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  */
79 static 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;
84 static 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. */
87 static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
88 static struct fasync_struct *fasync;
89 static ATOMIC_NOTIFIER_HEAD(random_ready_notifier);
90 
91 /* Control how we warn userspace. */
92 static struct ratelimit_state urandom_warning =
93 	RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE);
94 static int ratelimit_disable __read_mostly =
95 	IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
96 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
97 MODULE_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  */
rng_is_initialized(void)108 bool rng_is_initialized(void)
109 {
110 	return crng_ready();
111 }
112 EXPORT_SYMBOL(rng_is_initialized);
113 
crng_set_ready(struct work_struct * work)114 static 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. */
120 static 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  */
wait_for_random_bytes(void)132 int 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 }
144 EXPORT_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  */
execute_with_initialized_rng(struct notifier_block * nb)152 int __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 
201 enum {
202 	CRNG_RESEED_START_INTERVAL = HZ,
203 	CRNG_RESEED_INTERVAL = 60 * HZ
204 };
205 
206 static 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 
214 struct crng {
215 	u8 key[CHACHA_KEY_SIZE];
216 	unsigned long generation;
217 	local_lock_t lock;
218 };
219 
220 static 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  */
crng_reseed_interval(void)230 static 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. */
246 static void extract_entropy(void *buf, size_t len);
247 
248 /* This extracts a new crng key from the input pool. */
crng_reseed(struct work_struct * work)249 static 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  */
crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE],u32 chacha_state[CHACHA_STATE_WORDS],u8 * random_data,size_t random_data_len)294 static 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  */
crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],u8 * random_data,size_t random_data_len)317 static 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 
_get_random_bytes(void * buf,size_t len)375 static 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  */
get_random_bytes(void * buf,size_t len)414 void get_random_bytes(void *buf, size_t len)
415 {
416 	warn_unseeded_randomness();
417 	_get_random_bytes(buf, len);
418 }
419 EXPORT_SYMBOL(get_random_bytes);
420 
get_random_bytes_user(struct iov_iter * iter)421 static 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));
465 out_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)						\
478 struct 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 										\
492 static DEFINE_PER_CPU(struct batch_ ##type, batched_entropy_ ##type) = {	\
493 	.lock = INIT_LOCAL_LOCK(batched_entropy_ ##type.lock),			\
494 	.position = UINT_MAX							\
495 };										\
496 										\
497 type 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 }										\
528 EXPORT_SYMBOL(get_random_ ##type);
529 
530 DEFINE_BATCHED_ENTROPY(u8)
DEFINE_BATCHED_ENTROPY(u16)531 DEFINE_BATCHED_ENTROPY(u16)
532 DEFINE_BATCHED_ENTROPY(u32)
533 DEFINE_BATCHED_ENTROPY(u64)
534 
535 u32 __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 }
568 EXPORT_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  */
random_prepare_cpu(unsigned int cpu)575 int __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 
610 enum {
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 
616 static 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 
_mix_pool_bytes(const void * buf,size_t len)628 static 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  */
mix_pool_bytes(const void * buf,size_t len)638 static 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  */
extract_entropy(void * buf,size_t len)651 static 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 
_credit_init_bits(size_t bits)703 static 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 
797 static bool trust_cpu __initdata = true;
798 static bool trust_bootloader __initdata = true;
parse_trust_cpu(char * arg)799 static int __init parse_trust_cpu(char *arg)
800 {
801 	return kstrtobool(arg, &trust_cpu);
802 }
parse_trust_bootloader(char * arg)803 static int __init parse_trust_bootloader(char *arg)
804 {
805 	return kstrtobool(arg, &trust_bootloader);
806 }
807 early_param("random.trust_cpu", parse_trust_cpu);
808 early_param("random.trust_bootloader", parse_trust_bootloader);
809 
random_pm_notification(struct notifier_block * nb,unsigned long action,void * data)810 static 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 
835 static 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  */
random_init_early(const char * command_line)841 void __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  */
random_init(void)882 void __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  */
add_device_randomness(const void * buf,size_t len)917 void 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 }
927 EXPORT_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  */
add_hwgenerator_randomness(const void * buf,size_t len,size_t entropy,bool sleep_after)934 void 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 }
946 EXPORT_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  */
add_bootloader_randomness(const void * buf,size_t len)952 void __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)
960 static 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  */
add_vmfork_randomness(const void * unique_vm_id,size_t len)967 void __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)
977 EXPORT_SYMBOL_GPL(add_vmfork_randomness);
978 #endif
979 
register_random_vmfork_notifier(struct notifier_block * nb)980 int __cold register_random_vmfork_notifier(struct notifier_block *nb)
981 {
982 	return blocking_notifier_chain_register(&vmfork_chain, nb);
983 }
984 EXPORT_SYMBOL_GPL(register_random_vmfork_notifier);
985 
unregister_random_vmfork_notifier(struct notifier_block * nb)986 int __cold unregister_random_vmfork_notifier(struct notifier_block *nb)
987 {
988 	return blocking_notifier_chain_unregister(&vmfork_chain, nb);
989 }
990 EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier);
991 #endif
992 
993 struct fast_pool {
994 	unsigned long pool[4];
995 	unsigned long last;
996 	unsigned int count;
997 	struct timer_list mix;
998 };
999 
1000 static void mix_interrupt_randomness(struct timer_list *work);
1001 
1002 static 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  */
fast_mix(unsigned long s[4],unsigned long v1,unsigned long v2)1019 static 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  */
random_online_cpu(unsigned int cpu)1034 int __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 
mix_interrupt_randomness(struct timer_list * work)1052 static 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 
add_interrupt_randomness(int irq)1088 void 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 }
1112 EXPORT_SYMBOL_GPL(add_interrupt_randomness);
1113 
1114 /* There is one of these per entropy source */
1115 struct 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  */
add_timer_randomness(struct timer_rand_state * state,unsigned int num)1127 static 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 
add_input_randomness(unsigned int type,unsigned int code,unsigned int value)1193 void 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 }
1206 EXPORT_SYMBOL_GPL(add_input_randomness);
1207 
1208 #ifdef CONFIG_BLOCK
add_disk_randomness(struct gendisk * disk)1209 void 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 }
1216 EXPORT_SYMBOL_GPL(add_disk_randomness);
1217 
rand_initialize_disk(struct gendisk * disk)1218 void __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 
1234 struct 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  */
entropy_timer(struct timer_list * timer)1252 static 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  */
try_to_generate_entropy(void)1266 static 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 
SYSCALL_DEFINE3(getrandom,char __user *,ubuf,size_t,len,unsigned int,flags)1364 SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
1365 {
1366 	struct iov_iter iter;
1367 	struct iovec iov;
1368 	int ret;
1369 
1370 	if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
1371 		return -EINVAL;
1372 
1373 	/*
1374 	 * Requesting insecure and blocking randomness at the same time makes
1375 	 * no sense.
1376 	 */
1377 	if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
1378 		return -EINVAL;
1379 
1380 	if (!crng_ready() && !(flags & GRND_INSECURE)) {
1381 		if (flags & GRND_NONBLOCK)
1382 			return -EAGAIN;
1383 		ret = wait_for_random_bytes();
1384 		if (unlikely(ret))
1385 			return ret;
1386 	}
1387 
1388 	ret = import_single_range(ITER_DEST, ubuf, len, &iov, &iter);
1389 	if (unlikely(ret))
1390 		return ret;
1391 	return get_random_bytes_user(&iter);
1392 }
1393 
random_poll(struct file * file,poll_table * wait)1394 static __poll_t random_poll(struct file *file, poll_table *wait)
1395 {
1396 	poll_wait(file, &crng_init_wait, wait);
1397 	return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
1398 }
1399 
write_pool_user(struct iov_iter * iter)1400 static ssize_t write_pool_user(struct iov_iter *iter)
1401 {
1402 	u8 block[BLAKE2S_BLOCK_SIZE];
1403 	ssize_t ret = 0;
1404 	size_t copied;
1405 
1406 	if (unlikely(!iov_iter_count(iter)))
1407 		return 0;
1408 
1409 	for (;;) {
1410 		copied = copy_from_iter(block, sizeof(block), iter);
1411 		ret += copied;
1412 		mix_pool_bytes(block, copied);
1413 		if (!iov_iter_count(iter) || copied != sizeof(block))
1414 			break;
1415 
1416 		BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
1417 		if (ret % PAGE_SIZE == 0) {
1418 			if (signal_pending(current))
1419 				break;
1420 			cond_resched();
1421 		}
1422 	}
1423 
1424 	memzero_explicit(block, sizeof(block));
1425 	return ret ? ret : -EFAULT;
1426 }
1427 
random_write_iter(struct kiocb * kiocb,struct iov_iter * iter)1428 static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter)
1429 {
1430 	return write_pool_user(iter);
1431 }
1432 
urandom_read_iter(struct kiocb * kiocb,struct iov_iter * iter)1433 static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1434 {
1435 	static int maxwarn = 10;
1436 
1437 	/*
1438 	 * Opportunistically attempt to initialize the RNG on platforms that
1439 	 * have fast cycle counters, but don't (for now) require it to succeed.
1440 	 */
1441 	if (!crng_ready())
1442 		try_to_generate_entropy();
1443 
1444 	if (!crng_ready()) {
1445 		if (!ratelimit_disable && maxwarn <= 0)
1446 			++urandom_warning.missed;
1447 		else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
1448 			--maxwarn;
1449 			pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
1450 				  current->comm, iov_iter_count(iter));
1451 		}
1452 	}
1453 
1454 	return get_random_bytes_user(iter);
1455 }
1456 
random_read_iter(struct kiocb * kiocb,struct iov_iter * iter)1457 static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1458 {
1459 	int ret;
1460 
1461 	if (!crng_ready() &&
1462 	    ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
1463 	     (kiocb->ki_filp->f_flags & O_NONBLOCK)))
1464 		return -EAGAIN;
1465 
1466 	ret = wait_for_random_bytes();
1467 	if (ret != 0)
1468 		return ret;
1469 	return get_random_bytes_user(iter);
1470 }
1471 
random_ioctl(struct file * f,unsigned int cmd,unsigned long arg)1472 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1473 {
1474 	int __user *p = (int __user *)arg;
1475 	int ent_count;
1476 
1477 	switch (cmd) {
1478 	case RNDGETENTCNT:
1479 		/* Inherently racy, no point locking. */
1480 		if (put_user(input_pool.init_bits, p))
1481 			return -EFAULT;
1482 		return 0;
1483 	case RNDADDTOENTCNT:
1484 		if (!capable(CAP_SYS_ADMIN))
1485 			return -EPERM;
1486 		if (get_user(ent_count, p))
1487 			return -EFAULT;
1488 		if (ent_count < 0)
1489 			return -EINVAL;
1490 		credit_init_bits(ent_count);
1491 		return 0;
1492 	case RNDADDENTROPY: {
1493 		struct iov_iter iter;
1494 		struct iovec iov;
1495 		ssize_t ret;
1496 		int len;
1497 
1498 		if (!capable(CAP_SYS_ADMIN))
1499 			return -EPERM;
1500 		if (get_user(ent_count, p++))
1501 			return -EFAULT;
1502 		if (ent_count < 0)
1503 			return -EINVAL;
1504 		if (get_user(len, p++))
1505 			return -EFAULT;
1506 		ret = import_single_range(ITER_SOURCE, p, len, &iov, &iter);
1507 		if (unlikely(ret))
1508 			return ret;
1509 		ret = write_pool_user(&iter);
1510 		if (unlikely(ret < 0))
1511 			return ret;
1512 		/* Since we're crediting, enforce that it was all written into the pool. */
1513 		if (unlikely(ret != len))
1514 			return -EFAULT;
1515 		credit_init_bits(ent_count);
1516 		return 0;
1517 	}
1518 	case RNDZAPENTCNT:
1519 	case RNDCLEARPOOL:
1520 		/* No longer has any effect. */
1521 		if (!capable(CAP_SYS_ADMIN))
1522 			return -EPERM;
1523 		return 0;
1524 	case RNDRESEEDCRNG:
1525 		if (!capable(CAP_SYS_ADMIN))
1526 			return -EPERM;
1527 		if (!crng_ready())
1528 			return -ENODATA;
1529 		crng_reseed(NULL);
1530 		return 0;
1531 	default:
1532 		return -EINVAL;
1533 	}
1534 }
1535 
random_fasync(int fd,struct file * filp,int on)1536 static int random_fasync(int fd, struct file *filp, int on)
1537 {
1538 	return fasync_helper(fd, filp, on, &fasync);
1539 }
1540 
1541 const struct file_operations random_fops = {
1542 	.read_iter = random_read_iter,
1543 	.write_iter = random_write_iter,
1544 	.poll = random_poll,
1545 	.unlocked_ioctl = random_ioctl,
1546 	.compat_ioctl = compat_ptr_ioctl,
1547 	.fasync = random_fasync,
1548 	.llseek = noop_llseek,
1549 	.splice_read = copy_splice_read,
1550 	.splice_write = iter_file_splice_write,
1551 };
1552 
1553 const struct file_operations urandom_fops = {
1554 	.read_iter = urandom_read_iter,
1555 	.write_iter = random_write_iter,
1556 	.unlocked_ioctl = random_ioctl,
1557 	.compat_ioctl = compat_ptr_ioctl,
1558 	.fasync = random_fasync,
1559 	.llseek = noop_llseek,
1560 	.splice_read = copy_splice_read,
1561 	.splice_write = iter_file_splice_write,
1562 };
1563 
1564 
1565 /********************************************************************
1566  *
1567  * Sysctl interface.
1568  *
1569  * These are partly unused legacy knobs with dummy values to not break
1570  * userspace and partly still useful things. They are usually accessible
1571  * in /proc/sys/kernel/random/ and are as follows:
1572  *
1573  * - boot_id - a UUID representing the current boot.
1574  *
1575  * - uuid - a random UUID, different each time the file is read.
1576  *
1577  * - poolsize - the number of bits of entropy that the input pool can
1578  *   hold, tied to the POOL_BITS constant.
1579  *
1580  * - entropy_avail - the number of bits of entropy currently in the
1581  *   input pool. Always <= poolsize.
1582  *
1583  * - write_wakeup_threshold - the amount of entropy in the input pool
1584  *   below which write polls to /dev/random will unblock, requesting
1585  *   more entropy, tied to the POOL_READY_BITS constant. It is writable
1586  *   to avoid breaking old userspaces, but writing to it does not
1587  *   change any behavior of the RNG.
1588  *
1589  * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL.
1590  *   It is writable to avoid breaking old userspaces, but writing
1591  *   to it does not change any behavior of the RNG.
1592  *
1593  ********************************************************************/
1594 
1595 #ifdef CONFIG_SYSCTL
1596 
1597 #include <linux/sysctl.h>
1598 
1599 static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ;
1600 static int sysctl_random_write_wakeup_bits = POOL_READY_BITS;
1601 static int sysctl_poolsize = POOL_BITS;
1602 static u8 sysctl_bootid[UUID_SIZE];
1603 
1604 /*
1605  * This function is used to return both the bootid UUID, and random
1606  * UUID. The difference is in whether table->data is NULL; if it is,
1607  * then a new UUID is generated and returned to the user.
1608  */
proc_do_uuid(struct ctl_table * table,int write,void * buf,size_t * lenp,loff_t * ppos)1609 static int proc_do_uuid(struct ctl_table *table, int write, void *buf,
1610 			size_t *lenp, loff_t *ppos)
1611 {
1612 	u8 tmp_uuid[UUID_SIZE], *uuid;
1613 	char uuid_string[UUID_STRING_LEN + 1];
1614 	struct ctl_table fake_table = {
1615 		.data = uuid_string,
1616 		.maxlen = UUID_STRING_LEN
1617 	};
1618 
1619 	if (write)
1620 		return -EPERM;
1621 
1622 	uuid = table->data;
1623 	if (!uuid) {
1624 		uuid = tmp_uuid;
1625 		generate_random_uuid(uuid);
1626 	} else {
1627 		static DEFINE_SPINLOCK(bootid_spinlock);
1628 
1629 		spin_lock(&bootid_spinlock);
1630 		if (!uuid[8])
1631 			generate_random_uuid(uuid);
1632 		spin_unlock(&bootid_spinlock);
1633 	}
1634 
1635 	snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
1636 	return proc_dostring(&fake_table, 0, buf, lenp, ppos);
1637 }
1638 
1639 /* The same as proc_dointvec, but writes don't change anything. */
proc_do_rointvec(struct ctl_table * table,int write,void * buf,size_t * lenp,loff_t * ppos)1640 static int proc_do_rointvec(struct ctl_table *table, int write, void *buf,
1641 			    size_t *lenp, loff_t *ppos)
1642 {
1643 	return write ? 0 : proc_dointvec(table, 0, buf, lenp, ppos);
1644 }
1645 
1646 static struct ctl_table random_table[] = {
1647 	{
1648 		.procname	= "poolsize",
1649 		.data		= &sysctl_poolsize,
1650 		.maxlen		= sizeof(int),
1651 		.mode		= 0444,
1652 		.proc_handler	= proc_dointvec,
1653 	},
1654 	{
1655 		.procname	= "entropy_avail",
1656 		.data		= &input_pool.init_bits,
1657 		.maxlen		= sizeof(int),
1658 		.mode		= 0444,
1659 		.proc_handler	= proc_dointvec,
1660 	},
1661 	{
1662 		.procname	= "write_wakeup_threshold",
1663 		.data		= &sysctl_random_write_wakeup_bits,
1664 		.maxlen		= sizeof(int),
1665 		.mode		= 0644,
1666 		.proc_handler	= proc_do_rointvec,
1667 	},
1668 	{
1669 		.procname	= "urandom_min_reseed_secs",
1670 		.data		= &sysctl_random_min_urandom_seed,
1671 		.maxlen		= sizeof(int),
1672 		.mode		= 0644,
1673 		.proc_handler	= proc_do_rointvec,
1674 	},
1675 	{
1676 		.procname	= "boot_id",
1677 		.data		= &sysctl_bootid,
1678 		.mode		= 0444,
1679 		.proc_handler	= proc_do_uuid,
1680 	},
1681 	{
1682 		.procname	= "uuid",
1683 		.mode		= 0444,
1684 		.proc_handler	= proc_do_uuid,
1685 	},
1686 	{ }
1687 };
1688 
1689 /*
1690  * random_init() is called before sysctl_init(),
1691  * so we cannot call register_sysctl_init() in random_init()
1692  */
random_sysctls_init(void)1693 static int __init random_sysctls_init(void)
1694 {
1695 	register_sysctl_init("kernel/random", random_table);
1696 	return 0;
1697 }
1698 device_initcall(random_sysctls_init);
1699 #endif
1700