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 */
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_input_randomness(unsigned int type, unsigned int code,
129 * unsigned int value);
130 * void add_interrupt_randomness(int irq);
131 * void add_disk_randomness(struct gendisk *disk);
132 *
133 * void random_input_words(__u32 *buf, size_t wordcount, int ent_count)
134 * int random_input_wait(void);
135 *
136 * add_input_randomness() uses the input layer interrupt timing, as well as
137 * the event type information from the hardware.
138 *
139 * add_interrupt_randomness() uses the inter-interrupt timing as random
140 * inputs to the entropy pool. Note that not all interrupts are good
141 * sources of randomness! For example, the timer interrupts is not a
142 * good choice, because the periodicity of the interrupts is too
143 * regular, and hence predictable to an attacker. Network Interface
144 * Controller interrupts are a better measure, since the timing of the
145 * NIC interrupts are more unpredictable.
146 *
147 * add_disk_randomness() uses what amounts to the seek time of block
148 * layer request events, on a per-disk_devt basis, as input to the
149 * entropy pool. Note that high-speed solid state drives with very low
150 * seek times do not make for good sources of entropy, as their seek
151 * times are usually fairly consistent.
152 *
153 * random_input_words() just provides a raw block of entropy to the input
154 * pool, such as from a hardware entropy generator.
155 *
156 * random_input_wait() suspends the caller until such time as the
157 * entropy pool falls below the write threshold, and returns a count of how
158 * much entropy (in bits) is needed to sustain the pool.
159 *
160 * All of these routines try to estimate how many bits of randomness a
161 * particular randomness source. They do this by keeping track of the
162 * first and second order deltas of the event timings.
163 *
164 * Ensuring unpredictability at system startup
165 * ============================================
166 *
167 * When any operating system starts up, it will go through a sequence
168 * of actions that are fairly predictable by an adversary, especially
169 * if the start-up does not involve interaction with a human operator.
170 * This reduces the actual number of bits of unpredictability in the
171 * entropy pool below the value in entropy_count. In order to
172 * counteract this effect, it helps to carry information in the
173 * entropy pool across shut-downs and start-ups. To do this, put the
174 * following lines an appropriate script which is run during the boot
175 * sequence:
176 *
177 * echo "Initializing random number generator..."
178 * random_seed=/var/run/random-seed
179 * # Carry a random seed from start-up to start-up
180 * # Load and then save the whole entropy pool
181 * if [ -f $random_seed ]; then
182 * cat $random_seed >/dev/urandom
183 * else
184 * touch $random_seed
185 * fi
186 * chmod 600 $random_seed
187 * dd if=/dev/urandom of=$random_seed count=1 bs=512
188 *
189 * and the following lines in an appropriate script which is run as
190 * the system is shutdown:
191 *
192 * # Carry a random seed from shut-down to start-up
193 * # Save the whole entropy pool
194 * echo "Saving random seed..."
195 * random_seed=/var/run/random-seed
196 * touch $random_seed
197 * chmod 600 $random_seed
198 * dd if=/dev/urandom of=$random_seed count=1 bs=512
199 *
200 * For example, on most modern systems using the System V init
201 * scripts, such code fragments would be found in
202 * /etc/rc.d/init.d/random. On older Linux systems, the correct script
203 * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0.
204 *
205 * Effectively, these commands cause the contents of the entropy pool
206 * to be saved at shut-down time and reloaded into the entropy pool at
207 * start-up. (The 'dd' in the addition to the bootup script is to
208 * make sure that /etc/random-seed is different for every start-up,
209 * even if the system crashes without executing rc.0.) Even with
210 * complete knowledge of the start-up activities, predicting the state
211 * of the entropy pool requires knowledge of the previous history of
212 * the system.
213 *
214 * Configuring the /dev/random driver under Linux
215 * ==============================================
216 *
217 * The /dev/random driver under Linux uses minor numbers 8 and 9 of
218 * the /dev/mem major number (#1). So if your system does not have
219 * /dev/random and /dev/urandom created already, they can be created
220 * by using the commands:
221 *
222 * mknod /dev/random c 1 8
223 * mknod /dev/urandom c 1 9
224 *
225 * Acknowledgements:
226 * =================
227 *
228 * Ideas for constructing this random number generator were derived
229 * from Pretty Good Privacy's random number generator, and from private
230 * discussions with Phil Karn. Colin Plumb provided a faster random
231 * number generator, which speed up the mixing function of the entropy
232 * pool, taken from PGPfone. Dale Worley has also contributed many
233 * useful ideas and suggestions to improve this driver.
234 *
235 * Any flaws in the design are solely my responsibility, and should
236 * not be attributed to the Phil, Colin, or any of authors of PGP.
237 *
238 * Further background information on this topic may be obtained from
239 * RFC 1750, "Randomness Recommendations for Security", by Donald
240 * Eastlake, Steve Crocker, and Jeff Schiller.
241 */
243 #include <linux/utsname.h>
244 #include <linux/module.h>
245 #include <linux/kernel.h>
246 #include <linux/major.h>
247 #include <linux/string.h>
248 #include <linux/fcntl.h>
249 #include <linux/slab.h>
250 #include <linux/random.h>
251 #include <linux/poll.h>
252 #include <linux/init.h>
253 #include <linux/fs.h>
254 #include <linux/genhd.h>
255 #include <linux/interrupt.h>
256 #include <linux/mm.h>
257 #include <linux/spinlock.h>
258 #include <linux/percpu.h>
259 #include <linux/cryptohash.h>
260 #include <linux/fips.h>
262 #ifdef CONFIG_GENERIC_HARDIRQS
263 # include <linux/irq.h>
264 #endif
266 #include <asm/processor.h>
267 #include <asm/uaccess.h>
268 #include <asm/irq.h>
269 #include <asm/io.h>
271 /*
272 * Configuration information
273 */
274 #define INPUT_POOL_WORDS 128
275 #define OUTPUT_POOL_WORDS 32
276 #define SEC_XFER_SIZE 512
277 #define EXTRACT_SIZE 10
279 /*
280 * The minimum number of bits of entropy before we wake up a read on
281 * /dev/random. Should be enough to do a significant reseed.
282 */
283 static int random_read_wakeup_thresh = 64;
285 /*
286 * If the entropy count falls under this number of bits, then we
287 * should wake up processes which are selecting or polling on write
288 * access to /dev/random.
289 */
290 static int random_write_wakeup_thresh = 128;
292 /*
293 * When the input pool goes over trickle_thresh, start dropping most
294 * samples to avoid wasting CPU time and reduce lock contention.
295 */
297 static int trickle_thresh __read_mostly = INPUT_POOL_WORDS * 28;
299 static DEFINE_PER_CPU(int, trickle_count);
301 /*
302 * A pool of size .poolwords is stirred with a primitive polynomial
303 * of degree .poolwords over GF(2). The taps for various sizes are
304 * defined below. They are chosen to be evenly spaced (minimum RMS
305 * distance from evenly spaced; the numbers in the comments are a
306 * scaled squared error sum) except for the last tap, which is 1 to
307 * get the twisting happening as fast as possible.
308 */
309 static struct poolinfo {
310 int poolwords;
311 int tap1, tap2, tap3, tap4, tap5;
312 } poolinfo_table[] = {
313 /* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */
314 { 128, 103, 76, 51, 25, 1 },
315 /* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */
316 { 32, 26, 20, 14, 7, 1 },
317 #if 0
318 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */
319 { 2048, 1638, 1231, 819, 411, 1 },
321 /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
322 { 1024, 817, 615, 412, 204, 1 },
324 /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
325 { 1024, 819, 616, 410, 207, 2 },
327 /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
328 { 512, 411, 308, 208, 104, 1 },
330 /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
331 { 512, 409, 307, 206, 102, 2 },
332 /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
333 { 512, 409, 309, 205, 103, 2 },
335 /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
336 { 256, 205, 155, 101, 52, 1 },
338 /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
339 { 128, 103, 78, 51, 27, 2 },
341 /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
342 { 64, 52, 39, 26, 14, 1 },
343 #endif
344 };
346 #define POOLBITS poolwords*32
347 #define POOLBYTES poolwords*4
349 /*
350 * For the purposes of better mixing, we use the CRC-32 polynomial as
351 * well to make a twisted Generalized Feedback Shift Reigster
352 *
353 * (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR generators. ACM
354 * Transactions on Modeling and Computer Simulation 2(3):179-194.
355 * Also see M. Matsumoto & Y. Kurita, 1994. Twisted GFSR generators
356 * II. ACM Transactions on Mdeling and Computer Simulation 4:254-266)
357 *
358 * Thanks to Colin Plumb for suggesting this.
359 *
360 * We have not analyzed the resultant polynomial to prove it primitive;
361 * in fact it almost certainly isn't. Nonetheless, the irreducible factors
362 * of a random large-degree polynomial over GF(2) are more than large enough
363 * that periodicity is not a concern.
364 *
365 * The input hash is much less sensitive than the output hash. All
366 * that we want of it is that it be a good non-cryptographic hash;
367 * i.e. it not produce collisions when fed "random" data of the sort
368 * we expect to see. As long as the pool state differs for different
369 * inputs, we have preserved the input entropy and done a good job.
370 * The fact that an intelligent attacker can construct inputs that
371 * will produce controlled alterations to the pool's state is not
372 * important because we don't consider such inputs to contribute any
373 * randomness. The only property we need with respect to them is that
374 * the attacker can't increase his/her knowledge of the pool's state.
375 * Since all additions are reversible (knowing the final state and the
376 * input, you can reconstruct the initial state), if an attacker has
377 * any uncertainty about the initial state, he/she can only shuffle
378 * that uncertainty about, but never cause any collisions (which would
379 * decrease the uncertainty).
380 *
381 * The chosen system lets the state of the pool be (essentially) the input
382 * modulo the generator polymnomial. Now, for random primitive polynomials,
383 * this is a universal class of hash functions, meaning that the chance
384 * of a collision is limited by the attacker's knowledge of the generator
385 * polynomail, so if it is chosen at random, an attacker can never force
386 * a collision. Here, we use a fixed polynomial, but we *can* assume that
387 * ###--> it is unknown to the processes generating the input entropy. <-###
388 * Because of this important property, this is a good, collision-resistant
389 * hash; hash collisions will occur no more often than chance.
390 */
392 /*
393 * Static global variables
394 */
395 static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
396 static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
397 static struct fasync_struct *fasync;
399 #if 0
400 static int debug;
401 module_param(debug, bool, 0644);
402 #define DEBUG_ENT(fmt, arg...) do { \
403 if (debug) \
404 printk(KERN_DEBUG "random %04d %04d %04d: " \
405 fmt,\
406 input_pool.entropy_count,\
407 blocking_pool.entropy_count,\
408 nonblocking_pool.entropy_count,\
409 ## arg); } while (0)
410 #else
411 #define DEBUG_ENT(fmt, arg...) do {} while (0)
412 #endif
414 /**********************************************************************
415 *
416 * OS independent entropy store. Here are the functions which handle
417 * storing entropy in an entropy pool.
418 *
419 **********************************************************************/
421 struct entropy_store;
422 struct entropy_store {
423 /* read-only data: */
424 struct poolinfo *poolinfo;
425 __u32 *pool;
426 const char *name;
427 struct entropy_store *pull;
428 int limit;
430 /* read-write data: */
431 spinlock_t lock;
432 unsigned add_ptr;
433 int entropy_count;
434 int input_rotate;
435 __u8 last_data[EXTRACT_SIZE];
436 };
438 static __u32 input_pool_data[INPUT_POOL_WORDS];
439 static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
440 static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
442 static struct entropy_store input_pool = {
443 .poolinfo = &poolinfo_table[0],
444 .name = "input",
445 .limit = 1,
446 .lock = __SPIN_LOCK_UNLOCKED(&input_pool.lock),
447 .pool = input_pool_data
448 };
450 static struct entropy_store blocking_pool = {
451 .poolinfo = &poolinfo_table[1],
452 .name = "blocking",
453 .limit = 1,
454 .pull = &input_pool,
455 .lock = __SPIN_LOCK_UNLOCKED(&blocking_pool.lock),
456 .pool = blocking_pool_data
457 };
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 };
467 /*
468 * This function adds bytes into the entropy "pool". It does not
469 * update the entropy estimate. The caller should call
470 * credit_entropy_bits if this is appropriate.
471 *
472 * The pool is stirred with a primitive polynomial of the appropriate
473 * degree, and then twisted. We twist by three bits at a time because
474 * it's cheap to do so and helps slightly in the expected case where
475 * the entropy is concentrated in the low-order bits.
476 */
477 static void mix_pool_bytes_extract(struct entropy_store *r, const void *in,
478 int nbytes, __u8 out[64])
479 {
480 static __u32 const twist_table[8] = {
481 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
482 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
483 unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
484 int input_rotate;
485 int wordmask = r->poolinfo->poolwords - 1;
486 const char *bytes = in;
487 __u32 w;
488 unsigned long flags;
490 /* Taps are constant, so we can load them without holding r->lock. */
491 tap1 = r->poolinfo->tap1;
492 tap2 = r->poolinfo->tap2;
493 tap3 = r->poolinfo->tap3;
494 tap4 = r->poolinfo->tap4;
495 tap5 = r->poolinfo->tap5;
497 spin_lock_irqsave(&r->lock, flags);
498 input_rotate = r->input_rotate;
499 i = r->add_ptr;
501 /* mix one byte at a time to simplify size handling and churn faster */
502 while (nbytes--) {
503 w = rol32(*bytes++, input_rotate & 31);
504 i = (i - 1) & wordmask;
506 /* XOR in the various taps */
507 w ^= r->pool[i];
508 w ^= r->pool[(i + tap1) & wordmask];
509 w ^= r->pool[(i + tap2) & wordmask];
510 w ^= r->pool[(i + tap3) & wordmask];
511 w ^= r->pool[(i + tap4) & wordmask];
512 w ^= r->pool[(i + tap5) & wordmask];
514 /* Mix the result back in with a twist */
515 r->pool[i] = (w >> 3) ^ twist_table[w & 7];
517 /*
518 * Normally, we add 7 bits of rotation to the pool.
519 * At the beginning of the pool, add an extra 7 bits
520 * rotation, so that successive passes spread the
521 * input bits across the pool evenly.
522 */
523 input_rotate += i ? 7 : 14;
524 }
526 r->input_rotate = input_rotate;
527 r->add_ptr = i;
529 if (out)
530 for (j = 0; j < 16; j++)
531 ((__u32 *)out)[j] = r->pool[(i - j) & wordmask];
533 spin_unlock_irqrestore(&r->lock, flags);
534 }
536 static void mix_pool_bytes(struct entropy_store *r, const void *in, int bytes)
537 {
538 mix_pool_bytes_extract(r, in, bytes, NULL);
539 }
541 /*
542 * Credit (or debit) the entropy store with n bits of entropy
543 */
544 static void credit_entropy_bits(struct entropy_store *r, int nbits)
545 {
546 unsigned long flags;
547 int entropy_count;
549 if (!nbits)
550 return;
552 spin_lock_irqsave(&r->lock, flags);
554 DEBUG_ENT("added %d entropy credits to %s\n", nbits, r->name);
555 entropy_count = r->entropy_count;
556 entropy_count += nbits;
557 if (entropy_count < 0) {
558 DEBUG_ENT("negative entropy/overflow\n");
559 entropy_count = 0;
560 } else if (entropy_count > r->poolinfo->POOLBITS)
561 entropy_count = r->poolinfo->POOLBITS;
562 r->entropy_count = entropy_count;
564 /* should we wake readers? */
565 if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {
566 wake_up_interruptible(&random_read_wait);
567 kill_fasync(&fasync, SIGIO, POLL_IN);
568 }
569 spin_unlock_irqrestore(&r->lock, flags);
570 }
572 /*********************************************************************
573 *
574 * Entropy input management
575 *
576 *********************************************************************/
578 /* There is one of these per entropy source */
579 struct timer_rand_state {
580 cycles_t last_time;
581 long last_delta, last_delta2;
582 unsigned dont_count_entropy:1;
583 };
585 #ifndef CONFIG_GENERIC_HARDIRQS
587 static struct timer_rand_state *irq_timer_state[NR_IRQS];
589 static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
590 {
591 return irq_timer_state[irq];
592 }
594 static void set_timer_rand_state(unsigned int irq,
595 struct timer_rand_state *state)
596 {
597 irq_timer_state[irq] = state;
598 }
600 #else
602 static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
603 {
604 struct irq_desc *desc;
606 desc = irq_to_desc(irq);
608 return desc->timer_rand_state;
609 }
611 static void set_timer_rand_state(unsigned int irq,
612 struct timer_rand_state *state)
613 {
614 struct irq_desc *desc;
616 desc = irq_to_desc(irq);
618 desc->timer_rand_state = state;
619 }
620 #endif
622 static struct timer_rand_state input_timer_state;
624 /*
625 * This function adds entropy to the entropy "pool" by using timing
626 * delays. It uses the timer_rand_state structure to make an estimate
627 * of how many bits of entropy this call has added to the pool.
628 *
629 * The number "num" is also added to the pool - it should somehow describe
630 * the type of event which just happened. This is currently 0-255 for
631 * keyboard scan codes, and 256 upwards for interrupts.
632 *
633 */
634 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
635 {
636 struct {
637 cycles_t cycles;
638 long jiffies;
639 unsigned num;
640 } sample;
641 long delta, delta2, delta3;
643 preempt_disable();
644 /* if over the trickle threshold, use only 1 in 4096 samples */
645 if (input_pool.entropy_count > trickle_thresh &&
646 ((__this_cpu_inc_return(trickle_count) - 1) & 0xfff))
647 goto out;
649 sample.jiffies = jiffies;
650 sample.cycles = get_cycles();
651 sample.num = num;
652 mix_pool_bytes(&input_pool, &sample, sizeof(sample));
654 /*
655 * Calculate number of bits of randomness we probably added.
656 * We take into account the first, second and third-order deltas
657 * in order to make our estimate.
658 */
660 if (!state->dont_count_entropy) {
661 delta = sample.jiffies - state->last_time;
662 state->last_time = sample.jiffies;
664 delta2 = delta - state->last_delta;
665 state->last_delta = delta;
667 delta3 = delta2 - state->last_delta2;
668 state->last_delta2 = delta2;
670 if (delta < 0)
671 delta = -delta;
672 if (delta2 < 0)
673 delta2 = -delta2;
674 if (delta3 < 0)
675 delta3 = -delta3;
676 if (delta > delta2)
677 delta = delta2;
678 if (delta > delta3)
679 delta = delta3;
681 /*
682 * delta is now minimum absolute delta.
683 * Round down by 1 bit on general principles,
684 * and limit entropy entimate to 12 bits.
685 */
686 credit_entropy_bits(&input_pool,
687 min_t(int, fls(delta>>1), 11));
688 }
689 out:
690 preempt_enable();
691 }
693 void add_input_randomness(unsigned int type, unsigned int code,
694 unsigned int value)
695 {
696 static unsigned char last_value;
698 /* ignore autorepeat and the like */
699 if (value == last_value)
700 return;
702 DEBUG_ENT("input event\n");
703 last_value = value;
704 add_timer_randomness(&input_timer_state,
705 (type << 4) ^ code ^ (code >> 4) ^ value);
706 }
707 EXPORT_SYMBOL_GPL(add_input_randomness);
709 void add_interrupt_randomness(int irq)
710 {
711 struct timer_rand_state *state;
713 state = get_timer_rand_state(irq);
715 if (state == NULL)
716 return;
718 DEBUG_ENT("irq event %d\n", irq);
719 add_timer_randomness(state, 0x100 + irq);
720 }
722 #ifdef CONFIG_BLOCK
723 void add_disk_randomness(struct gendisk *disk)
724 {
725 if (!disk || !disk->random)
726 return;
727 /* first major is 1, so we get >= 0x200 here */
728 DEBUG_ENT("disk event %d:%d\n",
729 MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));
731 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
732 }
733 #endif
735 /*
736 * random_input_words - add bulk entropy to pool
737 *
738 * @buf: buffer to add
739 * @wordcount: number of __u32 words to add
740 * @ent_count: total amount of entropy (in bits) to credit
741 *
742 * this provides bulk input of entropy to the input pool
743 *
744 */
745 void random_input_words(__u32 *buf, size_t wordcount, int ent_count)
746 {
747 mix_pool_bytes(&input_pool, buf, wordcount*4);
749 credit_entropy_bits(&input_pool, ent_count);
751 DEBUG_ENT("crediting %d bits => %d\n",
752 ent_count, input_pool.entropy_count);
753 /*
754 * Wake up waiting processes if we have enough
755 * entropy.
756 */
757 if (input_pool.entropy_count >= random_read_wakeup_thresh)
758 wake_up_interruptible(&random_read_wait);
759 }
760 EXPORT_SYMBOL(random_input_words);
762 /*
763 * random_input_wait - wait until random needs entropy
764 *
765 * this function sleeps until the /dev/random subsystem actually
766 * needs more entropy, and then return the amount of entropy
767 * that it would be nice to have added to the system.
768 */
769 int random_input_wait(void)
770 {
771 int count;
773 wait_event_interruptible(random_write_wait,
774 input_pool.entropy_count < random_write_wakeup_thresh);
776 count = random_write_wakeup_thresh - input_pool.entropy_count;
778 /* likely we got woken up due to a signal */
779 if (count <= 0) count = random_read_wakeup_thresh;
781 DEBUG_ENT("requesting %d bits from input_wait()er %d<%d\n",
782 count,
783 input_pool.entropy_count, random_write_wakeup_thresh);
785 return count;
786 }
787 EXPORT_SYMBOL(random_input_wait);
790 #define EXTRACT_SIZE 10
792 /*********************************************************************
793 *
794 * Entropy extraction routines
795 *
796 *********************************************************************/
798 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
799 size_t nbytes, int min, int rsvd);
801 /*
802 * This utility inline function is responsible for transferring entropy
803 * from the primary pool to the secondary extraction pool. We make
804 * sure we pull enough for a 'catastrophic reseed'.
805 */
806 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
807 {
808 __u32 tmp[OUTPUT_POOL_WORDS];
810 if (r->pull && r->entropy_count < nbytes * 8 &&
811 r->entropy_count < r->poolinfo->POOLBITS) {
812 /* If we're limited, always leave two wakeup worth's BITS */
813 int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
814 int bytes = nbytes;
816 /* pull at least as many as BYTES as wakeup BITS */
817 bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
818 /* but never more than the buffer size */
819 bytes = min_t(int, bytes, sizeof(tmp));
821 DEBUG_ENT("going to reseed %s with %d bits "
822 "(%d of %d requested)\n",
823 r->name, bytes * 8, nbytes * 8, r->entropy_count);
825 bytes = extract_entropy(r->pull, tmp, bytes,
826 random_read_wakeup_thresh / 8, rsvd);
827 mix_pool_bytes(r, tmp, bytes);
828 credit_entropy_bits(r, bytes*8);
829 }
830 }
832 /*
833 * These functions extracts randomness from the "entropy pool", and
834 * returns it in a buffer.
835 *
836 * The min parameter specifies the minimum amount we can pull before
837 * failing to avoid races that defeat catastrophic reseeding while the
838 * reserved parameter indicates how much entropy we must leave in the
839 * pool after each pull to avoid starving other readers.
840 *
841 * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
842 */
844 static size_t account(struct entropy_store *r, size_t nbytes, int min,
845 int reserved)
846 {
847 unsigned long flags;
849 /* Hold lock while accounting */
850 spin_lock_irqsave(&r->lock, flags);
852 BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
853 DEBUG_ENT("trying to extract %d bits from %s\n",
854 nbytes * 8, r->name);
856 /* Can we pull enough? */
857 if (r->entropy_count / 8 < min + reserved) {
858 nbytes = 0;
859 } else {
860 /* If limited, never pull more than available */
861 if (r->limit && nbytes + reserved >= r->entropy_count / 8)
862 nbytes = r->entropy_count/8 - reserved;
864 if (r->entropy_count / 8 >= nbytes + reserved)
865 r->entropy_count -= nbytes*8;
866 else
867 r->entropy_count = reserved;
869 if (r->entropy_count < random_write_wakeup_thresh) {
870 wake_up_interruptible(&random_write_wait);
871 kill_fasync(&fasync, SIGIO, POLL_OUT);
872 }
873 }
875 DEBUG_ENT("debiting %d entropy credits from %s%s\n",
876 nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
878 spin_unlock_irqrestore(&r->lock, flags);
880 return nbytes;
881 }
883 static void extract_buf(struct entropy_store *r, __u8 *out)
884 {
885 int i;
886 __u32 hash[5], workspace[SHA_WORKSPACE_WORDS];
887 __u8 extract[64];
889 /* Generate a hash across the pool, 16 words (512 bits) at a time */
890 sha_init(hash);
891 for (i = 0; i < r->poolinfo->poolwords; i += 16)
892 sha_transform(hash, (__u8 *)(r->pool + i), workspace);
894 /*
895 * We mix the hash back into the pool to prevent backtracking
896 * attacks (where the attacker knows the state of the pool
897 * plus the current outputs, and attempts to find previous
898 * ouputs), unless the hash function can be inverted. By
899 * mixing at least a SHA1 worth of hash data back, we make
900 * brute-forcing the feedback as hard as brute-forcing the
901 * hash.
902 */
903 mix_pool_bytes_extract(r, hash, sizeof(hash), extract);
905 /*
906 * To avoid duplicates, we atomically extract a portion of the
907 * pool while mixing, and hash one final time.
908 */
909 sha_transform(hash, extract, workspace);
910 memset(extract, 0, sizeof(extract));
911 memset(workspace, 0, sizeof(workspace));
913 /*
914 * In case the hash function has some recognizable output
915 * pattern, we fold it in half. Thus, we always feed back
916 * twice as much data as we output.
917 */
918 hash[0] ^= hash[3];
919 hash[1] ^= hash[4];
920 hash[2] ^= rol32(hash[2], 16);
921 memcpy(out, hash, EXTRACT_SIZE);
922 memset(hash, 0, sizeof(hash));
923 }
925 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
926 size_t nbytes, int min, int reserved)
927 {
928 ssize_t ret = 0, i;
929 __u8 tmp[EXTRACT_SIZE];
930 unsigned long flags;
932 xfer_secondary_pool(r, nbytes);
933 nbytes = account(r, nbytes, min, reserved);
935 while (nbytes) {
936 extract_buf(r, tmp);
938 if (fips_enabled) {
939 spin_lock_irqsave(&r->lock, flags);
940 if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
941 panic("Hardware RNG duplicated output!\n");
942 memcpy(r->last_data, tmp, EXTRACT_SIZE);
943 spin_unlock_irqrestore(&r->lock, flags);
944 }
945 i = min_t(int, nbytes, EXTRACT_SIZE);
946 memcpy(buf, tmp, i);
947 nbytes -= i;
948 buf += i;
949 ret += i;
950 }
952 /* Wipe data just returned from memory */
953 memset(tmp, 0, sizeof(tmp));
955 return ret;
956 }
958 static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
959 size_t nbytes)
960 {
961 ssize_t ret = 0, i;
962 __u8 tmp[EXTRACT_SIZE];
964 xfer_secondary_pool(r, nbytes);
965 nbytes = account(r, nbytes, 0, 0);
967 while (nbytes) {
968 if (need_resched()) {
969 if (signal_pending(current)) {
970 if (ret == 0)
971 ret = -ERESTARTSYS;
972 break;
973 }
974 schedule();
975 }
977 extract_buf(r, tmp);
978 i = min_t(int, nbytes, EXTRACT_SIZE);
979 if (copy_to_user(buf, tmp, i)) {
980 ret = -EFAULT;
981 break;
982 }
984 nbytes -= i;
985 buf += i;
986 ret += i;
987 }
989 /* Wipe data just returned from memory */
990 memset(tmp, 0, sizeof(tmp));
992 return ret;
993 }
995 /*
996 * This function is the exported kernel interface. It returns some
997 * number of good random numbers, suitable for seeding TCP sequence
998 * numbers, etc.
999 */
1000 void get_random_bytes(void *buf, int nbytes)
1001 {
1002 char *p = buf;
1004 while (nbytes) {
1005 unsigned long v;
1006 int chunk = min(nbytes, (int)sizeof(unsigned long));
1008 if (!arch_get_random_long(&v))
1009 break;
1011 memcpy(p, &v, chunk);
1012 p += chunk;
1013 nbytes -= chunk;
1014 }
1016 extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
1017 }
1018 EXPORT_SYMBOL(get_random_bytes);
1020 /*
1021 * init_std_data - initialize pool with system data
1022 *
1023 * @r: pool to initialize
1024 *
1025 * This function clears the pool's entropy count and mixes some system
1026 * data into the pool to prepare it for use. The pool is not cleared
1027 * as that can only decrease the entropy in the pool.
1028 */
1029 static void init_std_data(struct entropy_store *r)
1030 {
1031 ktime_t now;
1032 unsigned long flags;
1034 spin_lock_irqsave(&r->lock, flags);
1035 r->entropy_count = 0;
1036 spin_unlock_irqrestore(&r->lock, flags);
1038 now = ktime_get_real();
1039 mix_pool_bytes(r, &now, sizeof(now));
1040 mix_pool_bytes(r, utsname(), sizeof(*(utsname())));
1041 }
1043 static int rand_initialize(void)
1044 {
1045 init_std_data(&input_pool);
1046 init_std_data(&blocking_pool);
1047 init_std_data(&nonblocking_pool);
1048 return 0;
1049 }
1050 module_init(rand_initialize);
1052 void rand_initialize_irq(int irq)
1053 {
1054 struct timer_rand_state *state;
1056 state = get_timer_rand_state(irq);
1058 if (state)
1059 return;
1061 /*
1062 * If kzalloc returns null, we just won't use that entropy
1063 * source.
1064 */
1065 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1066 if (state)
1067 set_timer_rand_state(irq, state);
1068 }
1070 #ifdef CONFIG_BLOCK
1071 void rand_initialize_disk(struct gendisk *disk)
1072 {
1073 struct timer_rand_state *state;
1075 /*
1076 * If kzalloc returns null, we just won't use that entropy
1077 * source.
1078 */
1079 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1080 if (state)
1081 disk->random = state;
1082 }
1083 #endif
1085 static ssize_t
1086 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1087 {
1088 ssize_t n, retval = 0, count = 0;
1090 if (nbytes == 0)
1091 return 0;
1093 while (nbytes > 0) {
1094 n = nbytes;
1095 if (n > SEC_XFER_SIZE)
1096 n = SEC_XFER_SIZE;
1098 DEBUG_ENT("reading %d bits\n", n*8);
1100 n = extract_entropy_user(&blocking_pool, buf, n);
1102 DEBUG_ENT("read got %d bits (%d still needed)\n",
1103 n*8, (nbytes-n)*8);
1105 if (n == 0) {
1106 if (file->f_flags & O_NONBLOCK) {
1107 retval = -EAGAIN;
1108 break;
1109 }
1111 DEBUG_ENT("sleeping?\n");
1113 wait_event_interruptible(random_read_wait,
1114 input_pool.entropy_count >=
1115 random_read_wakeup_thresh);
1117 DEBUG_ENT("awake\n");
1119 if (signal_pending(current)) {
1120 retval = -ERESTARTSYS;
1121 break;
1122 }
1124 continue;
1125 }
1127 if (n < 0) {
1128 retval = n;
1129 break;
1130 }
1131 count += n;
1132 buf += n;
1133 nbytes -= n;
1134 break; /* This break makes the device work */
1135 /* like a named pipe */
1136 }
1138 return (count ? count : retval);
1139 }
1141 static ssize_t
1142 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1143 {
1144 return extract_entropy_user(&nonblocking_pool, buf, nbytes);
1145 }
1147 static unsigned int
1148 random_poll(struct file *file, poll_table * wait)
1149 {
1150 unsigned int mask;
1152 poll_wait(file, &random_read_wait, wait);
1153 poll_wait(file, &random_write_wait, wait);
1154 mask = 0;
1155 if (input_pool.entropy_count >= random_read_wakeup_thresh)
1156 mask |= POLLIN | POLLRDNORM;
1157 if (input_pool.entropy_count < random_write_wakeup_thresh)
1158 mask |= POLLOUT | POLLWRNORM;
1159 return mask;
1160 }
1162 static int
1163 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1164 {
1165 size_t bytes;
1166 __u32 buf[16];
1167 const char __user *p = buffer;
1169 while (count > 0) {
1170 bytes = min(count, sizeof(buf));
1171 if (copy_from_user(&buf, p, bytes))
1172 return -EFAULT;
1174 count -= bytes;
1175 p += bytes;
1177 mix_pool_bytes(r, buf, bytes);
1178 cond_resched();
1179 }
1181 return 0;
1182 }
1184 static ssize_t random_write(struct file *file, const char __user *buffer,
1185 size_t count, loff_t *ppos)
1186 {
1187 size_t ret;
1189 ret = write_pool(&blocking_pool, buffer, count);
1190 if (ret)
1191 return ret;
1192 ret = write_pool(&nonblocking_pool, buffer, count);
1193 if (ret)
1194 return ret;
1196 return (ssize_t)count;
1197 }
1199 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1200 {
1201 int size, ent_count;
1202 int __user *p = (int __user *)arg;
1203 int retval;
1205 switch (cmd) {
1206 case RNDGETENTCNT:
1207 /* inherently racy, no point locking */
1208 if (put_user(input_pool.entropy_count, p))
1209 return -EFAULT;
1210 return 0;
1211 case RNDADDTOENTCNT:
1212 if (!capable(CAP_SYS_ADMIN))
1213 return -EPERM;
1214 if (get_user(ent_count, p))
1215 return -EFAULT;
1216 credit_entropy_bits(&input_pool, ent_count);
1217 return 0;
1218 case RNDADDENTROPY:
1219 if (!capable(CAP_SYS_ADMIN))
1220 return -EPERM;
1221 if (get_user(ent_count, p++))
1222 return -EFAULT;
1223 if (ent_count < 0)
1224 return -EINVAL;
1225 if (get_user(size, p++))
1226 return -EFAULT;
1227 retval = write_pool(&input_pool, (const char __user *)p,
1228 size);
1229 if (retval < 0)
1230 return retval;
1231 credit_entropy_bits(&input_pool, ent_count);
1232 return 0;
1233 case RNDZAPENTCNT:
1234 case RNDCLEARPOOL:
1235 /* Clear the entropy pool counters. */
1236 if (!capable(CAP_SYS_ADMIN))
1237 return -EPERM;
1238 rand_initialize();
1239 return 0;
1240 default:
1241 return -EINVAL;
1242 }
1243 }
1245 static int random_fasync(int fd, struct file *filp, int on)
1246 {
1247 return fasync_helper(fd, filp, on, &fasync);
1248 }
1250 const struct file_operations random_fops = {
1251 .read = random_read,
1252 .write = random_write,
1253 .poll = random_poll,
1254 .unlocked_ioctl = random_ioctl,
1255 .fasync = random_fasync,
1256 .llseek = noop_llseek,
1257 };
1259 const struct file_operations urandom_fops = {
1260 .read = urandom_read,
1261 .write = random_write,
1262 .unlocked_ioctl = random_ioctl,
1263 .fasync = random_fasync,
1264 .llseek = noop_llseek,
1265 };
1267 /***************************************************************
1268 * Random UUID interface
1269 *
1270 * Used here for a Boot ID, but can be useful for other kernel
1271 * drivers.
1272 ***************************************************************/
1274 /*
1275 * Generate random UUID
1276 */
1277 void generate_random_uuid(unsigned char uuid_out[16])
1278 {
1279 get_random_bytes(uuid_out, 16);
1280 /* Set UUID version to 4 --- truly random generation */
1281 uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1282 /* Set the UUID variant to DCE */
1283 uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1284 }
1285 EXPORT_SYMBOL(generate_random_uuid);
1287 /********************************************************************
1288 *
1289 * Sysctl interface
1290 *
1291 ********************************************************************/
1293 #ifdef CONFIG_SYSCTL
1295 #include <linux/sysctl.h>
1297 static int min_read_thresh = 8, min_write_thresh;
1298 static int max_read_thresh = INPUT_POOL_WORDS * 32;
1299 static int max_write_thresh = INPUT_POOL_WORDS * 32;
1300 static char sysctl_bootid[16];
1302 /*
1303 * These functions is used to return both the bootid UUID, and random
1304 * UUID. The difference is in whether table->data is NULL; if it is,
1305 * then a new UUID is generated and returned to the user.
1306 *
1307 * If the user accesses this via the proc interface, it will be returned
1308 * as an ASCII string in the standard UUID format. If accesses via the
1309 * sysctl system call, it is returned as 16 bytes of binary data.
1310 */
1311 static int proc_do_uuid(ctl_table *table, int write,
1312 void __user *buffer, size_t *lenp, loff_t *ppos)
1313 {
1314 ctl_table fake_table;
1315 unsigned char buf[64], tmp_uuid[16], *uuid;
1317 uuid = table->data;
1318 if (!uuid) {
1319 uuid = tmp_uuid;
1320 uuid[8] = 0;
1321 }
1322 if (uuid[8] == 0)
1323 generate_random_uuid(uuid);
1325 sprintf(buf, "%pU", uuid);
1327 fake_table.data = buf;
1328 fake_table.maxlen = sizeof(buf);
1330 return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1331 }
1333 static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1334 ctl_table random_table[] = {
1335 {
1336 .procname = "poolsize",
1337 .data = &sysctl_poolsize,
1338 .maxlen = sizeof(int),
1339 .mode = 0444,
1340 .proc_handler = proc_dointvec,
1341 },
1342 {
1343 .procname = "entropy_avail",
1344 .maxlen = sizeof(int),
1345 .mode = 0444,
1346 .proc_handler = proc_dointvec,
1347 .data = &input_pool.entropy_count,
1348 },
1349 {
1350 .procname = "read_wakeup_threshold",
1351 .data = &random_read_wakeup_thresh,
1352 .maxlen = sizeof(int),
1353 .mode = 0644,
1354 .proc_handler = proc_dointvec_minmax,
1355 .extra1 = &min_read_thresh,
1356 .extra2 = &max_read_thresh,
1357 },
1358 {
1359 .procname = "write_wakeup_threshold",
1360 .data = &random_write_wakeup_thresh,
1361 .maxlen = sizeof(int),
1362 .mode = 0644,
1363 .proc_handler = proc_dointvec_minmax,
1364 .extra1 = &min_write_thresh,
1365 .extra2 = &max_write_thresh,
1366 },
1367 {
1368 .procname = "boot_id",
1369 .data = &sysctl_bootid,
1370 .maxlen = 16,
1371 .mode = 0444,
1372 .proc_handler = proc_do_uuid,
1373 },
1374 {
1375 .procname = "uuid",
1376 .maxlen = 16,
1377 .mode = 0444,
1378 .proc_handler = proc_do_uuid,
1379 },
1380 { }
1381 };
1382 #endif /* CONFIG_SYSCTL */
1384 static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1386 static int __init random_int_secret_init(void)
1387 {
1388 get_random_bytes(random_int_secret, sizeof(random_int_secret));
1389 return 0;
1390 }
1391 late_initcall(random_int_secret_init);
1393 /*
1394 * Get a random word for internal kernel use only. Similar to urandom but
1395 * with the goal of minimal entropy pool depletion. As a result, the random
1396 * value is not cryptographically secure but for several uses the cost of
1397 * depleting entropy is too high
1398 */
1399 DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1400 unsigned int get_random_int(void)
1401 {
1402 __u32 *hash;
1403 unsigned int ret;
1405 if (arch_get_random_int(&ret))
1406 return ret;
1408 hash = get_cpu_var(get_random_int_hash);
1410 hash[0] += current->pid + jiffies + get_cycles();
1411 md5_transform(hash, random_int_secret);
1412 ret = hash[0];
1413 put_cpu_var(get_random_int_hash);
1415 return ret;
1416 }
1418 /*
1419 * randomize_range() returns a start address such that
1420 *
1421 * [...... <range> .....]
1422 * start end
1423 *
1424 * a <range> with size "len" starting at the return value is inside in the
1425 * area defined by [start, end], but is otherwise randomized.
1426 */
1427 unsigned long
1428 randomize_range(unsigned long start, unsigned long end, unsigned long len)
1429 {
1430 unsigned long range = end - len - start;
1432 if (end <= start + len)
1433 return 0;
1434 return PAGE_ALIGN(get_random_int() % range + start);
1435 }