summaryrefslogtreecommitdiffstats
path: root/drivers/char/random.c
blob: 4a9c79391dee93ae19048aa25729fe500deb6ddf (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
/*
 * Copyright (C) 2017-2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
 * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All rights reserved.
 *
 * This driver produces cryptographically secure pseudorandom data. It is divided
 * into roughly six sections, each with a section header:
 *
 *   - Initialization and readiness waiting.
 *   - Fast key erasure RNG, the "crng".
 *   - Entropy accumulation and extraction routines.
 *   - Entropy collection routines.
 *   - Userspace reader/writer interfaces.
 *   - Sysctl interface.
 *
 * The high level overview is that there is one input pool, into which
 * various pieces of data are hashed. Prior to initialization, some of that
 * data is then "credited" as having a certain number of bits of entropy.
 * When enough bits of entropy are available, the hash is finalized and
 * handed as a key to a stream cipher that expands it indefinitely for
 * various consumers. This key is periodically refreshed as the various
 * entropy collectors, described below, add data to the input pool.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/utsname.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/string.h>
#include <linux/fcntl.h>
#include <linux/slab.h>
#include <linux/random.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/interrupt.h>
#include <linux/mm.h>
#include <linux/nodemask.h>
#include <linux/spinlock.h>
#include <linux/kthread.h>
#include <linux/percpu.h>
#include <linux/ptrace.h>
#include <linux/workqueue.h>
#include <linux/irq.h>
#include <linux/ratelimit.h>
#include <linux/syscalls.h>
#include <linux/completion.h>
#include <linux/uuid.h>
#include <linux/uaccess.h>
#include <linux/suspend.h>
#include <linux/siphash.h>
#include <linux/sched/isolation.h>
#include <crypto/chacha.h>
#include <crypto/blake2s.h>
#include <asm/archrandom.h>
#include <asm/processor.h>
#include <asm/irq.h>
#include <asm/irq_regs.h>
#include <asm/io.h>

/*********************************************************************
 *
 * Initialization and readiness waiting.
 *
 * Much of the RNG infrastructure is devoted to various dependencies
 * being able to wait until the RNG has collected enough entropy and
 * is ready for safe consumption.
 *
 *********************************************************************/

/*
 * crng_init is protected by base_crng->lock, and only increases
 * its value (from empty->early->ready).
 */
static enum {
	CRNG_EMPTY = 0, /* Little to no entropy collected */
	CRNG_EARLY = 1, /* At least POOL_EARLY_BITS collected */
	CRNG_READY = 2  /* Fully initialized with POOL_READY_BITS collected */
} crng_init __read_mostly = CRNG_EMPTY;
static DEFINE_STATIC_KEY_FALSE(crng_is_ready);
#define crng_ready() (static_branch_likely(&crng_is_ready) || crng_init >= CRNG_READY)
/* Various types of waiters for crng_init->CRNG_READY transition. */
static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
static struct fasync_struct *fasync;
static ATOMIC_NOTIFIER_HEAD(random_ready_notifier);

/* Control how we warn userspace. */
static struct ratelimit_state urandom_warning =
	RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE);
static int ratelimit_disable __read_mostly =
	IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");

/*
 * Returns whether or not the input pool has been seeded and thus guaranteed
 * to supply cryptographically secure random numbers. This applies to: the
 * /dev/urandom device, the get_random_bytes function, and the get_random_{u8,
 * u16,u32,u64,long} family of functions.
 *
 * Returns: true if the input pool has been seeded.
 *          false if the input pool has not been seeded.
 */
bool rng_is_initialized(void)
{
	return crng_ready();
}
EXPORT_SYMBOL(rng_is_initialized);

static void __cold crng_set_ready(struct work_struct *work)
{
	static_branch_enable(&crng_is_ready);
}

/* Used by wait_for_random_bytes(), and considered an entropy collector, below. */
static void try_to_generate_entropy(void);

/*
 * Wait for the input pool to be seeded and thus guaranteed to supply
 * cryptographically secure random numbers. This applies to: the /dev/urandom
 * device, the get_random_bytes function, and the get_random_{u8,u16,u32,u64,
 * long} family of functions. Using any of these functions without first
 * calling this function forfeits the guarantee of security.
 *
 * Returns: 0 if the input pool has been seeded.
 *          -ERESTARTSYS if the function was interrupted by a signal.
 */
int wait_for_random_bytes(void)
{
	while (!crng_ready()) {
		int ret;

		try_to_generate_entropy();
		ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
		if (ret)
			return ret > 0 ? 0 : ret;
	}
	return 0;
}
EXPORT_SYMBOL(wait_for_random_bytes);

/*
 * Add a callback function that will be invoked when the crng is initialised,
 * or immediately if it already has been. Only use this is you are absolutely
 * sure it is required. Most users should instead be able to test
 * `rng_is_initialized()` on demand, or make use of `get_random_bytes_wait()`.
 */
int __cold execute_with_initialized_rng(struct notifier_block *nb)
{
	unsigned long flags;
	int ret = 0;

	spin_lock_irqsave(&random_ready_notifier.lock, flags);
	if (crng_ready())
		nb->notifier_call(nb, 0, NULL);
	else
		ret = raw_notifier_chain_register((struct raw_notifier_head *)&random_ready_notifier.head, nb);
	spin_unlock_irqrestore(&random_ready_notifier.lock, flags);
	return ret;
}

#define warn_unseeded_randomness() \
	if (IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) && !crng_ready()) \
		printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", \
				__func__, (void *)_RET_IP_, crng_init)


/*********************************************************************
 *
 * Fast key erasure RNG, the "crng".
 *
 * These functions expand entropy from the entropy extractor into
 * long streams for external consumption using the "fast key erasure"
 * RNG described at <https://blog.cr.yp.to/20170723-random.html>.
 *
 * There are a few exported interfaces for use by other drivers:
 *
 *	void get_random_bytes(void *buf, size_t len)
 *	u8 get_random_u8()
 *	u16 get_random_u16()
 *	u32 get_random_u32()
 *	u32 get_random_u32_below(u32 ceil)
 *	u32 get_random_u32_above(u32 floor)
 *	u32 get_random_u32_inclusive(u32 floor, u32 ceil)
 *	u64 get_random_u64()
 *	unsigned long get_random_long()
 *
 * These interfaces will return the requested number of random bytes
 * into the given buffer or as a return value. This is equivalent to
 * a read from /dev/urandom. The u8, u16, u32, u64, long family of
 * functions may be higher performance for one-off random integers,
 * because they do a bit of buffering and do not invoke reseeding
 * until the buffer is emptied.
 *
 *********************************************************************/

enum {
	CRNG_RESEED_START_INTERVAL = HZ,
	CRNG_RESEED_INTERVAL = 60 * HZ
};

static struct {
	u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long));
	unsigned long generation;
	spinlock_t lock;
} base_crng = {
	.lock = __SPIN_LOCK_UNLOCKED(base_crng.lock)
};

struct crng {
	u8 key[CHACHA_KEY_SIZE];
	unsigned long generation;
	local_lock_t lock;
};

static DEFINE_PER_CPU(struct crng, crngs) = {
	.generation = ULONG_MAX,
	.lock = INIT_LOCAL_LOCK(crngs.lock),
};

/*
 * Return the interval until the next reseeding, which is normally
 * CRNG_RESEED_INTERVAL, but during early boot, it is at an interval
 * proportional to the uptime.
 */
static unsigned int crng_reseed_interval(void)
{
	static bool early_boot = true;

	if (unlikely(READ_ONCE(early_boot))) {
		time64_t uptime = ktime_get_seconds();
		if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2)
			WRITE_ONCE(early_boot, false);
		else
			return max_t(unsigned int, CRNG_RESEED_START_INTERVAL,
				     (unsigned int)uptime / 2 * HZ);
	}
	return CRNG_RESEED_INTERVAL;
}

/* Used by crng_reseed() and crng_make_state() to extract a new seed from the input pool. */
static void extract_entropy(void *buf, size_t len);

/* This extracts a new crng key from the input pool. */
static void crng_reseed(struct work_struct *work)
{
	static DECLARE_DELAYED_WORK(next_reseed, crng_reseed);
	unsigned long flags;
	unsigned long next_gen;
	u8 key[CHACHA_KEY_SIZE];

	/* Immediately schedule the next reseeding, so that it fires sooner rather than later. */
	if (likely(system_unbound_wq))
		queue_delayed_work(system_unbound_wq, &next_reseed, crng_reseed_interval());

	extract_entropy(key, sizeof(key));

	/*
	 * We copy the new key into the base_crng, overwriting the old one,
	 * and update the generation counter. We avoid hitting ULONG_MAX,
	 * because the per-cpu crngs are initialized to ULONG_MAX, so this
	 * forces new CPUs that come online to always initialize.
	 */
	spin_lock_irqsave(&base_crng.lock, flags);
	memcpy(base_crng.key, key, sizeof(base_crng.key));
	next_gen = base_crng.generation + 1;
	if (next_gen == ULONG_MAX)
		++next_gen;
	WRITE_ONCE(base_crng.generation, next_gen);
	if (!static_branch_likely(&crng_is_ready))
		crng_init = CRNG_READY;
	spin_unlock_irqrestore(&base_crng.lock, flags);
	memzero_explicit(key, sizeof(key));
}

/*
 * This generates a ChaCha block using the provided key, and then
 * immediately overwrites that key with half the block. It returns
 * the resultant ChaCha state to the user, along with the second
 * half of the block containing 32 bytes of random data that may
 * be used; random_data_len may not be greater than 32.
 *
 * The returned ChaCha state contains within it a copy of the old
 * key value, at index 4, so the state should always be zeroed out
 * immediately after using in order to maintain forward secrecy.
 * If the state cannot be erased in a timely manner, then it is
 * safer to set the random_data parameter to &chacha_state[4] so
 * that this function overwrites it before returning.
 */
static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE],
				  u32 chacha_state[CHACHA_STATE_WORDS],
				  u8 *random_data, size_t random_data_len)
{
	u8 first_block[CHACHA_BLOCK_SIZE];

	BUG_ON(random_data_len > 32);

	chacha_init_consts(chacha_state);
	memcpy(&chacha_state[4], key, CHACHA_KEY_SIZE);
	memset(&chacha_state[12], 0, sizeof(u32) * 4);
	chacha20_block(chacha_state, first_block);

	memcpy(key, first_block, CHACHA_KEY_SIZE);
	memcpy(random_data, first_block + CHACHA_KEY_SIZE, random_data_len);
	memzero_explicit(first_block, sizeof(first_block));
}

/*
 * This function returns a ChaCha state that you may use for generating
 * random data. It also returns up to 32 bytes on its own of random data
 * that may be used; random_data_len may not be greater than 32.
 */
static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
			    u8 *random_data, size_t random_data_len)
{
	unsigned long flags;
	struct crng *crng;

	BUG_ON(random_data_len > 32);

	/*
	 * For the fast path, we check whether we're ready, unlocked first, and
	 * then re-check once locked later. In the case where we're really not
	 * ready, we do fast key erasure with the base_crng directly, extracting
	 * when crng_init is CRNG_EMPTY.
	 */
	if (!crng_ready()) {
		bool ready;

		spin_lock_irqsave(&base_crng.lock, flags);
		ready = crng_ready();
		if (!ready) {
			if (crng_init == CRNG_EMPTY)
				extract_entropy(base_crng.key, sizeof(base_crng.key));
			crng_fast_key_erasure(base_crng.key, chacha_state,
					      random_data, random_data_len);
		}
		spin_unlock_irqrestore(&base_crng.lock, flags);
		if (!ready)
			return;
	}

	local_lock_irqsave(&crngs.lock, flags);
	crng = raw_cpu_ptr(&crngs);

	/*
	 * If our per-cpu crng is older than the base_crng, then it means
	 * somebody reseeded the base_crng. In that case, we do fast key
	 * erasure on the base_crng, and use its output as the new key
	 * for our per-cpu crng. This brings us up to date with base_crng.
	 */
	if (unlikely(crng->generation != READ_ONCE(base_crng.generation))) {
		spin_lock(&base_crng.lock);
		crng_fast_key_erasure(base_crng.key, chacha_state,
				      crng->key, sizeof(crng->key));
		crng->generation = base_crng.generation;
		spin_unlock(&base_crng.lock);
	}

	/*
	 * Finally, when we've made it this far, our per-cpu crng has an up
	 * to date key, and we can do fast key erasure with it to produce
	 * some random data and a ChaCha state for the caller. All other
	 * branches of this function are "unlikely", so most of the time we
	 * should wind up here immediately.
	 */
	crng_fast_key_erasure(crng->key, chacha_state, random_data, random_data_len);
	local_unlock_irqrestore(&crngs.lock, flags);
}

static void _get_random_bytes(void *buf, size_t len)
{
	u32 chacha_state[CHACHA_STATE_WORDS];
	u8 tmp[CHACHA_BLOCK_SIZE];
	size_t first_block_len;

	if (!len)
		return;

	first_block_len = min_t(size_t, 32, len);
	crng_make_state(chacha_state, buf, first_block_len);
	len -= first_block_len;
	buf += first_block_len;

	while (len) {
		if (len < CHACHA_BLOCK_SIZE) {
			chacha20_block(chacha_state, tmp);
			memcpy(buf, tmp, len);
			memzero_explicit(tmp, sizeof(tmp));
			break;
		}

		chacha20_block(chacha_state, buf);
		if (unlikely(chacha_state[12] == 0))
			++chacha_state[13];
		len -= CHACHA_BLOCK_SIZE;
		buf += CHACHA_BLOCK_SIZE;
	}

	memzero_explicit(chacha_state, sizeof(chacha_state));
}

/*
 * This returns random bytes in arbitrary quantities. The quality of the
 * random bytes is good as /dev/urandom. In order to ensure that the
 * randomness provided by this function is okay, the function
 * wait_for_random_bytes() should be called and return 0 at least once
 * at any point prior.
 */
void get_random_bytes(void *buf, size_t len)
{
	warn_unseeded_randomness();
	_get_random_bytes(buf, len);
}
EXPORT_SYMBOL(get_random_bytes);

static ssize_t get_random_bytes_user(struct iov_iter *iter)
{
	u32 chacha_state[CHACHA_STATE_WORDS];
	u8 block[CHACHA_BLOCK_SIZE];
	size_t ret = 0, copied;

	if (unlikely(!iov_iter_count(iter)))
		return 0;

	/*
	 * Immediately overwrite the ChaCha key at index 4 with random
	 * bytes, in case userspace causes copy_to_iter() below to sleep
	 * forever, so that we still retain forward secrecy in that case.
	 */
	crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA_KEY_SIZE);
	/*
	 * However, if we're doing a read of len <= 32, we don't need to
	 * use chacha_state after, so we can simply return those bytes to
	 * the user directly.
	 */
	if (iov_iter_count(iter) <= CHACHA_KEY_SIZE) {
		ret = copy_to_iter(&chacha_state[4], CHACHA_KEY_SIZE, iter);
		goto out_zero_chacha;
	}

	for (;;) {
		chacha20_block(chacha_state, block);
		if (unlikely(chacha_state[12] == 0))
			++chacha_state[13];

		copied = copy_to_iter(block, sizeof(block), iter);
		ret += copied;
		if (!iov_iter_count(iter) || copied != sizeof(block))
			break;

		BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
		if (ret % PAGE_SIZE == 0) {
			if (signal_pending(current))
				break;
			cond_resched();
		}
	}

	memzero_explicit(block, sizeof(block));
out_zero_chacha:
	memzero_explicit(chacha_state, sizeof(chacha_state));
	return ret ? ret : -EFAULT;
}

/*
 * Batched entropy returns random integers. The quality of the random
 * number is good as /dev/urandom. In order to ensure that the randomness
 * provided by this function is okay, the function wait_for_random_bytes()
 * should be called and return 0 at least once at any point prior.
 */

#define DEFINE_BATCHED_ENTROPY(type)						\
struct batch_ ##type {								\
	/*									\
	 * We make this 1.5x a ChaCha block, so that we get the			\
	 * remaining 32 bytes from fast key erasure, plus one full		\
	 * block from the detached ChaCha state. We can increase		\
	 * the size of this later if needed so long as we keep the		\
	 * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE.		\
	 */									\
	type entropy[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(type))];		\
	local_lock_t lock;							\
	unsigned long generation;						\
	unsigned int position;							\
};										\
										\
static DEFINE_PER_CPU(struct batch_ ##type, batched_entropy_ ##type) = {	\
	.lock = INIT_LOCAL_LOCK(batched_entropy_ ##type.lock),			\
	.position = UINT_MAX							\
};										\
										\
type get_random_ ##type(void)							\
{										\
	type ret;								\
	unsigned long flags;							\
	struct batch_ ##type *batch;						\
	unsigned long next_gen;							\
										\
	warn_unseeded_randomness();						\
										\
	if  (!crng_ready()) {							\
		_get_random_bytes(&ret, sizeof(ret));				\
		return ret;							\
	}									\
										\
	local_lock_irqsave(&batched_entropy_ ##type.lock, flags);		\
	batch = raw_cpu_ptr(&batched_entropy_##type);				\
										\
	next_gen = READ_ONCE(base_crng.generation);				\
	if (batch->position >= ARRAY_SIZE(batch->entropy) ||			\
	    next_gen != batch->generation) {					\
		_get_random_bytes(batch->entropy, sizeof(batch->entropy));	\
		batch->position = 0;						\
		batch->generation = next_gen;					\
	}									\
										\
	ret = batch->entropy[batch->position];					\
	batch->entropy[batch->position] = 0;					\
	++batch->position;							\
	local_unlock_irqrestore(&batched_entropy_ ##type.lock, flags);		\
	return ret;								\
}										\
EXPORT_SYMBOL(get_random_ ##type);

DEFINE_BATCHED_ENTROPY(u8)
DEFINE_BATCHED_ENTROPY(u16)
DEFINE_BATCHED_ENTROPY(u32)
DEFINE_BATCHED_ENTROPY(u64)

u32 __get_random_u32_below(u32 ceil)
{
	/*
	 * This is the slow path for variable ceil. It is still fast, most of
	 * the time, by doing traditional reciprocal multiplication and
	 * opportunistically comparing the lower half to ceil itself, before
	 * falling back to computing a larger bound, and then rejecting samples
	 * whose lower half would indicate a range indivisible by ceil. The use
	 * of `-ceil % ceil` is analogous to `2^32 % ceil`, but is computable
	 * in 32-bits.
	 */
	u32 rand = get_random_u32();
	u64 mult;

	/*
	 * This function is technically undefined for ceil == 0, and in fact
	 * for the non-underscored constant version in the header, we build bug
	 * on that. But for the non-constant case, it's convenient to have that
	 * evaluate to being a straight call to get_random_u32(), so that
	 * get_random_u32_inclusive() can work over its whole range without
	 * undefined behavior.
	 */
	if (unlikely(!ceil))
		return rand;

	mult = (u64)ceil * rand;
	if (unlikely((u32)mult < ceil)) {
		u32 bound = -ceil % ceil;
		while (unlikely((u32)mult < bound))
			mult = (u64)ceil * get_random_u32();
	}
	return mult >> 32;
}
EXPORT_SYMBOL(__get_random_u32_below);

#ifdef CONFIG_SMP
/*
 * This function is called when the CPU is coming up, with entry
 * CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP.
 */
int __cold random_prepare_cpu(unsigned int cpu)
{
	/*
	 * When the cpu comes back online, immediately invalidate both
	 * the per-cpu crng and all batches, so that we serve fresh
	 * randomness.
	 */
	per_cpu_ptr(&crngs, cpu)->generation = ULONG_MAX;
	per_cpu_ptr(&batched_entropy_u8, cpu)->position = UINT_MAX;
	per_cpu_ptr(&batched_entropy_u16, cpu)->position = UINT_MAX;
	per_cpu_ptr(&batched_entropy_u32, cpu)->position = UINT_MAX;
	per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX;
	return 0;
}
#endif


/**********************************************************************
 *
 * Entropy accumulation and extraction routines.
 *
 * Callers may add entropy via:
 *
 *     static void mix_pool_bytes(const void *buf, size_t len)
 *
 * After which, if added entropy should be credited:
 *
 *     static void credit_init_bits(size_t bits)
 *
 * Finally, extract entropy via:
 *
 *     static void extract_entropy(void *buf, size_t len)
 *
 **********************************************************************/

enum {
	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
	POOL_READY_BITS = POOL_BITS, /* When crng_init->CRNG_READY */
	POOL_EARLY_BITS = POOL_READY_BITS / 2 /* When crng_init->CRNG_EARLY */
};

static struct {
	struct blake2s_state hash;
	spinlock_t lock;
	unsigned int init_bits;
} input_pool = {
	.hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE),
		    BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4,
		    BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 },
	.hash.outlen = BLAKE2S_HASH_SIZE,
	.lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
};

static void _mix_pool_bytes(const void *buf, size_t len)
{
	blake2s_update(&input_pool.hash, buf, len);
}

/*
 * This function adds bytes into the input pool. It does not
 * update the initialization bit counter; the caller should call
 * credit_init_bits if this is appropriate.
 */
static void mix_pool_bytes(const void *buf, size_t len)
{
	unsigned long flags;

	spin_lock_irqsave(&input_pool.lock, flags);
	_mix_pool_bytes(buf, len);
	spin_unlock_irqrestore(&input_pool.lock, flags);
}

/*
 * This is an HKDF-like construction for using the hashed collected entropy
 * as a PRF key, that's then expanded block-by-block.
 */
static void extract_entropy(void *buf, size_t len)
{
	unsigned long flags;
	u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
	struct {
		unsigned long rdseed[32 / sizeof(long)];
		size_t counter;
	} block;
	size_t i, longs;

	for (i = 0; i < ARRAY_SIZE(block.rdseed);) {
		longs = arch_get_random_seed_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
		if (longs) {
			i += longs;
			continue;
		}
		longs = arch_get_random_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
		if (longs) {
			i += longs;
			continue;
		}
		block.rdseed[i++] = random_get_entropy();
	}

	spin_lock_irqsave(&input_pool.lock, flags);

	/* seed = HASHPRF(last_key, entropy_input) */
	blake2s_final(&input_pool.hash, seed);

	/* next_key = HASHPRF(seed, RDSEED || 0) */
	block.counter = 0;
	blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
	blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));

	spin_unlock_irqrestore(&input_pool.lock, flags);
	memzero_explicit(next_key, sizeof(next_key));

	while (len) {
		i = min_t(size_t, len, BLAKE2S_HASH_SIZE);
		/* output = HASHPRF(seed, RDSEED || ++counter) */
		++block.counter;
		blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
		len -= i;
		buf += i;
	}

	memzero_explicit(seed, sizeof(seed));
	memzero_explicit(&block, sizeof(block));
}

#define credit_init_bits(bits) if (!crng_ready()) _credit_init_bits(bits)

static void __cold _credit_init_bits(size_t bits)
{
	static struct execute_work set_ready;
	unsigned int new, orig, add;
	unsigned long flags;

	if (!bits)
		return;

	add = min_t(size_t, bits, POOL_BITS);

	orig = READ_ONCE(input_pool.init_bits);
	do {
		new = min_t(unsigned int, POOL_BITS, orig + add);
	} while (!try_cmpxchg(&input_pool.init_bits, &orig, new));

	if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
		crng_reseed(NULL); /* Sets crng_init to CRNG_READY under base_crng.lock. */
		if (static_key_initialized)
			execute_in_process_context(crng_set_ready, &set_ready);
		atomic_notifier_call_chain(&random_ready_notifier, 0, NULL);
		wake_up_interruptible(&crng_init_wait);
		kill_fasync(&fasync, SIGIO, POLL_IN);
		pr_notice("crng init done\n");
		if (urandom_warning.missed)
			pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
				  urandom_warning.missed);
	} else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
		spin_lock_irqsave(&base_crng.lock, flags);
		/* Check if crng_init is CRNG_EMPTY, to avoid race with crng_reseed(). */
		if (crng_init == CRNG_EMPTY) {
			extract_entropy(base_crng.key, sizeof(base_crng.key));
			crng_init = CRNG_EARLY;
		}
		spin_unlock_irqrestore(&base_crng.lock, flags);
	}
}


/**********************************************************************
 *
 * Entropy collection routines.
 *
 * The following exported functions are used for pushing entropy into
 * the above entropy accumulation routines:
 *
 *	void add_device_randomness(const void *buf, size_t len);
 *	void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy, bool sleep_after);
 *	void add_bootloader_randomness(const void *buf, size_t len);
 *	void add_vmfork_randomness(const void *unique_vm_id, size_t len);
 *	void add_interrupt_randomness(int irq);
 *	void add_input_randomness(unsigned int type, unsigned int code, unsigned int value);
 *	void add_disk_randomness(struct gendisk *disk);
 *
 * add_device_randomness() adds data to the input pool that
 * is likely to differ between two devices (or possibly even per boot).
 * This would be things like MAC addresses or serial numbers, or the
 * read-out of the RTC. This does *not* credit any actual entropy to
 * the pool, but it initializes the pool to different values for devices
 * that might otherwise be identical and have very little entropy
 * available to them (particularly common in the embedded world).
 *
 * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
 * entropy as specified by the caller. If the entropy pool is full it will
 * block until more entropy is needed.
 *
 * add_bootloader_randomness() is called by bootloader drivers, such as EFI
 * and device tree, and credits its input depending on whether or not the
 * command line option 'random.trust_bootloader'.
 *
 * add_vmfork_randomness() adds a unique (but not necessarily secret) ID
 * representing the current instance of a VM to the pool, without crediting,
 * and then force-reseeds the crng so that it takes effect immediately.
 *
 * add_interrupt_randomness() uses the interrupt timing as random
 * inputs to the entropy pool. Using the cycle counters and the irq source
 * as inputs, it feeds the input pool roughly once a second or after 64
 * interrupts, crediting 1 bit of entropy for whichever comes first.
 *
 * add_input_randomness() uses the input layer interrupt timing, as well
 * as the event type information from the hardware.
 *
 * add_disk_randomness() uses what amounts to the seek time of block
 * layer request events, on a per-disk_devt basis, as input to the
 * entropy pool. Note that high-speed solid state drives with very low
 * seek times do not make for good sources of entropy, as their seek
 * times are usually fairly consistent.
 *
 * The last two routines try to estimate how many bits of entropy
 * to credit. They do this by keeping track of the first and second
 * order deltas of the event timings.
 *
 **********************************************************************/

static bool trust_cpu __initdata = true;
static bool trust_bootloader __initdata = true;
static int __init parse_trust_cpu(char *arg)
{
	return kstrtobool(arg, &trust_cpu);
}
static int __init parse_trust_bootloader(char *arg)
{
	return kstrtobool(arg, &trust_bootloader);
}
early_param("random.trust_cpu", parse_trust_cpu);
early_param("random.trust_bootloader", parse_trust_bootloader);

static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data)
{
	unsigned long flags, entropy = random_get_entropy();

	/*
	 * Encode a representation of how long the system has been suspended,
	 * in a way that is distinct from prior system suspends.
	 */
	ktime_t stamps[] = { ktime_get(), ktime_get_boottime(), ktime_get_real() };

	spin_lock_irqsave(&input_pool.lock, flags);
	_mix_pool_bytes(&action, sizeof(action));
	_mix_pool_bytes(stamps, sizeof(stamps));
	_mix_pool_bytes(&entropy, sizeof(entropy));
	spin_unlock_irqrestore(&input_pool.lock, flags);

	if (crng_ready() && (action == PM_RESTORE_PREPARE ||
	    (action == PM_POST_SUSPEND && !IS_ENABLED(CONFIG_PM_AUTOSLEEP) &&
	     !IS_ENABLED(CONFIG_PM_USERSPACE_AUTOSLEEP)))) {
		crng_reseed(NULL);
		pr_notice("crng reseeded on system resumption\n");
	}
	return 0;
}

static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification };

/*
 * This is called extremely early, before time keeping functionality is
 * available, but arch randomness is. Interrupts are not yet enabled.
 */
void __init random_init_early(const char *command_line)
{
	unsigned long entropy[BLAKE2S_BLOCK_SIZE / sizeof(long)];
	size_t i, longs, arch_bits;

#if defined(LATENT_ENTROPY_PLUGIN)
	static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
	_mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
#endif

	for (i = 0, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) {
		longs = arch_get_random_seed_longs(entropy, ARRAY_SIZE(entropy) - i);
		if (longs) {
			_mix_pool_bytes(entropy, sizeof(*entropy) * longs);
			i += longs;
			continue;
		}
		longs = arch_get_random_longs(entropy, ARRAY_SIZE(entropy) - i);
		if (longs) {
			_mix_pool_bytes(entropy, sizeof(*entropy) * longs);
			i += longs;
			continue;
		}
		arch_bits -= sizeof(*entropy) * 8;
		++i;
	}

	_mix_pool_bytes(init_utsname(), sizeof(*(init_utsname())));
	_mix_pool_bytes(command_line, strlen(command_line));

	/* Reseed if already seeded by earlier phases. */
	if (crng_ready())
		crng_reseed(NULL);
	else if (trust_cpu)
		_credit_init_bits(arch_bits);
}

/*
 * This is called a little bit after the prior function, and now there is
 * access to timestamps counters. Interrupts are not yet enabled.
 */
void __init random_init(void)
{
	unsigned long entropy = random_get_entropy();
	ktime_t now = ktime_get_real();

	_mix_pool_bytes(&now, sizeof(now));
	_mix_pool_bytes(&entropy, sizeof(entropy));
	add_latent_entropy();

	/*
	 * If we were initialized by the cpu or bootloader before jump labels
	 * are initialized, then we should enable the static branch here, where
	 * it's guaranteed that jump labels have been initialized.
	 */
	if (!static_branch_likely(&crng_is_ready) && crng_init >= CRNG_READY)
		crng_set_ready(NULL);

	/* Reseed if already seeded by earlier phases. */
	if (crng_ready())
		crng_reseed(NULL);

	WARN_ON(register_pm_notifier(&pm_notifier));

	WARN(!entropy, "Missing cycle counter and fallback timer; RNG "
		       "entropy collection will consequently suffer.");
}

/*
 * Add device- or boot-specific data to the input pool to help
 * initialize it.
 *
 * None of this adds any entropy; it is meant to avoid the problem of
 * the entropy pool having similar initial state across largely
 * identical devices.
 */
void add_device_randomness(const void *buf, size_t len)
{
	unsigned long entropy = random_get_entropy();
	unsigned long flags;

	spin_lock_irqsave(&input_pool.lock, flags);
	_mix_pool_bytes(&entropy, sizeof(entropy));
	_mix_pool_bytes(buf, len);
	spin_unlock_irqrestore(&input_pool.lock, flags);
}
EXPORT_SYMBOL(add_device_randomness);

/*
 * Interface for in-kernel drivers of true hardware RNGs. Those devices
 * may produce endless random bits, so this function will sleep for
 * some amount of time after, if the sleep_after parameter is true.
 */
void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy, bool sleep_after)
{
	mix_pool_bytes(buf, len);
	credit_init_bits(entropy);

	/*
	 * Throttle writing to once every reseed interval, unless we're not yet
	 * initialized or no entropy is credited.
	 */
	if (sleep_after && !kthread_should_stop() && (crng_ready() || !entropy))
		schedule_timeout_interruptible(crng_reseed_interval());
}
EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);

/*
 * Handle random seed passed by bootloader, and credit it depending
 * on the command line option 'random.trust_bootloader'.
 */
void __init add_bootloader_randomness(const void *buf, size_t len)
{
	mix_pool_bytes(buf, len);
	if (trust_bootloader)
		credit_init_bits(len * 8);
}

#if IS_ENABLED(CONFIG_VMGENID)
static BLOCKING_NOTIFIER_HEAD(vmfork_chain);

/*
 * Handle a new unique VM ID, which is unique, not secret, so we
 * don't credit it, but we do immediately force a reseed after so
 * that it's used by the crng posthaste.
 */
void __cold add_vmfork_randomness(const void *unique_vm_id, size_t len)
{
	add_device_randomness(unique_vm_id, len);
	if (crng_ready()) {
		crng_reseed(NULL);
		pr_notice("crng reseeded due to virtual machine fork\n");
	}
	blocking_notifier_call_chain(&vmfork_chain, 0, NULL);
}
#if IS_MODULE(CONFIG_VMGENID)
EXPORT_SYMBOL_GPL(add_vmfork_randomness);
#endif

int __cold register_random_vmfork_notifier(struct notifier_block *nb)
{
	return blocking_notifier_chain_register(&vmfork_chain, nb);
}
EXPORT_SYMBOL_GPL(register_random_vmfork_notifier);

int __cold unregister_random_vmfork_notifier(struct notifier_block *nb)
{
	return blocking_notifier_chain_unregister(&vmfork_chain, nb);
}
EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier);
#endif

struct fast_pool {
	unsigned long pool[4];
	unsigned long last;
	unsigned int count;
	struct timer_list mix;
};

static void mix_interrupt_randomness(struct timer_list *work);

static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = {
#ifdef CONFIG_64BIT
#define FASTMIX_PERM SIPHASH_PERMUTATION
	.pool = { SIPHASH_CONST_0, SIPHASH_CONST_1, SIPHASH_CONST_2, SIPHASH_CONST_3 },
#else
#define FASTMIX_PERM HSIPHASH_PERMUTATION
	.pool = { HSIPHASH_CONST_0, HSIPHASH_CONST_1, HSIPHASH_CONST_2, HSIPHASH_CONST_3 },
#endif
	.mix = __TIMER_INITIALIZER(mix_interrupt_randomness, 0)
};

/*
 * This is [Half]SipHash-1-x, starting from an empty key. Because
 * the key is fixed, it assumes that its inputs are non-malicious,
 * and therefore this has no security on its own. s represents the
 * four-word SipHash state, while v represents a two-word input.
 */
static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long v2)
{
	s[3] ^= v1;
	FASTMIX_PERM(s[0], s[1], s[2], s[3]);
	s[0] ^= v1;
	s[3] ^= v2;
	FASTMIX_PERM(s[0], s[1], s[2], s[3]);
	s[0] ^= v2;
}

#ifdef CONFIG_SMP
/*
 * This function is called when the CPU has just come online, with
 * entry CPUHP_AP_RANDOM_ONLINE, just after CPUHP_AP_WORKQUEUE_ONLINE.
 */
int __cold random_online_cpu(unsigned int cpu)
{
	/*
	 * During CPU shutdown and before CPU onlining, add_interrupt_
	 * randomness() may schedule mix_interrupt_randomness(), and
	 * set the MIX_INFLIGHT flag. However, because the worker can
	 * be scheduled on a different CPU during this period, that
	 * flag will never be cleared. For that reason, we zero out
	 * the flag here, which runs just after workqueues are onlined
	 * for the CPU again. This also has the effect of setting the
	 * irq randomness count to zero so that new accumulated irqs
	 * are fresh.
	 */
	per_cpu_ptr(&irq_randomness, cpu)->count = 0;
	return 0;
}
#endif

static void mix_interrupt_randomness(struct timer_list *work)
{
	struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix);
	/*
	 * The size of the copied stack pool is explicitly 2 longs so that we
	 * only ever ingest half of the siphash output each time, retaining
	 * the other half as the next "key" that carries over. The entropy is
	 * supposed to be sufficiently dispersed between bits so on average
	 * we don't wind up "losing" some.
	 */
	unsigned long pool[2];
	unsigned int count;

	/* Check to see if we're running on the wrong CPU due to hotplug. */
	local_irq_disable();
	if (fast_pool != this_cpu_ptr(&irq_randomness)) {
		local_irq_enable();
		return;
	}

	/*
	 * Copy the pool to the stack so that the mixer always has a
	 * consistent view, before we reenable irqs again.
	 */
	memcpy(pool, fast_pool->pool, sizeof(pool));
	count = fast_pool->count;
	fast_pool->count = 0;
	fast_pool->last = jiffies;
	local_irq_enable();

	mix_pool_bytes(pool, sizeof(pool));
	credit_init_bits(clamp_t(unsigned int, (count & U16_MAX) / 64, 1, sizeof(pool) * 8));

	memzero_explicit(pool, sizeof(pool));
}

void add_interrupt_randomness(int irq)
{
	enum { MIX_INFLIGHT = 1U << 31 };
	unsigned long entropy = random_get_entropy();
	struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
	struct pt_regs *regs = get_irq_regs();
	unsigned int new_count;

	fast_mix(fast_pool->pool, entropy,
		 (regs ? instruction_pointer(regs) : _RET_IP_) ^ swab(irq));
	new_count = ++fast_pool->count;

	if (new_count & MIX_INFLIGHT)
		return;

	if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ))
		return;

	fast_pool->count |= MIX_INFLIGHT;
	if (!timer_pending(&fast_pool->mix)) {
		fast_pool->mix.expires = jiffies;
		add_timer_on(&fast_pool->mix, raw_smp_processor_id());
	}
}
EXPORT_SYMBOL_GPL(add_interrupt_randomness);

/* There is one of these per entropy source */
struct timer_rand_state {
	unsigned long last_time;
	long last_delta, last_delta2;
};

/*
 * This function adds entropy to the entropy "pool" by using timing
 * delays. It uses the timer_rand_state structure to make an estimate
 * of how many bits of entropy this call has added to the pool. The
 * value "num" is also added to the pool; it should somehow describe
 * the type of event that just happened.
 */
static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
{
	unsigned long entropy = random_get_entropy(), now = jiffies, flags;
	long delta, delta2, delta3;
	unsigned int bits;

	/*
	 * If we're in a hard IRQ, add_interrupt_randomness() will be called
	 * sometime after, so mix into the fast pool.
	 */
	if (in_hardirq()) {
		fast_mix(this_cpu_ptr(&irq_randomness)->pool, entropy, num);
	} else {
		spin_lock_irqsave(&input_pool.lock, flags);
		_mix_pool_bytes(&entropy, sizeof(entropy));
		_mix_pool_bytes(&num, sizeof(num));
		spin_unlock_irqrestore(&input_pool.lock, flags);
	}

	if (crng_ready())
		return;

	/*
	 * Calculate number of bits of randomness we probably added.
	 * We take into account the first, second and third-order deltas
	 * in order to make our estimate.
	 */
	delta = now - READ_ONCE(state->last_time);
	WRITE_ONCE(state->last_time, now);

	delta2 = delta - READ_ONCE(state->last_delta);
	WRITE_ONCE(state->last_delta, delta);

	delta3 = delta2 - READ_ONCE(state->last_delta2);
	WRITE_ONCE(state->last_delta2, delta2);

	if (delta < 0)
		delta = -delta;
	if (delta2 < 0)
		delta2 = -delta2;
	if (delta3 < 0)
		delta3 = -delta3;
	if (delta > delta2)
		delta = delta2;
	if (delta > delta3)
		delta = delta3;

	/*
	 * delta is now minimum absolute delta. Round down by 1 bit
	 * on general principles, and limit entropy estimate to 11 bits.
	 */
	bits = min(fls(delta >> 1), 11);

	/*
	 * As mentioned above, if we're in a hard IRQ, add_interrupt_randomness()
	 * will run after this, which uses a different crediting scheme of 1 bit
	 * per every 64 interrupts. In order to let that function do accounting
	 * close to the one in this function, we credit a full 64/64 bit per bit,
	 * and then subtract one to account for the extra one added.
	 */
	if (in_hardirq())
		this_cpu_ptr(&irq_randomness)->count += max(1u, bits * 64) - 1;
	else
		_credit_init_bits(bits);
}

void add_input_randomness(unsigned int type, unsigned int code, unsigned int value)
{
	static unsigned char last_value;
	static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES };

	/* Ignore autorepeat and the like. */
	if (value == last_value)
		return;

	last_value = value;
	add_timer_randomness(&input_timer_state,
			     (type << 4) ^ code ^ (code >> 4) ^ value);
}
EXPORT_SYMBOL_GPL(add_input_randomness);

#ifdef CONFIG_BLOCK
void add_disk_randomness(struct gendisk *disk)
{
	if (!disk || !disk->random)
		return;
	/* First major is 1, so we get >= 0x200 here. */
	add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
}
EXPORT_SYMBOL_GPL(add_disk_randomness);

void __cold rand_initialize_disk(struct gendisk *disk)
{
	struct timer_rand_state *state;

	/*
	 * If kzalloc returns null, we just won't use that entropy
	 * source.
	 */
	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
	if (state) {
		state->last_time = INITIAL_JIFFIES;
		disk->random = state;
	}
}
#endif

struct entropy_timer_state {
	unsigned long entropy;
	struct timer_list timer;
	atomic_t samples;
	unsigned int samples_per_bit;
};

/*
 * Each time the timer fires, we expect that we got an unpredictable jump in
 * the cycle counter. Even if the timer is running on another CPU, the timer
 * activity will be touching the stack of the CPU that is generating entropy.
 *
 * Note that we don't re-arm the timer in the timer itself - we are happy to be
 * scheduled away, since that just makes the load more complex, but we do not
 * want the timer to keep ticking unless the entropy loop is running.
 *
 * So the re-arming always happens in the entropy loop itself.
 */
static void __cold entropy_timer(struct timer_list *timer)
{
	struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer);
	unsigned long entropy = random_get_entropy();

	mix_pool_bytes(&entropy, sizeof(entropy));
	if (atomic_inc_return(&state->samples) % state->samples_per_bit == 0)
		credit_init_bits(1);
}

/*
 * If we have an actual cycle counter, see if we can generate enough entropy
 * with timing noise.
 */
static void __cold try_to_generate_entropy(void)
{
	enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = HZ / 15 };
	u8 stack_bytes[sizeof(struct entropy_timer_state) + SMP_CACHE_BYTES - 1];
	struct entropy_timer_state *stack = PTR_ALIGN((void *)stack_bytes, SMP_CACHE_BYTES);
	unsigned int i, num_different = 0;
	unsigned long last = random_get_entropy();
	int cpu = -1;

	for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
		stack->entropy = random_get_entropy();
		if (stack->entropy != last)
			++num_different;
		last = stack->entropy;
	}
	stack->samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1);
	if (stack->samples_per_bit > MAX_SAMPLES_PER_BIT)
		return;

	atomic_set(&stack->samples, 0);
	timer_setup_on_stack(&stack->timer, entropy_timer, 0);
	while (!crng_ready() && !signal_pending(current)) {
		/*
		 * Check !timer_pending() and then ensure that any previous callback has finished
		 * executing by checking try_to_del_timer_sync(), before queueing the next one.
		 */
		if (!timer_pending(&stack->timer) && try_to_del_timer_sync(&stack->timer) >= 0) {
			struct cpumask timer_cpus;
			unsigned int num_cpus;

			/*
			 * Preemption must be disabled here, both to read the current CPU number
			 * and to avoid scheduling a timer on a dead CPU.
			 */
			preempt_disable();

			/* Only schedule callbacks on timer CPUs that are online. */
			cpumask_and(&timer_cpus, housekeeping_cpumask(HK_TYPE_TIMER), cpu_online_mask);
			num_cpus = cpumask_weight(&timer_cpus);
			/* In very bizarre case of misconfiguration, fallback to all online. */
			if (unlikely(num_cpus == 0)) {
				timer_cpus = *cpu_online_mask;
				num_cpus = cpumask_weight(&timer_cpus);
			}

			/* Basic CPU round-robin, which avoids the current CPU. */
			do {
				cpu = cpumask_next(cpu, &timer_cpus);
				if (cpu >= nr_cpu_ids)
					cpu = cpumask_first(&timer_cpus);
			} while (cpu == smp_processor_id() && num_cpus > 1);

			/* Expiring the timer at `jiffies` means it's the next tick. */
			stack->timer.expires = jiffies;

			add_timer_on(&stack->timer, cpu);

			preempt_enable();
		}
		mix_pool_bytes(&stack->entropy, sizeof(stack->entropy));
		schedule();
		stack->entropy = random_get_entropy();
	}
	mix_pool_bytes(&stack->entropy, sizeof(stack->entropy));

	del_timer_sync(&stack->timer);
	destroy_timer_on_stack(&stack->timer);
}


/**********************************************************************
 *
 * Userspace reader/writer interfaces.
 *
 * getrandom(2) is the primary modern interface into the RNG and should
 * be used in preference to anything else.
 *
 * Reading from /dev/random has the same functionality as calling
 * getrandom(2) with flags=0. In earlier versions, however, it had
 * vastly different semantics and should therefore be avoided, to
 * prevent backwards compatibility issues.
 *
 * Reading from /dev/urandom has the same functionality as calling
 * getrandom(2) with flags=GRND_INSECURE. Because it does not block
 * waiting for the RNG to be ready, it should not be used.
 *
 * Writing to either /dev/random or /dev/urandom adds entropy to
 * the input pool but does not credit it.
 *
 * Polling on /dev/random indicates when the RNG is initialized, on
 * the read side, and when it wants new entropy, on the write side.
 *
 * Both /dev/random and /dev/urandom have the same set of ioctls for
 * adding entropy, getting the entropy count, zeroing the count, and
 * reseeding the crng.
 *
 **********************************************************************/

SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
{
	struct iov_iter iter;
	struct iovec iov;
	int ret;

	if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
		return -EINVAL;

	/*
	 * Requesting insecure and blocking randomness at the same time makes
	 * no sense.
	 */
	if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
		return -EINVAL;

	if (!crng_ready() && !(flags & GRND_INSECURE)) {
		if (flags & GRND_NONBLOCK)
			return -EAGAIN;
		ret = wait_for_random_bytes();
		if (unlikely(ret))
			return ret;
	}

	ret = import_single_range(ITER_DEST, ubuf, len, &iov, &iter);
	if (unlikely(ret))
		return ret;
	return get_random_bytes_user(&iter);
}

static __poll_t random_poll(struct file *file, poll_table *wait)
{
	poll_wait(file, &crng_init_wait, wait);
	return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM;
}

static ssize_t write_pool_user(struct iov_iter *iter)
{
	u8 block[BLAKE2S_BLOCK_SIZE];
	ssize_t ret = 0;
	size_t copied;

	if (unlikely(!iov_iter_count(iter)))
		return 0;

	for (;;) {
		copied = copy_from_iter(block, sizeof(block), iter);
		ret += copied;
		mix_pool_bytes(block, copied);
		if (!iov_iter_count(iter) || copied != sizeof(block))
			break;

		BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
		if (ret % PAGE_SIZE == 0) {
			if (signal_pending(current))
				break;
			cond_resched();
		}
	}

	memzero_explicit(block, sizeof(block));
	return ret ? ret : -EFAULT;
}

static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter)
{
	return write_pool_user(iter);
}

static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
{
	static int maxwarn = 10;

	/*
	 * Opportunistically attempt to initialize the RNG on platforms that
	 * have fast cycle counters, but don't (for now) require it to succeed.
	 */
	if (!crng_ready())
		try_to_generate_entropy();

	if (!crng_ready()) {
		if (!ratelimit_disable && maxwarn <= 0)
			++urandom_warning.missed;
		else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
			--maxwarn;
			pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
				  current->comm, iov_iter_count(iter));
		}
	}

	return get_random_bytes_user(iter);
}

static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
{
	int ret;

	if (!crng_ready() &&
	    ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
	     (kiocb->ki_filp->f_flags & O_NONBLOCK)))
		return -EAGAIN;

	ret = wait_for_random_bytes();
	if (ret != 0)
		return ret;
	return get_random_bytes_user(iter);
}

static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
{
	int __user *p = (int __user *)arg;
	int ent_count;

	switch (cmd) {
	case RNDGETENTCNT:
		/* Inherently racy, no point locking. */
		if (put_user(input_pool.init_bits, p))
			return -EFAULT;
		return 0;
	case RNDADDTOENTCNT:
		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
		if (get_user(ent_count, p))
			return -EFAULT;
		if (ent_count < 0)
			return -EINVAL;
		credit_init_bits(ent_count);
		return 0;
	case RNDADDENTROPY: {
		struct iov_iter iter;
		struct iovec iov;
		ssize_t ret;
		int len;

		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
		if (get_user(ent_count, p++))
			return -EFAULT;
		if (ent_count < 0)
			return -EINVAL;
		if (get_user(len, p++))
			return -EFAULT;
		ret = import_single_range(ITER_SOURCE, p, len, &iov, &iter);
		if (unlikely(ret))
			return ret;
		ret = write_pool_user(&iter);
		if (unlikely(ret < 0))
			return ret;
		/* Since we're crediting, enforce that it was all written into the pool. */
		if (unlikely(ret != len))
			return -EFAULT;
		credit_init_bits(ent_count);
		return 0;
	}
	case RNDZAPENTCNT:
	case RNDCLEARPOOL:
		/* No longer has any effect. */
		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
		return 0;
	case RNDRESEEDCRNG:
		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
		if (!crng_ready())
			return -ENODATA;
		crng_reseed(NULL);
		return 0;
	default:
		return -EINVAL;
	}
}

static int random_fasync(int fd, struct file *filp, int on)
{
	return fasync_helper(fd, filp, on, &fasync);
}

const struct file_operations random_fops = {
	.read_iter = random_read_iter,
	.write_iter = random_write_iter,
	.poll = random_poll,
	.unlocked_ioctl = random_ioctl,
	.compat_ioctl = compat_ptr_ioctl,
	.fasync = random_fasync,
	.llseek = noop_llseek,
	.splice_read = copy_splice_read,
	.splice_write = iter_file_splice_write,
};

const struct file_operations urandom_fops = {
	.read_iter = urandom_read_iter,
	.write_iter = random_write_iter,
	.unlocked_ioctl = random_ioctl,
	.compat_ioctl = compat_ptr_ioctl,
	.fasync = random_fasync,
	.llseek = noop_llseek,
	.splice_read = copy_splice_read,
	.splice_write = iter_file_splice_write,
};


/********************************************************************
 *
 * Sysctl interface.
 *
 * These are partly unused legacy knobs with dummy values to not break
 * userspace and partly still useful things. They are usually accessible
 * in /proc/sys/kernel/random/ and are as follows:
 *
 * - boot_id - a UUID representing the current boot.
 *
 * - uuid - a random UUID, different each time the file is read.
 *
 * - poolsize - the number of bits of entropy that the input pool can
 *   hold, tied to the POOL_BITS constant.
 *
 * - entropy_avail - the number of bits of entropy currently in the
 *   input pool. Always <= poolsize.
 *
 * - write_wakeup_threshold - the amount of entropy in the input pool
 *   below which write polls to /dev/random will unblock, requesting
 *   more entropy, tied to the POOL_READY_BITS constant. It is writable
 *   to avoid breaking old userspaces, but writing to it does not
 *   change any behavior of the RNG.
 *
 * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL.
 *   It is writable to avoid breaking old userspaces, but writing
 *   to it does not change any behavior of the RNG.
 *
 ********************************************************************/

#ifdef CONFIG_SYSCTL

#include <linux/sysctl.h>

static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ;
static int sysctl_random_write_wakeup_bits = POOL_READY_BITS;
static int sysctl_poolsize = POOL_BITS;
static u8 sysctl_bootid[UUID_SIZE];

/*
 * This function is used to return both the bootid UUID, and random
 * UUID. The difference is in whether table->data is NULL; if it is,
 * then a new UUID is generated and returned to the user.
 */
static int proc_do_uuid(struct ctl_table *table, int write, void *buf,
			size_t *lenp, loff_t *ppos)
{
	u8 tmp_uuid[UUID_SIZE], *uuid;
	char uuid_string[UUID_STRING_LEN + 1];
	struct ctl_table fake_table = {
		.data = uuid_string,
		.maxlen = UUID_STRING_LEN
	};

	if (write)
		return -EPERM;

	uuid = table->data;
	if (!uuid) {
		uuid = tmp_uuid;
		generate_random_uuid(uuid);
	} else {
		static DEFINE_SPINLOCK(bootid_spinlock);

		spin_lock(&bootid_spinlock);
		if (!uuid[8])
			generate_random_uuid(uuid);
		spin_unlock(&bootid_spinlock);
	}

	snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
	return proc_dostring(&fake_table, 0, buf, lenp, ppos);
}

/* The same as proc_dointvec, but writes don't change anything. */
static int proc_do_rointvec(struct ctl_table *table, int write, void *buf,
			    size_t *lenp, loff_t *ppos)
{
	return write ? 0 : proc_dointvec(table, 0, buf, lenp, ppos);
}

static struct ctl_table random_table[] = {
	{
		.procname	= "poolsize",
		.data		= &sysctl_poolsize,
		.maxlen		= sizeof(int),
		.mode		= 0444,
		.proc_handler	= proc_dointvec,
	},
	{
		.procname	= "entropy_avail",
		.data		= &input_pool.init_bits,
		.maxlen		= sizeof(int),
		.mode		= 0444,
		.proc_handler	= proc_dointvec,
	},
	{
		.procname	= "write_wakeup_threshold",
		.data		= &sysctl_random_write_wakeup_bits,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= proc_do_rointvec,
	},
	{
		.procname	= "urandom_min_reseed_secs",
		.data		= &sysctl_random_min_urandom_seed,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= proc_do_rointvec,
	},
	{
		.procname	= "boot_id",
		.data		= &sysctl_bootid,
		.mode		= 0444,
		.proc_handler	= proc_do_uuid,
	},
	{
		.procname	= "uuid",
		.mode		= 0444,
		.proc_handler	= proc_do_uuid,
	},
};

/*
 * random_init() is called before sysctl_init(),
 * so we cannot call register_sysctl_init() in random_init()
 */
static int __init random_sysctls_init(void)
{
	register_sysctl_init("kernel/random", random_table);
	return 0;
}
device_initcall(random_sysctls_init);
#endif