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1// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
2/*
3 * Copyright (C) 2017-2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
4 * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
5 * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All rights reserved.
6 *
7 * This driver produces cryptographically secure pseudorandom data. It is divided
8 * into roughly six sections, each with a section header:
9 *
10 * - Initialization and readiness waiting.
11 * - Fast key erasure RNG, the "crng".
12 * - Entropy accumulation and extraction routines.
13 * - Entropy collection routines.
14 * - Userspace reader/writer interfaces.
15 * - Sysctl interface.
16 *
17 * The high level overview is that there is one input pool, into which
18 * various pieces of data are hashed. Prior to initialization, some of that
19 * data is then "credited" as having a certain number of bits of entropy.
20 * When enough bits of entropy are available, the hash is finalized and
21 * handed as a key to a stream cipher that expands it indefinitely for
22 * various consumers. This key is periodically refreshed as the various
23 * entropy collectors, described below, add data to the input pool.
24 */
25
26#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
27
28#include <linux/utsname.h>
29#include <linux/module.h>
30#include <linux/kernel.h>
31#include <linux/major.h>
32#include <linux/string.h>
33#include <linux/fcntl.h>
34#include <linux/slab.h>
35#include <linux/random.h>
36#include <linux/poll.h>
37#include <linux/init.h>
38#include <linux/fs.h>
39#include <linux/blkdev.h>
40#include <linux/interrupt.h>
41#include <linux/mm.h>
42#include <linux/nodemask.h>
43#include <linux/spinlock.h>
44#include <linux/kthread.h>
45#include <linux/percpu.h>
46#include <linux/ptrace.h>
47#include <linux/workqueue.h>
48#include <linux/irq.h>
49#include <linux/ratelimit.h>
50#include <linux/syscalls.h>
51#include <linux/completion.h>
52#include <linux/uuid.h>
53#include <linux/uaccess.h>
54#include <linux/suspend.h>
55#include <linux/siphash.h>
56#include <linux/sched/isolation.h>
57#include <crypto/chacha.h>
58#include <crypto/blake2s.h>
59#include <asm/archrandom.h>
60#include <asm/processor.h>
61#include <asm/irq.h>
62#include <asm/irq_regs.h>
63#include <asm/io.h>
64
65/*********************************************************************
66 *
67 * Initialization and readiness waiting.
68 *
69 * Much of the RNG infrastructure is devoted to various dependencies
70 * being able to wait until the RNG has collected enough entropy and
71 * is ready for safe consumption.
72 *
73 *********************************************************************/
74
75/*
76 * crng_init is protected by base_crng->lock, and only increases
77 * its value (from empty->early->ready).
78 */
79static enum {
80 CRNG_EMPTY = 0, /* Little to no entropy collected */
81 CRNG_EARLY = 1, /* At least POOL_EARLY_BITS collected */
82 CRNG_READY = 2 /* Fully initialized with POOL_READY_BITS collected */
83} crng_init __read_mostly = CRNG_EMPTY;
84static DEFINE_STATIC_KEY_FALSE(crng_is_ready);
85#define crng_ready() (static_branch_likely(&crng_is_ready) || crng_init >= CRNG_READY)
86/* Various types of waiters for crng_init->CRNG_READY transition. */
87static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
88static struct fasync_struct *fasync;
89static ATOMIC_NOTIFIER_HEAD(random_ready_notifier);
90
91/* Control how we warn userspace. */
92static struct ratelimit_state urandom_warning =
93 RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE);
94static int ratelimit_disable __read_mostly =
95 IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
96module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
97MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
98
99/*
100 * Returns whether or not the input pool has been seeded and thus guaranteed
101 * to supply cryptographically secure random numbers. This applies to: the
102 * /dev/urandom device, the get_random_bytes function, and the get_random_{u8,
103 * u16,u32,u64,long} family of functions.
104 *
105 * Returns: true if the input pool has been seeded.
106 * false if the input pool has not been seeded.
107 */
108bool rng_is_initialized(void)
109{
110 return crng_ready();
111}
112EXPORT_SYMBOL(rng_is_initialized);
113
114static void __cold crng_set_ready(struct work_struct *work)
115{
116 static_branch_enable(&crng_is_ready);
117}
118
119/* Used by wait_for_random_bytes(), and considered an entropy collector, below. */
120static void try_to_generate_entropy(void);
121
122/*
123 * Wait for the input pool to be seeded and thus guaranteed to supply
124 * cryptographically secure random numbers. This applies to: the /dev/urandom
125 * device, the get_random_bytes function, and the get_random_{u8,u16,u32,u64,
126 * long} family of functions. Using any of these functions without first
127 * calling this function forfeits the guarantee of security.
128 *
129 * Returns: 0 if the input pool has been seeded.
130 * -ERESTARTSYS if the function was interrupted by a signal.
131 */
132int wait_for_random_bytes(void)
133{
134 while (!crng_ready()) {
135 int ret;
136
137 try_to_generate_entropy();
138 ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
139 if (ret)
140 return ret > 0 ? 0 : ret;
141 }
142 return 0;
143}
144EXPORT_SYMBOL(wait_for_random_bytes);
145
146/*
147 * Add a callback function that will be invoked when the crng is initialised,
148 * or immediately if it already has been. Only use this is you are absolutely
149 * sure it is required. Most users should instead be able to test
150 * `rng_is_initialized()` on demand, or make use of `get_random_bytes_wait()`.
151 */
152int __cold execute_with_initialized_rng(struct notifier_block *nb)
153{
154 unsigned long flags;
155 int ret = 0;
156
157 spin_lock_irqsave(&random_ready_notifier.lock, flags);
158 if (crng_ready())
159 nb->notifier_call(nb, 0, NULL);
160 else
161 ret = raw_notifier_chain_register((struct raw_notifier_head *)&random_ready_notifier.head, nb);
162 spin_unlock_irqrestore(&random_ready_notifier.lock, flags);
163 return ret;
164}
165
166#define warn_unseeded_randomness() \
167 if (IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) && !crng_ready()) \
168 printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", \
169 __func__, (void *)_RET_IP_, crng_init)
170
171
172/*********************************************************************
173 *
174 * Fast key erasure RNG, the "crng".
175 *
176 * These functions expand entropy from the entropy extractor into
177 * long streams for external consumption using the "fast key erasure"
178 * RNG described at <https://blog.cr.yp.to/20170723-random.html>.
179 *
180 * There are a few exported interfaces for use by other drivers:
181 *
182 * void get_random_bytes(void *buf, size_t len)
183 * u8 get_random_u8()
184 * u16 get_random_u16()
185 * u32 get_random_u32()
186 * u32 get_random_u32_below(u32 ceil)
187 * u32 get_random_u32_above(u32 floor)
188 * u32 get_random_u32_inclusive(u32 floor, u32 ceil)
189 * u64 get_random_u64()
190 * unsigned long get_random_long()
191 *
192 * These interfaces will return the requested number of random bytes
193 * into the given buffer or as a return value. This is equivalent to
194 * a read from /dev/urandom. The u8, u16, u32, u64, long family of
195 * functions may be higher performance for one-off random integers,
196 * because they do a bit of buffering and do not invoke reseeding
197 * until the buffer is emptied.
198 *
199 *********************************************************************/
200
201enum {
202 CRNG_RESEED_START_INTERVAL = HZ,
203 CRNG_RESEED_INTERVAL = 60 * HZ
204};
205
206static struct {
207 u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long));
208 unsigned long generation;
209 spinlock_t lock;
210} base_crng = {
211 .lock = __SPIN_LOCK_UNLOCKED(base_crng.lock)
212};
213
214struct crng {
215 u8 key[CHACHA_KEY_SIZE];
216 unsigned long generation;
217 local_lock_t lock;
218};
219
220static DEFINE_PER_CPU(struct crng, crngs) = {
221 .generation = ULONG_MAX,
222 .lock = INIT_LOCAL_LOCK(crngs.lock),
223};
224
225/*
226 * Return the interval until the next reseeding, which is normally
227 * CRNG_RESEED_INTERVAL, but during early boot, it is at an interval
228 * proportional to the uptime.
229 */
230static unsigned int crng_reseed_interval(void)
231{
232 static bool early_boot = true;
233
234 if (unlikely(READ_ONCE(early_boot))) {
235 time64_t uptime = ktime_get_seconds();
236 if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2)
237 WRITE_ONCE(early_boot, false);
238 else
239 return max_t(unsigned int, CRNG_RESEED_START_INTERVAL,
240 (unsigned int)uptime / 2 * HZ);
241 }
242 return CRNG_RESEED_INTERVAL;
243}
244
245/* Used by crng_reseed() and crng_make_state() to extract a new seed from the input pool. */
246static void extract_entropy(void *buf, size_t len);
247
248/* This extracts a new crng key from the input pool. */
249static void crng_reseed(struct work_struct *work)
250{
251 static DECLARE_DELAYED_WORK(next_reseed, crng_reseed);
252 unsigned long flags;
253 unsigned long next_gen;
254 u8 key[CHACHA_KEY_SIZE];
255
256 /* Immediately schedule the next reseeding, so that it fires sooner rather than later. */
257 if (likely(system_unbound_wq))
258 queue_delayed_work(system_unbound_wq, &next_reseed, crng_reseed_interval());
259
260 extract_entropy(key, sizeof(key));
261
262 /*
263 * We copy the new key into the base_crng, overwriting the old one,
264 * and update the generation counter. We avoid hitting ULONG_MAX,
265 * because the per-cpu crngs are initialized to ULONG_MAX, so this
266 * forces new CPUs that come online to always initialize.
267 */
268 spin_lock_irqsave(&base_crng.lock, flags);
269 memcpy(base_crng.key, key, sizeof(base_crng.key));
270 next_gen = base_crng.generation + 1;
271 if (next_gen == ULONG_MAX)
272 ++next_gen;
273 WRITE_ONCE(base_crng.generation, next_gen);
274 if (!static_branch_likely(&crng_is_ready))
275 crng_init = CRNG_READY;
276 spin_unlock_irqrestore(&base_crng.lock, flags);
277 memzero_explicit(key, sizeof(key));
278}
279
280/*
281 * This generates a ChaCha block using the provided key, and then
282 * immediately overwrites that key with half the block. It returns
283 * the resultant ChaCha state to the user, along with the second
284 * half of the block containing 32 bytes of random data that may
285 * be used; random_data_len may not be greater than 32.
286 *
287 * The returned ChaCha state contains within it a copy of the old
288 * key value, at index 4, so the state should always be zeroed out
289 * immediately after using in order to maintain forward secrecy.
290 * If the state cannot be erased in a timely manner, then it is
291 * safer to set the random_data parameter to &chacha_state[4] so
292 * that this function overwrites it before returning.
293 */
294static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE],
295 u32 chacha_state[CHACHA_STATE_WORDS],
296 u8 *random_data, size_t random_data_len)
297{
298 u8 first_block[CHACHA_BLOCK_SIZE];
299
300 BUG_ON(random_data_len > 32);
301
302 chacha_init_consts(chacha_state);
303 memcpy(&chacha_state[4], key, CHACHA_KEY_SIZE);
304 memset(&chacha_state[12], 0, sizeof(u32) * 4);
305 chacha20_block(chacha_state, first_block);
306
307 memcpy(key, first_block, CHACHA_KEY_SIZE);
308 memcpy(random_data, first_block + CHACHA_KEY_SIZE, random_data_len);
309 memzero_explicit(first_block, sizeof(first_block));
310}
311
312/*
313 * This function returns a ChaCha state that you may use for generating
314 * random data. It also returns up to 32 bytes on its own of random data
315 * that may be used; random_data_len may not be greater than 32.
316 */
317static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
318 u8 *random_data, size_t random_data_len)
319{
320 unsigned long flags;
321 struct crng *crng;
322
323 BUG_ON(random_data_len > 32);
324
325 /*
326 * For the fast path, we check whether we're ready, unlocked first, and
327 * then re-check once locked later. In the case where we're really not
328 * ready, we do fast key erasure with the base_crng directly, extracting
329 * when crng_init is CRNG_EMPTY.
330 */
331 if (!crng_ready()) {
332 bool ready;
333
334 spin_lock_irqsave(&base_crng.lock, flags);
335 ready = crng_ready();
336 if (!ready) {
337 if (crng_init == CRNG_EMPTY)
338 extract_entropy(base_crng.key, sizeof(base_crng.key));
339 crng_fast_key_erasure(base_crng.key, chacha_state,
340 random_data, random_data_len);
341 }
342 spin_unlock_irqrestore(&base_crng.lock, flags);
343 if (!ready)
344 return;
345 }
346
347 local_lock_irqsave(&crngs.lock, flags);
348 crng = raw_cpu_ptr(&crngs);
349
350 /*
351 * If our per-cpu crng is older than the base_crng, then it means
352 * somebody reseeded the base_crng. In that case, we do fast key
353 * erasure on the base_crng, and use its output as the new key
354 * for our per-cpu crng. This brings us up to date with base_crng.
355 */
356 if (unlikely(crng->generation != READ_ONCE(base_crng.generation))) {
357 spin_lock(&base_crng.lock);
358 crng_fast_key_erasure(base_crng.key, chacha_state,
359 crng->key, sizeof(crng->key));
360 crng->generation = base_crng.generation;
361 spin_unlock(&base_crng.lock);
362 }
363
364 /*
365 * Finally, when we've made it this far, our per-cpu crng has an up
366 * to date key, and we can do fast key erasure with it to produce
367 * some random data and a ChaCha state for the caller. All other
368 * branches of this function are "unlikely", so most of the time we
369 * should wind up here immediately.
370 */
371 crng_fast_key_erasure(crng->key, chacha_state, random_data, random_data_len);
372 local_unlock_irqrestore(&crngs.lock, flags);
373}
374
375static void _get_random_bytes(void *buf, size_t len)
376{
377 u32 chacha_state[CHACHA_STATE_WORDS];
378 u8 tmp[CHACHA_BLOCK_SIZE];
379 size_t first_block_len;
380
381 if (!len)
382 return;
383
384 first_block_len = min_t(size_t, 32, len);
385 crng_make_state(chacha_state, buf, first_block_len);
386 len -= first_block_len;
387 buf += first_block_len;
388
389 while (len) {
390 if (len < CHACHA_BLOCK_SIZE) {
391 chacha20_block(chacha_state, tmp);
392 memcpy(buf, tmp, len);
393 memzero_explicit(tmp, sizeof(tmp));
394 break;
395 }
396
397 chacha20_block(chacha_state, buf);
398 if (unlikely(chacha_state[12] == 0))
399 ++chacha_state[13];
400 len -= CHACHA_BLOCK_SIZE;
401 buf += CHACHA_BLOCK_SIZE;
402 }
403
404 memzero_explicit(chacha_state, sizeof(chacha_state));
405}
406
407/*
408 * This returns random bytes in arbitrary quantities. The quality of the
409 * random bytes is good as /dev/urandom. In order to ensure that the
410 * randomness provided by this function is okay, the function
411 * wait_for_random_bytes() should be called and return 0 at least once
412 * at any point prior.
413 */
414void get_random_bytes(void *buf, size_t len)
415{
416 warn_unseeded_randomness();
417 _get_random_bytes(buf, len);
418}
419EXPORT_SYMBOL(get_random_bytes);
420
421static ssize_t get_random_bytes_user(struct iov_iter *iter)
422{
423 u32 chacha_state[CHACHA_STATE_WORDS];
424 u8 block[CHACHA_BLOCK_SIZE];
425 size_t ret = 0, copied;
426
427 if (unlikely(!iov_iter_count(iter)))
428 return 0;
429
430 /*
431 * Immediately overwrite the ChaCha key at index 4 with random
432 * bytes, in case userspace causes copy_to_iter() below to sleep
433 * forever, so that we still retain forward secrecy in that case.
434 */
435 crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA_KEY_SIZE);
436 /*
437 * However, if we're doing a read of len <= 32, we don't need to
438 * use chacha_state after, so we can simply return those bytes to
439 * the user directly.
440 */
441 if (iov_iter_count(iter) <= CHACHA_KEY_SIZE) {
442 ret = copy_to_iter(&chacha_state[4], CHACHA_KEY_SIZE, iter);
443 goto out_zero_chacha;
444 }
445
446 for (;;) {
447 chacha20_block(chacha_state, block);
448 if (unlikely(chacha_state[12] == 0))
449 ++chacha_state[13];
450
451 copied = copy_to_iter(block, sizeof(block), iter);
452 ret += copied;
453 if (!iov_iter_count(iter) || copied != sizeof(block))
454 break;
455
456 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
457 if (ret % PAGE_SIZE == 0) {
458 if (signal_pending(current))
459 break;
460 cond_resched();
461 }
462 }
463
464 memzero_explicit(block, sizeof(block));
465out_zero_chacha:
466 memzero_explicit(chacha_state, sizeof(chacha_state));
467 return ret ? ret : -EFAULT;
468}
469
470/*
471 * Batched entropy returns random integers. The quality of the random
472 * number is good as /dev/urandom. In order to ensure that the randomness
473 * provided by this function is okay, the function wait_for_random_bytes()
474 * should be called and return 0 at least once at any point prior.
475 */
476
477#define DEFINE_BATCHED_ENTROPY(type) \
478struct batch_ ##type { \
479 /* \
480 * We make this 1.5x a ChaCha block, so that we get the \
481 * remaining 32 bytes from fast key erasure, plus one full \
482 * block from the detached ChaCha state. We can increase \
483 * the size of this later if needed so long as we keep the \
484 * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE. \
485 */ \
486 type entropy[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(type))]; \
487 local_lock_t lock; \
488 unsigned long generation; \
489 unsigned int position; \
490}; \
491 \
492static DEFINE_PER_CPU(struct batch_ ##type, batched_entropy_ ##type) = { \
493 .lock = INIT_LOCAL_LOCK(batched_entropy_ ##type.lock), \
494 .position = UINT_MAX \
495}; \
496 \
497type get_random_ ##type(void) \
498{ \
499 type ret; \
500 unsigned long flags; \
501 struct batch_ ##type *batch; \
502 unsigned long next_gen; \
503 \
504 warn_unseeded_randomness(); \
505 \
506 if (!crng_ready()) { \
507 _get_random_bytes(&ret, sizeof(ret)); \
508 return ret; \
509 } \
510 \
511 local_lock_irqsave(&batched_entropy_ ##type.lock, flags); \
512 batch = raw_cpu_ptr(&batched_entropy_##type); \
513 \
514 next_gen = READ_ONCE(base_crng.generation); \
515 if (batch->position >= ARRAY_SIZE(batch->entropy) || \
516 next_gen != batch->generation) { \
517 _get_random_bytes(batch->entropy, sizeof(batch->entropy)); \
518 batch->position = 0; \
519 batch->generation = next_gen; \
520 } \
521 \
522 ret = batch->entropy[batch->position]; \
523 batch->entropy[batch->position] = 0; \
524 ++batch->position; \
525 local_unlock_irqrestore(&batched_entropy_ ##type.lock, flags); \
526 return ret; \
527} \
528EXPORT_SYMBOL(get_random_ ##type);
529
530DEFINE_BATCHED_ENTROPY(u8)
531DEFINE_BATCHED_ENTROPY(u16)
532DEFINE_BATCHED_ENTROPY(u32)
533DEFINE_BATCHED_ENTROPY(u64)
534
535u32 __get_random_u32_below(u32 ceil)
536{
537 /*
538 * This is the slow path for variable ceil. It is still fast, most of
539 * the time, by doing traditional reciprocal multiplication and
540 * opportunistically comparing the lower half to ceil itself, before
541 * falling back to computing a larger bound, and then rejecting samples
542 * whose lower half would indicate a range indivisible by ceil. The use
543 * of `-ceil % ceil` is analogous to `2^32 % ceil`, but is computable
544 * in 32-bits.
545 */
546 u32 rand = get_random_u32();
547 u64 mult;
548
549 /*
550 * This function is technically undefined for ceil == 0, and in fact
551 * for the non-underscored constant version in the header, we build bug
552 * on that. But for the non-constant case, it's convenient to have that
553 * evaluate to being a straight call to get_random_u32(), so that
554 * get_random_u32_inclusive() can work over its whole range without
555 * undefined behavior.
556 */
557 if (unlikely(!ceil))
558 return rand;
559
560 mult = (u64)ceil * rand;
561 if (unlikely((u32)mult < ceil)) {
562 u32 bound = -ceil % ceil;
563 while (unlikely((u32)mult < bound))
564 mult = (u64)ceil * get_random_u32();
565 }
566 return mult >> 32;
567}
568EXPORT_SYMBOL(__get_random_u32_below);
569
570#ifdef CONFIG_SMP
571/*
572 * This function is called when the CPU is coming up, with entry
573 * CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP.
574 */
575int __cold random_prepare_cpu(unsigned int cpu)
576{
577 /*
578 * When the cpu comes back online, immediately invalidate both
579 * the per-cpu crng and all batches, so that we serve fresh
580 * randomness.
581 */
582 per_cpu_ptr(&crngs, cpu)->generation = ULONG_MAX;
583 per_cpu_ptr(&batched_entropy_u8, cpu)->position = UINT_MAX;
584 per_cpu_ptr(&batched_entropy_u16, cpu)->position = UINT_MAX;
585 per_cpu_ptr(&batched_entropy_u32, cpu)->position = UINT_MAX;
586 per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX;
587 return 0;
588}
589#endif
590
591
592/**********************************************************************
593 *
594 * Entropy accumulation and extraction routines.
595 *
596 * Callers may add entropy via:
597 *
598 * static void mix_pool_bytes(const void *buf, size_t len)
599 *
600 * After which, if added entropy should be credited:
601 *
602 * static void credit_init_bits(size_t bits)
603 *
604 * Finally, extract entropy via:
605 *
606 * static void extract_entropy(void *buf, size_t len)
607 *
608 **********************************************************************/
609
610enum {
611 POOL_BITS = BLAKE2S_HASH_SIZE * 8,
612 POOL_READY_BITS = POOL_BITS, /* When crng_init->CRNG_READY */
613 POOL_EARLY_BITS = POOL_READY_BITS / 2 /* When crng_init->CRNG_EARLY */
614};
615
616static struct {
617 struct blake2s_state hash;
618 spinlock_t lock;
619 unsigned int init_bits;
620} input_pool = {
621 .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE),
622 BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4,
623 BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 },
624 .hash.outlen = BLAKE2S_HASH_SIZE,
625 .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
626};
627
628static void _mix_pool_bytes(const void *buf, size_t len)
629{
630 blake2s_update(&input_pool.hash, buf, len);
631}
632
633/*
634 * This function adds bytes into the input pool. It does not
635 * update the initialization bit counter; the caller should call
636 * credit_init_bits if this is appropriate.
637 */
638static void mix_pool_bytes(const void *buf, size_t len)
639{
640 unsigned long flags;
641
642 spin_lock_irqsave(&input_pool.lock, flags);
643 _mix_pool_bytes(buf, len);
644 spin_unlock_irqrestore(&input_pool.lock, flags);
645}
646
647/*
648 * This is an HKDF-like construction for using the hashed collected entropy
649 * as a PRF key, that's then expanded block-by-block.
650 */
651static void extract_entropy(void *buf, size_t len)
652{
653 unsigned long flags;
654 u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
655 struct {
656 unsigned long rdseed[32 / sizeof(long)];
657 size_t counter;
658 } block;
659 size_t i, longs;
660
661 for (i = 0; i < ARRAY_SIZE(block.rdseed);) {
662 longs = arch_get_random_seed_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
663 if (longs) {
664 i += longs;
665 continue;
666 }
667 longs = arch_get_random_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
668 if (longs) {
669 i += longs;
670 continue;
671 }
672 block.rdseed[i++] = random_get_entropy();
673 }
674
675 spin_lock_irqsave(&input_pool.lock, flags);
676
677 /* seed = HASHPRF(last_key, entropy_input) */
678 blake2s_final(&input_pool.hash, seed);
679
680 /* next_key = HASHPRF(seed, RDSEED || 0) */
681 block.counter = 0;
682 blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
683 blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
684
685 spin_unlock_irqrestore(&input_pool.lock, flags);
686 memzero_explicit(next_key, sizeof(next_key));
687
688 while (len) {
689 i = min_t(size_t, len, BLAKE2S_HASH_SIZE);
690 /* output = HASHPRF(seed, RDSEED || ++counter) */
691 ++block.counter;
692 blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
693 len -= i;
694 buf += i;
695 }
696
697 memzero_explicit(seed, sizeof(seed));
698 memzero_explicit(&block, sizeof(block));
699}
700
701#define credit_init_bits(bits) if (!crng_ready()) _credit_init_bits(bits)
702
703static void __cold _credit_init_bits(size_t bits)
704{
705 static struct execute_work set_ready;
706 unsigned int new, orig, add;
707 unsigned long flags;
708
709 if (!bits)
710 return;
711
712 add = min_t(size_t, bits, POOL_BITS);
713
714 orig = READ_ONCE(input_pool.init_bits);
715 do {
716 new = min_t(unsigned int, POOL_BITS, orig + add);
717 } while (!try_cmpxchg(&input_pool.init_bits, &orig, new));
718
719 if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
720 crng_reseed(NULL); /* Sets crng_init to CRNG_READY under base_crng.lock. */
721 if (static_key_initialized)
722 execute_in_process_context(crng_set_ready, &set_ready);
723 atomic_notifier_call_chain(&random_ready_notifier, 0, NULL);
724 wake_up_interruptible(&crng_init_wait);
725 kill_fasync(&fasync, SIGIO, POLL_IN);
726 pr_notice("crng init done\n");
727 if (urandom_warning.missed)
728 pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
729 urandom_warning.missed);
730 } else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
731 spin_lock_irqsave(&base_crng.lock, flags);
732 /* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */
733 if (crng_init == CRNG_EMPTY) {
734 extract_entropy(base_crng.key, sizeof(base_crng.key));
735 crng_init = CRNG_EARLY;
736 }
737 spin_unlock_irqrestore(&base_crng.lock, flags);
738 }
739}
740
741
742/**********************************************************************
743 *
744 * Entropy collection routines.
745 *
746 * The following exported functions are used for pushing entropy into
747 * the above entropy accumulation routines:
748 *
749 * void add_device_randomness(const void *buf, size_t len);
750 * void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy, bool sleep_after);
751 * void add_bootloader_randomness(const void *buf, size_t len);
752 * void add_vmfork_randomness(const void *unique_vm_id, size_t len);
753 * void add_interrupt_randomness(int irq);
754 * void add_input_randomness(unsigned int type, unsigned int code, unsigned int value);
755 * void add_disk_randomness(struct gendisk *disk);
756 *
757 * add_device_randomness() adds data to the input pool that
758 * is likely to differ between two devices (or possibly even per boot).
759 * This would be things like MAC addresses or serial numbers, or the
760 * read-out of the RTC. This does *not* credit any actual entropy to
761 * the pool, but it initializes the pool to different values for devices
762 * that might otherwise be identical and have very little entropy
763 * available to them (particularly common in the embedded world).
764 *
765 * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
766 * entropy as specified by the caller. If the entropy pool is full it will
767 * block until more entropy is needed.
768 *
769 * add_bootloader_randomness() is called by bootloader drivers, such as EFI
770 * and device tree, and credits its input depending on whether or not the
771 * command line option 'random.trust_bootloader'.
772 *
773 * add_vmfork_randomness() adds a unique (but not necessarily secret) ID
774 * representing the current instance of a VM to the pool, without crediting,
775 * and then force-reseeds the crng so that it takes effect immediately.
776 *
777 * add_interrupt_randomness() uses the interrupt timing as random
778 * inputs to the entropy pool. Using the cycle counters and the irq source
779 * as inputs, it feeds the input pool roughly once a second or after 64
780 * interrupts, crediting 1 bit of entropy for whichever comes first.
781 *
782 * add_input_randomness() uses the input layer interrupt timing, as well
783 * as the event type information from the hardware.
784 *
785 * add_disk_randomness() uses what amounts to the seek time of block
786 * layer request events, on a per-disk_devt basis, as input to the
787 * entropy pool. Note that high-speed solid state drives with very low
788 * seek times do not make for good sources of entropy, as their seek
789 * times are usually fairly consistent.
790 *
791 * The last two routines try to estimate how many bits of entropy
792 * to credit. They do this by keeping track of the first and second
793 * order deltas of the event timings.
794 *
795 **********************************************************************/
796
797static bool trust_cpu __initdata = true;
798static bool trust_bootloader __initdata = true;
799static int __init parse_trust_cpu(char *arg)
800{
801 return kstrtobool(arg, &trust_cpu);
802}
803static int __init parse_trust_bootloader(char *arg)
804{
805 return kstrtobool(arg, &trust_bootloader);
806}
807early_param("random.trust_cpu", parse_trust_cpu);
808early_param("random.trust_bootloader", parse_trust_bootloader);
809
810static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data)
811{
812 unsigned long flags, entropy = random_get_entropy();
813
814 /*
815 * Encode a representation of how long the system has been suspended,
816 * in a way that is distinct from prior system suspends.
817 */
818 ktime_t stamps[] = { ktime_get(), ktime_get_boottime(), ktime_get_real() };
819
820 spin_lock_irqsave(&input_pool.lock, flags);
821 _mix_pool_bytes(&action, sizeof(action));
822 _mix_pool_bytes(stamps, sizeof(stamps));
823 _mix_pool_bytes(&entropy, sizeof(entropy));
824 spin_unlock_irqrestore(&input_pool.lock, flags);
825
826 if (crng_ready() && (action == PM_RESTORE_PREPARE ||
827 (action == PM_POST_SUSPEND && !IS_ENABLED(CONFIG_PM_AUTOSLEEP) &&
828 !IS_ENABLED(CONFIG_PM_USERSPACE_AUTOSLEEP)))) {
829 crng_reseed(NULL);
830 pr_notice("crng reseeded on system resumption\n");
831 }
832 return 0;
833}
834
835static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification };
836
837/*
838 * This is called extremely early, before time keeping functionality is
839 * available, but arch randomness is. Interrupts are not yet enabled.
840 */
841void __init random_init_early(const char *command_line)
842{
843 unsigned long entropy[BLAKE2S_BLOCK_SIZE / sizeof(long)];
844 size_t i, longs, arch_bits;
845
846#if defined(LATENT_ENTROPY_PLUGIN)
847 static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
848 _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
849#endif
850
851 for (i = 0, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) {
852 longs = arch_get_random_seed_longs(entropy, ARRAY_SIZE(entropy) - i);
853 if (longs) {
854 _mix_pool_bytes(entropy, sizeof(*entropy) * longs);
855 i += longs;
856 continue;
857 }
858 longs = arch_get_random_longs(entropy, ARRAY_SIZE(entropy) - i);
859 if (longs) {
860 _mix_pool_bytes(entropy, sizeof(*entropy) * longs);
861 i += longs;
862 continue;
863 }
864 arch_bits -= sizeof(*entropy) * 8;
865 ++i;
866 }
867
868 _mix_pool_bytes(init_utsname(), sizeof(*(init_utsname())));
869 _mix_pool_bytes(command_line, strlen(command_line));
870
871 /* Reseed if already seeded by earlier phases. */
872 if (crng_ready())
873 crng_reseed(NULL);
874 else if (trust_cpu)
875 _credit_init_bits(arch_bits);
876}
877
878/*
879 * This is called a little bit after the prior function, and now there is
880 * access to timestamps counters. Interrupts are not yet enabled.
881 */
882void __init random_init(void)
883{
884 unsigned long entropy = random_get_entropy();
885 ktime_t now = ktime_get_real();
886
887 _mix_pool_bytes(&now, sizeof(now));
888 _mix_pool_bytes(&entropy, sizeof(entropy));
889 add_latent_entropy();
890
891 /*
892 * If we were initialized by the cpu or bootloader before jump labels
893 * are initialized, then we should enable the static branch here, where
894 * it's guaranteed that jump labels have been initialized.
895 */
896 if (!static_branch_likely(&crng_is_ready) && crng_init >= CRNG_READY)
897 crng_set_ready(NULL);
898
899 /* Reseed if already seeded by earlier phases. */
900 if (crng_ready())
901 crng_reseed(NULL);
902
903 WARN_ON(register_pm_notifier(&pm_notifier));
904
905 WARN(!entropy, "Missing cycle counter and fallback timer; RNG "
906 "entropy collection will consequently suffer.");
907}
908
909/*
910 * Add device- or boot-specific data to the input pool to help
911 * initialize it.
912 *
913 * None of this adds any entropy; it is meant to avoid the problem of
914 * the entropy pool having similar initial state across largely
915 * identical devices.
916 */
917void add_device_randomness(const void *buf, size_t len)
918{
919 unsigned long entropy = random_get_entropy();
920 unsigned long flags;
921
922 spin_lock_irqsave(&input_pool.lock, flags);
923 _mix_pool_bytes(&entropy, sizeof(entropy));
924 _mix_pool_bytes(buf, len);
925 spin_unlock_irqrestore(&input_pool.lock, flags);
926}
927EXPORT_SYMBOL(add_device_randomness);
928
929/*
930 * Interface for in-kernel drivers of true hardware RNGs. Those devices
931 * may produce endless random bits, so this function will sleep for
932 * some amount of time after, if the sleep_after parameter is true.
933 */
934void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy, bool sleep_after)
935{
936 mix_pool_bytes(buf, len);
937 credit_init_bits(entropy);
938
939 /*
940 * Throttle writing to once every reseed interval, unless we're not yet
941 * initialized or no entropy is credited.
942 */
943 if (sleep_after && !kthread_should_stop() && (crng_ready() || !entropy))
944 schedule_timeout_interruptible(crng_reseed_interval());
945}
946EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
947
948/*
949 * Handle random seed passed by bootloader, and credit it depending
950 * on the command line option 'random.trust_bootloader'.
951 */
952void __init add_bootloader_randomness(const void *buf, size_t len)
953{
954 mix_pool_bytes(buf, len);
955 if (trust_bootloader)
956 credit_init_bits(len * 8);
957}
958
959#if IS_ENABLED(CONFIG_VMGENID)
960static BLOCKING_NOTIFIER_HEAD(vmfork_chain);
961
962/*
963 * Handle a new unique VM ID, which is unique, not secret, so we
964 * don't credit it, but we do immediately force a reseed after so
965 * that it's used by the crng posthaste.
966 */
967void __cold add_vmfork_randomness(const void *unique_vm_id, size_t len)
968{
969 add_device_randomness(unique_vm_id, len);
970 if (crng_ready()) {
971 crng_reseed(NULL);
972 pr_notice("crng reseeded due to virtual machine fork\n");
973 }
974 blocking_notifier_call_chain(&vmfork_chain, 0, NULL);
975}
976#if IS_MODULE(CONFIG_VMGENID)
977EXPORT_SYMBOL_GPL(add_vmfork_randomness);
978#endif
979
980int __cold register_random_vmfork_notifier(struct notifier_block *nb)
981{
982 return blocking_notifier_chain_register(&vmfork_chain, nb);
983}
984EXPORT_SYMBOL_GPL(register_random_vmfork_notifier);
985
986int __cold unregister_random_vmfork_notifier(struct notifier_block *nb)
987{
988 return blocking_notifier_chain_unregister(&vmfork_chain, nb);
989}
990EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier);
991#endif
992
993struct fast_pool {
994 unsigned long pool[4];
995 unsigned long last;
996 unsigned int count;
997 struct timer_list mix;
998};
999
1000static void mix_interrupt_randomness(struct timer_list *work);
1001
1002static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = {
1003#ifdef CONFIG_64BIT
1004#define FASTMIX_PERM SIPHASH_PERMUTATION
1005 .pool = { SIPHASH_CONST_0, SIPHASH_CONST_1, SIPHASH_CONST_2, SIPHASH_CONST_3 },
1006#else
1007#define FASTMIX_PERM HSIPHASH_PERMUTATION
1008 .pool = { HSIPHASH_CONST_0, HSIPHASH_CONST_1, HSIPHASH_CONST_2, HSIPHASH_CONST_3 },
1009#endif
1010 .mix = __TIMER_INITIALIZER(mix_interrupt_randomness, 0)
1011};
1012
1013/*
1014 * This is [Half]SipHash-1-x, starting from an empty key. Because
1015 * the key is fixed, it assumes that its inputs are non-malicious,
1016 * and therefore this has no security on its own. s represents the
1017 * four-word SipHash state, while v represents a two-word input.
1018 */
1019static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long v2)
1020{
1021 s[3] ^= v1;
1022 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1023 s[0] ^= v1;
1024 s[3] ^= v2;
1025 FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1026 s[0] ^= v2;
1027}
1028
1029#ifdef CONFIG_SMP
1030/*
1031 * This function is called when the CPU has just come online, with
1032 * entry CPUHP_AP_RANDOM_ONLINE, just after CPUHP_AP_WORKQUEUE_ONLINE.
1033 */
1034int __cold random_online_cpu(unsigned int cpu)
1035{
1036 /*
1037 * During CPU shutdown and before CPU onlining, add_interrupt_
1038 * randomness() may schedule mix_interrupt_randomness(), and
1039 * set the MIX_INFLIGHT flag. However, because the worker can
1040 * be scheduled on a different CPU during this period, that
1041 * flag will never be cleared. For that reason, we zero out
1042 * the flag here, which runs just after workqueues are onlined
1043 * for the CPU again. This also has the effect of setting the
1044 * irq randomness count to zero so that new accumulated irqs
1045 * are fresh.
1046 */
1047 per_cpu_ptr(&irq_randomness, cpu)->count = 0;
1048 return 0;
1049}
1050#endif
1051
1052static void mix_interrupt_randomness(struct timer_list *work)
1053{
1054 struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix);
1055 /*
1056 * The size of the copied stack pool is explicitly 2 longs so that we
1057 * only ever ingest half of the siphash output each time, retaining
1058 * the other half as the next "key" that carries over. The entropy is
1059 * supposed to be sufficiently dispersed between bits so on average
1060 * we don't wind up "losing" some.
1061 */
1062 unsigned long pool[2];
1063 unsigned int count;
1064
1065 /* Check to see if we're running on the wrong CPU due to hotplug. */
1066 local_irq_disable();
1067 if (fast_pool != this_cpu_ptr(&irq_randomness)) {
1068 local_irq_enable();
1069 return;
1070 }
1071
1072 /*
1073 * Copy the pool to the stack so that the mixer always has a
1074 * consistent view, before we reenable irqs again.
1075 */
1076 memcpy(pool, fast_pool->pool, sizeof(pool));
1077 count = fast_pool->count;
1078 fast_pool->count = 0;
1079 fast_pool->last = jiffies;
1080 local_irq_enable();
1081
1082 mix_pool_bytes(pool, sizeof(pool));
1083 credit_init_bits(clamp_t(unsigned int, (count & U16_MAX) / 64, 1, sizeof(pool) * 8));
1084
1085 memzero_explicit(pool, sizeof(pool));
1086}
1087
1088void add_interrupt_randomness(int irq)
1089{
1090 enum { MIX_INFLIGHT = 1U << 31 };
1091 unsigned long entropy = random_get_entropy();
1092 struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
1093 struct pt_regs *regs = get_irq_regs();
1094 unsigned int new_count;
1095
1096 fast_mix(fast_pool->pool, entropy,
1097 (regs ? instruction_pointer(regs) : _RET_IP_) ^ swab(irq));
1098 new_count = ++fast_pool->count;
1099
1100 if (new_count & MIX_INFLIGHT)
1101 return;
1102
1103 if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ))
1104 return;
1105
1106 fast_pool->count |= MIX_INFLIGHT;
1107 if (!timer_pending(&fast_pool->mix)) {
1108 fast_pool->mix.expires = jiffies;
1109 add_timer_on(&fast_pool->mix, raw_smp_processor_id());
1110 }
1111}
1112EXPORT_SYMBOL_GPL(add_interrupt_randomness);
1113
1114/* There is one of these per entropy source */
1115struct timer_rand_state {
1116 unsigned long last_time;
1117 long last_delta, last_delta2;
1118};
1119
1120/*
1121 * This function adds entropy to the entropy "pool" by using timing
1122 * delays. It uses the timer_rand_state structure to make an estimate
1123 * of how many bits of entropy this call has added to the pool. The
1124 * value "num" is also added to the pool; it should somehow describe
1125 * the type of event that just happened.
1126 */
1127static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
1128{
1129 unsigned long entropy = random_get_entropy(), now = jiffies, flags;
1130 long delta, delta2, delta3;
1131 unsigned int bits;
1132
1133 /*
1134 * If we're in a hard IRQ, add_interrupt_randomness() will be called
1135 * sometime after, so mix into the fast pool.
1136 */
1137 if (in_hardirq()) {
1138 fast_mix(this_cpu_ptr(&irq_randomness)->pool, entropy, num);
1139 } else {
1140 spin_lock_irqsave(&input_pool.lock, flags);
1141 _mix_pool_bytes(&entropy, sizeof(entropy));
1142 _mix_pool_bytes(&num, sizeof(num));
1143 spin_unlock_irqrestore(&input_pool.lock, flags);
1144 }
1145
1146 if (crng_ready())
1147 return;
1148
1149 /*
1150 * Calculate number of bits of randomness we probably added.
1151 * We take into account the first, second and third-order deltas
1152 * in order to make our estimate.
1153 */
1154 delta = now - READ_ONCE(state->last_time);
1155 WRITE_ONCE(state->last_time, now);
1156
1157 delta2 = delta - READ_ONCE(state->last_delta);
1158 WRITE_ONCE(state->last_delta, delta);
1159
1160 delta3 = delta2 - READ_ONCE(state->last_delta2);
1161 WRITE_ONCE(state->last_delta2, delta2);
1162
1163 if (delta < 0)
1164 delta = -delta;
1165 if (delta2 < 0)
1166 delta2 = -delta2;
1167 if (delta3 < 0)
1168 delta3 = -delta3;
1169 if (delta > delta2)
1170 delta = delta2;
1171 if (delta > delta3)
1172 delta = delta3;
1173
1174 /*
1175 * delta is now minimum absolute delta. Round down by 1 bit
1176 * on general principles, and limit entropy estimate to 11 bits.
1177 */
1178 bits = min(fls(delta >> 1), 11);
1179
1180 /*
1181 * As mentioned above, if we're in a hard IRQ, add_interrupt_randomness()
1182 * will run after this, which uses a different crediting scheme of 1 bit
1183 * per every 64 interrupts. In order to let that function do accounting
1184 * close to the one in this function, we credit a full 64/64 bit per bit,
1185 * and then subtract one to account for the extra one added.
1186 */
1187 if (in_hardirq())
1188 this_cpu_ptr(&irq_randomness)->count += max(1u, bits * 64) - 1;
1189 else
1190 _credit_init_bits(bits);
1191}
1192
1193void add_input_randomness(unsigned int type, unsigned int code, unsigned int value)
1194{
1195 static unsigned char last_value;
1196 static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES };
1197
1198 /* Ignore autorepeat and the like. */
1199 if (value == last_value)
1200 return;
1201
1202 last_value = value;
1203 add_timer_randomness(&input_timer_state,
1204 (type << 4) ^ code ^ (code >> 4) ^ value);
1205}
1206EXPORT_SYMBOL_GPL(add_input_randomness);
1207
1208#ifdef CONFIG_BLOCK
1209void add_disk_randomness(struct gendisk *disk)
1210{
1211 if (!disk || !disk->random)
1212 return;
1213 /* First major is 1, so we get >= 0x200 here. */
1214 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
1215}
1216EXPORT_SYMBOL_GPL(add_disk_randomness);
1217
1218void __cold rand_initialize_disk(struct gendisk *disk)
1219{
1220 struct timer_rand_state *state;
1221
1222 /*
1223 * If kzalloc returns null, we just won't use that entropy
1224 * source.
1225 */
1226 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1227 if (state) {
1228 state->last_time = INITIAL_JIFFIES;
1229 disk->random = state;
1230 }
1231}
1232#endif
1233
1234struct entropy_timer_state {
1235 unsigned long entropy;
1236 struct timer_list timer;
1237 atomic_t samples;
1238 unsigned int samples_per_bit;
1239};
1240
1241/*
1242 * Each time the timer fires, we expect that we got an unpredictable jump in
1243 * the cycle counter. Even if the timer is running on another CPU, the timer
1244 * activity will be touching the stack of the CPU that is generating entropy.
1245 *
1246 * Note that we don't re-arm the timer in the timer itself - we are happy to be
1247 * scheduled away, since that just makes the load more complex, but we do not
1248 * want the timer to keep ticking unless the entropy loop is running.
1249 *
1250 * So the re-arming always happens in the entropy loop itself.
1251 */
1252static void __cold entropy_timer(struct timer_list *timer)
1253{
1254 struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer);
1255 unsigned long entropy = random_get_entropy();
1256
1257 mix_pool_bytes(&entropy, sizeof(entropy));
1258 if (atomic_inc_return(&state->samples) % state->samples_per_bit == 0)
1259 credit_init_bits(1);
1260}
1261
1262/*
1263 * If we have an actual cycle counter, see if we can generate enough entropy
1264 * with timing noise.
1265 */
1266static void __cold try_to_generate_entropy(void)
1267{
1268 enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = HZ / 15 };
1269 u8 stack_bytes[sizeof(struct entropy_timer_state) + SMP_CACHE_BYTES - 1];
1270 struct entropy_timer_state *stack = PTR_ALIGN((void *)stack_bytes, SMP_CACHE_BYTES);
1271 unsigned int i, num_different = 0;
1272 unsigned long last = random_get_entropy();
1273 int cpu = -1;
1274
1275 for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
1276 stack->entropy = random_get_entropy();
1277 if (stack->entropy != last)
1278 ++num_different;
1279 last = stack->entropy;
1280 }
1281 stack->samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1);
1282 if (stack->samples_per_bit > MAX_SAMPLES_PER_BIT)
1283 return;
1284
1285 atomic_set(&stack->samples, 0);
1286 timer_setup_on_stack(&stack->timer, entropy_timer, 0);
1287 while (!crng_ready() && !signal_pending(current)) {
1288 /*
1289 * Check !timer_pending() and then ensure that any previous callback has finished
1290 * executing by checking try_to_del_timer_sync(), before queueing the next one.
1291 */
1292 if (!timer_pending(&stack->timer) && try_to_del_timer_sync(&stack->timer) >= 0) {
1293 struct cpumask timer_cpus;
1294 unsigned int num_cpus;
1295
1296 /*
1297 * Preemption must be disabled here, both to read the current CPU number
1298 * and to avoid scheduling a timer on a dead CPU.
1299 */
1300 preempt_disable();
1301
1302 /* Only schedule callbacks on timer CPUs that are online. */
1303 cpumask_and(&timer_cpus, housekeeping_cpumask(HK_TYPE_TIMER), cpu_online_mask);
1304 num_cpus = cpumask_weight(&timer_cpus);
1305 /* In very bizarre case of misconfiguration, fallback to all online. */
1306 if (unlikely(num_cpus == 0)) {
1307 timer_cpus = *cpu_online_mask;
1308 num_cpus = cpumask_weight(&timer_cpus);
1309 }
1310
1311 /* Basic CPU round-robin, which avoids the current CPU. */
1312 do {
1313 cpu = cpumask_next(cpu, &timer_cpus);
1314 if (cpu >= nr_cpu_ids)
1315 cpu = cpumask_first(&timer_cpus);
1316 } while (cpu == smp_processor_id() && num_cpus > 1);
1317
1318 /* Expiring the timer at `jiffies` means it's the next tick. */
1319 stack->timer.expires = jiffies;
1320
1321 add_timer_on(&stack->timer, cpu);
1322
1323 preempt_enable();
1324 }
1325 mix_pool_bytes(&stack->entropy, sizeof(stack->entropy));
1326 schedule();
1327 stack->entropy = random_get_entropy();
1328 }
1329 mix_pool_bytes(&stack->entropy, sizeof(stack->entropy));
1330
1331 del_timer_sync(&stack->timer);
1332 destroy_timer_on_stack(&stack->timer);
1333}
1334
1335
1336/**********************************************************************
1337 *
1338 * Userspace reader/writer interfaces.
1339 *
1340 * getrandom(2) is the primary modern interface into the RNG and should
1341 * be used in preference to anything else.
1342 *
1343 * Reading from /dev/random has the same functionality as calling
1344 * getrandom(2) with flags=0. In earlier versions, however, it had
1345 * vastly different semantics and should therefore be avoided, to
1346 * prevent backwards compatibility issues.
1347 *
1348 * Reading from /dev/urandom has the same functionality as calling
1349 * getrandom(2) with flags=GRND_INSECURE. Because it does not block
1350 * waiting for the RNG to be ready, it should not be used.
1351 *
1352 * Writing to either /dev/random or /dev/urandom adds entropy to
1353 * the input pool but does not credit it.
1354 *
1355 * Polling on /dev/random indicates when the RNG is initialized, on
1356 * the read side, and when it wants new entropy, on the write side.
1357 *
1358 * Both /dev/random and /dev/urandom have the same set of ioctls for
1359 * adding entropy, getting the entropy count, zeroing the count, and
1360 * reseeding the crng.
1361 *
1362 **********************************************************************/
1363
1364SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
1365{
1366 struct iov_iter iter;
1367 int ret;
1368
1369 if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
1370 return -EINVAL;
1371
1372 /*
1373 * Requesting insecure and blocking randomness at the same time makes
1374 * no sense.
1375 */
1376 if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
1377 return -EINVAL;
1378
1379 if (!crng_ready() && !(flags & GRND_INSECURE)) {
1380 if (flags & GRND_NONBLOCK)
1381 return -EAGAIN;
1382 ret = wait_for_random_bytes();
1383 if (unlikely(ret))
1384 return ret;
1385 }
1386
1387 ret = import_ubuf(ITER_DEST, ubuf, len, &iter);
1388 if (unlikely(ret))
1389 return ret;
1390 return get_random_bytes_user(&iter);
1391}
1392
1393static __poll_t random_poll(struct file *file, poll_table *wait)
1394{
1395 poll_wait(file, &crng_init_wait, wait);
1396 return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
1397}
1398
1399static ssize_t write_pool_user(struct iov_iter *iter)
1400{
1401 u8 block[BLAKE2S_BLOCK_SIZE];
1402 ssize_t ret = 0;
1403 size_t copied;
1404
1405 if (unlikely(!iov_iter_count(iter)))
1406 return 0;
1407
1408 for (;;) {
1409 copied = copy_from_iter(block, sizeof(block), iter);
1410 ret += copied;
1411 mix_pool_bytes(block, copied);
1412 if (!iov_iter_count(iter) || copied != sizeof(block))
1413 break;
1414
1415 BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
1416 if (ret % PAGE_SIZE == 0) {
1417 if (signal_pending(current))
1418 break;
1419 cond_resched();
1420 }
1421 }
1422
1423 memzero_explicit(block, sizeof(block));
1424 return ret ? ret : -EFAULT;
1425}
1426
1427static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter)
1428{
1429 return write_pool_user(iter);
1430}
1431
1432static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1433{
1434 static int maxwarn = 10;
1435
1436 /*
1437 * Opportunistically attempt to initialize the RNG on platforms that
1438 * have fast cycle counters, but don't (for now) require it to succeed.
1439 */
1440 if (!crng_ready())
1441 try_to_generate_entropy();
1442
1443 if (!crng_ready()) {
1444 if (!ratelimit_disable && maxwarn <= 0)
1445 ++urandom_warning.missed;
1446 else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
1447 --maxwarn;
1448 pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
1449 current->comm, iov_iter_count(iter));
1450 }
1451 }
1452
1453 return get_random_bytes_user(iter);
1454}
1455
1456static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1457{
1458 int ret;
1459
1460 if (!crng_ready() &&
1461 ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
1462 (kiocb->ki_filp->f_flags & O_NONBLOCK)))
1463 return -EAGAIN;
1464
1465 ret = wait_for_random_bytes();
1466 if (ret != 0)
1467 return ret;
1468 return get_random_bytes_user(iter);
1469}
1470
1471static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1472{
1473 int __user *p = (int __user *)arg;
1474 int ent_count;
1475
1476 switch (cmd) {
1477 case RNDGETENTCNT:
1478 /* Inherently racy, no point locking. */
1479 if (put_user(input_pool.init_bits, p))
1480 return -EFAULT;
1481 return 0;
1482 case RNDADDTOENTCNT:
1483 if (!capable(CAP_SYS_ADMIN))
1484 return -EPERM;
1485 if (get_user(ent_count, p))
1486 return -EFAULT;
1487 if (ent_count < 0)
1488 return -EINVAL;
1489 credit_init_bits(ent_count);
1490 return 0;
1491 case RNDADDENTROPY: {
1492 struct iov_iter iter;
1493 ssize_t ret;
1494 int len;
1495
1496 if (!capable(CAP_SYS_ADMIN))
1497 return -EPERM;
1498 if (get_user(ent_count, p++))
1499 return -EFAULT;
1500 if (ent_count < 0)
1501 return -EINVAL;
1502 if (get_user(len, p++))
1503 return -EFAULT;
1504 ret = import_ubuf(ITER_SOURCE, p, len, &iter);
1505 if (unlikely(ret))
1506 return ret;
1507 ret = write_pool_user(&iter);
1508 if (unlikely(ret < 0))
1509 return ret;
1510 /* Since we're crediting, enforce that it was all written into the pool. */
1511 if (unlikely(ret != len))
1512 return -EFAULT;
1513 credit_init_bits(ent_count);
1514 return 0;
1515 }
1516 case RNDZAPENTCNT:
1517 case RNDCLEARPOOL:
1518 /* No longer has any effect. */
1519 if (!capable(CAP_SYS_ADMIN))
1520 return -EPERM;
1521 return 0;
1522 case RNDRESEEDCRNG:
1523 if (!capable(CAP_SYS_ADMIN))
1524 return -EPERM;
1525 if (!crng_ready())
1526 return -ENODATA;
1527 crng_reseed(NULL);
1528 return 0;
1529 default:
1530 return -EINVAL;
1531 }
1532}
1533
1534static int random_fasync(int fd, struct file *filp, int on)
1535{
1536 return fasync_helper(fd, filp, on, &fasync);
1537}
1538
1539const struct file_operations random_fops = {
1540 .read_iter = random_read_iter,
1541 .write_iter = random_write_iter,
1542 .poll = random_poll,
1543 .unlocked_ioctl = random_ioctl,
1544 .compat_ioctl = compat_ptr_ioctl,
1545 .fasync = random_fasync,
1546 .llseek = noop_llseek,
1547 .splice_read = copy_splice_read,
1548 .splice_write = iter_file_splice_write,
1549};
1550
1551const struct file_operations urandom_fops = {
1552 .read_iter = urandom_read_iter,
1553 .write_iter = random_write_iter,
1554 .unlocked_ioctl = random_ioctl,
1555 .compat_ioctl = compat_ptr_ioctl,
1556 .fasync = random_fasync,
1557 .llseek = noop_llseek,
1558 .splice_read = copy_splice_read,
1559 .splice_write = iter_file_splice_write,
1560};
1561
1562
1563/********************************************************************
1564 *
1565 * Sysctl interface.
1566 *
1567 * These are partly unused legacy knobs with dummy values to not break
1568 * userspace and partly still useful things. They are usually accessible
1569 * in /proc/sys/kernel/random/ and are as follows:
1570 *
1571 * - boot_id - a UUID representing the current boot.
1572 *
1573 * - uuid - a random UUID, different each time the file is read.
1574 *
1575 * - poolsize - the number of bits of entropy that the input pool can
1576 * hold, tied to the POOL_BITS constant.
1577 *
1578 * - entropy_avail - the number of bits of entropy currently in the
1579 * input pool. Always <= poolsize.
1580 *
1581 * - write_wakeup_threshold - the amount of entropy in the input pool
1582 * below which write polls to /dev/random will unblock, requesting
1583 * more entropy, tied to the POOL_READY_BITS constant. It is writable
1584 * to avoid breaking old userspaces, but writing to it does not
1585 * change any behavior of the RNG.
1586 *
1587 * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL.
1588 * It is writable to avoid breaking old userspaces, but writing
1589 * to it does not change any behavior of the RNG.
1590 *
1591 ********************************************************************/
1592
1593#ifdef CONFIG_SYSCTL
1594
1595#include <linux/sysctl.h>
1596
1597static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ;
1598static int sysctl_random_write_wakeup_bits = POOL_READY_BITS;
1599static int sysctl_poolsize = POOL_BITS;
1600static u8 sysctl_bootid[UUID_SIZE];
1601
1602/*
1603 * This function is used to return both the bootid UUID, and random
1604 * UUID. The difference is in whether table->data is NULL; if it is,
1605 * then a new UUID is generated and returned to the user.
1606 */
1607static int proc_do_uuid(struct ctl_table *table, int write, void *buf,
1608 size_t *lenp, loff_t *ppos)
1609{
1610 u8 tmp_uuid[UUID_SIZE], *uuid;
1611 char uuid_string[UUID_STRING_LEN + 1];
1612 struct ctl_table fake_table = {
1613 .data = uuid_string,
1614 .maxlen = UUID_STRING_LEN
1615 };
1616
1617 if (write)
1618 return -EPERM;
1619
1620 uuid = table->data;
1621 if (!uuid) {
1622 uuid = tmp_uuid;
1623 generate_random_uuid(uuid);
1624 } else {
1625 static DEFINE_SPINLOCK(bootid_spinlock);
1626
1627 spin_lock(&bootid_spinlock);
1628 if (!uuid[8])
1629 generate_random_uuid(uuid);
1630 spin_unlock(&bootid_spinlock);
1631 }
1632
1633 snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
1634 return proc_dostring(&fake_table, 0, buf, lenp, ppos);
1635}
1636
1637/* The same as proc_dointvec, but writes don't change anything. */
1638static int proc_do_rointvec(struct ctl_table *table, int write, void *buf,
1639 size_t *lenp, loff_t *ppos)
1640{
1641 return write ? 0 : proc_dointvec(table, 0, buf, lenp, ppos);
1642}
1643
1644static struct ctl_table random_table[] = {
1645 {
1646 .procname = "poolsize",
1647 .data = &sysctl_poolsize,
1648 .maxlen = sizeof(int),
1649 .mode = 0444,
1650 .proc_handler = proc_dointvec,
1651 },
1652 {
1653 .procname = "entropy_avail",
1654 .data = &input_pool.init_bits,
1655 .maxlen = sizeof(int),
1656 .mode = 0444,
1657 .proc_handler = proc_dointvec,
1658 },
1659 {
1660 .procname = "write_wakeup_threshold",
1661 .data = &sysctl_random_write_wakeup_bits,
1662 .maxlen = sizeof(int),
1663 .mode = 0644,
1664 .proc_handler = proc_do_rointvec,
1665 },
1666 {
1667 .procname = "urandom_min_reseed_secs",
1668 .data = &sysctl_random_min_urandom_seed,
1669 .maxlen = sizeof(int),
1670 .mode = 0644,
1671 .proc_handler = proc_do_rointvec,
1672 },
1673 {
1674 .procname = "boot_id",
1675 .data = &sysctl_bootid,
1676 .mode = 0444,
1677 .proc_handler = proc_do_uuid,
1678 },
1679 {
1680 .procname = "uuid",
1681 .mode = 0444,
1682 .proc_handler = proc_do_uuid,
1683 },
1684};
1685
1686/*
1687 * random_init() is called before sysctl_init(),
1688 * so we cannot call register_sysctl_init() in random_init()
1689 */
1690static int __init random_sysctls_init(void)
1691{
1692 register_sysctl_init("kernel/random", random_table);
1693 return 0;
1694}
1695device_initcall(random_sysctls_init);
1696#endif
1/*
2 * random.c -- A strong random number generator
3 *
4 * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
5 *
6 * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All
7 * rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, and the entire permission notice in its entirety,
14 * including the disclaimer of warranties.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. The name of the author may not be used to endorse or promote
19 * products derived from this software without specific prior
20 * written permission.
21 *
22 * ALTERNATIVELY, this product may be distributed under the terms of
23 * the GNU General Public License, in which case the provisions of the GPL are
24 * required INSTEAD OF the above restrictions. (This clause is
25 * necessary due to a potential bad interaction between the GPL and
26 * the restrictions contained in a BSD-style copyright.)
27 *
28 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
29 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
30 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
31 * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
32 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
33 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
34 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
35 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
36 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
38 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
39 * DAMAGE.
40 */
41
42/*
43 * (now, with legal B.S. out of the way.....)
44 *
45 * This routine gathers environmental noise from device drivers, etc.,
46 * and returns good random numbers, suitable for cryptographic use.
47 * Besides the obvious cryptographic uses, these numbers are also good
48 * for seeding TCP sequence numbers, and other places where it is
49 * desirable to have numbers which are not only random, but hard to
50 * predict by an attacker.
51 *
52 * Theory of operation
53 * ===================
54 *
55 * Computers are very predictable devices. Hence it is extremely hard
56 * to produce truly random numbers on a computer --- as opposed to
57 * pseudo-random numbers, which can easily generated by using a
58 * algorithm. Unfortunately, it is very easy for attackers to guess
59 * the sequence of pseudo-random number generators, and for some
60 * applications this is not acceptable. So instead, we must try to
61 * gather "environmental noise" from the computer's environment, which
62 * must be hard for outside attackers to observe, and use that to
63 * generate random numbers. In a Unix environment, this is best done
64 * from inside the kernel.
65 *
66 * Sources of randomness from the environment include inter-keyboard
67 * timings, inter-interrupt timings from some interrupts, and other
68 * events which are both (a) non-deterministic and (b) hard for an
69 * outside observer to measure. Randomness from these sources are
70 * added to an "entropy pool", which is mixed using a CRC-like function.
71 * This is not cryptographically strong, but it is adequate assuming
72 * the randomness is not chosen maliciously, and it is fast enough that
73 * the overhead of doing it on every interrupt is very reasonable.
74 * As random bytes are mixed into the entropy pool, the routines keep
75 * an *estimate* of how many bits of randomness have been stored into
76 * the random number generator's internal state.
77 *
78 * When random bytes are desired, they are obtained by taking the SHA
79 * hash of the contents of the "entropy pool". The SHA hash avoids
80 * exposing the internal state of the entropy pool. It is believed to
81 * be computationally infeasible to derive any useful information
82 * about the input of SHA from its output. Even if it is possible to
83 * analyze SHA in some clever way, as long as the amount of data
84 * returned from the generator is less than the inherent entropy in
85 * the pool, the output data is totally unpredictable. For this
86 * reason, the routine decreases its internal estimate of how many
87 * bits of "true randomness" are contained in the entropy pool as it
88 * outputs random numbers.
89 *
90 * If this estimate goes to zero, the routine can still generate
91 * random numbers; however, an attacker may (at least in theory) be
92 * able to infer the future output of the generator from prior
93 * outputs. This requires successful cryptanalysis of SHA, which is
94 * not believed to be feasible, but there is a remote possibility.
95 * Nonetheless, these numbers should be useful for the vast majority
96 * of purposes.
97 *
98 * Exported interfaces ---- output
99 * ===============================
100 *
101 * There are three exported interfaces; the first is one designed to
102 * be used from within the kernel:
103 *
104 * void get_random_bytes(void *buf, int nbytes);
105 *
106 * This interface will return the requested number of random bytes,
107 * and place it in the requested buffer.
108 *
109 * The two other interfaces are two character devices /dev/random and
110 * /dev/urandom. /dev/random is suitable for use when very high
111 * quality randomness is desired (for example, for key generation or
112 * one-time pads), as it will only return a maximum of the number of
113 * bits of randomness (as estimated by the random number generator)
114 * contained in the entropy pool.
115 *
116 * The /dev/urandom device does not have this limit, and will return
117 * as many bytes as are requested. As more and more random bytes are
118 * requested without giving time for the entropy pool to recharge,
119 * this will result in random numbers that are merely cryptographically
120 * strong. For many applications, however, this is acceptable.
121 *
122 * Exported interfaces ---- input
123 * ==============================
124 *
125 * The current exported interfaces for gathering environmental noise
126 * from the devices are:
127 *
128 * void add_device_randomness(const void *buf, unsigned int size);
129 * void add_input_randomness(unsigned int type, unsigned int code,
130 * unsigned int value);
131 * void add_interrupt_randomness(int irq, int irq_flags);
132 * void add_disk_randomness(struct gendisk *disk);
133 *
134 * add_device_randomness() is for adding data to the random pool that
135 * is likely to differ between two devices (or possibly even per boot).
136 * This would be things like MAC addresses or serial numbers, or the
137 * read-out of the RTC. This does *not* add any actual entropy to the
138 * pool, but it initializes the pool to different values for devices
139 * that might otherwise be identical and have very little entropy
140 * available to them (particularly common in the embedded world).
141 *
142 * add_input_randomness() uses the input layer interrupt timing, as well as
143 * the event type information from the hardware.
144 *
145 * add_interrupt_randomness() uses the interrupt timing as random
146 * inputs to the entropy pool. Using the cycle counters and the irq source
147 * as inputs, it feeds the randomness roughly once a second.
148 *
149 * add_disk_randomness() uses what amounts to the seek time of block
150 * layer request events, on a per-disk_devt basis, as input to the
151 * entropy pool. Note that high-speed solid state drives with very low
152 * seek times do not make for good sources of entropy, as their seek
153 * times are usually fairly consistent.
154 *
155 * All of these routines try to estimate how many bits of randomness a
156 * particular randomness source. They do this by keeping track of the
157 * first and second order deltas of the event timings.
158 *
159 * Ensuring unpredictability at system startup
160 * ============================================
161 *
162 * When any operating system starts up, it will go through a sequence
163 * of actions that are fairly predictable by an adversary, especially
164 * if the start-up does not involve interaction with a human operator.
165 * This reduces the actual number of bits of unpredictability in the
166 * entropy pool below the value in entropy_count. In order to
167 * counteract this effect, it helps to carry information in the
168 * entropy pool across shut-downs and start-ups. To do this, put the
169 * following lines an appropriate script which is run during the boot
170 * sequence:
171 *
172 * echo "Initializing random number generator..."
173 * random_seed=/var/run/random-seed
174 * # Carry a random seed from start-up to start-up
175 * # Load and then save the whole entropy pool
176 * if [ -f $random_seed ]; then
177 * cat $random_seed >/dev/urandom
178 * else
179 * touch $random_seed
180 * fi
181 * chmod 600 $random_seed
182 * dd if=/dev/urandom of=$random_seed count=1 bs=512
183 *
184 * and the following lines in an appropriate script which is run as
185 * the system is shutdown:
186 *
187 * # Carry a random seed from shut-down to start-up
188 * # Save the whole entropy pool
189 * echo "Saving random seed..."
190 * random_seed=/var/run/random-seed
191 * touch $random_seed
192 * chmod 600 $random_seed
193 * dd if=/dev/urandom of=$random_seed count=1 bs=512
194 *
195 * For example, on most modern systems using the System V init
196 * scripts, such code fragments would be found in
197 * /etc/rc.d/init.d/random. On older Linux systems, the correct script
198 * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0.
199 *
200 * Effectively, these commands cause the contents of the entropy pool
201 * to be saved at shut-down time and reloaded into the entropy pool at
202 * start-up. (The 'dd' in the addition to the bootup script is to
203 * make sure that /etc/random-seed is different for every start-up,
204 * even if the system crashes without executing rc.0.) Even with
205 * complete knowledge of the start-up activities, predicting the state
206 * of the entropy pool requires knowledge of the previous history of
207 * the system.
208 *
209 * Configuring the /dev/random driver under Linux
210 * ==============================================
211 *
212 * The /dev/random driver under Linux uses minor numbers 8 and 9 of
213 * the /dev/mem major number (#1). So if your system does not have
214 * /dev/random and /dev/urandom created already, they can be created
215 * by using the commands:
216 *
217 * mknod /dev/random c 1 8
218 * mknod /dev/urandom c 1 9
219 *
220 * Acknowledgements:
221 * =================
222 *
223 * Ideas for constructing this random number generator were derived
224 * from Pretty Good Privacy's random number generator, and from private
225 * discussions with Phil Karn. Colin Plumb provided a faster random
226 * number generator, which speed up the mixing function of the entropy
227 * pool, taken from PGPfone. Dale Worley has also contributed many
228 * useful ideas and suggestions to improve this driver.
229 *
230 * Any flaws in the design are solely my responsibility, and should
231 * not be attributed to the Phil, Colin, or any of authors of PGP.
232 *
233 * Further background information on this topic may be obtained from
234 * RFC 1750, "Randomness Recommendations for Security", by Donald
235 * Eastlake, Steve Crocker, and Jeff Schiller.
236 */
237
238#include <linux/utsname.h>
239#include <linux/module.h>
240#include <linux/kernel.h>
241#include <linux/major.h>
242#include <linux/string.h>
243#include <linux/fcntl.h>
244#include <linux/slab.h>
245#include <linux/random.h>
246#include <linux/poll.h>
247#include <linux/init.h>
248#include <linux/fs.h>
249#include <linux/genhd.h>
250#include <linux/interrupt.h>
251#include <linux/mm.h>
252#include <linux/spinlock.h>
253#include <linux/percpu.h>
254#include <linux/cryptohash.h>
255#include <linux/fips.h>
256#include <linux/ptrace.h>
257#include <linux/kmemcheck.h>
258
259#ifdef CONFIG_GENERIC_HARDIRQS
260# include <linux/irq.h>
261#endif
262
263#include <asm/processor.h>
264#include <asm/uaccess.h>
265#include <asm/irq.h>
266#include <asm/irq_regs.h>
267#include <asm/io.h>
268
269#define CREATE_TRACE_POINTS
270#include <trace/events/random.h>
271
272/*
273 * Configuration information
274 */
275#define INPUT_POOL_WORDS 128
276#define OUTPUT_POOL_WORDS 32
277#define SEC_XFER_SIZE 512
278#define EXTRACT_SIZE 10
279
280#define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))
281
282/*
283 * The minimum number of bits of entropy before we wake up a read on
284 * /dev/random. Should be enough to do a significant reseed.
285 */
286static int random_read_wakeup_thresh = 64;
287
288/*
289 * If the entropy count falls under this number of bits, then we
290 * should wake up processes which are selecting or polling on write
291 * access to /dev/random.
292 */
293static int random_write_wakeup_thresh = 128;
294
295/*
296 * When the input pool goes over trickle_thresh, start dropping most
297 * samples to avoid wasting CPU time and reduce lock contention.
298 */
299
300static int trickle_thresh __read_mostly = INPUT_POOL_WORDS * 28;
301
302static DEFINE_PER_CPU(int, trickle_count);
303
304/*
305 * A pool of size .poolwords is stirred with a primitive polynomial
306 * of degree .poolwords over GF(2). The taps for various sizes are
307 * defined below. They are chosen to be evenly spaced (minimum RMS
308 * distance from evenly spaced; the numbers in the comments are a
309 * scaled squared error sum) except for the last tap, which is 1 to
310 * get the twisting happening as fast as possible.
311 */
312static struct poolinfo {
313 int poolwords;
314 int tap1, tap2, tap3, tap4, tap5;
315} poolinfo_table[] = {
316 /* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */
317 { 128, 103, 76, 51, 25, 1 },
318 /* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */
319 { 32, 26, 20, 14, 7, 1 },
320#if 0
321 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */
322 { 2048, 1638, 1231, 819, 411, 1 },
323
324 /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
325 { 1024, 817, 615, 412, 204, 1 },
326
327 /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
328 { 1024, 819, 616, 410, 207, 2 },
329
330 /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
331 { 512, 411, 308, 208, 104, 1 },
332
333 /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
334 { 512, 409, 307, 206, 102, 2 },
335 /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
336 { 512, 409, 309, 205, 103, 2 },
337
338 /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
339 { 256, 205, 155, 101, 52, 1 },
340
341 /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
342 { 128, 103, 78, 51, 27, 2 },
343
344 /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
345 { 64, 52, 39, 26, 14, 1 },
346#endif
347};
348
349#define POOLBITS poolwords*32
350#define POOLBYTES poolwords*4
351
352/*
353 * For the purposes of better mixing, we use the CRC-32 polynomial as
354 * well to make a twisted Generalized Feedback Shift Reigster
355 *
356 * (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR generators. ACM
357 * Transactions on Modeling and Computer Simulation 2(3):179-194.
358 * Also see M. Matsumoto & Y. Kurita, 1994. Twisted GFSR generators
359 * II. ACM Transactions on Mdeling and Computer Simulation 4:254-266)
360 *
361 * Thanks to Colin Plumb for suggesting this.
362 *
363 * We have not analyzed the resultant polynomial to prove it primitive;
364 * in fact it almost certainly isn't. Nonetheless, the irreducible factors
365 * of a random large-degree polynomial over GF(2) are more than large enough
366 * that periodicity is not a concern.
367 *
368 * The input hash is much less sensitive than the output hash. All
369 * that we want of it is that it be a good non-cryptographic hash;
370 * i.e. it not produce collisions when fed "random" data of the sort
371 * we expect to see. As long as the pool state differs for different
372 * inputs, we have preserved the input entropy and done a good job.
373 * The fact that an intelligent attacker can construct inputs that
374 * will produce controlled alterations to the pool's state is not
375 * important because we don't consider such inputs to contribute any
376 * randomness. The only property we need with respect to them is that
377 * the attacker can't increase his/her knowledge of the pool's state.
378 * Since all additions are reversible (knowing the final state and the
379 * input, you can reconstruct the initial state), if an attacker has
380 * any uncertainty about the initial state, he/she can only shuffle
381 * that uncertainty about, but never cause any collisions (which would
382 * decrease the uncertainty).
383 *
384 * The chosen system lets the state of the pool be (essentially) the input
385 * modulo the generator polymnomial. Now, for random primitive polynomials,
386 * this is a universal class of hash functions, meaning that the chance
387 * of a collision is limited by the attacker's knowledge of the generator
388 * polynomail, so if it is chosen at random, an attacker can never force
389 * a collision. Here, we use a fixed polynomial, but we *can* assume that
390 * ###--> it is unknown to the processes generating the input entropy. <-###
391 * Because of this important property, this is a good, collision-resistant
392 * hash; hash collisions will occur no more often than chance.
393 */
394
395/*
396 * Static global variables
397 */
398static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
399static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
400static struct fasync_struct *fasync;
401
402#if 0
403static bool debug;
404module_param(debug, bool, 0644);
405#define DEBUG_ENT(fmt, arg...) do { \
406 if (debug) \
407 printk(KERN_DEBUG "random %04d %04d %04d: " \
408 fmt,\
409 input_pool.entropy_count,\
410 blocking_pool.entropy_count,\
411 nonblocking_pool.entropy_count,\
412 ## arg); } while (0)
413#else
414#define DEBUG_ENT(fmt, arg...) do {} while (0)
415#endif
416
417/**********************************************************************
418 *
419 * OS independent entropy store. Here are the functions which handle
420 * storing entropy in an entropy pool.
421 *
422 **********************************************************************/
423
424struct entropy_store;
425struct entropy_store {
426 /* read-only data: */
427 struct poolinfo *poolinfo;
428 __u32 *pool;
429 const char *name;
430 struct entropy_store *pull;
431 int limit;
432
433 /* read-write data: */
434 spinlock_t lock;
435 unsigned add_ptr;
436 unsigned input_rotate;
437 int entropy_count;
438 int entropy_total;
439 unsigned int initialized:1;
440 __u8 last_data[EXTRACT_SIZE];
441};
442
443static __u32 input_pool_data[INPUT_POOL_WORDS];
444static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
445static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
446
447static struct entropy_store input_pool = {
448 .poolinfo = &poolinfo_table[0],
449 .name = "input",
450 .limit = 1,
451 .lock = __SPIN_LOCK_UNLOCKED(&input_pool.lock),
452 .pool = input_pool_data
453};
454
455static struct entropy_store blocking_pool = {
456 .poolinfo = &poolinfo_table[1],
457 .name = "blocking",
458 .limit = 1,
459 .pull = &input_pool,
460 .lock = __SPIN_LOCK_UNLOCKED(&blocking_pool.lock),
461 .pool = blocking_pool_data
462};
463
464static struct entropy_store nonblocking_pool = {
465 .poolinfo = &poolinfo_table[1],
466 .name = "nonblocking",
467 .pull = &input_pool,
468 .lock = __SPIN_LOCK_UNLOCKED(&nonblocking_pool.lock),
469 .pool = nonblocking_pool_data
470};
471
472static __u32 const twist_table[8] = {
473 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
474 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
475
476/*
477 * This function adds bytes into the entropy "pool". It does not
478 * update the entropy estimate. The caller should call
479 * credit_entropy_bits if this is appropriate.
480 *
481 * The pool is stirred with a primitive polynomial of the appropriate
482 * degree, and then twisted. We twist by three bits at a time because
483 * it's cheap to do so and helps slightly in the expected case where
484 * the entropy is concentrated in the low-order bits.
485 */
486static void _mix_pool_bytes(struct entropy_store *r, const void *in,
487 int nbytes, __u8 out[64])
488{
489 unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
490 int input_rotate;
491 int wordmask = r->poolinfo->poolwords - 1;
492 const char *bytes = in;
493 __u32 w;
494
495 tap1 = r->poolinfo->tap1;
496 tap2 = r->poolinfo->tap2;
497 tap3 = r->poolinfo->tap3;
498 tap4 = r->poolinfo->tap4;
499 tap5 = r->poolinfo->tap5;
500
501 smp_rmb();
502 input_rotate = ACCESS_ONCE(r->input_rotate);
503 i = ACCESS_ONCE(r->add_ptr);
504
505 /* mix one byte at a time to simplify size handling and churn faster */
506 while (nbytes--) {
507 w = rol32(*bytes++, input_rotate & 31);
508 i = (i - 1) & wordmask;
509
510 /* XOR in the various taps */
511 w ^= r->pool[i];
512 w ^= r->pool[(i + tap1) & wordmask];
513 w ^= r->pool[(i + tap2) & wordmask];
514 w ^= r->pool[(i + tap3) & wordmask];
515 w ^= r->pool[(i + tap4) & wordmask];
516 w ^= r->pool[(i + tap5) & wordmask];
517
518 /* Mix the result back in with a twist */
519 r->pool[i] = (w >> 3) ^ twist_table[w & 7];
520
521 /*
522 * Normally, we add 7 bits of rotation to the pool.
523 * At the beginning of the pool, add an extra 7 bits
524 * rotation, so that successive passes spread the
525 * input bits across the pool evenly.
526 */
527 input_rotate += i ? 7 : 14;
528 }
529
530 ACCESS_ONCE(r->input_rotate) = input_rotate;
531 ACCESS_ONCE(r->add_ptr) = i;
532 smp_wmb();
533
534 if (out)
535 for (j = 0; j < 16; j++)
536 ((__u32 *)out)[j] = r->pool[(i - j) & wordmask];
537}
538
539static void __mix_pool_bytes(struct entropy_store *r, const void *in,
540 int nbytes, __u8 out[64])
541{
542 trace_mix_pool_bytes_nolock(r->name, nbytes, _RET_IP_);
543 _mix_pool_bytes(r, in, nbytes, out);
544}
545
546static void mix_pool_bytes(struct entropy_store *r, const void *in,
547 int nbytes, __u8 out[64])
548{
549 unsigned long flags;
550
551 trace_mix_pool_bytes(r->name, nbytes, _RET_IP_);
552 spin_lock_irqsave(&r->lock, flags);
553 _mix_pool_bytes(r, in, nbytes, out);
554 spin_unlock_irqrestore(&r->lock, flags);
555}
556
557struct fast_pool {
558 __u32 pool[4];
559 unsigned long last;
560 unsigned short count;
561 unsigned char rotate;
562 unsigned char last_timer_intr;
563};
564
565/*
566 * This is a fast mixing routine used by the interrupt randomness
567 * collector. It's hardcoded for an 128 bit pool and assumes that any
568 * locks that might be needed are taken by the caller.
569 */
570static void fast_mix(struct fast_pool *f, const void *in, int nbytes)
571{
572 const char *bytes = in;
573 __u32 w;
574 unsigned i = f->count;
575 unsigned input_rotate = f->rotate;
576
577 while (nbytes--) {
578 w = rol32(*bytes++, input_rotate & 31) ^ f->pool[i & 3] ^
579 f->pool[(i + 1) & 3];
580 f->pool[i & 3] = (w >> 3) ^ twist_table[w & 7];
581 input_rotate += (i++ & 3) ? 7 : 14;
582 }
583 f->count = i;
584 f->rotate = input_rotate;
585}
586
587/*
588 * Credit (or debit) the entropy store with n bits of entropy
589 */
590static void credit_entropy_bits(struct entropy_store *r, int nbits)
591{
592 int entropy_count, orig;
593
594 if (!nbits)
595 return;
596
597 DEBUG_ENT("added %d entropy credits to %s\n", nbits, r->name);
598retry:
599 entropy_count = orig = ACCESS_ONCE(r->entropy_count);
600 entropy_count += nbits;
601
602 if (entropy_count < 0) {
603 DEBUG_ENT("negative entropy/overflow\n");
604 entropy_count = 0;
605 } else if (entropy_count > r->poolinfo->POOLBITS)
606 entropy_count = r->poolinfo->POOLBITS;
607 if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
608 goto retry;
609
610 if (!r->initialized && nbits > 0) {
611 r->entropy_total += nbits;
612 if (r->entropy_total > 128)
613 r->initialized = 1;
614 }
615
616 trace_credit_entropy_bits(r->name, nbits, entropy_count,
617 r->entropy_total, _RET_IP_);
618
619 /* should we wake readers? */
620 if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {
621 wake_up_interruptible(&random_read_wait);
622 kill_fasync(&fasync, SIGIO, POLL_IN);
623 }
624}
625
626/*********************************************************************
627 *
628 * Entropy input management
629 *
630 *********************************************************************/
631
632/* There is one of these per entropy source */
633struct timer_rand_state {
634 cycles_t last_time;
635 long last_delta, last_delta2;
636 unsigned dont_count_entropy:1;
637};
638
639/*
640 * Add device- or boot-specific data to the input and nonblocking
641 * pools to help initialize them to unique values.
642 *
643 * None of this adds any entropy, it is meant to avoid the
644 * problem of the nonblocking pool having similar initial state
645 * across largely identical devices.
646 */
647void add_device_randomness(const void *buf, unsigned int size)
648{
649 unsigned long time = get_cycles() ^ jiffies;
650
651 mix_pool_bytes(&input_pool, buf, size, NULL);
652 mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
653 mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
654 mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
655}
656EXPORT_SYMBOL(add_device_randomness);
657
658static struct timer_rand_state input_timer_state;
659
660/*
661 * This function adds entropy to the entropy "pool" by using timing
662 * delays. It uses the timer_rand_state structure to make an estimate
663 * of how many bits of entropy this call has added to the pool.
664 *
665 * The number "num" is also added to the pool - it should somehow describe
666 * the type of event which just happened. This is currently 0-255 for
667 * keyboard scan codes, and 256 upwards for interrupts.
668 *
669 */
670static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
671{
672 struct {
673 long jiffies;
674 unsigned cycles;
675 unsigned num;
676 } sample;
677 long delta, delta2, delta3;
678
679 preempt_disable();
680 /* if over the trickle threshold, use only 1 in 4096 samples */
681 if (input_pool.entropy_count > trickle_thresh &&
682 ((__this_cpu_inc_return(trickle_count) - 1) & 0xfff))
683 goto out;
684
685 sample.jiffies = jiffies;
686 sample.cycles = get_cycles();
687 sample.num = num;
688 mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
689
690 /*
691 * Calculate number of bits of randomness we probably added.
692 * We take into account the first, second and third-order deltas
693 * in order to make our estimate.
694 */
695
696 if (!state->dont_count_entropy) {
697 delta = sample.jiffies - state->last_time;
698 state->last_time = sample.jiffies;
699
700 delta2 = delta - state->last_delta;
701 state->last_delta = delta;
702
703 delta3 = delta2 - state->last_delta2;
704 state->last_delta2 = delta2;
705
706 if (delta < 0)
707 delta = -delta;
708 if (delta2 < 0)
709 delta2 = -delta2;
710 if (delta3 < 0)
711 delta3 = -delta3;
712 if (delta > delta2)
713 delta = delta2;
714 if (delta > delta3)
715 delta = delta3;
716
717 /*
718 * delta is now minimum absolute delta.
719 * Round down by 1 bit on general principles,
720 * and limit entropy entimate to 12 bits.
721 */
722 credit_entropy_bits(&input_pool,
723 min_t(int, fls(delta>>1), 11));
724 }
725out:
726 preempt_enable();
727}
728
729void add_input_randomness(unsigned int type, unsigned int code,
730 unsigned int value)
731{
732 static unsigned char last_value;
733
734 /* ignore autorepeat and the like */
735 if (value == last_value)
736 return;
737
738 DEBUG_ENT("input event\n");
739 last_value = value;
740 add_timer_randomness(&input_timer_state,
741 (type << 4) ^ code ^ (code >> 4) ^ value);
742}
743EXPORT_SYMBOL_GPL(add_input_randomness);
744
745static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
746
747void add_interrupt_randomness(int irq, int irq_flags)
748{
749 struct entropy_store *r;
750 struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
751 struct pt_regs *regs = get_irq_regs();
752 unsigned long now = jiffies;
753 __u32 input[4], cycles = get_cycles();
754
755 input[0] = cycles ^ jiffies;
756 input[1] = irq;
757 if (regs) {
758 __u64 ip = instruction_pointer(regs);
759 input[2] = ip;
760 input[3] = ip >> 32;
761 }
762
763 fast_mix(fast_pool, input, sizeof(input));
764
765 if ((fast_pool->count & 1023) &&
766 !time_after(now, fast_pool->last + HZ))
767 return;
768
769 fast_pool->last = now;
770
771 r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
772 __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
773 /*
774 * If we don't have a valid cycle counter, and we see
775 * back-to-back timer interrupts, then skip giving credit for
776 * any entropy.
777 */
778 if (cycles == 0) {
779 if (irq_flags & __IRQF_TIMER) {
780 if (fast_pool->last_timer_intr)
781 return;
782 fast_pool->last_timer_intr = 1;
783 } else
784 fast_pool->last_timer_intr = 0;
785 }
786 credit_entropy_bits(r, 1);
787}
788
789#ifdef CONFIG_BLOCK
790void add_disk_randomness(struct gendisk *disk)
791{
792 if (!disk || !disk->random)
793 return;
794 /* first major is 1, so we get >= 0x200 here */
795 DEBUG_ENT("disk event %d:%d\n",
796 MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));
797
798 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
799}
800#endif
801
802/*********************************************************************
803 *
804 * Entropy extraction routines
805 *
806 *********************************************************************/
807
808static ssize_t extract_entropy(struct entropy_store *r, void *buf,
809 size_t nbytes, int min, int rsvd);
810
811/*
812 * This utility inline function is responsible for transferring entropy
813 * from the primary pool to the secondary extraction pool. We make
814 * sure we pull enough for a 'catastrophic reseed'.
815 */
816static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
817{
818 __u32 tmp[OUTPUT_POOL_WORDS];
819
820 if (r->pull && r->entropy_count < nbytes * 8 &&
821 r->entropy_count < r->poolinfo->POOLBITS) {
822 /* If we're limited, always leave two wakeup worth's BITS */
823 int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
824 int bytes = nbytes;
825
826 /* pull at least as many as BYTES as wakeup BITS */
827 bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
828 /* but never more than the buffer size */
829 bytes = min_t(int, bytes, sizeof(tmp));
830
831 DEBUG_ENT("going to reseed %s with %d bits "
832 "(%d of %d requested)\n",
833 r->name, bytes * 8, nbytes * 8, r->entropy_count);
834
835 bytes = extract_entropy(r->pull, tmp, bytes,
836 random_read_wakeup_thresh / 8, rsvd);
837 mix_pool_bytes(r, tmp, bytes, NULL);
838 credit_entropy_bits(r, bytes*8);
839 }
840}
841
842/*
843 * These functions extracts randomness from the "entropy pool", and
844 * returns it in a buffer.
845 *
846 * The min parameter specifies the minimum amount we can pull before
847 * failing to avoid races that defeat catastrophic reseeding while the
848 * reserved parameter indicates how much entropy we must leave in the
849 * pool after each pull to avoid starving other readers.
850 *
851 * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
852 */
853
854static size_t account(struct entropy_store *r, size_t nbytes, int min,
855 int reserved)
856{
857 unsigned long flags;
858
859 /* Hold lock while accounting */
860 spin_lock_irqsave(&r->lock, flags);
861
862 BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
863 DEBUG_ENT("trying to extract %d bits from %s\n",
864 nbytes * 8, r->name);
865
866 /* Can we pull enough? */
867 if (r->entropy_count / 8 < min + reserved) {
868 nbytes = 0;
869 } else {
870 /* If limited, never pull more than available */
871 if (r->limit && nbytes + reserved >= r->entropy_count / 8)
872 nbytes = r->entropy_count/8 - reserved;
873
874 if (r->entropy_count / 8 >= nbytes + reserved)
875 r->entropy_count -= nbytes*8;
876 else
877 r->entropy_count = reserved;
878
879 if (r->entropy_count < random_write_wakeup_thresh) {
880 wake_up_interruptible(&random_write_wait);
881 kill_fasync(&fasync, SIGIO, POLL_OUT);
882 }
883 }
884
885 DEBUG_ENT("debiting %d entropy credits from %s%s\n",
886 nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
887
888 spin_unlock_irqrestore(&r->lock, flags);
889
890 return nbytes;
891}
892
893static void extract_buf(struct entropy_store *r, __u8 *out)
894{
895 int i;
896 union {
897 __u32 w[5];
898 unsigned long l[LONGS(EXTRACT_SIZE)];
899 } hash;
900 __u32 workspace[SHA_WORKSPACE_WORDS];
901 __u8 extract[64];
902 unsigned long flags;
903
904 /* Generate a hash across the pool, 16 words (512 bits) at a time */
905 sha_init(hash.w);
906 spin_lock_irqsave(&r->lock, flags);
907 for (i = 0; i < r->poolinfo->poolwords; i += 16)
908 sha_transform(hash.w, (__u8 *)(r->pool + i), workspace);
909
910 /*
911 * We mix the hash back into the pool to prevent backtracking
912 * attacks (where the attacker knows the state of the pool
913 * plus the current outputs, and attempts to find previous
914 * ouputs), unless the hash function can be inverted. By
915 * mixing at least a SHA1 worth of hash data back, we make
916 * brute-forcing the feedback as hard as brute-forcing the
917 * hash.
918 */
919 __mix_pool_bytes(r, hash.w, sizeof(hash.w), extract);
920 spin_unlock_irqrestore(&r->lock, flags);
921
922 /*
923 * To avoid duplicates, we atomically extract a portion of the
924 * pool while mixing, and hash one final time.
925 */
926 sha_transform(hash.w, extract, workspace);
927 memset(extract, 0, sizeof(extract));
928 memset(workspace, 0, sizeof(workspace));
929
930 /*
931 * In case the hash function has some recognizable output
932 * pattern, we fold it in half. Thus, we always feed back
933 * twice as much data as we output.
934 */
935 hash.w[0] ^= hash.w[3];
936 hash.w[1] ^= hash.w[4];
937 hash.w[2] ^= rol32(hash.w[2], 16);
938
939 /*
940 * If we have a architectural hardware random number
941 * generator, mix that in, too.
942 */
943 for (i = 0; i < LONGS(EXTRACT_SIZE); i++) {
944 unsigned long v;
945 if (!arch_get_random_long(&v))
946 break;
947 hash.l[i] ^= v;
948 }
949
950 memcpy(out, &hash, EXTRACT_SIZE);
951 memset(&hash, 0, sizeof(hash));
952}
953
954static ssize_t extract_entropy(struct entropy_store *r, void *buf,
955 size_t nbytes, int min, int reserved)
956{
957 ssize_t ret = 0, i;
958 __u8 tmp[EXTRACT_SIZE];
959
960 trace_extract_entropy(r->name, nbytes, r->entropy_count, _RET_IP_);
961 xfer_secondary_pool(r, nbytes);
962 nbytes = account(r, nbytes, min, reserved);
963
964 while (nbytes) {
965 extract_buf(r, tmp);
966
967 if (fips_enabled) {
968 unsigned long flags;
969
970 spin_lock_irqsave(&r->lock, flags);
971 if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
972 panic("Hardware RNG duplicated output!\n");
973 memcpy(r->last_data, tmp, EXTRACT_SIZE);
974 spin_unlock_irqrestore(&r->lock, flags);
975 }
976 i = min_t(int, nbytes, EXTRACT_SIZE);
977 memcpy(buf, tmp, i);
978 nbytes -= i;
979 buf += i;
980 ret += i;
981 }
982
983 /* Wipe data just returned from memory */
984 memset(tmp, 0, sizeof(tmp));
985
986 return ret;
987}
988
989static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
990 size_t nbytes)
991{
992 ssize_t ret = 0, i;
993 __u8 tmp[EXTRACT_SIZE];
994
995 trace_extract_entropy_user(r->name, nbytes, r->entropy_count, _RET_IP_);
996 xfer_secondary_pool(r, nbytes);
997 nbytes = account(r, nbytes, 0, 0);
998
999 while (nbytes) {
1000 if (need_resched()) {
1001 if (signal_pending(current)) {
1002 if (ret == 0)
1003 ret = -ERESTARTSYS;
1004 break;
1005 }
1006 schedule();
1007 }
1008
1009 extract_buf(r, tmp);
1010 i = min_t(int, nbytes, EXTRACT_SIZE);
1011 if (copy_to_user(buf, tmp, i)) {
1012 ret = -EFAULT;
1013 break;
1014 }
1015
1016 nbytes -= i;
1017 buf += i;
1018 ret += i;
1019 }
1020
1021 /* Wipe data just returned from memory */
1022 memset(tmp, 0, sizeof(tmp));
1023
1024 return ret;
1025}
1026
1027/*
1028 * This function is the exported kernel interface. It returns some
1029 * number of good random numbers, suitable for key generation, seeding
1030 * TCP sequence numbers, etc. It does not use the hw random number
1031 * generator, if available; use get_random_bytes_arch() for that.
1032 */
1033void get_random_bytes(void *buf, int nbytes)
1034{
1035 extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
1036}
1037EXPORT_SYMBOL(get_random_bytes);
1038
1039/*
1040 * This function will use the architecture-specific hardware random
1041 * number generator if it is available. The arch-specific hw RNG will
1042 * almost certainly be faster than what we can do in software, but it
1043 * is impossible to verify that it is implemented securely (as
1044 * opposed, to, say, the AES encryption of a sequence number using a
1045 * key known by the NSA). So it's useful if we need the speed, but
1046 * only if we're willing to trust the hardware manufacturer not to
1047 * have put in a back door.
1048 */
1049void get_random_bytes_arch(void *buf, int nbytes)
1050{
1051 char *p = buf;
1052
1053 trace_get_random_bytes(nbytes, _RET_IP_);
1054 while (nbytes) {
1055 unsigned long v;
1056 int chunk = min(nbytes, (int)sizeof(unsigned long));
1057
1058 if (!arch_get_random_long(&v))
1059 break;
1060
1061 memcpy(p, &v, chunk);
1062 p += chunk;
1063 nbytes -= chunk;
1064 }
1065
1066 if (nbytes)
1067 extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
1068}
1069EXPORT_SYMBOL(get_random_bytes_arch);
1070
1071
1072/*
1073 * init_std_data - initialize pool with system data
1074 *
1075 * @r: pool to initialize
1076 *
1077 * This function clears the pool's entropy count and mixes some system
1078 * data into the pool to prepare it for use. The pool is not cleared
1079 * as that can only decrease the entropy in the pool.
1080 */
1081static void init_std_data(struct entropy_store *r)
1082{
1083 int i;
1084 ktime_t now = ktime_get_real();
1085 unsigned long rv;
1086
1087 r->entropy_count = 0;
1088 r->entropy_total = 0;
1089 mix_pool_bytes(r, &now, sizeof(now), NULL);
1090 for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof(rv)) {
1091 if (!arch_get_random_long(&rv))
1092 break;
1093 mix_pool_bytes(r, &rv, sizeof(rv), NULL);
1094 }
1095 mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
1096}
1097
1098/*
1099 * Note that setup_arch() may call add_device_randomness()
1100 * long before we get here. This allows seeding of the pools
1101 * with some platform dependent data very early in the boot
1102 * process. But it limits our options here. We must use
1103 * statically allocated structures that already have all
1104 * initializations complete at compile time. We should also
1105 * take care not to overwrite the precious per platform data
1106 * we were given.
1107 */
1108static int rand_initialize(void)
1109{
1110 init_std_data(&input_pool);
1111 init_std_data(&blocking_pool);
1112 init_std_data(&nonblocking_pool);
1113 return 0;
1114}
1115module_init(rand_initialize);
1116
1117#ifdef CONFIG_BLOCK
1118void rand_initialize_disk(struct gendisk *disk)
1119{
1120 struct timer_rand_state *state;
1121
1122 /*
1123 * If kzalloc returns null, we just won't use that entropy
1124 * source.
1125 */
1126 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1127 if (state)
1128 disk->random = state;
1129}
1130#endif
1131
1132static ssize_t
1133random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1134{
1135 ssize_t n, retval = 0, count = 0;
1136
1137 if (nbytes == 0)
1138 return 0;
1139
1140 while (nbytes > 0) {
1141 n = nbytes;
1142 if (n > SEC_XFER_SIZE)
1143 n = SEC_XFER_SIZE;
1144
1145 DEBUG_ENT("reading %d bits\n", n*8);
1146
1147 n = extract_entropy_user(&blocking_pool, buf, n);
1148
1149 DEBUG_ENT("read got %d bits (%d still needed)\n",
1150 n*8, (nbytes-n)*8);
1151
1152 if (n == 0) {
1153 if (file->f_flags & O_NONBLOCK) {
1154 retval = -EAGAIN;
1155 break;
1156 }
1157
1158 DEBUG_ENT("sleeping?\n");
1159
1160 wait_event_interruptible(random_read_wait,
1161 input_pool.entropy_count >=
1162 random_read_wakeup_thresh);
1163
1164 DEBUG_ENT("awake\n");
1165
1166 if (signal_pending(current)) {
1167 retval = -ERESTARTSYS;
1168 break;
1169 }
1170
1171 continue;
1172 }
1173
1174 if (n < 0) {
1175 retval = n;
1176 break;
1177 }
1178 count += n;
1179 buf += n;
1180 nbytes -= n;
1181 break; /* This break makes the device work */
1182 /* like a named pipe */
1183 }
1184
1185 return (count ? count : retval);
1186}
1187
1188static ssize_t
1189urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1190{
1191 return extract_entropy_user(&nonblocking_pool, buf, nbytes);
1192}
1193
1194static unsigned int
1195random_poll(struct file *file, poll_table * wait)
1196{
1197 unsigned int mask;
1198
1199 poll_wait(file, &random_read_wait, wait);
1200 poll_wait(file, &random_write_wait, wait);
1201 mask = 0;
1202 if (input_pool.entropy_count >= random_read_wakeup_thresh)
1203 mask |= POLLIN | POLLRDNORM;
1204 if (input_pool.entropy_count < random_write_wakeup_thresh)
1205 mask |= POLLOUT | POLLWRNORM;
1206 return mask;
1207}
1208
1209static int
1210write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1211{
1212 size_t bytes;
1213 __u32 buf[16];
1214 const char __user *p = buffer;
1215
1216 while (count > 0) {
1217 bytes = min(count, sizeof(buf));
1218 if (copy_from_user(&buf, p, bytes))
1219 return -EFAULT;
1220
1221 count -= bytes;
1222 p += bytes;
1223
1224 mix_pool_bytes(r, buf, bytes, NULL);
1225 cond_resched();
1226 }
1227
1228 return 0;
1229}
1230
1231static ssize_t random_write(struct file *file, const char __user *buffer,
1232 size_t count, loff_t *ppos)
1233{
1234 size_t ret;
1235
1236 ret = write_pool(&blocking_pool, buffer, count);
1237 if (ret)
1238 return ret;
1239 ret = write_pool(&nonblocking_pool, buffer, count);
1240 if (ret)
1241 return ret;
1242
1243 return (ssize_t)count;
1244}
1245
1246static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1247{
1248 int size, ent_count;
1249 int __user *p = (int __user *)arg;
1250 int retval;
1251
1252 switch (cmd) {
1253 case RNDGETENTCNT:
1254 /* inherently racy, no point locking */
1255 if (put_user(input_pool.entropy_count, p))
1256 return -EFAULT;
1257 return 0;
1258 case RNDADDTOENTCNT:
1259 if (!capable(CAP_SYS_ADMIN))
1260 return -EPERM;
1261 if (get_user(ent_count, p))
1262 return -EFAULT;
1263 credit_entropy_bits(&input_pool, ent_count);
1264 return 0;
1265 case RNDADDENTROPY:
1266 if (!capable(CAP_SYS_ADMIN))
1267 return -EPERM;
1268 if (get_user(ent_count, p++))
1269 return -EFAULT;
1270 if (ent_count < 0)
1271 return -EINVAL;
1272 if (get_user(size, p++))
1273 return -EFAULT;
1274 retval = write_pool(&input_pool, (const char __user *)p,
1275 size);
1276 if (retval < 0)
1277 return retval;
1278 credit_entropy_bits(&input_pool, ent_count);
1279 return 0;
1280 case RNDZAPENTCNT:
1281 case RNDCLEARPOOL:
1282 /* Clear the entropy pool counters. */
1283 if (!capable(CAP_SYS_ADMIN))
1284 return -EPERM;
1285 rand_initialize();
1286 return 0;
1287 default:
1288 return -EINVAL;
1289 }
1290}
1291
1292static int random_fasync(int fd, struct file *filp, int on)
1293{
1294 return fasync_helper(fd, filp, on, &fasync);
1295}
1296
1297const struct file_operations random_fops = {
1298 .read = random_read,
1299 .write = random_write,
1300 .poll = random_poll,
1301 .unlocked_ioctl = random_ioctl,
1302 .fasync = random_fasync,
1303 .llseek = noop_llseek,
1304};
1305
1306const struct file_operations urandom_fops = {
1307 .read = urandom_read,
1308 .write = random_write,
1309 .unlocked_ioctl = random_ioctl,
1310 .fasync = random_fasync,
1311 .llseek = noop_llseek,
1312};
1313
1314/***************************************************************
1315 * Random UUID interface
1316 *
1317 * Used here for a Boot ID, but can be useful for other kernel
1318 * drivers.
1319 ***************************************************************/
1320
1321/*
1322 * Generate random UUID
1323 */
1324void generate_random_uuid(unsigned char uuid_out[16])
1325{
1326 get_random_bytes(uuid_out, 16);
1327 /* Set UUID version to 4 --- truly random generation */
1328 uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1329 /* Set the UUID variant to DCE */
1330 uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1331}
1332EXPORT_SYMBOL(generate_random_uuid);
1333
1334/********************************************************************
1335 *
1336 * Sysctl interface
1337 *
1338 ********************************************************************/
1339
1340#ifdef CONFIG_SYSCTL
1341
1342#include <linux/sysctl.h>
1343
1344static int min_read_thresh = 8, min_write_thresh;
1345static int max_read_thresh = INPUT_POOL_WORDS * 32;
1346static int max_write_thresh = INPUT_POOL_WORDS * 32;
1347static char sysctl_bootid[16];
1348
1349/*
1350 * These functions is used to return both the bootid UUID, and random
1351 * UUID. The difference is in whether table->data is NULL; if it is,
1352 * then a new UUID is generated and returned to the user.
1353 *
1354 * If the user accesses this via the proc interface, it will be returned
1355 * as an ASCII string in the standard UUID format. If accesses via the
1356 * sysctl system call, it is returned as 16 bytes of binary data.
1357 */
1358static int proc_do_uuid(ctl_table *table, int write,
1359 void __user *buffer, size_t *lenp, loff_t *ppos)
1360{
1361 ctl_table fake_table;
1362 unsigned char buf[64], tmp_uuid[16], *uuid;
1363
1364 uuid = table->data;
1365 if (!uuid) {
1366 uuid = tmp_uuid;
1367 generate_random_uuid(uuid);
1368 } else {
1369 static DEFINE_SPINLOCK(bootid_spinlock);
1370
1371 spin_lock(&bootid_spinlock);
1372 if (!uuid[8])
1373 generate_random_uuid(uuid);
1374 spin_unlock(&bootid_spinlock);
1375 }
1376
1377 sprintf(buf, "%pU", uuid);
1378
1379 fake_table.data = buf;
1380 fake_table.maxlen = sizeof(buf);
1381
1382 return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1383}
1384
1385static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1386ctl_table random_table[] = {
1387 {
1388 .procname = "poolsize",
1389 .data = &sysctl_poolsize,
1390 .maxlen = sizeof(int),
1391 .mode = 0444,
1392 .proc_handler = proc_dointvec,
1393 },
1394 {
1395 .procname = "entropy_avail",
1396 .maxlen = sizeof(int),
1397 .mode = 0444,
1398 .proc_handler = proc_dointvec,
1399 .data = &input_pool.entropy_count,
1400 },
1401 {
1402 .procname = "read_wakeup_threshold",
1403 .data = &random_read_wakeup_thresh,
1404 .maxlen = sizeof(int),
1405 .mode = 0644,
1406 .proc_handler = proc_dointvec_minmax,
1407 .extra1 = &min_read_thresh,
1408 .extra2 = &max_read_thresh,
1409 },
1410 {
1411 .procname = "write_wakeup_threshold",
1412 .data = &random_write_wakeup_thresh,
1413 .maxlen = sizeof(int),
1414 .mode = 0644,
1415 .proc_handler = proc_dointvec_minmax,
1416 .extra1 = &min_write_thresh,
1417 .extra2 = &max_write_thresh,
1418 },
1419 {
1420 .procname = "boot_id",
1421 .data = &sysctl_bootid,
1422 .maxlen = 16,
1423 .mode = 0444,
1424 .proc_handler = proc_do_uuid,
1425 },
1426 {
1427 .procname = "uuid",
1428 .maxlen = 16,
1429 .mode = 0444,
1430 .proc_handler = proc_do_uuid,
1431 },
1432 { }
1433};
1434#endif /* CONFIG_SYSCTL */
1435
1436static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1437
1438static int __init random_int_secret_init(void)
1439{
1440 get_random_bytes(random_int_secret, sizeof(random_int_secret));
1441 return 0;
1442}
1443late_initcall(random_int_secret_init);
1444
1445/*
1446 * Get a random word for internal kernel use only. Similar to urandom but
1447 * with the goal of minimal entropy pool depletion. As a result, the random
1448 * value is not cryptographically secure but for several uses the cost of
1449 * depleting entropy is too high
1450 */
1451DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1452unsigned int get_random_int(void)
1453{
1454 __u32 *hash;
1455 unsigned int ret;
1456
1457 if (arch_get_random_int(&ret))
1458 return ret;
1459
1460 hash = get_cpu_var(get_random_int_hash);
1461
1462 hash[0] += current->pid + jiffies + get_cycles();
1463 md5_transform(hash, random_int_secret);
1464 ret = hash[0];
1465 put_cpu_var(get_random_int_hash);
1466
1467 return ret;
1468}
1469
1470/*
1471 * randomize_range() returns a start address such that
1472 *
1473 * [...... <range> .....]
1474 * start end
1475 *
1476 * a <range> with size "len" starting at the return value is inside in the
1477 * area defined by [start, end], but is otherwise randomized.
1478 */
1479unsigned long
1480randomize_range(unsigned long start, unsigned long end, unsigned long len)
1481{
1482 unsigned long range = end - len - start;
1483
1484 if (end <= start + len)
1485 return 0;
1486 return PAGE_ALIGN(get_random_int() % range + start);
1487}