m)
755 pr_notice("%d urandom warning(s) missed due to ratelimiting\n", m);
756 } else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
757 spin_lock_irqsave(&base_crng.lock, flags);
758 /* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */
759 if (crng_init == CRNG_EMPTY) {
760 extract_entropy(buf: base_crng.key, len: sizeof(base_crng.key));
761 crng_init = CRNG_EARLY;
762 }
763 spin_unlock_irqrestore(lock: &base_crng.lock, flags);
764 }
765}
766
767
768/**********************************************************************
769 *
770 * Entropy collection routines.
771 *
772 * The following exported functions are used for pushing entropy into
773 * the above entropy accumulation routines:
774 *
775 * void add_device_randomness(const void *buf, size_t len);
776 * void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy, bool sleep_after);
777 * void add_bootloader_randomness(const void *buf, size_t len);
778 * void add_vmfork_randomness(const void *unique_vm_id, size_t len);
779 * void add_interrupt_randomness(int irq);
780 * void add_input_randomness(unsigned int type, unsigned int code, unsigned int value);
781 * void add_disk_randomness(struct gendisk *disk);
782 *
783 * add_device_randomness() adds data to the input pool that
784 * is likely to differ between two devices (or possibly even per boot).
785 * This would be things like MAC addresses or serial numbers, or the
786 * read-out of the RTC. This does *not* credit any actual entropy to
787 * the pool, but it initializes the pool to different values for devices
788 * that might otherwise be identical and have very little entropy
789 * available to them (particularly common in the embedded world).
790 *
791 * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
792 * entropy as specified by the caller. If the entropy pool is full it will
793 * block until more entropy is needed.
794 *
795 * add_bootloader_randomness() is called by bootloader drivers, such as EFI
796 * and device tree, and credits its input depending on whether or not the
797 * command line option 'random.trust_bootloader'.
798 *
799 * add_vmfork_randomness() adds a unique (but not necessarily secret) ID
800 * representing the current instance of a VM to the pool, without crediting,
801 * and then force-reseeds the crng so that it takes effect immediately.
802 *
803 * add_interrupt_randomness() uses the interrupt timing as random
804 * inputs to the entropy pool. Using the cycle counters and the irq source
805 * as inputs, it feeds the input pool roughly once a second or after 64
806 * interrupts, crediting 1 bit of entropy for whichever comes first.
807 *
808 * add_input_randomness() uses the input layer interrupt timing, as well
809 * as the event type information from the hardware.
810 *
811 * add_disk_randomness() uses what amounts to the seek time of block
812 * layer request events, on a per-disk_devt basis, as input to the
813 * entropy pool. Note that high-speed solid state drives with very low
814 * seek times do not make for good sources of entropy, as their seek
815 * times are usually fairly consistent.
816 *
817 * The last two routines try to estimate how many bits of entropy
818 * to credit. They do this by keeping track of the first and second
819 * order deltas of the event timings.
820 *
821 **********************************************************************/
822
823static bool trust_cpu __initdata = true;
824static bool trust_bootloader __initdata = true;
825static int __init parse_trust_cpu(char *arg)
826{
827 return kstrtobool(s: arg, res: &trust_cpu);
828}
829static int __init parse_trust_bootloader(char *arg)
830{
831 return kstrtobool(s: arg, res: &trust_bootloader);
832}
833early_param("random.trust_cpu", parse_trust_cpu);
834early_param("random.trust_bootloader", parse_trust_bootloader);
835
836static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data)
837{
838 unsigned long flags, entropy = random_get_entropy();
839
840 /*
841 * Encode a representation of how long the system has been suspended,
842 * in a way that is distinct from prior system suspends.
843 */
844 ktime_t stamps[] = { ktime_get(), ktime_get_boottime(), ktime_get_real() };
845
846 spin_lock_irqsave(&input_pool.lock, flags);
847 _mix_pool_bytes(buf: &action, len: sizeof(action));
848 _mix_pool_bytes(buf: stamps, len: sizeof(stamps));
849 _mix_pool_bytes(buf: &entropy, len: sizeof(entropy));
850 spin_unlock_irqrestore(lock: &input_pool.lock, flags);
851
852 if (crng_ready() && (action == PM_RESTORE_PREPARE ||
853 (action == PM_POST_SUSPEND && !IS_ENABLED(CONFIG_PM_AUTOSLEEP) &&
854 !IS_ENABLED(CONFIG_PM_USERSPACE_AUTOSLEEP)))) {
855 crng_reseed(NULL);
856 pr_notice("crng reseeded on system resumption\n");
857 }
858 return 0;
859}
860
861static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification };
862
863/*
864 * This is called extremely early, before time keeping functionality is
865 * available, but arch randomness is. Interrupts are not yet enabled.
866 */
867void __init random_init_early(const char *command_line)
868{
869 unsigned long entropy[BLAKE2S_BLOCK_SIZE / sizeof(long)];
870 size_t i, longs, arch_bits;
871
872#if defined(LATENT_ENTROPY_PLUGIN)
873 static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
874 _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
875#endif
876
877 for (i = 0, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) {
878 longs = arch_get_random_seed_longs(v: entropy, ARRAY_SIZE(entropy) - i);
879 if (longs) {
880 _mix_pool_bytes(buf: entropy, len: sizeof(*entropy) * longs);
881 i += longs;
882 continue;
883 }
884 longs = arch_get_random_longs(v: entropy, ARRAY_SIZE(entropy) - i);
885 if (longs) {
886 _mix_pool_bytes(buf: entropy, len: sizeof(*entropy) * longs);
887 i += longs;
888 continue;
889 }
890 arch_bits -= sizeof(*entropy) * 8;
891 ++i;
892 }
893
894 _mix_pool_bytes(buf: init_utsname(), len: sizeof(*(init_utsname())));
895 _mix_pool_bytes(buf: command_line, len: strlen(command_line));
896
897 /* Reseed if already seeded by earlier phases. */
898 if (crng_ready())
899 crng_reseed(NULL);
900 else if (trust_cpu)
901 _credit_init_bits(bits: arch_bits);
902}
903
904/*
905 * This is called a little bit after the prior function, and now there is
906 * access to timestamps counters. Interrupts are not yet enabled.
907 */
908void __init random_init(void)
909{
910 unsigned long entropy = random_get_entropy();
911 ktime_t now = ktime_get_real();
912
913 _mix_pool_bytes(buf: &now, len: sizeof(now));
914 _mix_pool_bytes(buf: &entropy, len: sizeof(entropy));
915 add_latent_entropy();
916
917 /*
918 * If we were initialized by the cpu or bootloader before jump labels
919 * or workqueues are initialized, then we should enable the static
920 * branch here, where it's guaranteed that these have been initialized.
921 */
922 if (!static_branch_likely(&crng_is_ready) && crng_init >= CRNG_READY)
923 crng_set_ready(NULL);
924
925 /* Reseed if already seeded by earlier phases. */
926 if (crng_ready())
927 crng_reseed(NULL);
928
929 WARN_ON(register_pm_notifier(&pm_notifier));
930
931 WARN(!entropy, "Missing cycle counter and fallback timer; RNG "
932 "entropy collection will consequently suffer.");
933}
934
935/*
936 * Add device- or boot-specific data to the input pool to help
937 * initialize it.
938 *
939 * None of this adds any entropy; it is meant to avoid the problem of
940 * the entropy pool having similar initial state across largely
941 * identical devices.
942 */
943void add_device_randomness(const void *buf, size_t len)
944{
945 unsigned long entropy = random_get_entropy();
946 unsigned long flags;
947
948 spin_lock_irqsave(&input_pool.lock, flags);
949 _mix_pool_bytes(buf: &entropy, len: sizeof(entropy));
950 _mix_pool_bytes(buf, len);
951 spin_unlock_irqrestore(lock: &input_pool.lock, flags);
952}
953EXPORT_SYMBOL(add_device_randomness);
954
955/*
956 * Interface for in-kernel drivers of true hardware RNGs. Those devices
957 * may produce endless random bits, so this function will sleep for
958 * some amount of time after, if the sleep_after parameter is true.
959 */
960void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy, bool sleep_after)
961{
962 mix_pool_bytes(buf, len);
963 credit_init_bits(entropy);
964
965 /*
966 * Throttle writing to once every reseed interval, unless we're not yet
967 * initialized or no entropy is credited.
968 */
969 if (sleep_after && !kthread_should_stop() && (crng_ready() || !entropy))
970 schedule_timeout_interruptible(timeout: crng_reseed_interval());
971}
972EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
973
974/*
975 * Handle random seed passed by bootloader, and credit it depending
976 * on the command line option 'random.trust_bootloader'.
977 */
978void __init add_bootloader_randomness(const void *buf, size_t len)
979{
980 mix_pool_bytes(buf, len);
981 if (trust_bootloader)
982 credit_init_bits(len * 8);
983}
984
985#if IS_ENABLED(CONFIG_VMGENID)
986static BLOCKING_NOTIFIER_HEAD(vmfork_chain);
987
988/*
989 * Handle a new unique VM ID, which is unique, not secret, so we
990 * don't credit it, but we do immediately force a reseed after so
991 * that it's used by the crng posthaste.
992 */
993void __cold add_vmfork_randomness(const void *unique_vm_id, size_t len)
994{
995 add_device_randomness(unique_vm_id, len);
996 if (crng_ready()) {
997 crng_reseed(NULL);
998 pr_notice("crng reseeded due to virtual machine fork\n");
999 }
1000 blocking_notifier_call_chain(&vmfork_chain, 0, NULL);
1001}
1002#if IS_MODULE(CONFIG_VMGENID)
1003EXPORT_SYMBOL_GPL(add_vmfork_randomness);
1004#endif
1005
1006int __cold register_random_vmfork_notifier(struct notifier_block *nb)
1007{
1008 return blocking_notifier_chain_register(&vmfork_chain, nb);
1009}
1010EXPORT_SYMBOL_GPL(register_random_vmfork_notifier);
1011
1012int __cold unregister_random_vmfork_notifier(struct notifier_block *nb)
1013{
1014 return blocking_notifier_chain_unregister(&vmfork_chain, nb);
1015}
1016EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier);
1017#endif
1018
1019struct fast_pool {
1020 unsigned long pool[4];
1021 unsigned long last;
1022 unsigned int count;
1023 struct timer_list mix;
1024};
1025
1026static void mix_interrupt_randomness(struct timer_list *work);
1027
1028static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = {
1029#ifdef CONFIG_64BIT
1030#define FASTMIX_PERM SIPHASH_PERMUTATION
1031 .pool = { SIPHASH_CONST_0, SIPHASH_CONST_1, SIPHASH_CONST_2, SIPHASH_CONST_3 },
1032#else
1033#define FASTMIX_PERM HSIPHASH_PERMUTATION
1034 .pool = { HSIPHASH_CONST_0, HSIPHASH_CONST_1, HSIPHASH_CONST_2, HSIPHASH_CONST_3 },
1035#endif
1036 .mix = __TIMER_INITIALIZER(mix_interrupt_randomness, 0)
1037};
1038
1039/*
1040 * This is [Half]SipHash-1-x, starting from an empty key. Because
1041 * the key is fixed, it assumes that its inputs are non-malicious,
1042 * and therefore this has no security on its own. s represents the
1043 * four-word SipHash state, while v represents a two-word input.
1044 */
1045static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long v2)
1046{
1047 s[3] ^= v1;
1048 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1049 s[0] ^= v1;
1050 s[3] ^= v2;
1051 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1052 s[0] ^= v2;
1053}
1054
1055#ifdef CONFIG_SMP
1056/*
1057 * This function is called when the CPU has just come online, with
1058 * entry CPUHP_AP_RANDOM_ONLINE, just after CPUHP_AP_WORKQUEUE_ONLINE.
1059 */
1060int __cold random_online_cpu(unsigned int cpu)
1061{
1062 /*
1063 * During CPU shutdown and before CPU onlining, add_interrupt_
1064 * randomness() may schedule mix_interrupt_randomness(), and
1065 * set the MIX_INFLIGHT flag. However, because the worker can
1066 * be scheduled on a different CPU during this period, that
1067 * flag will never be cleared. For that reason, we zero out
1068 * the flag here, which runs just after workqueues are onlined
1069 * for the CPU again. This also has the effect of setting the
1070 * irq randomness count to zero so that new accumulated irqs
1071 * are fresh.
1072 */
1073 per_cpu_ptr(&irq_randomness, cpu)->count = 0;
1074 return 0;
1075}
1076#endif
1077
1078static void mix_interrupt_randomness(struct timer_list *work)
1079{
1080 struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix);
1081 /*
1082 * The size of the copied stack pool is explicitly 2 longs so that we
1083 * only ever ingest half of the siphash output each time, retaining
1084 * the other half as the next "key" that carries over. The entropy is
1085 * supposed to be sufficiently dispersed between bits so on average
1086 * we don't wind up "losing" some.
1087 */
1088 unsigned long pool[2];
1089 unsigned int count;
1090
1091 /* Check to see if we're running on the wrong CPU due to hotplug. */
1092 local_irq_disable();
1093 if (fast_pool != this_cpu_ptr(&irq_randomness)) {
1094 local_irq_enable();
1095 return;
1096 }
1097
1098 /*
1099 * Copy the pool to the stack so that the mixer always has a
1100 * consistent view, before we reenable irqs again.
1101 */
1102 memcpy(to: pool, from: fast_pool->pool, len: sizeof(pool));
1103 count = fast_pool->count;
1104 fast_pool->count = 0;
1105 fast_pool->last = jiffies;
1106 local_irq_enable();
1107
1108 mix_pool_bytes(buf: pool, len: sizeof(pool));
1109 credit_init_bits(clamp_t(unsigned int, (count & U16_MAX) / 64, 1, sizeof(pool) * 8));
1110
1111 memzero_explicit(s: pool, count: sizeof(pool));
1112}
1113
1114void add_interrupt_randomness(int irq)
1115{
1116 enum { MIX_INFLIGHT = 1U << 31 };
1117 unsigned long entropy = random_get_entropy();
1118 struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
1119 struct pt_regs *regs = get_irq_regs();
1120 unsigned int new_count;
1121
1122 fast_mix(s: fast_pool->pool, v1: entropy,
1123 v2: (regs ? instruction_pointer(regs) : _RET_IP_) ^ swab(y: irq));
1124 new_count = ++fast_pool->count;
1125
1126 if (new_count & MIX_INFLIGHT)
1127 return;
1128
1129 if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ))
1130 return;
1131
1132 fast_pool->count |= MIX_INFLIGHT;
1133 if (!timer_pending(timer: &fast_pool->mix)) {
1134 fast_pool->mix.expires = jiffies;
1135 add_timer_on(timer: &fast_pool->mix, raw_smp_processor_id());
1136 }
1137}
1138EXPORT_SYMBOL_GPL(add_interrupt_randomness);
1139
1140/* There is one of these per entropy source */
1141struct timer_rand_state {
1142 unsigned long last_time;
1143 long last_delta, last_delta2;
1144};
1145
1146/*
1147 * This function adds entropy to the entropy "pool" by using timing
1148 * delays. It uses the timer_rand_state structure to make an estimate
1149 * of how many bits of entropy this call has added to the pool. The
1150 * value "num" is also added to the pool; it should somehow describe
1151 * the type of event that just happened.
1152 */
1153static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
1154{
1155 unsigned long entropy = random_get_entropy(), now = jiffies, flags;
1156 long delta, delta2, delta3;
1157 unsigned int bits;
1158
1159 /*
1160 * If we're in a hard IRQ, add_interrupt_randomness() will be called
1161 * sometime after, so mix into the fast pool.
1162 */
1163 if (in_hardirq()) {
1164 fast_mix(this_cpu_ptr(&irq_randomness)->pool, v1: entropy, v2: num);
1165 } else {
1166 spin_lock_irqsave(&input_pool.lock, flags);
1167 _mix_pool_bytes(buf: &entropy, len: sizeof(entropy));
1168 _mix_pool_bytes(buf: &num, len: sizeof(num));
1169 spin_unlock_irqrestore(lock: &input_pool.lock, flags);
1170 }
1171
1172 if (crng_ready())
1173 return;
1174
1175 /*
1176 * Calculate number of bits of randomness we probably added.
1177 * We take into account the first, second and third-order deltas
1178 * in order to make our estimate.
1179 */
1180 delta = now - READ_ONCE(state->last_time);
1181 WRITE_ONCE(state->last_time, now);
1182
1183 delta2 = delta - READ_ONCE(state->last_delta);
1184 WRITE_ONCE(state->last_delta, delta);
1185
1186 delta3 = delta2 - READ_ONCE(state->last_delta2);
1187 WRITE_ONCE(state->last_delta2, delta2);
1188
1189 if (delta < 0)
1190 delta = -delta;
1191 if (delta2 < 0)
1192 delta2 = -delta2;
1193 if (delta3 < 0)
1194 delta3 = -delta3;
1195 if (delta > delta2)
1196 delta = delta2;
1197 if (delta > delta3)
1198 delta = delta3;
1199
1200 /*
1201 * delta is now minimum absolute delta. Round down by 1 bit
1202 * on general principles, and limit entropy estimate to 11 bits.
1203 */
1204 bits = min(fls(delta >> 1), 11);
1205
1206 /*
1207 * As mentioned above, if we're in a hard IRQ, add_interrupt_randomness()
1208 * will run after this, which uses a different crediting scheme of 1 bit
1209 * per every 64 interrupts. In order to let that function do accounting
1210 * close to the one in this function, we credit a full 64/64 bit per bit,
1211 * and then subtract one to account for the extra one added.
1212 */
1213 if (in_hardirq())
1214 this_cpu_ptr(&irq_randomness)->count += max(1u, bits * 64) - 1;
1215 else
1216 _credit_init_bits(bits);
1217}
1218
1219void add_input_randomness(unsigned int type, unsigned int code, unsigned int value)
1220{
1221 static unsigned char last_value;
1222 static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES };
1223
1224 /* Ignore autorepeat and the like. */
1225 if (value == last_value)
1226 return;
1227
1228 last_value = value;
1229 add_timer_randomness(state: &input_timer_state,
1230 num: (type << 4) ^ code ^ (code >> 4) ^ value);
1231}
1232EXPORT_SYMBOL_GPL(add_input_randomness);
1233
1234#ifdef CONFIG_BLOCK
1235void add_disk_randomness(struct gendisk *disk)
1236{
1237 if (!disk || !disk->random)
1238 return;
1239 /* First major is 1, so we get >= 0x200 here. */
1240 add_timer_randomness(state: disk->random, num: 0x100 + disk_devt(disk));
1241}
1242EXPORT_SYMBOL_GPL(add_disk_randomness);
1243
1244void __cold rand_initialize_disk(struct gendisk *disk)
1245{
1246 struct timer_rand_state *state;
1247
1248 /*
1249 * If kzalloc returns null, we just won't use that entropy
1250 * source.
1251 */
1252 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1253 if (state) {
1254 state->last_time = INITIAL_JIFFIES;
1255 disk->random = state;
1256 }
1257}
1258#endif
1259
1260struct entropy_timer_state {
1261 unsigned long entropy;
1262 struct timer_list timer;
1263 atomic_t samples;
1264 unsigned int samples_per_bit;
1265};
1266
1267/*
1268 * Each time the timer fires, we expect that we got an unpredictable jump in
1269 * the cycle counter. Even if the timer is running on another CPU, the timer
1270 * activity will be touching the stack of the CPU that is generating entropy.
1271 *
1272 * Note that we don't re-arm the timer in the timer itself - we are happy to be
1273 * scheduled away, since that just makes the load more complex, but we do not
1274 * want the timer to keep ticking unless the entropy loop is running.
1275 *
1276 * So the re-arming always happens in the entropy loop itself.
1277 */
1278static void __cold entropy_timer(struct timer_list *timer)
1279{
1280 struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer);
1281 unsigned long entropy = random_get_entropy();
1282
1283 mix_pool_bytes(buf: &entropy, len: sizeof(entropy));
1284 if (atomic_inc_return(v: &state->samples) % state->samples_per_bit == 0)
1285 credit_init_bits(1);
1286}
1287
1288/*
1289 * If we have an actual cycle counter, see if we can generate enough entropy
1290 * with timing noise.
1291 */
1292static void __cold try_to_generate_entropy(void)
1293{
1294 enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = HZ / 15 };
1295 u8 stack_bytes[sizeof(struct entropy_timer_state) + SMP_CACHE_BYTES - 1];
1296 struct entropy_timer_state *stack = PTR_ALIGN((void *)stack_bytes, SMP_CACHE_BYTES);
1297 unsigned int i, num_different = 0;
1298 unsigned long last = random_get_entropy();
1299 int cpu = -1;
1300
1301 for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
1302 stack->entropy = random_get_entropy();
1303 if (stack->entropy != last)
1304 ++num_different;
1305 last = stack->entropy;
1306 }
1307 stack->samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1);
1308 if (stack->samples_per_bit > MAX_SAMPLES_PER_BIT)
1309 return;
1310
1311 atomic_set(v: &stack->samples, i: 0);
1312 timer_setup_on_stack(&stack->timer, entropy_timer, 0);
1313 while (!crng_ready() && !signal_pending(current)) {
1314 /*
1315 * Check !timer_pending() and then ensure that any previous callback has finished
1316 * executing by checking timer_delete_sync_try(), before queueing the next one.
1317 */
1318 if (!timer_pending(timer: &stack->timer) && timer_delete_sync_try(timer: &stack->timer) >= 0) {
1319 struct cpumask timer_cpus;
1320 unsigned int num_cpus;
1321
1322 /*
1323 * Preemption must be disabled here, both to read the current CPU number
1324 * and to avoid scheduling a timer on a dead CPU.
1325 */
1326 preempt_disable();
1327
1328 /* Only schedule callbacks on timer CPUs that are online. */
1329 cpumask_and(dstp: &timer_cpus, src1p: housekeeping_cpumask(type: HK_TYPE_TIMER), cpu_online_mask);
1330 num_cpus = cpumask_weight(srcp: &timer_cpus);
1331 /* In very bizarre case of misconfiguration, fallback to all online. */
1332 if (unlikely(num_cpus == 0)) {
1333 timer_cpus = *cpu_online_mask;
1334 num_cpus = cpumask_weight(srcp: &timer_cpus);
1335 }
1336
1337 /* Basic CPU round-robin, which avoids the current CPU. */
1338 do {
1339 cpu = cpumask_next(n: cpu, srcp: &timer_cpus);
1340 if (cpu >= nr_cpu_ids)
1341 cpu = cpumask_first(srcp: &timer_cpus);
1342 } while (cpu == smp_processor_id() && num_cpus > 1);
1343
1344 /* Expiring the timer at `jiffies` means it's the next tick. */
1345 stack->timer.expires = jiffies;
1346
1347 add_timer_on(timer: &stack->timer, cpu);
1348
1349 preempt_enable();
1350 }
1351 mix_pool_bytes(buf: &stack->entropy, len: sizeof(stack->entropy));
1352 schedule();
1353 stack->entropy = random_get_entropy();
1354 }
1355 mix_pool_bytes(buf: &stack->entropy, len: sizeof(stack->entropy));
1356
1357 timer_delete_sync(timer: &stack->timer);
1358 timer_destroy_on_stack(timer: &stack->timer);
1359}
1360
1361
1362/**********************************************************************
1363 *
1364 * Userspace reader/writer interfaces.
1365 *
1366 * getrandom(2) is the primary modern interface into the RNG and should
1367 * be used in preference to anything else.
1368 *
1369 * Reading from /dev/random has the same functionality as calling
1370 * getrandom(2) with flags=0. In earlier versions, however, it had
1371 * vastly different semantics and should therefore be avoided, to
1372 * prevent backwards compatibility issues.
1373 *
1374 * Reading from /dev/urandom has the same functionality as calling
1375 * getrandom(2) with flags=GRND_INSECURE. Because it does not block
1376 * waiting for the RNG to be ready, it should not be used.
1377 *
1378 * Writing to either /dev/random or /dev/urandom adds entropy to
1379 * the input pool but does not credit it.
1380 *
1381 * Polling on /dev/random indicates when the RNG is initialized, on
1382 * the read side, and when it wants new entropy, on the write side.
1383 *
1384 * Both /dev/random and /dev/urandom have the same set of ioctls for
1385 * adding entropy, getting the entropy count, zeroing the count, and
1386 * reseeding the crng.
1387 *
1388 **********************************************************************/
1389
1390SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
1391{
1392 struct iov_iter iter;
1393 int ret;
1394
1395 if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
1396 return -EINVAL;
1397
1398 /*
1399 * Requesting insecure and blocking randomness at the same time makes
1400 * no sense.
1401 */
1402 if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
1403 return -EINVAL;
1404
1405 if (!crng_ready() && !(flags & GRND_INSECURE)) {
1406 if (flags & GRND_NONBLOCK)
1407 return -EAGAIN;
1408 ret = wait_for_random_bytes();
1409 if (unlikely(ret))
1410 return ret;
1411 }
1412
1413 ret = import_ubuf(ITER_DEST, buf: ubuf, len, i: &iter);
1414 if (unlikely(ret))
1415 return ret;
1416 return get_random_bytes_user(iter: &iter);
1417}
1418
1419static __poll_t random_poll(struct file *file, poll_table *wait)
1420{
1421 poll_wait(filp: file, wait_address: &crng_init_wait, p: wait);
1422 return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
1423}
1424
1425static ssize_t write_pool_user(struct iov_iter *iter)
1426{
1427 u8 block[BLAKE2S_BLOCK_SIZE];
1428 ssize_t ret = 0;
1429 size_t copied;
1430
1431 if (unlikely(!iov_iter_count(iter)))
1432 return 0;
1433
1434 for (;;) {
1435 copied = copy_from_iter(addr: block, bytes: sizeof(block), i: iter);
1436 ret += copied;
1437 mix_pool_bytes(buf: block, len: copied);
1438 if (!iov_iter_count(i: iter) || copied != sizeof(block))
1439 break;
1440
1441 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
1442 if (ret % PAGE_SIZE == 0) {
1443 if (signal_pending(current))
1444 break;
1445 cond_resched();
1446 }
1447 }
1448
1449 memzero_explicit(s: block, count: sizeof(block));
1450 return ret ? ret : -EFAULT;
1451}
1452
1453static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter)
1454{
1455 return write_pool_user(iter);
1456}
1457
1458static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1459{
1460 static int maxwarn = 10;
1461
1462 /*
1463 * Opportunistically attempt to initialize the RNG on platforms that
1464 * have fast cycle counters, but don't (for now) require it to succeed.
1465 */
1466 if (!crng_ready())
1467 try_to_generate_entropy();
1468
1469 if (!crng_ready()) {
1470 if (!ratelimit_disable && maxwarn <= 0)
1471 ratelimit_state_inc_miss(rs: &urandom_warning);
1472 else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
1473 --maxwarn;
1474 pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
1475 current->comm, iov_iter_count(iter));
1476 }
1477 }
1478
1479 return get_random_bytes_user(iter);
1480}
1481
1482static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1483{
1484 int ret;
1485
1486 if (!crng_ready() &&
1487 ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
1488 (kiocb->ki_filp->f_flags & O_NONBLOCK)))
1489 return -EAGAIN;
1490
1491 ret = wait_for_random_bytes();
1492 if (ret != 0)
1493 return ret;
1494 return get_random_bytes_user(iter);
1495}
1496
1497static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1498{
1499 int __user *p = (int __user *)arg;
1500 int ent_count;
1501
1502 switch (cmd) {
1503 case RNDGETENTCNT:
1504 /* Inherently racy, no point locking. */
1505 if (put_user(input_pool.init_bits, p))
1506 return -EFAULT;
1507 return 0;
1508 case RNDADDTOENTCNT:
1509 if (!capable(CAP_SYS_ADMIN))
1510 return -EPERM;
1511 if (get_user(ent_count, p))
1512 return -EFAULT;
1513 if (ent_count < 0)
1514 return -EINVAL;
1515 credit_init_bits(ent_count);
1516 return 0;
1517 case RNDADDENTROPY: {
1518 struct iov_iter iter;
1519 ssize_t ret;
1520 int len;
1521
1522 if (!capable(CAP_SYS_ADMIN))
1523 return -EPERM;
1524 if (get_user(ent_count, p++))
1525 return -EFAULT;
1526 if (ent_count < 0)
1527 return -EINVAL;
1528 if (get_user(len, p++))
1529 return -EFAULT;
1530 ret = import_ubuf(ITER_SOURCE, buf: p, len, i: &iter);
1531 if (unlikely(ret))
1532 return ret;
1533 ret = write_pool_user(iter: &iter);
1534 if (unlikely(ret < 0))
1535 return ret;
1536 /* Since we're crediting, enforce that it was all written into the pool. */
1537 if (unlikely(ret != len))
1538 return -EFAULT;
1539 credit_init_bits(ent_count);
1540 return 0;
1541 }
1542 case RNDZAPENTCNT:
1543 case RNDCLEARPOOL:
1544 /* No longer has any effect. */
1545 if (!capable(CAP_SYS_ADMIN))
1546 return -EPERM;
1547 return 0;
1548 case RNDRESEEDCRNG:
1549 if (!capable(CAP_SYS_ADMIN))
1550 return -EPERM;
1551 if (!crng_ready())
1552 return -ENODATA;
1553 crng_reseed(NULL);
1554 return 0;
1555 default:
1556 return -EINVAL;
1557 }
1558}
1559
1560static int random_fasync(int fd, struct file *filp, int on)
1561{
1562 return fasync_helper(fd, filp, on, &fasync);
1563}
1564
1565const struct file_operations random_fops = {
1566 .read_iter = random_read_iter,
1567 .write_iter = random_write_iter,
1568 .poll = random_poll,
1569 .unlocked_ioctl = random_ioctl,
1570 .compat_ioctl = compat_ptr_ioctl,
1571 .fasync = random_fasync,
1572 .llseek = noop_llseek,
1573 .splice_read = copy_splice_read,
1574 .splice_write = iter_file_splice_write,
1575};
1576
1577const struct file_operations urandom_fops = {
1578 .read_iter = urandom_read_iter,
1579 .write_iter = random_write_iter,
1580 .unlocked_ioctl = random_ioctl,
1581 .compat_ioctl = compat_ptr_ioctl,
1582 .fasync = random_fasync,
1583 .llseek = noop_llseek,
1584 .splice_read = copy_splice_read,
1585 .splice_write = iter_file_splice_write,
1586};
1587
1588
1589/********************************************************************
1590 *
1591 * Sysctl interface.
1592 *
1593 * These are partly unused legacy knobs with dummy values to not break
1594 * userspace and partly still useful things. They are usually accessible
1595 * in /proc/sys/kernel/random/ and are as follows:
1596 *
1597 * - boot_id - a UUID representing the current boot.
1598 *
1599 * - uuid - a random UUID, different each time the file is read.
1600 *
1601 * - poolsize - the number of bits of entropy that the input pool can
1602 * hold, tied to the POOL_BITS constant.
1603 *
1604 * - entropy_avail - the number of bits of entropy currently in the
1605 * input pool. Always <= poolsize.
1606 *
1607 * - write_wakeup_threshold - the amount of entropy in the input pool
1608 * below which write polls to /dev/random will unblock, requesting
1609 * more entropy, tied to the POOL_READY_BITS constant. It is writable
1610 * to avoid breaking old userspaces, but writing to it does not
1611 * change any behavior of the RNG.
1612 *
1613 * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL.
1614 * It is writable to avoid breaking old userspaces, but writing
1615 * to it does not change any behavior of the RNG.
1616 *
1617 ********************************************************************/
1618
1619#ifdef CONFIG_SYSCTL
1620
1621#include <linux/sysctl.h>
1622
1623static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ;
1624static int sysctl_random_write_wakeup_bits = POOL_READY_BITS;
1625static int sysctl_poolsize = POOL_BITS;
1626static u8 sysctl_bootid[UUID_SIZE];
1627
1628/*
1629 * This function is used to return both the bootid UUID, and random
1630 * UUID. The difference is in whether table->data is NULL; if it is,
1631 * then a new UUID is generated and returned to the user.
1632 */
1633static int proc_do_uuid(const struct ctl_table *table, int write, void *buf,
1634 size_t *lenp, loff_t *ppos)
1635{
1636 u8 tmp_uuid[UUID_SIZE], *uuid;
1637 char uuid_string[UUID_STRING_LEN + 1];
1638 struct ctl_table fake_table = {
1639 .data = uuid_string,
1640 .maxlen = UUID_STRING_LEN
1641 };
1642
1643 if (write)
1644 return -EPERM;
1645
1646 uuid = table->data;
1647 if (!uuid) {
1648 uuid = tmp_uuid;
1649 generate_random_uuid(uuid);
1650 } else {
1651 static DEFINE_SPINLOCK(bootid_spinlock);
1652
1653 spin_lock(lock: &bootid_spinlock);
1654 if (!uuid[8])
1655 generate_random_uuid(uuid);
1656 spin_unlock(lock: &bootid_spinlock);
1657 }
1658
1659 snprintf(buf: uuid_string, size: sizeof(uuid_string), fmt: "%pU", uuid);
1660 return proc_dostring(&fake_table, 0, buf, lenp, ppos);
1661}
1662
1663/* The same as proc_dointvec, but writes don't change anything. */
1664static int proc_do_rointvec(const struct ctl_table *table, int write, void *buf,
1665 size_t *lenp, loff_t *ppos)
1666{
1667 return write ? 0 : proc_dointvec(table, 0, buf, lenp, ppos);
1668}
1669
1670static const struct ctl_table random_table[] = {
1671 {
1672 .procname = "poolsize",
1673 .data = &sysctl_poolsize,
1674 .maxlen = sizeof(int),
1675 .mode = 0444,
1676 .proc_handler = proc_dointvec,
1677 },
1678 {
1679 .procname = "entropy_avail",
1680 .data = &input_pool.init_bits,
1681 .maxlen = sizeof(int),
1682 .mode = 0444,
1683 .proc_handler = proc_dointvec,
1684 },
1685 {
1686 .procname = "write_wakeup_threshold",
1687 .data = &sysctl_random_write_wakeup_bits,
1688 .maxlen = sizeof(int),
1689 .mode = 0644,
1690 .proc_handler = proc_do_rointvec,
1691 },
1692 {
1693 .procname = "urandom_min_reseed_secs",
1694 .data = &sysctl_random_min_urandom_seed,
1695 .maxlen = sizeof(int),
1696 .mode = 0644,
1697 .proc_handler = proc_do_rointvec,
1698 },
1699 {
1700 .procname = "boot_id",
1701 .data = &sysctl_bootid,
1702 .mode = 0444,
1703 .proc_handler = proc_do_uuid,
1704 },
1705 {
1706 .procname = "uuid",
1707 .mode = 0444,
1708 .proc_handler = proc_do_uuid,
1709 },
1710};
1711
1712/*
1713 * random_init() is called before sysctl_init(),
1714 * so we cannot call register_sysctl_init() in random_init()
1715 */
1716static int __init random_sysctls_init(void)
1717{
1718 register_sysctl_init("kernel/random", random_table);
1719 return 0;
1720}
1721device_initcall(random_sysctls_init);
1722#endif
1723