xref: /openbmc/linux/drivers/char/random.c (revision b34e08d5)
1 /*
2  * random.c -- A strong random number generator
3  *
4  * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
5  *
6  * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999.  All
7  * rights reserved.
8  *
9  * Redistribution and use in source and binary forms, with or without
10  * modification, are permitted provided that the following conditions
11  * are met:
12  * 1. Redistributions of source code must retain the above copyright
13  *    notice, and the entire permission notice in its entirety,
14  *    including the disclaimer of warranties.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  * 3. The name of the author may not be used to endorse or promote
19  *    products derived from this software without specific prior
20  *    written permission.
21  *
22  * ALTERNATIVELY, this product may be distributed under the terms of
23  * the GNU General Public License, in which case the provisions of the GPL are
24  * required INSTEAD OF the above restrictions.  (This clause is
25  * necessary due to a potential bad interaction between the GPL and
26  * the restrictions contained in a BSD-style copyright.)
27  *
28  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
29  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
30  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
31  * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
32  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
33  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
34  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
35  * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
36  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
38  * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
39  * DAMAGE.
40  */
41 
42 /*
43  * (now, with legal B.S. out of the way.....)
44  *
45  * This routine gathers environmental noise from device drivers, etc.,
46  * and returns good random numbers, suitable for cryptographic use.
47  * Besides the obvious cryptographic uses, these numbers are also good
48  * for seeding TCP sequence numbers, and other places where it is
49  * desirable to have numbers which are not only random, but hard to
50  * predict by an attacker.
51  *
52  * Theory of operation
53  * ===================
54  *
55  * Computers are very predictable devices.  Hence it is extremely hard
56  * to produce truly random numbers on a computer --- as opposed to
57  * pseudo-random numbers, which can easily generated by using a
58  * algorithm.  Unfortunately, it is very easy for attackers to guess
59  * the sequence of pseudo-random number generators, and for some
60  * applications this is not acceptable.  So instead, we must try to
61  * gather "environmental noise" from the computer's environment, which
62  * must be hard for outside attackers to observe, and use that to
63  * generate random numbers.  In a Unix environment, this is best done
64  * from inside the kernel.
65  *
66  * Sources of randomness from the environment include inter-keyboard
67  * timings, inter-interrupt timings from some interrupts, and other
68  * events which are both (a) non-deterministic and (b) hard for an
69  * outside observer to measure.  Randomness from these sources are
70  * added to an "entropy pool", which is mixed using a CRC-like function.
71  * This is not cryptographically strong, but it is adequate assuming
72  * the randomness is not chosen maliciously, and it is fast enough that
73  * the overhead of doing it on every interrupt is very reasonable.
74  * As random bytes are mixed into the entropy pool, the routines keep
75  * an *estimate* of how many bits of randomness have been stored into
76  * the random number generator's internal state.
77  *
78  * When random bytes are desired, they are obtained by taking the SHA
79  * hash of the contents of the "entropy pool".  The SHA hash avoids
80  * exposing the internal state of the entropy pool.  It is believed to
81  * be computationally infeasible to derive any useful information
82  * about the input of SHA from its output.  Even if it is possible to
83  * analyze SHA in some clever way, as long as the amount of data
84  * returned from the generator is less than the inherent entropy in
85  * the pool, the output data is totally unpredictable.  For this
86  * reason, the routine decreases its internal estimate of how many
87  * bits of "true randomness" are contained in the entropy pool as it
88  * outputs random numbers.
89  *
90  * If this estimate goes to zero, the routine can still generate
91  * random numbers; however, an attacker may (at least in theory) be
92  * able to infer the future output of the generator from prior
93  * outputs.  This requires successful cryptanalysis of SHA, which is
94  * not believed to be feasible, but there is a remote possibility.
95  * Nonetheless, these numbers should be useful for the vast majority
96  * of purposes.
97  *
98  * Exported interfaces ---- output
99  * ===============================
100  *
101  * There are three exported interfaces; the first is one designed to
102  * be used from within the kernel:
103  *
104  * 	void get_random_bytes(void *buf, int nbytes);
105  *
106  * This interface will return the requested number of random bytes,
107  * and place it in the requested buffer.
108  *
109  * The two other interfaces are two character devices /dev/random and
110  * /dev/urandom.  /dev/random is suitable for use when very high
111  * quality randomness is desired (for example, for key generation or
112  * one-time pads), as it will only return a maximum of the number of
113  * bits of randomness (as estimated by the random number generator)
114  * contained in the entropy pool.
115  *
116  * The /dev/urandom device does not have this limit, and will return
117  * as many bytes as are requested.  As more and more random bytes are
118  * requested without giving time for the entropy pool to recharge,
119  * this will result in random numbers that are merely cryptographically
120  * strong.  For many applications, however, this is acceptable.
121  *
122  * Exported interfaces ---- input
123  * ==============================
124  *
125  * The current exported interfaces for gathering environmental noise
126  * from the devices are:
127  *
128  *	void add_device_randomness(const void *buf, unsigned int size);
129  * 	void add_input_randomness(unsigned int type, unsigned int code,
130  *                                unsigned int value);
131  *	void add_interrupt_randomness(int irq, int irq_flags);
132  * 	void add_disk_randomness(struct gendisk *disk);
133  *
134  * add_device_randomness() is for adding data to the random pool that
135  * is likely to differ between two devices (or possibly even per boot).
136  * This would be things like MAC addresses or serial numbers, or the
137  * read-out of the RTC. This does *not* add any actual entropy to the
138  * pool, but it initializes the pool to different values for devices
139  * that might otherwise be identical and have very little entropy
140  * available to them (particularly common in the embedded world).
141  *
142  * add_input_randomness() uses the input layer interrupt timing, as well as
143  * the event type information from the hardware.
144  *
145  * add_interrupt_randomness() uses the interrupt timing as random
146  * inputs to the entropy pool. Using the cycle counters and the irq source
147  * as inputs, it feeds the randomness roughly once a second.
148  *
149  * add_disk_randomness() uses what amounts to the seek time of block
150  * layer request events, on a per-disk_devt basis, as input to the
151  * entropy pool. Note that high-speed solid state drives with very low
152  * seek times do not make for good sources of entropy, as their seek
153  * times are usually fairly consistent.
154  *
155  * All of these routines try to estimate how many bits of randomness a
156  * particular randomness source.  They do this by keeping track of the
157  * first and second order deltas of the event timings.
158  *
159  * Ensuring unpredictability at system startup
160  * ============================================
161  *
162  * When any operating system starts up, it will go through a sequence
163  * of actions that are fairly predictable by an adversary, especially
164  * if the start-up does not involve interaction with a human operator.
165  * This reduces the actual number of bits of unpredictability in the
166  * entropy pool below the value in entropy_count.  In order to
167  * counteract this effect, it helps to carry information in the
168  * entropy pool across shut-downs and start-ups.  To do this, put the
169  * following lines an appropriate script which is run during the boot
170  * sequence:
171  *
172  *	echo "Initializing random number generator..."
173  *	random_seed=/var/run/random-seed
174  *	# Carry a random seed from start-up to start-up
175  *	# Load and then save the whole entropy pool
176  *	if [ -f $random_seed ]; then
177  *		cat $random_seed >/dev/urandom
178  *	else
179  *		touch $random_seed
180  *	fi
181  *	chmod 600 $random_seed
182  *	dd if=/dev/urandom of=$random_seed count=1 bs=512
183  *
184  * and the following lines in an appropriate script which is run as
185  * the system is shutdown:
186  *
187  *	# Carry a random seed from shut-down to start-up
188  *	# Save the whole entropy pool
189  *	echo "Saving random seed..."
190  *	random_seed=/var/run/random-seed
191  *	touch $random_seed
192  *	chmod 600 $random_seed
193  *	dd if=/dev/urandom of=$random_seed count=1 bs=512
194  *
195  * For example, on most modern systems using the System V init
196  * scripts, such code fragments would be found in
197  * /etc/rc.d/init.d/random.  On older Linux systems, the correct script
198  * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0.
199  *
200  * Effectively, these commands cause the contents of the entropy pool
201  * to be saved at shut-down time and reloaded into the entropy pool at
202  * start-up.  (The 'dd' in the addition to the bootup script is to
203  * make sure that /etc/random-seed is different for every start-up,
204  * even if the system crashes without executing rc.0.)  Even with
205  * complete knowledge of the start-up activities, predicting the state
206  * of the entropy pool requires knowledge of the previous history of
207  * the system.
208  *
209  * Configuring the /dev/random driver under Linux
210  * ==============================================
211  *
212  * The /dev/random driver under Linux uses minor numbers 8 and 9 of
213  * the /dev/mem major number (#1).  So if your system does not have
214  * /dev/random and /dev/urandom created already, they can be created
215  * by using the commands:
216  *
217  * 	mknod /dev/random c 1 8
218  * 	mknod /dev/urandom c 1 9
219  *
220  * Acknowledgements:
221  * =================
222  *
223  * Ideas for constructing this random number generator were derived
224  * from Pretty Good Privacy's random number generator, and from private
225  * discussions with Phil Karn.  Colin Plumb provided a faster random
226  * number generator, which speed up the mixing function of the entropy
227  * pool, taken from PGPfone.  Dale Worley has also contributed many
228  * useful ideas and suggestions to improve this driver.
229  *
230  * Any flaws in the design are solely my responsibility, and should
231  * not be attributed to the Phil, Colin, or any of authors of PGP.
232  *
233  * Further background information on this topic may be obtained from
234  * RFC 1750, "Randomness Recommendations for Security", by Donald
235  * Eastlake, Steve Crocker, and Jeff Schiller.
236  */
237 
238 #include <linux/utsname.h>
239 #include <linux/module.h>
240 #include <linux/kernel.h>
241 #include <linux/major.h>
242 #include <linux/string.h>
243 #include <linux/fcntl.h>
244 #include <linux/slab.h>
245 #include <linux/random.h>
246 #include <linux/poll.h>
247 #include <linux/init.h>
248 #include <linux/fs.h>
249 #include <linux/genhd.h>
250 #include <linux/interrupt.h>
251 #include <linux/mm.h>
252 #include <linux/spinlock.h>
253 #include <linux/percpu.h>
254 #include <linux/cryptohash.h>
255 #include <linux/fips.h>
256 #include <linux/ptrace.h>
257 #include <linux/kmemcheck.h>
258 #include <linux/workqueue.h>
259 #include <linux/irq.h>
260 
261 #include <asm/processor.h>
262 #include <asm/uaccess.h>
263 #include <asm/irq.h>
264 #include <asm/irq_regs.h>
265 #include <asm/io.h>
266 
267 #define CREATE_TRACE_POINTS
268 #include <trace/events/random.h>
269 
270 /*
271  * Configuration information
272  */
273 #define INPUT_POOL_SHIFT	12
274 #define INPUT_POOL_WORDS	(1 << (INPUT_POOL_SHIFT-5))
275 #define OUTPUT_POOL_SHIFT	10
276 #define OUTPUT_POOL_WORDS	(1 << (OUTPUT_POOL_SHIFT-5))
277 #define SEC_XFER_SIZE		512
278 #define EXTRACT_SIZE		10
279 
280 #define DEBUG_RANDOM_BOOT 0
281 
282 #define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))
283 
284 /*
285  * To allow fractional bits to be tracked, the entropy_count field is
286  * denominated in units of 1/8th bits.
287  *
288  * 2*(ENTROPY_SHIFT + log2(poolbits)) must <= 31, or the multiply in
289  * credit_entropy_bits() needs to be 64 bits wide.
290  */
291 #define ENTROPY_SHIFT 3
292 #define ENTROPY_BITS(r) ((r)->entropy_count >> ENTROPY_SHIFT)
293 
294 /*
295  * The minimum number of bits of entropy before we wake up a read on
296  * /dev/random.  Should be enough to do a significant reseed.
297  */
298 static int random_read_wakeup_bits = 64;
299 
300 /*
301  * If the entropy count falls under this number of bits, then we
302  * should wake up processes which are selecting or polling on write
303  * access to /dev/random.
304  */
305 static int random_write_wakeup_bits = 28 * OUTPUT_POOL_WORDS;
306 
307 /*
308  * The minimum number of seconds between urandom pool reseeding.  We
309  * do this to limit the amount of entropy that can be drained from the
310  * input pool even if there are heavy demands on /dev/urandom.
311  */
312 static int random_min_urandom_seed = 60;
313 
314 /*
315  * Originally, we used a primitive polynomial of degree .poolwords
316  * over GF(2).  The taps for various sizes are defined below.  They
317  * were chosen to be evenly spaced except for the last tap, which is 1
318  * to get the twisting happening as fast as possible.
319  *
320  * For the purposes of better mixing, we use the CRC-32 polynomial as
321  * well to make a (modified) twisted Generalized Feedback Shift
322  * Register.  (See M. Matsumoto & Y. Kurita, 1992.  Twisted GFSR
323  * generators.  ACM Transactions on Modeling and Computer Simulation
324  * 2(3):179-194.  Also see M. Matsumoto & Y. Kurita, 1994.  Twisted
325  * GFSR generators II.  ACM Transactions on Modeling and Computer
326  * Simulation 4:254-266)
327  *
328  * Thanks to Colin Plumb for suggesting this.
329  *
330  * The mixing operation is much less sensitive than the output hash,
331  * where we use SHA-1.  All that we want of mixing operation is that
332  * it be a good non-cryptographic hash; i.e. it not produce collisions
333  * when fed "random" data of the sort we expect to see.  As long as
334  * the pool state differs for different inputs, we have preserved the
335  * input entropy and done a good job.  The fact that an intelligent
336  * attacker can construct inputs that will produce controlled
337  * alterations to the pool's state is not important because we don't
338  * consider such inputs to contribute any randomness.  The only
339  * property we need with respect to them is that the attacker can't
340  * increase his/her knowledge of the pool's state.  Since all
341  * additions are reversible (knowing the final state and the input,
342  * you can reconstruct the initial state), if an attacker has any
343  * uncertainty about the initial state, he/she can only shuffle that
344  * uncertainty about, but never cause any collisions (which would
345  * decrease the uncertainty).
346  *
347  * Our mixing functions were analyzed by Lacharme, Roeck, Strubel, and
348  * Videau in their paper, "The Linux Pseudorandom Number Generator
349  * Revisited" (see: http://eprint.iacr.org/2012/251.pdf).  In their
350  * paper, they point out that we are not using a true Twisted GFSR,
351  * since Matsumoto & Kurita used a trinomial feedback polynomial (that
352  * is, with only three taps, instead of the six that we are using).
353  * As a result, the resulting polynomial is neither primitive nor
354  * irreducible, and hence does not have a maximal period over
355  * GF(2**32).  They suggest a slight change to the generator
356  * polynomial which improves the resulting TGFSR polynomial to be
357  * irreducible, which we have made here.
358  */
359 static struct poolinfo {
360 	int poolbitshift, poolwords, poolbytes, poolbits, poolfracbits;
361 #define S(x) ilog2(x)+5, (x), (x)*4, (x)*32, (x) << (ENTROPY_SHIFT+5)
362 	int tap1, tap2, tap3, tap4, tap5;
363 } poolinfo_table[] = {
364 	/* was: x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 */
365 	/* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */
366 	{ S(128),	104,	76,	51,	25,	1 },
367 	/* was: x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 */
368 	/* x^32 + x^26 + x^19 + x^14 + x^7 + x + 1 */
369 	{ S(32),	26,	19,	14,	7,	1 },
370 #if 0
371 	/* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1  -- 115 */
372 	{ S(2048),	1638,	1231,	819,	411,	1 },
373 
374 	/* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
375 	{ S(1024),	817,	615,	412,	204,	1 },
376 
377 	/* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
378 	{ S(1024),	819,	616,	410,	207,	2 },
379 
380 	/* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
381 	{ S(512),	411,	308,	208,	104,	1 },
382 
383 	/* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
384 	{ S(512),	409,	307,	206,	102,	2 },
385 	/* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
386 	{ S(512),	409,	309,	205,	103,	2 },
387 
388 	/* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
389 	{ S(256),	205,	155,	101,	52,	1 },
390 
391 	/* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
392 	{ S(128),	103,	78,	51,	27,	2 },
393 
394 	/* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
395 	{ S(64),	52,	39,	26,	14,	1 },
396 #endif
397 };
398 
399 /*
400  * Static global variables
401  */
402 static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
403 static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
404 static struct fasync_struct *fasync;
405 
406 /**********************************************************************
407  *
408  * OS independent entropy store.   Here are the functions which handle
409  * storing entropy in an entropy pool.
410  *
411  **********************************************************************/
412 
413 struct entropy_store;
414 struct entropy_store {
415 	/* read-only data: */
416 	const struct poolinfo *poolinfo;
417 	__u32 *pool;
418 	const char *name;
419 	struct entropy_store *pull;
420 	struct work_struct push_work;
421 
422 	/* read-write data: */
423 	unsigned long last_pulled;
424 	spinlock_t lock;
425 	unsigned short add_ptr;
426 	unsigned short input_rotate;
427 	int entropy_count;
428 	int entropy_total;
429 	unsigned int initialized:1;
430 	unsigned int limit:1;
431 	unsigned int last_data_init:1;
432 	__u8 last_data[EXTRACT_SIZE];
433 };
434 
435 static void push_to_pool(struct work_struct *work);
436 static __u32 input_pool_data[INPUT_POOL_WORDS];
437 static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
438 static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
439 
440 static struct entropy_store input_pool = {
441 	.poolinfo = &poolinfo_table[0],
442 	.name = "input",
443 	.limit = 1,
444 	.lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
445 	.pool = input_pool_data
446 };
447 
448 static struct entropy_store blocking_pool = {
449 	.poolinfo = &poolinfo_table[1],
450 	.name = "blocking",
451 	.limit = 1,
452 	.pull = &input_pool,
453 	.lock = __SPIN_LOCK_UNLOCKED(blocking_pool.lock),
454 	.pool = blocking_pool_data,
455 	.push_work = __WORK_INITIALIZER(blocking_pool.push_work,
456 					push_to_pool),
457 };
458 
459 static struct entropy_store nonblocking_pool = {
460 	.poolinfo = &poolinfo_table[1],
461 	.name = "nonblocking",
462 	.pull = &input_pool,
463 	.lock = __SPIN_LOCK_UNLOCKED(nonblocking_pool.lock),
464 	.pool = nonblocking_pool_data,
465 	.push_work = __WORK_INITIALIZER(nonblocking_pool.push_work,
466 					push_to_pool),
467 };
468 
469 static __u32 const twist_table[8] = {
470 	0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
471 	0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
472 
473 /*
474  * This function adds bytes into the entropy "pool".  It does not
475  * update the entropy estimate.  The caller should call
476  * credit_entropy_bits if this is appropriate.
477  *
478  * The pool is stirred with a primitive polynomial of the appropriate
479  * degree, and then twisted.  We twist by three bits at a time because
480  * it's cheap to do so and helps slightly in the expected case where
481  * the entropy is concentrated in the low-order bits.
482  */
483 static void _mix_pool_bytes(struct entropy_store *r, const void *in,
484 			    int nbytes, __u8 out[64])
485 {
486 	unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
487 	int input_rotate;
488 	int wordmask = r->poolinfo->poolwords - 1;
489 	const char *bytes = in;
490 	__u32 w;
491 
492 	tap1 = r->poolinfo->tap1;
493 	tap2 = r->poolinfo->tap2;
494 	tap3 = r->poolinfo->tap3;
495 	tap4 = r->poolinfo->tap4;
496 	tap5 = r->poolinfo->tap5;
497 
498 	smp_rmb();
499 	input_rotate = ACCESS_ONCE(r->input_rotate);
500 	i = ACCESS_ONCE(r->add_ptr);
501 
502 	/* mix one byte at a time to simplify size handling and churn faster */
503 	while (nbytes--) {
504 		w = rol32(*bytes++, input_rotate);
505 		i = (i - 1) & wordmask;
506 
507 		/* XOR in the various taps */
508 		w ^= r->pool[i];
509 		w ^= r->pool[(i + tap1) & wordmask];
510 		w ^= r->pool[(i + tap2) & wordmask];
511 		w ^= r->pool[(i + tap3) & wordmask];
512 		w ^= r->pool[(i + tap4) & wordmask];
513 		w ^= r->pool[(i + tap5) & wordmask];
514 
515 		/* Mix the result back in with a twist */
516 		r->pool[i] = (w >> 3) ^ twist_table[w & 7];
517 
518 		/*
519 		 * Normally, we add 7 bits of rotation to the pool.
520 		 * At the beginning of the pool, add an extra 7 bits
521 		 * rotation, so that successive passes spread the
522 		 * input bits across the pool evenly.
523 		 */
524 		input_rotate = (input_rotate + (i ? 7 : 14)) & 31;
525 	}
526 
527 	ACCESS_ONCE(r->input_rotate) = input_rotate;
528 	ACCESS_ONCE(r->add_ptr) = i;
529 	smp_wmb();
530 
531 	if (out)
532 		for (j = 0; j < 16; j++)
533 			((__u32 *)out)[j] = r->pool[(i - j) & wordmask];
534 }
535 
536 static void __mix_pool_bytes(struct entropy_store *r, const void *in,
537 			     int nbytes, __u8 out[64])
538 {
539 	trace_mix_pool_bytes_nolock(r->name, nbytes, _RET_IP_);
540 	_mix_pool_bytes(r, in, nbytes, out);
541 }
542 
543 static void mix_pool_bytes(struct entropy_store *r, const void *in,
544 			   int nbytes, __u8 out[64])
545 {
546 	unsigned long flags;
547 
548 	trace_mix_pool_bytes(r->name, nbytes, _RET_IP_);
549 	spin_lock_irqsave(&r->lock, flags);
550 	_mix_pool_bytes(r, in, nbytes, out);
551 	spin_unlock_irqrestore(&r->lock, flags);
552 }
553 
554 struct fast_pool {
555 	__u32		pool[4];
556 	unsigned long	last;
557 	unsigned short	count;
558 	unsigned char	rotate;
559 	unsigned char	last_timer_intr;
560 };
561 
562 /*
563  * This is a fast mixing routine used by the interrupt randomness
564  * collector.  It's hardcoded for an 128 bit pool and assumes that any
565  * locks that might be needed are taken by the caller.
566  */
567 static void fast_mix(struct fast_pool *f, __u32 input[4])
568 {
569 	__u32		w;
570 	unsigned	input_rotate = f->rotate;
571 
572 	w = rol32(input[0], input_rotate) ^ f->pool[0] ^ f->pool[3];
573 	f->pool[0] = (w >> 3) ^ twist_table[w & 7];
574 	input_rotate = (input_rotate + 14) & 31;
575 	w = rol32(input[1], input_rotate) ^ f->pool[1] ^ f->pool[0];
576 	f->pool[1] = (w >> 3) ^ twist_table[w & 7];
577 	input_rotate = (input_rotate + 7) & 31;
578 	w = rol32(input[2], input_rotate) ^ f->pool[2] ^ f->pool[1];
579 	f->pool[2] = (w >> 3) ^ twist_table[w & 7];
580 	input_rotate = (input_rotate + 7) & 31;
581 	w = rol32(input[3], input_rotate) ^ f->pool[3] ^ f->pool[2];
582 	f->pool[3] = (w >> 3) ^ twist_table[w & 7];
583 	input_rotate = (input_rotate + 7) & 31;
584 
585 	f->rotate = input_rotate;
586 	f->count++;
587 }
588 
589 /*
590  * Credit (or debit) the entropy store with n bits of entropy.
591  * Use credit_entropy_bits_safe() if the value comes from userspace
592  * or otherwise should be checked for extreme values.
593  */
594 static void credit_entropy_bits(struct entropy_store *r, int nbits)
595 {
596 	int entropy_count, orig;
597 	const int pool_size = r->poolinfo->poolfracbits;
598 	int nfrac = nbits << ENTROPY_SHIFT;
599 
600 	if (!nbits)
601 		return;
602 
603 retry:
604 	entropy_count = orig = ACCESS_ONCE(r->entropy_count);
605 	if (nfrac < 0) {
606 		/* Debit */
607 		entropy_count += nfrac;
608 	} else {
609 		/*
610 		 * Credit: we have to account for the possibility of
611 		 * overwriting already present entropy.	 Even in the
612 		 * ideal case of pure Shannon entropy, new contributions
613 		 * approach the full value asymptotically:
614 		 *
615 		 * entropy <- entropy + (pool_size - entropy) *
616 		 *	(1 - exp(-add_entropy/pool_size))
617 		 *
618 		 * For add_entropy <= pool_size/2 then
619 		 * (1 - exp(-add_entropy/pool_size)) >=
620 		 *    (add_entropy/pool_size)*0.7869...
621 		 * so we can approximate the exponential with
622 		 * 3/4*add_entropy/pool_size and still be on the
623 		 * safe side by adding at most pool_size/2 at a time.
624 		 *
625 		 * The use of pool_size-2 in the while statement is to
626 		 * prevent rounding artifacts from making the loop
627 		 * arbitrarily long; this limits the loop to log2(pool_size)*2
628 		 * turns no matter how large nbits is.
629 		 */
630 		int pnfrac = nfrac;
631 		const int s = r->poolinfo->poolbitshift + ENTROPY_SHIFT + 2;
632 		/* The +2 corresponds to the /4 in the denominator */
633 
634 		do {
635 			unsigned int anfrac = min(pnfrac, pool_size/2);
636 			unsigned int add =
637 				((pool_size - entropy_count)*anfrac*3) >> s;
638 
639 			entropy_count += add;
640 			pnfrac -= anfrac;
641 		} while (unlikely(entropy_count < pool_size-2 && pnfrac));
642 	}
643 
644 	if (entropy_count < 0) {
645 		pr_warn("random: negative entropy/overflow: pool %s count %d\n",
646 			r->name, entropy_count);
647 		WARN_ON(1);
648 		entropy_count = 0;
649 	} else if (entropy_count > pool_size)
650 		entropy_count = pool_size;
651 	if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
652 		goto retry;
653 
654 	r->entropy_total += nbits;
655 	if (!r->initialized && r->entropy_total > 128) {
656 		r->initialized = 1;
657 		r->entropy_total = 0;
658 		if (r == &nonblocking_pool) {
659 			prandom_reseed_late();
660 			pr_notice("random: %s pool is initialized\n", r->name);
661 		}
662 	}
663 
664 	trace_credit_entropy_bits(r->name, nbits,
665 				  entropy_count >> ENTROPY_SHIFT,
666 				  r->entropy_total, _RET_IP_);
667 
668 	if (r == &input_pool) {
669 		int entropy_bits = entropy_count >> ENTROPY_SHIFT;
670 
671 		/* should we wake readers? */
672 		if (entropy_bits >= random_read_wakeup_bits) {
673 			wake_up_interruptible(&random_read_wait);
674 			kill_fasync(&fasync, SIGIO, POLL_IN);
675 		}
676 		/* If the input pool is getting full, send some
677 		 * entropy to the two output pools, flipping back and
678 		 * forth between them, until the output pools are 75%
679 		 * full.
680 		 */
681 		if (entropy_bits > random_write_wakeup_bits &&
682 		    r->initialized &&
683 		    r->entropy_total >= 2*random_read_wakeup_bits) {
684 			static struct entropy_store *last = &blocking_pool;
685 			struct entropy_store *other = &blocking_pool;
686 
687 			if (last == &blocking_pool)
688 				other = &nonblocking_pool;
689 			if (other->entropy_count <=
690 			    3 * other->poolinfo->poolfracbits / 4)
691 				last = other;
692 			if (last->entropy_count <=
693 			    3 * last->poolinfo->poolfracbits / 4) {
694 				schedule_work(&last->push_work);
695 				r->entropy_total = 0;
696 			}
697 		}
698 	}
699 }
700 
701 static void credit_entropy_bits_safe(struct entropy_store *r, int nbits)
702 {
703 	const int nbits_max = (int)(~0U >> (ENTROPY_SHIFT + 1));
704 
705 	/* Cap the value to avoid overflows */
706 	nbits = min(nbits,  nbits_max);
707 	nbits = max(nbits, -nbits_max);
708 
709 	credit_entropy_bits(r, nbits);
710 }
711 
712 /*********************************************************************
713  *
714  * Entropy input management
715  *
716  *********************************************************************/
717 
718 /* There is one of these per entropy source */
719 struct timer_rand_state {
720 	cycles_t last_time;
721 	long last_delta, last_delta2;
722 	unsigned dont_count_entropy:1;
723 };
724 
725 #define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, };
726 
727 /*
728  * Add device- or boot-specific data to the input and nonblocking
729  * pools to help initialize them to unique values.
730  *
731  * None of this adds any entropy, it is meant to avoid the
732  * problem of the nonblocking pool having similar initial state
733  * across largely identical devices.
734  */
735 void add_device_randomness(const void *buf, unsigned int size)
736 {
737 	unsigned long time = random_get_entropy() ^ jiffies;
738 	unsigned long flags;
739 
740 	trace_add_device_randomness(size, _RET_IP_);
741 	spin_lock_irqsave(&input_pool.lock, flags);
742 	_mix_pool_bytes(&input_pool, buf, size, NULL);
743 	_mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
744 	spin_unlock_irqrestore(&input_pool.lock, flags);
745 
746 	spin_lock_irqsave(&nonblocking_pool.lock, flags);
747 	_mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
748 	_mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
749 	spin_unlock_irqrestore(&nonblocking_pool.lock, flags);
750 }
751 EXPORT_SYMBOL(add_device_randomness);
752 
753 static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE;
754 
755 /*
756  * This function adds entropy to the entropy "pool" by using timing
757  * delays.  It uses the timer_rand_state structure to make an estimate
758  * of how many bits of entropy this call has added to the pool.
759  *
760  * The number "num" is also added to the pool - it should somehow describe
761  * the type of event which just happened.  This is currently 0-255 for
762  * keyboard scan codes, and 256 upwards for interrupts.
763  *
764  */
765 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
766 {
767 	struct entropy_store	*r;
768 	struct {
769 		long jiffies;
770 		unsigned cycles;
771 		unsigned num;
772 	} sample;
773 	long delta, delta2, delta3;
774 
775 	preempt_disable();
776 
777 	sample.jiffies = jiffies;
778 	sample.cycles = random_get_entropy();
779 	sample.num = num;
780 	r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
781 	mix_pool_bytes(r, &sample, sizeof(sample), NULL);
782 
783 	/*
784 	 * Calculate number of bits of randomness we probably added.
785 	 * We take into account the first, second and third-order deltas
786 	 * in order to make our estimate.
787 	 */
788 
789 	if (!state->dont_count_entropy) {
790 		delta = sample.jiffies - state->last_time;
791 		state->last_time = sample.jiffies;
792 
793 		delta2 = delta - state->last_delta;
794 		state->last_delta = delta;
795 
796 		delta3 = delta2 - state->last_delta2;
797 		state->last_delta2 = delta2;
798 
799 		if (delta < 0)
800 			delta = -delta;
801 		if (delta2 < 0)
802 			delta2 = -delta2;
803 		if (delta3 < 0)
804 			delta3 = -delta3;
805 		if (delta > delta2)
806 			delta = delta2;
807 		if (delta > delta3)
808 			delta = delta3;
809 
810 		/*
811 		 * delta is now minimum absolute delta.
812 		 * Round down by 1 bit on general principles,
813 		 * and limit entropy entimate to 12 bits.
814 		 */
815 		credit_entropy_bits(r, min_t(int, fls(delta>>1), 11));
816 	}
817 	preempt_enable();
818 }
819 
820 void add_input_randomness(unsigned int type, unsigned int code,
821 				 unsigned int value)
822 {
823 	static unsigned char last_value;
824 
825 	/* ignore autorepeat and the like */
826 	if (value == last_value)
827 		return;
828 
829 	last_value = value;
830 	add_timer_randomness(&input_timer_state,
831 			     (type << 4) ^ code ^ (code >> 4) ^ value);
832 	trace_add_input_randomness(ENTROPY_BITS(&input_pool));
833 }
834 EXPORT_SYMBOL_GPL(add_input_randomness);
835 
836 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
837 
838 void add_interrupt_randomness(int irq, int irq_flags)
839 {
840 	struct entropy_store	*r;
841 	struct fast_pool	*fast_pool = &__get_cpu_var(irq_randomness);
842 	struct pt_regs		*regs = get_irq_regs();
843 	unsigned long		now = jiffies;
844 	cycles_t		cycles = random_get_entropy();
845 	__u32			input[4], c_high, j_high;
846 	__u64			ip;
847 	unsigned long		seed;
848 	int			credit;
849 
850 	c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;
851 	j_high = (sizeof(now) > 4) ? now >> 32 : 0;
852 	input[0] = cycles ^ j_high ^ irq;
853 	input[1] = now ^ c_high;
854 	ip = regs ? instruction_pointer(regs) : _RET_IP_;
855 	input[2] = ip;
856 	input[3] = ip >> 32;
857 
858 	fast_mix(fast_pool, input);
859 
860 	if ((fast_pool->count & 63) && !time_after(now, fast_pool->last + HZ))
861 		return;
862 
863 	fast_pool->last = now;
864 
865 	r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
866 	__mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
867 
868 	/*
869 	 * If we don't have a valid cycle counter, and we see
870 	 * back-to-back timer interrupts, then skip giving credit for
871 	 * any entropy, otherwise credit 1 bit.
872 	 */
873 	credit = 1;
874 	if (cycles == 0) {
875 		if (irq_flags & __IRQF_TIMER) {
876 			if (fast_pool->last_timer_intr)
877 				credit = 0;
878 			fast_pool->last_timer_intr = 1;
879 		} else
880 			fast_pool->last_timer_intr = 0;
881 	}
882 
883 	/*
884 	 * If we have architectural seed generator, produce a seed and
885 	 * add it to the pool.  For the sake of paranoia count it as
886 	 * 50% entropic.
887 	 */
888 	if (arch_get_random_seed_long(&seed)) {
889 		__mix_pool_bytes(r, &seed, sizeof(seed), NULL);
890 		credit += sizeof(seed) * 4;
891 	}
892 
893 	credit_entropy_bits(r, credit);
894 }
895 
896 #ifdef CONFIG_BLOCK
897 void add_disk_randomness(struct gendisk *disk)
898 {
899 	if (!disk || !disk->random)
900 		return;
901 	/* first major is 1, so we get >= 0x200 here */
902 	add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
903 	trace_add_disk_randomness(disk_devt(disk), ENTROPY_BITS(&input_pool));
904 }
905 #endif
906 
907 /*********************************************************************
908  *
909  * Entropy extraction routines
910  *
911  *********************************************************************/
912 
913 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
914 			       size_t nbytes, int min, int rsvd);
915 
916 /*
917  * This utility inline function is responsible for transferring entropy
918  * from the primary pool to the secondary extraction pool. We make
919  * sure we pull enough for a 'catastrophic reseed'.
920  */
921 static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes);
922 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
923 {
924 	if (r->limit == 0 && random_min_urandom_seed) {
925 		unsigned long now = jiffies;
926 
927 		if (time_before(now,
928 				r->last_pulled + random_min_urandom_seed * HZ))
929 			return;
930 		r->last_pulled = now;
931 	}
932 	if (r->pull &&
933 	    r->entropy_count < (nbytes << (ENTROPY_SHIFT + 3)) &&
934 	    r->entropy_count < r->poolinfo->poolfracbits)
935 		_xfer_secondary_pool(r, nbytes);
936 }
937 
938 static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
939 {
940 	__u32	tmp[OUTPUT_POOL_WORDS];
941 
942 	/* For /dev/random's pool, always leave two wakeups' worth */
943 	int rsvd_bytes = r->limit ? 0 : random_read_wakeup_bits / 4;
944 	int bytes = nbytes;
945 
946 	/* pull at least as much as a wakeup */
947 	bytes = max_t(int, bytes, random_read_wakeup_bits / 8);
948 	/* but never more than the buffer size */
949 	bytes = min_t(int, bytes, sizeof(tmp));
950 
951 	trace_xfer_secondary_pool(r->name, bytes * 8, nbytes * 8,
952 				  ENTROPY_BITS(r), ENTROPY_BITS(r->pull));
953 	bytes = extract_entropy(r->pull, tmp, bytes,
954 				random_read_wakeup_bits / 8, rsvd_bytes);
955 	mix_pool_bytes(r, tmp, bytes, NULL);
956 	credit_entropy_bits(r, bytes*8);
957 }
958 
959 /*
960  * Used as a workqueue function so that when the input pool is getting
961  * full, we can "spill over" some entropy to the output pools.  That
962  * way the output pools can store some of the excess entropy instead
963  * of letting it go to waste.
964  */
965 static void push_to_pool(struct work_struct *work)
966 {
967 	struct entropy_store *r = container_of(work, struct entropy_store,
968 					      push_work);
969 	BUG_ON(!r);
970 	_xfer_secondary_pool(r, random_read_wakeup_bits/8);
971 	trace_push_to_pool(r->name, r->entropy_count >> ENTROPY_SHIFT,
972 			   r->pull->entropy_count >> ENTROPY_SHIFT);
973 }
974 
975 /*
976  * This function decides how many bytes to actually take from the
977  * given pool, and also debits the entropy count accordingly.
978  */
979 static size_t account(struct entropy_store *r, size_t nbytes, int min,
980 		      int reserved)
981 {
982 	int have_bytes;
983 	int entropy_count, orig;
984 	size_t ibytes;
985 
986 	BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
987 
988 	/* Can we pull enough? */
989 retry:
990 	entropy_count = orig = ACCESS_ONCE(r->entropy_count);
991 	have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);
992 	ibytes = nbytes;
993 	/* If limited, never pull more than available */
994 	if (r->limit)
995 		ibytes = min_t(size_t, ibytes, have_bytes - reserved);
996 	if (ibytes < min)
997 		ibytes = 0;
998 	entropy_count = max_t(int, 0,
999 			      entropy_count - (ibytes << (ENTROPY_SHIFT + 3)));
1000 	if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
1001 		goto retry;
1002 
1003 	trace_debit_entropy(r->name, 8 * ibytes);
1004 	if (ibytes &&
1005 	    (r->entropy_count >> ENTROPY_SHIFT) < random_write_wakeup_bits) {
1006 		wake_up_interruptible(&random_write_wait);
1007 		kill_fasync(&fasync, SIGIO, POLL_OUT);
1008 	}
1009 
1010 	return ibytes;
1011 }
1012 
1013 /*
1014  * This function does the actual extraction for extract_entropy and
1015  * extract_entropy_user.
1016  *
1017  * Note: we assume that .poolwords is a multiple of 16 words.
1018  */
1019 static void extract_buf(struct entropy_store *r, __u8 *out)
1020 {
1021 	int i;
1022 	union {
1023 		__u32 w[5];
1024 		unsigned long l[LONGS(20)];
1025 	} hash;
1026 	__u32 workspace[SHA_WORKSPACE_WORDS];
1027 	__u8 extract[64];
1028 	unsigned long flags;
1029 
1030 	/*
1031 	 * If we have an architectural hardware random number
1032 	 * generator, use it for SHA's initial vector
1033 	 */
1034 	sha_init(hash.w);
1035 	for (i = 0; i < LONGS(20); i++) {
1036 		unsigned long v;
1037 		if (!arch_get_random_long(&v))
1038 			break;
1039 		hash.l[i] = v;
1040 	}
1041 
1042 	/* Generate a hash across the pool, 16 words (512 bits) at a time */
1043 	spin_lock_irqsave(&r->lock, flags);
1044 	for (i = 0; i < r->poolinfo->poolwords; i += 16)
1045 		sha_transform(hash.w, (__u8 *)(r->pool + i), workspace);
1046 
1047 	/*
1048 	 * We mix the hash back into the pool to prevent backtracking
1049 	 * attacks (where the attacker knows the state of the pool
1050 	 * plus the current outputs, and attempts to find previous
1051 	 * ouputs), unless the hash function can be inverted. By
1052 	 * mixing at least a SHA1 worth of hash data back, we make
1053 	 * brute-forcing the feedback as hard as brute-forcing the
1054 	 * hash.
1055 	 */
1056 	__mix_pool_bytes(r, hash.w, sizeof(hash.w), extract);
1057 	spin_unlock_irqrestore(&r->lock, flags);
1058 
1059 	/*
1060 	 * To avoid duplicates, we atomically extract a portion of the
1061 	 * pool while mixing, and hash one final time.
1062 	 */
1063 	sha_transform(hash.w, extract, workspace);
1064 	memset(extract, 0, sizeof(extract));
1065 	memset(workspace, 0, sizeof(workspace));
1066 
1067 	/*
1068 	 * In case the hash function has some recognizable output
1069 	 * pattern, we fold it in half. Thus, we always feed back
1070 	 * twice as much data as we output.
1071 	 */
1072 	hash.w[0] ^= hash.w[3];
1073 	hash.w[1] ^= hash.w[4];
1074 	hash.w[2] ^= rol32(hash.w[2], 16);
1075 
1076 	memcpy(out, &hash, EXTRACT_SIZE);
1077 	memset(&hash, 0, sizeof(hash));
1078 }
1079 
1080 /*
1081  * This function extracts randomness from the "entropy pool", and
1082  * returns it in a buffer.
1083  *
1084  * The min parameter specifies the minimum amount we can pull before
1085  * failing to avoid races that defeat catastrophic reseeding while the
1086  * reserved parameter indicates how much entropy we must leave in the
1087  * pool after each pull to avoid starving other readers.
1088  */
1089 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
1090 				 size_t nbytes, int min, int reserved)
1091 {
1092 	ssize_t ret = 0, i;
1093 	__u8 tmp[EXTRACT_SIZE];
1094 	unsigned long flags;
1095 
1096 	/* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */
1097 	if (fips_enabled) {
1098 		spin_lock_irqsave(&r->lock, flags);
1099 		if (!r->last_data_init) {
1100 			r->last_data_init = 1;
1101 			spin_unlock_irqrestore(&r->lock, flags);
1102 			trace_extract_entropy(r->name, EXTRACT_SIZE,
1103 					      ENTROPY_BITS(r), _RET_IP_);
1104 			xfer_secondary_pool(r, EXTRACT_SIZE);
1105 			extract_buf(r, tmp);
1106 			spin_lock_irqsave(&r->lock, flags);
1107 			memcpy(r->last_data, tmp, EXTRACT_SIZE);
1108 		}
1109 		spin_unlock_irqrestore(&r->lock, flags);
1110 	}
1111 
1112 	trace_extract_entropy(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
1113 	xfer_secondary_pool(r, nbytes);
1114 	nbytes = account(r, nbytes, min, reserved);
1115 
1116 	while (nbytes) {
1117 		extract_buf(r, tmp);
1118 
1119 		if (fips_enabled) {
1120 			spin_lock_irqsave(&r->lock, flags);
1121 			if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
1122 				panic("Hardware RNG duplicated output!\n");
1123 			memcpy(r->last_data, tmp, EXTRACT_SIZE);
1124 			spin_unlock_irqrestore(&r->lock, flags);
1125 		}
1126 		i = min_t(int, nbytes, EXTRACT_SIZE);
1127 		memcpy(buf, tmp, i);
1128 		nbytes -= i;
1129 		buf += i;
1130 		ret += i;
1131 	}
1132 
1133 	/* Wipe data just returned from memory */
1134 	memset(tmp, 0, sizeof(tmp));
1135 
1136 	return ret;
1137 }
1138 
1139 /*
1140  * This function extracts randomness from the "entropy pool", and
1141  * returns it in a userspace buffer.
1142  */
1143 static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
1144 				    size_t nbytes)
1145 {
1146 	ssize_t ret = 0, i;
1147 	__u8 tmp[EXTRACT_SIZE];
1148 
1149 	trace_extract_entropy_user(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
1150 	xfer_secondary_pool(r, nbytes);
1151 	nbytes = account(r, nbytes, 0, 0);
1152 
1153 	while (nbytes) {
1154 		if (need_resched()) {
1155 			if (signal_pending(current)) {
1156 				if (ret == 0)
1157 					ret = -ERESTARTSYS;
1158 				break;
1159 			}
1160 			schedule();
1161 		}
1162 
1163 		extract_buf(r, tmp);
1164 		i = min_t(int, nbytes, EXTRACT_SIZE);
1165 		if (copy_to_user(buf, tmp, i)) {
1166 			ret = -EFAULT;
1167 			break;
1168 		}
1169 
1170 		nbytes -= i;
1171 		buf += i;
1172 		ret += i;
1173 	}
1174 
1175 	/* Wipe data just returned from memory */
1176 	memset(tmp, 0, sizeof(tmp));
1177 
1178 	return ret;
1179 }
1180 
1181 /*
1182  * This function is the exported kernel interface.  It returns some
1183  * number of good random numbers, suitable for key generation, seeding
1184  * TCP sequence numbers, etc.  It does not rely on the hardware random
1185  * number generator.  For random bytes direct from the hardware RNG
1186  * (when available), use get_random_bytes_arch().
1187  */
1188 void get_random_bytes(void *buf, int nbytes)
1189 {
1190 #if DEBUG_RANDOM_BOOT > 0
1191 	if (unlikely(nonblocking_pool.initialized == 0))
1192 		printk(KERN_NOTICE "random: %pF get_random_bytes called "
1193 		       "with %d bits of entropy available\n",
1194 		       (void *) _RET_IP_,
1195 		       nonblocking_pool.entropy_total);
1196 #endif
1197 	trace_get_random_bytes(nbytes, _RET_IP_);
1198 	extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
1199 }
1200 EXPORT_SYMBOL(get_random_bytes);
1201 
1202 /*
1203  * This function will use the architecture-specific hardware random
1204  * number generator if it is available.  The arch-specific hw RNG will
1205  * almost certainly be faster than what we can do in software, but it
1206  * is impossible to verify that it is implemented securely (as
1207  * opposed, to, say, the AES encryption of a sequence number using a
1208  * key known by the NSA).  So it's useful if we need the speed, but
1209  * only if we're willing to trust the hardware manufacturer not to
1210  * have put in a back door.
1211  */
1212 void get_random_bytes_arch(void *buf, int nbytes)
1213 {
1214 	char *p = buf;
1215 
1216 	trace_get_random_bytes_arch(nbytes, _RET_IP_);
1217 	while (nbytes) {
1218 		unsigned long v;
1219 		int chunk = min(nbytes, (int)sizeof(unsigned long));
1220 
1221 		if (!arch_get_random_long(&v))
1222 			break;
1223 
1224 		memcpy(p, &v, chunk);
1225 		p += chunk;
1226 		nbytes -= chunk;
1227 	}
1228 
1229 	if (nbytes)
1230 		extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
1231 }
1232 EXPORT_SYMBOL(get_random_bytes_arch);
1233 
1234 
1235 /*
1236  * init_std_data - initialize pool with system data
1237  *
1238  * @r: pool to initialize
1239  *
1240  * This function clears the pool's entropy count and mixes some system
1241  * data into the pool to prepare it for use. The pool is not cleared
1242  * as that can only decrease the entropy in the pool.
1243  */
1244 static void init_std_data(struct entropy_store *r)
1245 {
1246 	int i;
1247 	ktime_t now = ktime_get_real();
1248 	unsigned long rv;
1249 
1250 	r->last_pulled = jiffies;
1251 	mix_pool_bytes(r, &now, sizeof(now), NULL);
1252 	for (i = r->poolinfo->poolbytes; i > 0; i -= sizeof(rv)) {
1253 		if (!arch_get_random_seed_long(&rv) &&
1254 		    !arch_get_random_long(&rv))
1255 			rv = random_get_entropy();
1256 		mix_pool_bytes(r, &rv, sizeof(rv), NULL);
1257 	}
1258 	mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
1259 }
1260 
1261 /*
1262  * Note that setup_arch() may call add_device_randomness()
1263  * long before we get here. This allows seeding of the pools
1264  * with some platform dependent data very early in the boot
1265  * process. But it limits our options here. We must use
1266  * statically allocated structures that already have all
1267  * initializations complete at compile time. We should also
1268  * take care not to overwrite the precious per platform data
1269  * we were given.
1270  */
1271 static int rand_initialize(void)
1272 {
1273 	init_std_data(&input_pool);
1274 	init_std_data(&blocking_pool);
1275 	init_std_data(&nonblocking_pool);
1276 	return 0;
1277 }
1278 early_initcall(rand_initialize);
1279 
1280 #ifdef CONFIG_BLOCK
1281 void rand_initialize_disk(struct gendisk *disk)
1282 {
1283 	struct timer_rand_state *state;
1284 
1285 	/*
1286 	 * If kzalloc returns null, we just won't use that entropy
1287 	 * source.
1288 	 */
1289 	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1290 	if (state) {
1291 		state->last_time = INITIAL_JIFFIES;
1292 		disk->random = state;
1293 	}
1294 }
1295 #endif
1296 
1297 /*
1298  * Attempt an emergency refill using arch_get_random_seed_long().
1299  *
1300  * As with add_interrupt_randomness() be paranoid and only
1301  * credit the output as 50% entropic.
1302  */
1303 static int arch_random_refill(void)
1304 {
1305 	const unsigned int nlongs = 64;	/* Arbitrary number */
1306 	unsigned int n = 0;
1307 	unsigned int i;
1308 	unsigned long buf[nlongs];
1309 
1310 	if (!arch_has_random_seed())
1311 		return 0;
1312 
1313 	for (i = 0; i < nlongs; i++) {
1314 		if (arch_get_random_seed_long(&buf[n]))
1315 			n++;
1316 	}
1317 
1318 	if (n) {
1319 		unsigned int rand_bytes = n * sizeof(unsigned long);
1320 
1321 		mix_pool_bytes(&input_pool, buf, rand_bytes, NULL);
1322 		credit_entropy_bits(&input_pool, rand_bytes*4);
1323 	}
1324 
1325 	return n;
1326 }
1327 
1328 static ssize_t
1329 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1330 {
1331 	ssize_t n;
1332 
1333 	if (nbytes == 0)
1334 		return 0;
1335 
1336 	nbytes = min_t(size_t, nbytes, SEC_XFER_SIZE);
1337 	while (1) {
1338 		n = extract_entropy_user(&blocking_pool, buf, nbytes);
1339 		if (n < 0)
1340 			return n;
1341 		trace_random_read(n*8, (nbytes-n)*8,
1342 				  ENTROPY_BITS(&blocking_pool),
1343 				  ENTROPY_BITS(&input_pool));
1344 		if (n > 0)
1345 			return n;
1346 
1347 		/* Pool is (near) empty.  Maybe wait and retry. */
1348 
1349 		/* First try an emergency refill */
1350 		if (arch_random_refill())
1351 			continue;
1352 
1353 		if (file->f_flags & O_NONBLOCK)
1354 			return -EAGAIN;
1355 
1356 		wait_event_interruptible(random_read_wait,
1357 			ENTROPY_BITS(&input_pool) >=
1358 			random_read_wakeup_bits);
1359 		if (signal_pending(current))
1360 			return -ERESTARTSYS;
1361 	}
1362 }
1363 
1364 static ssize_t
1365 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1366 {
1367 	int ret;
1368 
1369 	if (unlikely(nonblocking_pool.initialized == 0))
1370 		printk_once(KERN_NOTICE "random: %s urandom read "
1371 			    "with %d bits of entropy available\n",
1372 			    current->comm, nonblocking_pool.entropy_total);
1373 
1374 	ret = extract_entropy_user(&nonblocking_pool, buf, nbytes);
1375 
1376 	trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool),
1377 			   ENTROPY_BITS(&input_pool));
1378 	return ret;
1379 }
1380 
1381 static unsigned int
1382 random_poll(struct file *file, poll_table * wait)
1383 {
1384 	unsigned int mask;
1385 
1386 	poll_wait(file, &random_read_wait, wait);
1387 	poll_wait(file, &random_write_wait, wait);
1388 	mask = 0;
1389 	if (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits)
1390 		mask |= POLLIN | POLLRDNORM;
1391 	if (ENTROPY_BITS(&input_pool) < random_write_wakeup_bits)
1392 		mask |= POLLOUT | POLLWRNORM;
1393 	return mask;
1394 }
1395 
1396 static int
1397 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1398 {
1399 	size_t bytes;
1400 	__u32 buf[16];
1401 	const char __user *p = buffer;
1402 
1403 	while (count > 0) {
1404 		bytes = min(count, sizeof(buf));
1405 		if (copy_from_user(&buf, p, bytes))
1406 			return -EFAULT;
1407 
1408 		count -= bytes;
1409 		p += bytes;
1410 
1411 		mix_pool_bytes(r, buf, bytes, NULL);
1412 		cond_resched();
1413 	}
1414 
1415 	return 0;
1416 }
1417 
1418 static ssize_t random_write(struct file *file, const char __user *buffer,
1419 			    size_t count, loff_t *ppos)
1420 {
1421 	size_t ret;
1422 
1423 	ret = write_pool(&blocking_pool, buffer, count);
1424 	if (ret)
1425 		return ret;
1426 	ret = write_pool(&nonblocking_pool, buffer, count);
1427 	if (ret)
1428 		return ret;
1429 
1430 	return (ssize_t)count;
1431 }
1432 
1433 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1434 {
1435 	int size, ent_count;
1436 	int __user *p = (int __user *)arg;
1437 	int retval;
1438 
1439 	switch (cmd) {
1440 	case RNDGETENTCNT:
1441 		/* inherently racy, no point locking */
1442 		ent_count = ENTROPY_BITS(&input_pool);
1443 		if (put_user(ent_count, p))
1444 			return -EFAULT;
1445 		return 0;
1446 	case RNDADDTOENTCNT:
1447 		if (!capable(CAP_SYS_ADMIN))
1448 			return -EPERM;
1449 		if (get_user(ent_count, p))
1450 			return -EFAULT;
1451 		credit_entropy_bits_safe(&input_pool, ent_count);
1452 		return 0;
1453 	case RNDADDENTROPY:
1454 		if (!capable(CAP_SYS_ADMIN))
1455 			return -EPERM;
1456 		if (get_user(ent_count, p++))
1457 			return -EFAULT;
1458 		if (ent_count < 0)
1459 			return -EINVAL;
1460 		if (get_user(size, p++))
1461 			return -EFAULT;
1462 		retval = write_pool(&input_pool, (const char __user *)p,
1463 				    size);
1464 		if (retval < 0)
1465 			return retval;
1466 		credit_entropy_bits_safe(&input_pool, ent_count);
1467 		return 0;
1468 	case RNDZAPENTCNT:
1469 	case RNDCLEARPOOL:
1470 		/*
1471 		 * Clear the entropy pool counters. We no longer clear
1472 		 * the entropy pool, as that's silly.
1473 		 */
1474 		if (!capable(CAP_SYS_ADMIN))
1475 			return -EPERM;
1476 		input_pool.entropy_count = 0;
1477 		nonblocking_pool.entropy_count = 0;
1478 		blocking_pool.entropy_count = 0;
1479 		return 0;
1480 	default:
1481 		return -EINVAL;
1482 	}
1483 }
1484 
1485 static int random_fasync(int fd, struct file *filp, int on)
1486 {
1487 	return fasync_helper(fd, filp, on, &fasync);
1488 }
1489 
1490 const struct file_operations random_fops = {
1491 	.read  = random_read,
1492 	.write = random_write,
1493 	.poll  = random_poll,
1494 	.unlocked_ioctl = random_ioctl,
1495 	.fasync = random_fasync,
1496 	.llseek = noop_llseek,
1497 };
1498 
1499 const struct file_operations urandom_fops = {
1500 	.read  = urandom_read,
1501 	.write = random_write,
1502 	.unlocked_ioctl = random_ioctl,
1503 	.fasync = random_fasync,
1504 	.llseek = noop_llseek,
1505 };
1506 
1507 /***************************************************************
1508  * Random UUID interface
1509  *
1510  * Used here for a Boot ID, but can be useful for other kernel
1511  * drivers.
1512  ***************************************************************/
1513 
1514 /*
1515  * Generate random UUID
1516  */
1517 void generate_random_uuid(unsigned char uuid_out[16])
1518 {
1519 	get_random_bytes(uuid_out, 16);
1520 	/* Set UUID version to 4 --- truly random generation */
1521 	uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1522 	/* Set the UUID variant to DCE */
1523 	uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1524 }
1525 EXPORT_SYMBOL(generate_random_uuid);
1526 
1527 /********************************************************************
1528  *
1529  * Sysctl interface
1530  *
1531  ********************************************************************/
1532 
1533 #ifdef CONFIG_SYSCTL
1534 
1535 #include <linux/sysctl.h>
1536 
1537 static int min_read_thresh = 8, min_write_thresh;
1538 static int max_read_thresh = OUTPUT_POOL_WORDS * 32;
1539 static int max_write_thresh = INPUT_POOL_WORDS * 32;
1540 static char sysctl_bootid[16];
1541 
1542 /*
1543  * This function is used to return both the bootid UUID, and random
1544  * UUID.  The difference is in whether table->data is NULL; if it is,
1545  * then a new UUID is generated and returned to the user.
1546  *
1547  * If the user accesses this via the proc interface, the UUID will be
1548  * returned as an ASCII string in the standard UUID format; if via the
1549  * sysctl system call, as 16 bytes of binary data.
1550  */
1551 static int proc_do_uuid(struct ctl_table *table, int write,
1552 			void __user *buffer, size_t *lenp, loff_t *ppos)
1553 {
1554 	struct ctl_table fake_table;
1555 	unsigned char buf[64], tmp_uuid[16], *uuid;
1556 
1557 	uuid = table->data;
1558 	if (!uuid) {
1559 		uuid = tmp_uuid;
1560 		generate_random_uuid(uuid);
1561 	} else {
1562 		static DEFINE_SPINLOCK(bootid_spinlock);
1563 
1564 		spin_lock(&bootid_spinlock);
1565 		if (!uuid[8])
1566 			generate_random_uuid(uuid);
1567 		spin_unlock(&bootid_spinlock);
1568 	}
1569 
1570 	sprintf(buf, "%pU", uuid);
1571 
1572 	fake_table.data = buf;
1573 	fake_table.maxlen = sizeof(buf);
1574 
1575 	return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1576 }
1577 
1578 /*
1579  * Return entropy available scaled to integral bits
1580  */
1581 static int proc_do_entropy(ctl_table *table, int write,
1582 			   void __user *buffer, size_t *lenp, loff_t *ppos)
1583 {
1584 	ctl_table fake_table;
1585 	int entropy_count;
1586 
1587 	entropy_count = *(int *)table->data >> ENTROPY_SHIFT;
1588 
1589 	fake_table.data = &entropy_count;
1590 	fake_table.maxlen = sizeof(entropy_count);
1591 
1592 	return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
1593 }
1594 
1595 static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1596 extern struct ctl_table random_table[];
1597 struct ctl_table random_table[] = {
1598 	{
1599 		.procname	= "poolsize",
1600 		.data		= &sysctl_poolsize,
1601 		.maxlen		= sizeof(int),
1602 		.mode		= 0444,
1603 		.proc_handler	= proc_dointvec,
1604 	},
1605 	{
1606 		.procname	= "entropy_avail",
1607 		.maxlen		= sizeof(int),
1608 		.mode		= 0444,
1609 		.proc_handler	= proc_do_entropy,
1610 		.data		= &input_pool.entropy_count,
1611 	},
1612 	{
1613 		.procname	= "read_wakeup_threshold",
1614 		.data		= &random_read_wakeup_bits,
1615 		.maxlen		= sizeof(int),
1616 		.mode		= 0644,
1617 		.proc_handler	= proc_dointvec_minmax,
1618 		.extra1		= &min_read_thresh,
1619 		.extra2		= &max_read_thresh,
1620 	},
1621 	{
1622 		.procname	= "write_wakeup_threshold",
1623 		.data		= &random_write_wakeup_bits,
1624 		.maxlen		= sizeof(int),
1625 		.mode		= 0644,
1626 		.proc_handler	= proc_dointvec_minmax,
1627 		.extra1		= &min_write_thresh,
1628 		.extra2		= &max_write_thresh,
1629 	},
1630 	{
1631 		.procname	= "urandom_min_reseed_secs",
1632 		.data		= &random_min_urandom_seed,
1633 		.maxlen		= sizeof(int),
1634 		.mode		= 0644,
1635 		.proc_handler	= proc_dointvec,
1636 	},
1637 	{
1638 		.procname	= "boot_id",
1639 		.data		= &sysctl_bootid,
1640 		.maxlen		= 16,
1641 		.mode		= 0444,
1642 		.proc_handler	= proc_do_uuid,
1643 	},
1644 	{
1645 		.procname	= "uuid",
1646 		.maxlen		= 16,
1647 		.mode		= 0444,
1648 		.proc_handler	= proc_do_uuid,
1649 	},
1650 	{ }
1651 };
1652 #endif 	/* CONFIG_SYSCTL */
1653 
1654 static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1655 
1656 int random_int_secret_init(void)
1657 {
1658 	get_random_bytes(random_int_secret, sizeof(random_int_secret));
1659 	return 0;
1660 }
1661 
1662 /*
1663  * Get a random word for internal kernel use only. Similar to urandom but
1664  * with the goal of minimal entropy pool depletion. As a result, the random
1665  * value is not cryptographically secure but for several uses the cost of
1666  * depleting entropy is too high
1667  */
1668 static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1669 unsigned int get_random_int(void)
1670 {
1671 	__u32 *hash;
1672 	unsigned int ret;
1673 
1674 	if (arch_get_random_int(&ret))
1675 		return ret;
1676 
1677 	hash = get_cpu_var(get_random_int_hash);
1678 
1679 	hash[0] += current->pid + jiffies + random_get_entropy();
1680 	md5_transform(hash, random_int_secret);
1681 	ret = hash[0];
1682 	put_cpu_var(get_random_int_hash);
1683 
1684 	return ret;
1685 }
1686 EXPORT_SYMBOL(get_random_int);
1687 
1688 /*
1689  * randomize_range() returns a start address such that
1690  *
1691  *    [...... <range> .....]
1692  *  start                  end
1693  *
1694  * a <range> with size "len" starting at the return value is inside in the
1695  * area defined by [start, end], but is otherwise randomized.
1696  */
1697 unsigned long
1698 randomize_range(unsigned long start, unsigned long end, unsigned long len)
1699 {
1700 	unsigned long range = end - len - start;
1701 
1702 	if (end <= start + len)
1703 		return 0;
1704 	return PAGE_ALIGN(get_random_int() % range + start);
1705 }
1706