Line data Source code
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 : */
108 0 : bool rng_is_initialized(void)
109 : {
110 0 : return crng_ready();
111 : }
112 : EXPORT_SYMBOL(rng_is_initialized);
113 :
114 0 : static void __cold crng_set_ready(struct work_struct *work)
115 : {
116 1 : static_branch_enable(&crng_is_ready);
117 0 : }
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 : */
132 0 : int wait_for_random_bytes(void)
133 : {
134 0 : while (!crng_ready()) {
135 : int ret;
136 :
137 0 : try_to_generate_entropy();
138 0 : ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
139 0 : if (ret)
140 0 : 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 : */
152 1 : int __cold execute_with_initialized_rng(struct notifier_block *nb)
153 : {
154 : unsigned long flags;
155 1 : int ret = 0;
156 :
157 1 : spin_lock_irqsave(&random_ready_notifier.lock, flags);
158 1 : if (crng_ready())
159 1 : nb->notifier_call(nb, 0, NULL);
160 : else
161 0 : ret = raw_notifier_chain_register((struct raw_notifier_head *)&random_ready_notifier.head, nb);
162 1 : spin_unlock_irqrestore(&random_ready_notifier.lock, flags);
163 1 : 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 : */
230 10 : static unsigned int crng_reseed_interval(void)
231 : {
232 : static bool early_boot = true;
233 :
234 10 : if (unlikely(READ_ONCE(early_boot))) {
235 10 : time64_t uptime = ktime_get_seconds();
236 10 : if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2)
237 0 : WRITE_ONCE(early_boot, false);
238 : else
239 10 : 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. */
249 12 : 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 12 : if (likely(system_unbound_wq))
258 10 : queue_delayed_work(system_unbound_wq, &next_reseed, crng_reseed_interval());
259 :
260 12 : 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 12 : spin_lock_irqsave(&base_crng.lock, flags);
269 12 : memcpy(base_crng.key, key, sizeof(base_crng.key));
270 12 : next_gen = base_crng.generation + 1;
271 12 : if (next_gen == ULONG_MAX)
272 0 : ++next_gen;
273 12 : WRITE_ONCE(base_crng.generation, next_gen);
274 12 : if (!static_branch_likely(&crng_is_ready))
275 2 : crng_init = CRNG_READY;
276 12 : spin_unlock_irqrestore(&base_crng.lock, flags);
277 12 : memzero_explicit(key, sizeof(key));
278 12 : }
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 : */
294 69 : 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 69 : BUG_ON(random_data_len > 32);
301 :
302 69 : chacha_init_consts(chacha_state);
303 69 : memcpy(&chacha_state[4], key, CHACHA_KEY_SIZE);
304 69 : memset(&chacha_state[12], 0, sizeof(u32) * 4);
305 69 : chacha20_block(chacha_state, first_block);
306 :
307 69 : memcpy(key, first_block, CHACHA_KEY_SIZE);
308 69 : memcpy(random_data, first_block + CHACHA_KEY_SIZE, random_data_len);
309 69 : memzero_explicit(first_block, sizeof(first_block));
310 69 : }
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 : */
317 68 : 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 68 : 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 68 : if (!crng_ready()) {
332 : bool ready;
333 :
334 0 : spin_lock_irqsave(&base_crng.lock, flags);
335 0 : ready = crng_ready();
336 0 : if (!ready) {
337 0 : if (crng_init == CRNG_EMPTY)
338 0 : extract_entropy(base_crng.key, sizeof(base_crng.key));
339 0 : crng_fast_key_erasure(base_crng.key, chacha_state,
340 : random_data, random_data_len);
341 : }
342 0 : spin_unlock_irqrestore(&base_crng.lock, flags);
343 0 : if (!ready)
344 : return;
345 : }
346 :
347 68 : local_lock_irqsave(&crngs.lock, flags);
348 68 : 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 68 : if (unlikely(crng->generation != READ_ONCE(base_crng.generation))) {
357 1 : spin_lock(&base_crng.lock);
358 1 : crng_fast_key_erasure(base_crng.key, chacha_state,
359 : crng->key, sizeof(crng->key));
360 1 : 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 68 : crng_fast_key_erasure(crng->key, chacha_state, random_data, random_data_len);
372 68 : local_unlock_irqrestore(&crngs.lock, flags);
373 : }
374 :
375 68 : 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 68 : if (!len)
382 0 : return;
383 :
384 68 : first_block_len = min_t(size_t, 32, len);
385 68 : crng_make_state(chacha_state, buf, first_block_len);
386 68 : len -= first_block_len;
387 68 : buf += first_block_len;
388 :
389 202 : while (len) {
390 131 : if (len < CHACHA_BLOCK_SIZE) {
391 65 : chacha20_block(chacha_state, tmp);
392 65 : memcpy(buf, tmp, len);
393 : memzero_explicit(tmp, sizeof(tmp));
394 : break;
395 : }
396 :
397 66 : chacha20_block(chacha_state, buf);
398 66 : if (unlikely(chacha_state[12] == 0))
399 0 : ++chacha_state[13];
400 66 : len -= CHACHA_BLOCK_SIZE;
401 66 : buf += CHACHA_BLOCK_SIZE;
402 : }
403 :
404 68 : 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 : */
414 67 : void get_random_bytes(void *buf, size_t len)
415 : {
416 : warn_unseeded_randomness();
417 67 : _get_random_bytes(buf, len);
418 67 : }
419 : EXPORT_SYMBOL(get_random_bytes);
420 :
421 0 : 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 0 : size_t ret = 0, copied;
426 :
427 0 : 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 0 : 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 0 : if (iov_iter_count(iter) <= CHACHA_KEY_SIZE) {
442 0 : ret = copy_to_iter(&chacha_state[4], CHACHA_KEY_SIZE, iter);
443 0 : goto out_zero_chacha;
444 : }
445 :
446 : for (;;) {
447 0 : chacha20_block(chacha_state, block);
448 0 : if (unlikely(chacha_state[12] == 0))
449 0 : ++chacha_state[13];
450 :
451 0 : copied = copy_to_iter(block, sizeof(block), iter);
452 0 : ret += copied;
453 0 : if (!iov_iter_count(iter) || copied != sizeof(block))
454 : break;
455 :
456 : BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
457 0 : if (ret % PAGE_SIZE == 0) {
458 0 : if (signal_pending(current))
459 : break;
460 0 : cond_resched();
461 : }
462 : }
463 :
464 : memzero_explicit(block, sizeof(block));
465 : out_zero_chacha:
466 0 : memzero_explicit(chacha_state, sizeof(chacha_state));
467 0 : 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 0 : DEFINE_BATCHED_ENTROPY(u8)
531 0 : DEFINE_BATCHED_ENTROPY(u16)
532 12 : DEFINE_BATCHED_ENTROPY(u32)
533 0 : DEFINE_BATCHED_ENTROPY(u64)
534 :
535 0 : 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 0 : 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 0 : if (unlikely(!ceil))
558 : return rand;
559 :
560 0 : mult = (u64)ceil * rand;
561 0 : if (unlikely((u32)mult < ceil)) {
562 0 : u32 bound = -ceil % ceil;
563 0 : while (unlikely((u32)mult < bound))
564 0 : mult = (u64)ceil * get_random_u32();
565 : }
566 0 : 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 : */
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 :
628 : static void _mix_pool_bytes(const void *buf, size_t len)
629 : {
630 1891 : 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 : */
638 30 : static void mix_pool_bytes(const void *buf, size_t len)
639 : {
640 : unsigned long flags;
641 :
642 30 : spin_lock_irqsave(&input_pool.lock, flags);
643 30 : _mix_pool_bytes(buf, len);
644 30 : spin_unlock_irqrestore(&input_pool.lock, flags);
645 30 : }
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 : */
651 12 : 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 36 : for (i = 0; i < ARRAY_SIZE(block.rdseed);) {
662 12 : longs = arch_get_random_seed_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
663 : if (longs) {
664 : i += longs;
665 : continue;
666 : }
667 24 : longs = arch_get_random_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
668 12 : if (longs) {
669 12 : i += longs;
670 12 : continue;
671 : }
672 0 : block.rdseed[i++] = random_get_entropy();
673 : }
674 :
675 12 : spin_lock_irqsave(&input_pool.lock, flags);
676 :
677 : /* seed = HASHPRF(last_key, entropy_input) */
678 12 : blake2s_final(&input_pool.hash, seed);
679 :
680 : /* next_key = HASHPRF(seed, RDSEED || 0) */
681 12 : block.counter = 0;
682 12 : blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
683 12 : blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
684 :
685 12 : spin_unlock_irqrestore(&input_pool.lock, flags);
686 : memzero_explicit(next_key, sizeof(next_key));
687 :
688 24 : while (len) {
689 12 : i = min_t(size_t, len, BLAKE2S_HASH_SIZE);
690 : /* output = HASHPRF(seed, RDSEED || ++counter) */
691 12 : ++block.counter;
692 12 : blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
693 12 : len -= i;
694 12 : buf += i;
695 : }
696 :
697 12 : memzero_explicit(seed, sizeof(seed));
698 12 : memzero_explicit(&block, sizeof(block));
699 12 : }
700 :
701 : #define credit_init_bits(bits) if (!crng_ready()) _credit_init_bits(bits)
702 :
703 1 : 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 1 : if (!bits)
710 : return;
711 :
712 1 : add = min_t(size_t, bits, POOL_BITS);
713 :
714 1 : orig = READ_ONCE(input_pool.init_bits);
715 : do {
716 1 : new = min_t(unsigned int, POOL_BITS, orig + add);
717 3 : } while (!try_cmpxchg(&input_pool.init_bits, &orig, new));
718 :
719 1 : if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
720 1 : crng_reseed(NULL); /* Sets crng_init to CRNG_READY under base_crng.lock. */
721 1 : if (static_key_initialized)
722 0 : execute_in_process_context(crng_set_ready, &set_ready);
723 1 : atomic_notifier_call_chain(&random_ready_notifier, 0, NULL);
724 1 : wake_up_interruptible(&crng_init_wait);
725 1 : kill_fasync(&fasync, SIGIO, POLL_IN);
726 1 : pr_notice("crng init done\n");
727 1 : if (urandom_warning.missed)
728 0 : pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
729 : urandom_warning.missed);
730 0 : } else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
731 0 : spin_lock_irqsave(&base_crng.lock, flags);
732 : /* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */
733 0 : if (crng_init == CRNG_EMPTY) {
734 0 : extract_entropy(base_crng.key, sizeof(base_crng.key));
735 0 : 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;
799 0 : static int __init parse_trust_cpu(char *arg)
800 : {
801 0 : return kstrtobool(arg, &trust_cpu);
802 : }
803 0 : static int __init parse_trust_bootloader(char *arg)
804 : {
805 0 : 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 :
810 0 : static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data)
811 : {
812 0 : 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 0 : ktime_t stamps[] = { ktime_get(), ktime_get_boottime(), ktime_get_real() };
819 :
820 0 : spin_lock_irqsave(&input_pool.lock, flags);
821 0 : _mix_pool_bytes(&action, sizeof(action));
822 0 : _mix_pool_bytes(stamps, sizeof(stamps));
823 0 : _mix_pool_bytes(&entropy, sizeof(entropy));
824 0 : spin_unlock_irqrestore(&input_pool.lock, flags);
825 :
826 0 : 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 0 : crng_reseed(NULL);
830 0 : pr_notice("crng reseeded on system resumption\n");
831 : }
832 0 : 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 : */
841 1 : 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 3 : for (i = 0, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) {
852 1 : 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 2 : longs = arch_get_random_longs(entropy, ARRAY_SIZE(entropy) - i);
859 1 : if (longs) {
860 2 : _mix_pool_bytes(entropy, sizeof(*entropy) * longs);
861 1 : i += longs;
862 1 : continue;
863 : }
864 0 : arch_bits -= sizeof(*entropy) * 8;
865 0 : ++i;
866 : }
867 :
868 2 : _mix_pool_bytes(init_utsname(), sizeof(*(init_utsname())));
869 2 : _mix_pool_bytes(command_line, strlen(command_line));
870 :
871 : /* Reseed if already seeded by earlier phases. */
872 1 : if (crng_ready())
873 1 : crng_reseed(NULL);
874 0 : else if (trust_cpu)
875 0 : _credit_init_bits(arch_bits);
876 1 : }
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 : */
882 1 : void __init random_init(void)
883 : {
884 1 : unsigned long entropy = random_get_entropy();
885 1 : ktime_t now = ktime_get_real();
886 :
887 1 : _mix_pool_bytes(&now, sizeof(now));
888 1 : _mix_pool_bytes(&entropy, sizeof(entropy));
889 1 : 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 1 : 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 1 : if (crng_ready())
901 1 : crng_reseed(NULL);
902 :
903 1 : WARN_ON(register_pm_notifier(&pm_notifier));
904 :
905 1 : WARN(!entropy, "Missing cycle counter and fallback timer; RNG "
906 : "entropy collection will consequently suffer.");
907 1 : }
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 : */
917 928 : void add_device_randomness(const void *buf, size_t len)
918 : {
919 928 : unsigned long entropy = random_get_entropy();
920 : unsigned long flags;
921 :
922 928 : spin_lock_irqsave(&input_pool.lock, flags);
923 928 : _mix_pool_bytes(&entropy, sizeof(entropy));
924 928 : _mix_pool_bytes(buf, len);
925 928 : spin_unlock_irqrestore(&input_pool.lock, flags);
926 928 : }
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 : */
934 0 : void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy, bool sleep_after)
935 : {
936 0 : mix_pool_bytes(buf, len);
937 0 : 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 0 : if (sleep_after && !kthread_should_stop() && (crng_ready() || !entropy))
944 0 : schedule_timeout_interruptible(crng_reseed_interval());
945 0 : }
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 : */
952 1 : void __init add_bootloader_randomness(const void *buf, size_t len)
953 : {
954 1 : mix_pool_bytes(buf, len);
955 1 : if (trust_bootloader)
956 1 : credit_init_bits(len * 8);
957 1 : }
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 : */
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 :
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 :
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 : */
1019 2943 : static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long v2)
1020 : {
1021 2943 : s[3] ^= v1;
1022 20601 : FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1023 2943 : s[0] ^= v1;
1024 2943 : s[3] ^= v2;
1025 20601 : FASTMIX_PERM(s[0], s[1], s[2], s[3]);
1026 2943 : s[0] ^= v2;
1027 2943 : }
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 : */
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 :
1052 29 : static void mix_interrupt_randomness(struct timer_list *work)
1053 : {
1054 29 : 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 29 : if (fast_pool != this_cpu_ptr(&irq_randomness)) {
1068 : local_irq_enable();
1069 0 : 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 29 : memcpy(pool, fast_pool->pool, sizeof(pool));
1077 29 : count = fast_pool->count;
1078 29 : fast_pool->count = 0;
1079 29 : fast_pool->last = jiffies;
1080 : local_irq_enable();
1081 :
1082 29 : mix_pool_bytes(pool, sizeof(pool));
1083 29 : credit_init_bits(clamp_t(unsigned int, (count & U16_MAX) / 64, 1, sizeof(pool) * 8));
1084 :
1085 29 : memzero_explicit(pool, sizeof(pool));
1086 : }
1087 :
1088 2943 : void add_interrupt_randomness(int irq)
1089 : {
1090 : enum { MIX_INFLIGHT = 1U << 31 };
1091 2943 : unsigned long entropy = random_get_entropy();
1092 2943 : struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
1093 2943 : struct pt_regs *regs = get_irq_regs();
1094 : unsigned int new_count;
1095 :
1096 2943 : fast_mix(fast_pool->pool, entropy,
1097 5886 : (regs ? instruction_pointer(regs) : _RET_IP_) ^ swab(irq));
1098 2943 : new_count = ++fast_pool->count;
1099 :
1100 2943 : if (new_count & MIX_INFLIGHT)
1101 : return;
1102 :
1103 2914 : if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ))
1104 : return;
1105 :
1106 29 : fast_pool->count |= MIX_INFLIGHT;
1107 58 : if (!timer_pending(&fast_pool->mix)) {
1108 29 : fast_pool->mix.expires = jiffies;
1109 29 : 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 : */
1127 0 : static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
1128 : {
1129 0 : 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 0 : if (in_hardirq()) {
1138 0 : fast_mix(this_cpu_ptr(&irq_randomness)->pool, entropy, num);
1139 : } else {
1140 0 : spin_lock_irqsave(&input_pool.lock, flags);
1141 0 : _mix_pool_bytes(&entropy, sizeof(entropy));
1142 0 : _mix_pool_bytes(&num, sizeof(num));
1143 : spin_unlock_irqrestore(&input_pool.lock, flags);
1144 : }
1145 :
1146 0 : if (crng_ready())
1147 0 : 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 0 : delta = now - READ_ONCE(state->last_time);
1155 0 : WRITE_ONCE(state->last_time, now);
1156 :
1157 0 : delta2 = delta - READ_ONCE(state->last_delta);
1158 0 : WRITE_ONCE(state->last_delta, delta);
1159 :
1160 0 : delta3 = delta2 - READ_ONCE(state->last_delta2);
1161 0 : WRITE_ONCE(state->last_delta2, delta2);
1162 :
1163 0 : if (delta < 0)
1164 0 : delta = -delta;
1165 0 : if (delta2 < 0)
1166 0 : delta2 = -delta2;
1167 0 : if (delta3 < 0)
1168 0 : delta3 = -delta3;
1169 0 : if (delta > delta2)
1170 0 : delta = delta2;
1171 0 : if (delta > delta3)
1172 0 : 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 0 : 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 0 : if (in_hardirq())
1188 0 : this_cpu_ptr(&irq_randomness)->count += max(1u, bits * 64) - 1;
1189 : else
1190 0 : _credit_init_bits(bits);
1191 : }
1192 :
1193 0 : 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 0 : if (value == last_value)
1200 : return;
1201 :
1202 0 : last_value = value;
1203 0 : add_timer_randomness(&input_timer_state,
1204 0 : (type << 4) ^ code ^ (code >> 4) ^ value);
1205 : }
1206 : EXPORT_SYMBOL_GPL(add_input_randomness);
1207 :
1208 : #ifdef CONFIG_BLOCK
1209 0 : void add_disk_randomness(struct gendisk *disk)
1210 : {
1211 0 : if (!disk || !disk->random)
1212 : return;
1213 : /* First major is 1, so we get >= 0x200 here. */
1214 0 : add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
1215 : }
1216 : EXPORT_SYMBOL_GPL(add_disk_randomness);
1217 :
1218 0 : 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 0 : state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1227 0 : if (state) {
1228 0 : state->last_time = INITIAL_JIFFIES;
1229 0 : disk->random = state;
1230 : }
1231 0 : }
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 : */
1252 0 : static void __cold entropy_timer(struct timer_list *timer)
1253 : {
1254 0 : struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer);
1255 0 : unsigned long entropy = random_get_entropy();
1256 :
1257 0 : mix_pool_bytes(&entropy, sizeof(entropy));
1258 0 : if (atomic_inc_return(&state->samples) % state->samples_per_bit == 0)
1259 0 : credit_init_bits(1);
1260 0 : }
1261 :
1262 : /*
1263 : * If we have an actual cycle counter, see if we can generate enough entropy
1264 : * with timing noise.
1265 : */
1266 0 : 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 0 : struct entropy_timer_state *stack = PTR_ALIGN((void *)stack_bytes, SMP_CACHE_BYTES);
1271 0 : unsigned int i, num_different = 0;
1272 0 : unsigned long last = random_get_entropy();
1273 0 : int cpu = -1;
1274 :
1275 0 : for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
1276 0 : stack->entropy = random_get_entropy();
1277 0 : if (stack->entropy != last)
1278 0 : ++num_different;
1279 0 : last = stack->entropy;
1280 : }
1281 0 : stack->samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1);
1282 0 : if (stack->samples_per_bit > MAX_SAMPLES_PER_BIT)
1283 0 : return;
1284 :
1285 0 : atomic_set(&stack->samples, 0);
1286 0 : timer_setup_on_stack(&stack->timer, entropy_timer, 0);
1287 0 : 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 0 : 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 0 : preempt_disable();
1301 :
1302 : /* Only schedule callbacks on timer CPUs that are online. */
1303 0 : cpumask_and(&timer_cpus, housekeeping_cpumask(HK_TYPE_TIMER), cpu_online_mask);
1304 0 : num_cpus = cpumask_weight(&timer_cpus);
1305 : /* In very bizarre case of misconfiguration, fallback to all online. */
1306 0 : if (unlikely(num_cpus == 0)) {
1307 0 : timer_cpus = *cpu_online_mask;
1308 0 : num_cpus = cpumask_weight(&timer_cpus);
1309 : }
1310 :
1311 : /* Basic CPU round-robin, which avoids the current CPU. */
1312 : do {
1313 0 : cpu = cpumask_next(cpu, &timer_cpus);
1314 0 : if (cpu >= nr_cpu_ids)
1315 0 : cpu = cpumask_first(&timer_cpus);
1316 0 : } while (cpu == smp_processor_id() && num_cpus > 1);
1317 :
1318 : /* Expiring the timer at `jiffies` means it's the next tick. */
1319 0 : stack->timer.expires = jiffies;
1320 :
1321 0 : add_timer_on(&stack->timer, cpu);
1322 :
1323 0 : preempt_enable();
1324 : }
1325 0 : mix_pool_bytes(&stack->entropy, sizeof(stack->entropy));
1326 0 : schedule();
1327 0 : stack->entropy = random_get_entropy();
1328 : }
1329 0 : mix_pool_bytes(&stack->entropy, sizeof(stack->entropy));
1330 :
1331 0 : del_timer_sync(&stack->timer);
1332 0 : 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 :
1364 0 : 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 0 : 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 0 : if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
1378 : return -EINVAL;
1379 :
1380 0 : if (!crng_ready() && !(flags & GRND_INSECURE)) {
1381 0 : if (flags & GRND_NONBLOCK)
1382 : return -EAGAIN;
1383 0 : ret = wait_for_random_bytes();
1384 0 : if (unlikely(ret))
1385 0 : return ret;
1386 : }
1387 :
1388 0 : ret = import_single_range(ITER_DEST, ubuf, len, &iov, &iter);
1389 0 : if (unlikely(ret))
1390 0 : return ret;
1391 0 : return get_random_bytes_user(&iter);
1392 : }
1393 :
1394 0 : static __poll_t random_poll(struct file *file, poll_table *wait)
1395 : {
1396 0 : poll_wait(file, &crng_init_wait, wait);
1397 0 : return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
1398 : }
1399 :
1400 0 : static ssize_t write_pool_user(struct iov_iter *iter)
1401 : {
1402 : u8 block[BLAKE2S_BLOCK_SIZE];
1403 0 : ssize_t ret = 0;
1404 : size_t copied;
1405 :
1406 0 : if (unlikely(!iov_iter_count(iter)))
1407 : return 0;
1408 :
1409 : for (;;) {
1410 0 : copied = copy_from_iter(block, sizeof(block), iter);
1411 0 : ret += copied;
1412 0 : mix_pool_bytes(block, copied);
1413 0 : if (!iov_iter_count(iter) || copied != sizeof(block))
1414 : break;
1415 :
1416 : BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
1417 0 : if (ret % PAGE_SIZE == 0) {
1418 0 : if (signal_pending(current))
1419 : break;
1420 0 : cond_resched();
1421 : }
1422 : }
1423 :
1424 0 : memzero_explicit(block, sizeof(block));
1425 0 : return ret ? ret : -EFAULT;
1426 : }
1427 :
1428 0 : static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter)
1429 : {
1430 0 : return write_pool_user(iter);
1431 : }
1432 :
1433 0 : 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 0 : if (!crng_ready())
1442 0 : try_to_generate_entropy();
1443 :
1444 0 : if (!crng_ready()) {
1445 0 : if (!ratelimit_disable && maxwarn <= 0)
1446 0 : ++urandom_warning.missed;
1447 0 : else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
1448 0 : --maxwarn;
1449 0 : pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
1450 : current->comm, iov_iter_count(iter));
1451 : }
1452 : }
1453 :
1454 0 : return get_random_bytes_user(iter);
1455 : }
1456 :
1457 0 : static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
1458 : {
1459 : int ret;
1460 :
1461 0 : if (!crng_ready() &&
1462 0 : ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
1463 0 : (kiocb->ki_filp->f_flags & O_NONBLOCK)))
1464 : return -EAGAIN;
1465 :
1466 0 : ret = wait_for_random_bytes();
1467 0 : if (ret != 0)
1468 0 : return ret;
1469 0 : return get_random_bytes_user(iter);
1470 : }
1471 :
1472 0 : static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1473 : {
1474 0 : int __user *p = (int __user *)arg;
1475 : int ent_count;
1476 :
1477 0 : switch (cmd) {
1478 : case RNDGETENTCNT:
1479 : /* Inherently racy, no point locking. */
1480 0 : if (put_user(input_pool.init_bits, p))
1481 : return -EFAULT;
1482 0 : return 0;
1483 : case RNDADDTOENTCNT:
1484 0 : if (!capable(CAP_SYS_ADMIN))
1485 : return -EPERM;
1486 0 : if (get_user(ent_count, p))
1487 : return -EFAULT;
1488 0 : if (ent_count < 0)
1489 : return -EINVAL;
1490 0 : 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 0 : if (!capable(CAP_SYS_ADMIN))
1499 : return -EPERM;
1500 0 : if (get_user(ent_count, p++))
1501 : return -EFAULT;
1502 0 : if (ent_count < 0)
1503 : return -EINVAL;
1504 0 : if (get_user(len, p++))
1505 : return -EFAULT;
1506 0 : ret = import_single_range(ITER_SOURCE, p, len, &iov, &iter);
1507 0 : if (unlikely(ret))
1508 : return ret;
1509 0 : ret = write_pool_user(&iter);
1510 0 : if (unlikely(ret < 0))
1511 : return ret;
1512 : /* Since we're crediting, enforce that it was all written into the pool. */
1513 0 : if (unlikely(ret != len))
1514 : return -EFAULT;
1515 0 : credit_init_bits(ent_count);
1516 : return 0;
1517 : }
1518 : case RNDZAPENTCNT:
1519 : case RNDCLEARPOOL:
1520 : /* No longer has any effect. */
1521 0 : if (!capable(CAP_SYS_ADMIN))
1522 : return -EPERM;
1523 0 : return 0;
1524 : case RNDRESEEDCRNG:
1525 0 : if (!capable(CAP_SYS_ADMIN))
1526 : return -EPERM;
1527 0 : if (!crng_ready())
1528 : return -ENODATA;
1529 0 : crng_reseed(NULL);
1530 0 : return 0;
1531 : default:
1532 : return -EINVAL;
1533 : }
1534 : }
1535 :
1536 0 : static int random_fasync(int fd, struct file *filp, int on)
1537 : {
1538 0 : 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 = generic_file_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 = generic_file_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 : */
1609 0 : 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 0 : struct ctl_table fake_table = {
1615 : .data = uuid_string,
1616 : .maxlen = UUID_STRING_LEN
1617 : };
1618 :
1619 0 : if (write)
1620 : return -EPERM;
1621 :
1622 0 : uuid = table->data;
1623 0 : if (!uuid) {
1624 0 : uuid = tmp_uuid;
1625 0 : generate_random_uuid(uuid);
1626 : } else {
1627 : static DEFINE_SPINLOCK(bootid_spinlock);
1628 :
1629 0 : spin_lock(&bootid_spinlock);
1630 0 : if (!uuid[8])
1631 0 : generate_random_uuid(uuid);
1632 : spin_unlock(&bootid_spinlock);
1633 : }
1634 :
1635 0 : snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
1636 0 : return proc_dostring(&fake_table, 0, buf, lenp, ppos);
1637 : }
1638 :
1639 : /* The same as proc_dointvec, but writes don't change anything. */
1640 0 : static int proc_do_rointvec(struct ctl_table *table, int write, void *buf,
1641 : size_t *lenp, loff_t *ppos)
1642 : {
1643 0 : 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 : */
1693 1 : static int __init random_sysctls_init(void)
1694 : {
1695 1 : register_sysctl_init("kernel/random", random_table);
1696 1 : return 0;
1697 : }
1698 : device_initcall(random_sysctls_init);
1699 : #endif
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