2 * random.c -- A strong random number generator
4 * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
6 * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
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
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.)
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
43 * (now, with legal B.S. out of the way.....)
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.
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.
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.
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.
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
98 * Exported interfaces ---- output
99 * ===============================
101 * There are three exported interfaces; the first is one designed to
102 * be used from within the kernel:
104 * void get_random_bytes(void *buf, int nbytes);
106 * This interface will return the requested number of random bytes,
107 * and place it in the requested buffer.
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.
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.
122 * Exported interfaces ---- input
123 * ==============================
125 * The current exported interfaces for gathering environmental noise
126 * from the devices are:
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);
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).
142 * add_input_randomness() uses the input layer interrupt timing, as well as
143 * the event type information from the hardware.
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.
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.
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.
159 * Ensuring unpredictability at system startup
160 * ============================================
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
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
181 * chmod 600 $random_seed
182 * dd if=/dev/urandom of=$random_seed count=1 bs=512
184 * and the following lines in an appropriate script which is run as
185 * the system is shutdown:
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
192 * chmod 600 $random_seed
193 * dd if=/dev/urandom of=$random_seed count=1 bs=512
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.
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
209 * Configuring the /dev/random driver under Linux
210 * ==============================================
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:
217 * mknod /dev/random c 1 8
218 * mknod /dev/urandom c 1 9
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.
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.
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.
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>
259 #ifdef CONFIG_GENERIC_HARDIRQS
260 # include <linux/irq.h>
263 #include <asm/processor.h>
264 #include <asm/uaccess.h>
266 #include <asm/irq_regs.h>
270 * Configuration information
272 #define INPUT_POOL_WORDS 128
273 #define OUTPUT_POOL_WORDS 32
274 #define SEC_XFER_SIZE 512
275 #define EXTRACT_SIZE 10
278 * The minimum number of bits of entropy before we wake up a read on
279 * /dev/random. Should be enough to do a significant reseed.
281 static int random_read_wakeup_thresh = 64;
284 * If the entropy count falls under this number of bits, then we
285 * should wake up processes which are selecting or polling on write
286 * access to /dev/random.
288 static int random_write_wakeup_thresh = 128;
291 * When the input pool goes over trickle_thresh, start dropping most
292 * samples to avoid wasting CPU time and reduce lock contention.
295 static int trickle_thresh __read_mostly = INPUT_POOL_WORDS * 28;
297 static DEFINE_PER_CPU(int, trickle_count);
300 * A pool of size .poolwords is stirred with a primitive polynomial
301 * of degree .poolwords over GF(2). The taps for various sizes are
302 * defined below. They are chosen to be evenly spaced (minimum RMS
303 * distance from evenly spaced; the numbers in the comments are a
304 * scaled squared error sum) except for the last tap, which is 1 to
305 * get the twisting happening as fast as possible.
307 static struct poolinfo {
309 int tap1, tap2, tap3, tap4, tap5;
310 } poolinfo_table[] = {
311 /* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */
312 { 128, 103, 76, 51, 25, 1 },
313 /* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */
314 { 32, 26, 20, 14, 7, 1 },
316 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */
317 { 2048, 1638, 1231, 819, 411, 1 },
319 /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
320 { 1024, 817, 615, 412, 204, 1 },
322 /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
323 { 1024, 819, 616, 410, 207, 2 },
325 /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
326 { 512, 411, 308, 208, 104, 1 },
328 /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
329 { 512, 409, 307, 206, 102, 2 },
330 /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
331 { 512, 409, 309, 205, 103, 2 },
333 /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
334 { 256, 205, 155, 101, 52, 1 },
336 /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
337 { 128, 103, 78, 51, 27, 2 },
339 /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
340 { 64, 52, 39, 26, 14, 1 },
344 #define POOLBITS poolwords*32
345 #define POOLBYTES poolwords*4
348 * For the purposes of better mixing, we use the CRC-32 polynomial as
349 * well to make a twisted Generalized Feedback Shift Reigster
351 * (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR generators. ACM
352 * Transactions on Modeling and Computer Simulation 2(3):179-194.
353 * Also see M. Matsumoto & Y. Kurita, 1994. Twisted GFSR generators
354 * II. ACM Transactions on Mdeling and Computer Simulation 4:254-266)
356 * Thanks to Colin Plumb for suggesting this.
358 * We have not analyzed the resultant polynomial to prove it primitive;
359 * in fact it almost certainly isn't. Nonetheless, the irreducible factors
360 * of a random large-degree polynomial over GF(2) are more than large enough
361 * that periodicity is not a concern.
363 * The input hash is much less sensitive than the output hash. All
364 * that we want of it is that it be a good non-cryptographic hash;
365 * i.e. it not produce collisions when fed "random" data of the sort
366 * we expect to see. As long as the pool state differs for different
367 * inputs, we have preserved the input entropy and done a good job.
368 * The fact that an intelligent attacker can construct inputs that
369 * will produce controlled alterations to the pool's state is not
370 * important because we don't consider such inputs to contribute any
371 * randomness. The only property we need with respect to them is that
372 * the attacker can't increase his/her knowledge of the pool's state.
373 * Since all additions are reversible (knowing the final state and the
374 * input, you can reconstruct the initial state), if an attacker has
375 * any uncertainty about the initial state, he/she can only shuffle
376 * that uncertainty about, but never cause any collisions (which would
377 * decrease the uncertainty).
379 * The chosen system lets the state of the pool be (essentially) the input
380 * modulo the generator polymnomial. Now, for random primitive polynomials,
381 * this is a universal class of hash functions, meaning that the chance
382 * of a collision is limited by the attacker's knowledge of the generator
383 * polynomail, so if it is chosen at random, an attacker can never force
384 * a collision. Here, we use a fixed polynomial, but we *can* assume that
385 * ###--> it is unknown to the processes generating the input entropy. <-###
386 * Because of this important property, this is a good, collision-resistant
387 * hash; hash collisions will occur no more often than chance.
391 * Static global variables
393 static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
394 static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
395 static struct fasync_struct *fasync;
399 module_param(debug, bool, 0644);
400 #define DEBUG_ENT(fmt, arg...) do { \
402 printk(KERN_DEBUG "random %04d %04d %04d: " \
404 input_pool.entropy_count,\
405 blocking_pool.entropy_count,\
406 nonblocking_pool.entropy_count,\
409 #define DEBUG_ENT(fmt, arg...) do {} while (0)
412 /**********************************************************************
414 * OS independent entropy store. Here are the functions which handle
415 * storing entropy in an entropy pool.
417 **********************************************************************/
419 struct entropy_store;
420 struct entropy_store {
421 /* read-only data: */
422 struct poolinfo *poolinfo;
425 struct entropy_store *pull;
428 /* read-write data: */
431 unsigned input_rotate;
434 unsigned int initialized:1;
435 __u8 last_data[EXTRACT_SIZE];
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],
446 .lock = __SPIN_LOCK_UNLOCKED(&input_pool.lock),
447 .pool = input_pool_data
450 static struct entropy_store blocking_pool = {
451 .poolinfo = &poolinfo_table[1],
455 .lock = __SPIN_LOCK_UNLOCKED(&blocking_pool.lock),
456 .pool = blocking_pool_data
459 static struct entropy_store nonblocking_pool = {
460 .poolinfo = &poolinfo_table[1],
461 .name = "nonblocking",
463 .lock = __SPIN_LOCK_UNLOCKED(&nonblocking_pool.lock),
464 .pool = nonblocking_pool_data
467 static __u32 const twist_table[8] = {
468 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
469 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
472 * This function adds bytes into the entropy "pool". It does not
473 * update the entropy estimate. The caller should call
474 * credit_entropy_bits if this is appropriate.
476 * The pool is stirred with a primitive polynomial of the appropriate
477 * degree, and then twisted. We twist by three bits at a time because
478 * it's cheap to do so and helps slightly in the expected case where
479 * the entropy is concentrated in the low-order bits.
481 static void __mix_pool_bytes(struct entropy_store *r, const void *in,
482 int nbytes, __u8 out[64])
484 unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
486 int wordmask = r->poolinfo->poolwords - 1;
487 const char *bytes = in;
490 tap1 = r->poolinfo->tap1;
491 tap2 = r->poolinfo->tap2;
492 tap3 = r->poolinfo->tap3;
493 tap4 = r->poolinfo->tap4;
494 tap5 = r->poolinfo->tap5;
497 input_rotate = ACCESS_ONCE(r->input_rotate);
498 i = ACCESS_ONCE(r->add_ptr);
500 /* mix one byte at a time to simplify size handling and churn faster */
502 w = rol32(*bytes++, input_rotate & 31);
503 i = (i - 1) & wordmask;
505 /* XOR in the various taps */
507 w ^= r->pool[(i + tap1) & wordmask];
508 w ^= r->pool[(i + tap2) & wordmask];
509 w ^= r->pool[(i + tap3) & wordmask];
510 w ^= r->pool[(i + tap4) & wordmask];
511 w ^= r->pool[(i + tap5) & wordmask];
513 /* Mix the result back in with a twist */
514 r->pool[i] = (w >> 3) ^ twist_table[w & 7];
517 * Normally, we add 7 bits of rotation to the pool.
518 * At the beginning of the pool, add an extra 7 bits
519 * rotation, so that successive passes spread the
520 * input bits across the pool evenly.
522 input_rotate += i ? 7 : 14;
525 ACCESS_ONCE(r->input_rotate) = input_rotate;
526 ACCESS_ONCE(r->add_ptr) = i;
530 for (j = 0; j < 16; j++)
531 ((__u32 *)out)[j] = r->pool[(i - j) & wordmask];
534 static void mix_pool_bytes(struct entropy_store *r, const void *in,
535 int nbytes, __u8 out[64])
539 spin_lock_irqsave(&r->lock, flags);
540 __mix_pool_bytes(r, in, nbytes, out);
541 spin_unlock_irqrestore(&r->lock, flags);
547 unsigned short count;
548 unsigned char rotate;
549 unsigned char last_timer_intr;
553 * This is a fast mixing routine used by the interrupt randomness
554 * collector. It's hardcoded for an 128 bit pool and assumes that any
555 * locks that might be needed are taken by the caller.
557 static void fast_mix(struct fast_pool *f, const void *in, int nbytes)
559 const char *bytes = in;
561 unsigned i = f->count;
562 unsigned input_rotate = f->rotate;
565 w = rol32(*bytes++, input_rotate & 31) ^ f->pool[i & 3] ^
566 f->pool[(i + 1) & 3];
567 f->pool[i & 3] = (w >> 3) ^ twist_table[w & 7];
568 input_rotate += (i++ & 3) ? 7 : 14;
571 f->rotate = input_rotate;
575 * Credit (or debit) the entropy store with n bits of entropy
577 static void credit_entropy_bits(struct entropy_store *r, int nbits)
579 int entropy_count, orig;
584 DEBUG_ENT("added %d entropy credits to %s\n", nbits, r->name);
586 entropy_count = orig = ACCESS_ONCE(r->entropy_count);
587 entropy_count += nbits;
588 if (entropy_count < 0) {
589 DEBUG_ENT("negative entropy/overflow\n");
591 } else if (entropy_count > r->poolinfo->POOLBITS)
592 entropy_count = r->poolinfo->POOLBITS;
593 if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
596 if (!r->initialized && nbits > 0) {
597 r->entropy_total += nbits;
598 if (r->entropy_total > 128)
602 /* should we wake readers? */
603 if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {
604 wake_up_interruptible(&random_read_wait);
605 kill_fasync(&fasync, SIGIO, POLL_IN);
609 /*********************************************************************
611 * Entropy input management
613 *********************************************************************/
615 /* There is one of these per entropy source */
616 struct timer_rand_state {
618 long last_delta, last_delta2;
619 unsigned dont_count_entropy:1;
622 #ifndef CONFIG_GENERIC_HARDIRQS
624 static struct timer_rand_state *irq_timer_state[NR_IRQS];
626 static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
628 return irq_timer_state[irq];
631 static void set_timer_rand_state(unsigned int irq,
632 struct timer_rand_state *state)
634 irq_timer_state[irq] = state;
639 static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
641 struct irq_desc *desc;
643 desc = irq_to_desc(irq);
645 return desc->timer_rand_state;
648 static void set_timer_rand_state(unsigned int irq,
649 struct timer_rand_state *state)
651 struct irq_desc *desc;
653 desc = irq_to_desc(irq);
655 desc->timer_rand_state = state;
660 * Add device- or boot-specific data to the input and nonblocking
661 * pools to help initialize them to unique values.
663 * None of this adds any entropy, it is meant to avoid the
664 * problem of the nonblocking pool having similar initial state
665 * across largely identical devices.
667 void add_device_randomness(const void *buf, unsigned int size)
669 unsigned long time = get_cycles() ^ jiffies;
671 mix_pool_bytes(&input_pool, buf, size, NULL);
672 mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
673 mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
674 mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
676 EXPORT_SYMBOL(add_device_randomness);
678 static struct timer_rand_state input_timer_state;
681 * This function adds entropy to the entropy "pool" by using timing
682 * delays. It uses the timer_rand_state structure to make an estimate
683 * of how many bits of entropy this call has added to the pool.
685 * The number "num" is also added to the pool - it should somehow describe
686 * the type of event which just happened. This is currently 0-255 for
687 * keyboard scan codes, and 256 upwards for interrupts.
690 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
697 long delta, delta2, delta3;
700 /* if over the trickle threshold, use only 1 in 4096 samples */
701 if (input_pool.entropy_count > trickle_thresh &&
702 ((__this_cpu_inc_return(trickle_count) - 1) & 0xfff))
705 sample.jiffies = jiffies;
706 sample.cycles = get_cycles();
708 mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
711 * Calculate number of bits of randomness we probably added.
712 * We take into account the first, second and third-order deltas
713 * in order to make our estimate.
716 if (!state->dont_count_entropy) {
717 delta = sample.jiffies - state->last_time;
718 state->last_time = sample.jiffies;
720 delta2 = delta - state->last_delta;
721 state->last_delta = delta;
723 delta3 = delta2 - state->last_delta2;
724 state->last_delta2 = delta2;
738 * delta is now minimum absolute delta.
739 * Round down by 1 bit on general principles,
740 * and limit entropy entimate to 12 bits.
742 credit_entropy_bits(&input_pool,
743 min_t(int, fls(delta>>1), 11));
749 void add_input_randomness(unsigned int type, unsigned int code,
752 static unsigned char last_value;
754 /* ignore autorepeat and the like */
755 if (value == last_value)
758 DEBUG_ENT("input event\n");
760 add_timer_randomness(&input_timer_state,
761 (type << 4) ^ code ^ (code >> 4) ^ value);
763 EXPORT_SYMBOL_GPL(add_input_randomness);
765 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
767 void add_interrupt_randomness(int irq, int irq_flags)
769 struct entropy_store *r;
770 struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
771 struct pt_regs *regs = get_irq_regs();
772 unsigned long now = jiffies;
773 __u32 input[4], cycles = get_cycles();
775 input[0] = cycles ^ jiffies;
778 __u64 ip = instruction_pointer(regs);
783 fast_mix(fast_pool, input, sizeof(input));
785 if ((fast_pool->count & 1023) &&
786 !time_after(now, fast_pool->last + HZ))
789 fast_pool->last = now;
791 r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
792 __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
794 * If we don't have a valid cycle counter, and we see
795 * back-to-back timer interrupts, then skip giving credit for
799 if (irq_flags & __IRQF_TIMER) {
800 if (fast_pool->last_timer_intr)
802 fast_pool->last_timer_intr = 1;
804 fast_pool->last_timer_intr = 0;
806 credit_entropy_bits(r, 1);
810 void add_disk_randomness(struct gendisk *disk)
812 if (!disk || !disk->random)
814 /* first major is 1, so we get >= 0x200 here */
815 DEBUG_ENT("disk event %d:%d\n",
816 MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));
818 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
822 /*********************************************************************
824 * Entropy extraction routines
826 *********************************************************************/
828 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
829 size_t nbytes, int min, int rsvd);
832 * This utility inline function is responsible for transferring entropy
833 * from the primary pool to the secondary extraction pool. We make
834 * sure we pull enough for a 'catastrophic reseed'.
836 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
839 __u32 tmp[OUTPUT_POOL_WORDS];
844 if (r->pull && r->entropy_count < nbytes * 8 &&
845 r->entropy_count < r->poolinfo->POOLBITS) {
846 /* If we're limited, always leave two wakeup worth's BITS */
847 int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
850 /* pull at least as many as BYTES as wakeup BITS */
851 bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
852 /* but never more than the buffer size */
853 bytes = min_t(int, bytes, sizeof(u.tmp));
855 DEBUG_ENT("going to reseed %s with %d bits "
856 "(%d of %d requested)\n",
857 r->name, bytes * 8, nbytes * 8, r->entropy_count);
859 bytes = extract_entropy(r->pull, u.tmp, bytes,
860 random_read_wakeup_thresh / 8, rsvd);
861 mix_pool_bytes(r, u.tmp, bytes, NULL);
862 credit_entropy_bits(r, bytes*8);
864 kmemcheck_mark_initialized(&u.hwrand, sizeof(u.hwrand));
865 for (i = 0; i < 4; i++)
866 if (arch_get_random_long(&u.hwrand[i]))
869 mix_pool_bytes(r, &u.hwrand, sizeof(u.hwrand), 0);
873 * These functions extracts randomness from the "entropy pool", and
874 * returns it in a buffer.
876 * The min parameter specifies the minimum amount we can pull before
877 * failing to avoid races that defeat catastrophic reseeding while the
878 * reserved parameter indicates how much entropy we must leave in the
879 * pool after each pull to avoid starving other readers.
881 * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
884 static size_t account(struct entropy_store *r, size_t nbytes, int min,
889 /* Hold lock while accounting */
890 spin_lock_irqsave(&r->lock, flags);
892 BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
893 DEBUG_ENT("trying to extract %d bits from %s\n",
894 nbytes * 8, r->name);
896 /* Can we pull enough? */
897 if (r->entropy_count / 8 < min + reserved) {
900 /* If limited, never pull more than available */
901 if (r->limit && nbytes + reserved >= r->entropy_count / 8)
902 nbytes = r->entropy_count/8 - reserved;
904 if (r->entropy_count / 8 >= nbytes + reserved)
905 r->entropy_count -= nbytes*8;
907 r->entropy_count = reserved;
909 if (r->entropy_count < random_write_wakeup_thresh) {
910 wake_up_interruptible(&random_write_wait);
911 kill_fasync(&fasync, SIGIO, POLL_OUT);
915 DEBUG_ENT("debiting %d entropy credits from %s%s\n",
916 nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
918 spin_unlock_irqrestore(&r->lock, flags);
923 static void extract_buf(struct entropy_store *r, __u8 *out)
926 __u32 hash[5], workspace[SHA_WORKSPACE_WORDS];
930 /* Generate a hash across the pool, 16 words (512 bits) at a time */
932 spin_lock_irqsave(&r->lock, flags);
933 for (i = 0; i < r->poolinfo->poolwords; i += 16)
934 sha_transform(hash, (__u8 *)(r->pool + i), workspace);
937 * We mix the hash back into the pool to prevent backtracking
938 * attacks (where the attacker knows the state of the pool
939 * plus the current outputs, and attempts to find previous
940 * ouputs), unless the hash function can be inverted. By
941 * mixing at least a SHA1 worth of hash data back, we make
942 * brute-forcing the feedback as hard as brute-forcing the
945 __mix_pool_bytes(r, hash, sizeof(hash), extract);
946 spin_unlock_irqrestore(&r->lock, flags);
949 * To avoid duplicates, we atomically extract a portion of the
950 * pool while mixing, and hash one final time.
952 sha_transform(hash, extract, workspace);
953 memset(extract, 0, sizeof(extract));
954 memset(workspace, 0, sizeof(workspace));
957 * In case the hash function has some recognizable output
958 * pattern, we fold it in half. Thus, we always feed back
959 * twice as much data as we output.
963 hash[2] ^= rol32(hash[2], 16);
964 memcpy(out, hash, EXTRACT_SIZE);
965 memset(hash, 0, sizeof(hash));
968 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
969 size_t nbytes, int min, int reserved)
972 __u8 tmp[EXTRACT_SIZE];
974 xfer_secondary_pool(r, nbytes);
975 nbytes = account(r, nbytes, min, reserved);
983 spin_lock_irqsave(&r->lock, flags);
984 if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
985 panic("Hardware RNG duplicated output!\n");
986 memcpy(r->last_data, tmp, EXTRACT_SIZE);
987 spin_unlock_irqrestore(&r->lock, flags);
989 i = min_t(int, nbytes, EXTRACT_SIZE);
996 /* Wipe data just returned from memory */
997 memset(tmp, 0, sizeof(tmp));
1002 static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
1006 __u8 tmp[EXTRACT_SIZE];
1008 xfer_secondary_pool(r, nbytes);
1009 nbytes = account(r, nbytes, 0, 0);
1012 if (need_resched()) {
1013 if (signal_pending(current)) {
1021 extract_buf(r, tmp);
1022 i = min_t(int, nbytes, EXTRACT_SIZE);
1023 if (copy_to_user(buf, tmp, i)) {
1033 /* Wipe data just returned from memory */
1034 memset(tmp, 0, sizeof(tmp));
1040 * This function is the exported kernel interface. It returns some
1041 * number of good random numbers, suitable for seeding TCP sequence
1044 void get_random_bytes(void *buf, int nbytes)
1050 int chunk = min(nbytes, (int)sizeof(unsigned long));
1052 if (!arch_get_random_long(&v))
1055 memcpy(p, &v, chunk);
1060 extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
1062 EXPORT_SYMBOL(get_random_bytes);
1065 * init_std_data - initialize pool with system data
1067 * @r: pool to initialize
1069 * This function clears the pool's entropy count and mixes some system
1070 * data into the pool to prepare it for use. The pool is not cleared
1071 * as that can only decrease the entropy in the pool.
1073 static void init_std_data(struct entropy_store *r)
1076 ktime_t now = ktime_get_real();
1079 r->entropy_count = 0;
1080 r->entropy_total = 0;
1081 mix_pool_bytes(r, &now, sizeof(now), NULL);
1082 for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof(rv)) {
1083 if (!arch_get_random_long(&rv))
1085 mix_pool_bytes(r, &rv, sizeof(rv), NULL);
1087 mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
1090 static int rand_initialize(void)
1092 init_std_data(&input_pool);
1093 init_std_data(&blocking_pool);
1094 init_std_data(&nonblocking_pool);
1097 module_init(rand_initialize);
1099 void rand_initialize_irq(int irq)
1101 struct timer_rand_state *state;
1103 state = get_timer_rand_state(irq);
1109 * If kzalloc returns null, we just won't use that entropy
1112 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1114 set_timer_rand_state(irq, state);
1118 void rand_initialize_disk(struct gendisk *disk)
1120 struct timer_rand_state *state;
1123 * If kzalloc returns null, we just won't use that entropy
1126 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1128 disk->random = state;
1133 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1135 ssize_t n, retval = 0, count = 0;
1140 while (nbytes > 0) {
1142 if (n > SEC_XFER_SIZE)
1145 DEBUG_ENT("reading %d bits\n", n*8);
1147 n = extract_entropy_user(&blocking_pool, buf, n);
1149 DEBUG_ENT("read got %d bits (%d still needed)\n",
1153 if (file->f_flags & O_NONBLOCK) {
1158 DEBUG_ENT("sleeping?\n");
1160 wait_event_interruptible(random_read_wait,
1161 input_pool.entropy_count >=
1162 random_read_wakeup_thresh);
1164 DEBUG_ENT("awake\n");
1166 if (signal_pending(current)) {
1167 retval = -ERESTARTSYS;
1181 break; /* This break makes the device work */
1182 /* like a named pipe */
1185 return (count ? count : retval);
1189 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1191 return extract_entropy_user(&nonblocking_pool, buf, nbytes);
1195 random_poll(struct file *file, poll_table * wait)
1199 poll_wait(file, &random_read_wait, wait);
1200 poll_wait(file, &random_write_wait, wait);
1202 if (input_pool.entropy_count >= random_read_wakeup_thresh)
1203 mask |= POLLIN | POLLRDNORM;
1204 if (input_pool.entropy_count < random_write_wakeup_thresh)
1205 mask |= POLLOUT | POLLWRNORM;
1210 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1214 const char __user *p = buffer;
1217 bytes = min(count, sizeof(buf));
1218 if (copy_from_user(&buf, p, bytes))
1224 mix_pool_bytes(r, buf, bytes, NULL);
1231 static ssize_t random_write(struct file *file, const char __user *buffer,
1232 size_t count, loff_t *ppos)
1236 ret = write_pool(&blocking_pool, buffer, count);
1239 ret = write_pool(&nonblocking_pool, buffer, count);
1243 return (ssize_t)count;
1246 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1248 int size, ent_count;
1249 int __user *p = (int __user *)arg;
1254 /* inherently racy, no point locking */
1255 if (put_user(input_pool.entropy_count, p))
1258 case RNDADDTOENTCNT:
1259 if (!capable(CAP_SYS_ADMIN))
1261 if (get_user(ent_count, p))
1263 credit_entropy_bits(&input_pool, ent_count);
1266 if (!capable(CAP_SYS_ADMIN))
1268 if (get_user(ent_count, p++))
1272 if (get_user(size, p++))
1274 retval = write_pool(&input_pool, (const char __user *)p,
1278 credit_entropy_bits(&input_pool, ent_count);
1282 /* Clear the entropy pool counters. */
1283 if (!capable(CAP_SYS_ADMIN))
1292 static int random_fasync(int fd, struct file *filp, int on)
1294 return fasync_helper(fd, filp, on, &fasync);
1297 const struct file_operations random_fops = {
1298 .read = random_read,
1299 .write = random_write,
1300 .poll = random_poll,
1301 .unlocked_ioctl = random_ioctl,
1302 .fasync = random_fasync,
1303 .llseek = noop_llseek,
1306 const struct file_operations urandom_fops = {
1307 .read = urandom_read,
1308 .write = random_write,
1309 .unlocked_ioctl = random_ioctl,
1310 .fasync = random_fasync,
1311 .llseek = noop_llseek,
1314 /***************************************************************
1315 * Random UUID interface
1317 * Used here for a Boot ID, but can be useful for other kernel
1319 ***************************************************************/
1322 * Generate random UUID
1324 void generate_random_uuid(unsigned char uuid_out[16])
1326 get_random_bytes(uuid_out, 16);
1327 /* Set UUID version to 4 --- truly random generation */
1328 uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1329 /* Set the UUID variant to DCE */
1330 uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1332 EXPORT_SYMBOL(generate_random_uuid);
1334 /********************************************************************
1338 ********************************************************************/
1340 #ifdef CONFIG_SYSCTL
1342 #include <linux/sysctl.h>
1344 static int min_read_thresh = 8, min_write_thresh;
1345 static int max_read_thresh = INPUT_POOL_WORDS * 32;
1346 static int max_write_thresh = INPUT_POOL_WORDS * 32;
1347 static char sysctl_bootid[16];
1350 * These functions is used to return both the bootid UUID, and random
1351 * UUID. The difference is in whether table->data is NULL; if it is,
1352 * then a new UUID is generated and returned to the user.
1354 * If the user accesses this via the proc interface, it will be returned
1355 * as an ASCII string in the standard UUID format. If accesses via the
1356 * sysctl system call, it is returned as 16 bytes of binary data.
1358 static int proc_do_uuid(ctl_table *table, int write,
1359 void __user *buffer, size_t *lenp, loff_t *ppos)
1361 ctl_table fake_table;
1362 unsigned char buf[64], tmp_uuid[16], *uuid;
1367 generate_random_uuid(uuid);
1369 static DEFINE_SPINLOCK(bootid_spinlock);
1371 spin_lock(&bootid_spinlock);
1373 generate_random_uuid(uuid);
1374 spin_unlock(&bootid_spinlock);
1377 sprintf(buf, "%pU", uuid);
1379 fake_table.data = buf;
1380 fake_table.maxlen = sizeof(buf);
1382 return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1385 static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1386 extern ctl_table random_table[];
1387 ctl_table random_table[] = {
1389 .procname = "poolsize",
1390 .data = &sysctl_poolsize,
1391 .maxlen = sizeof(int),
1393 .proc_handler = proc_dointvec,
1396 .procname = "entropy_avail",
1397 .maxlen = sizeof(int),
1399 .proc_handler = proc_dointvec,
1400 .data = &input_pool.entropy_count,
1403 .procname = "read_wakeup_threshold",
1404 .data = &random_read_wakeup_thresh,
1405 .maxlen = sizeof(int),
1407 .proc_handler = proc_dointvec_minmax,
1408 .extra1 = &min_read_thresh,
1409 .extra2 = &max_read_thresh,
1412 .procname = "write_wakeup_threshold",
1413 .data = &random_write_wakeup_thresh,
1414 .maxlen = sizeof(int),
1416 .proc_handler = proc_dointvec_minmax,
1417 .extra1 = &min_write_thresh,
1418 .extra2 = &max_write_thresh,
1421 .procname = "boot_id",
1422 .data = &sysctl_bootid,
1425 .proc_handler = proc_do_uuid,
1431 .proc_handler = proc_do_uuid,
1435 #endif /* CONFIG_SYSCTL */
1437 static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1439 static int __init random_int_secret_init(void)
1441 get_random_bytes(random_int_secret, sizeof(random_int_secret));
1444 late_initcall(random_int_secret_init);
1447 * Get a random word for internal kernel use only. Similar to urandom but
1448 * with the goal of minimal entropy pool depletion. As a result, the random
1449 * value is not cryptographically secure but for several uses the cost of
1450 * depleting entropy is too high
1452 static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1453 unsigned int get_random_int(void)
1458 if (arch_get_random_int(&ret))
1461 hash = get_cpu_var(get_random_int_hash);
1463 hash[0] += current->pid + jiffies + get_cycles();
1464 md5_transform(hash, random_int_secret);
1466 put_cpu_var(get_random_int_hash);
1472 * randomize_range() returns a start address such that
1474 * [...... <range> .....]
1477 * a <range> with size "len" starting at the return value is inside in the
1478 * area defined by [start, end], but is otherwise randomized.
1481 randomize_range(unsigned long start, unsigned long end, unsigned long len)
1483 unsigned long range = end - len - start;
1485 if (end <= start + len)
1487 return PAGE_ALIGN(get_random_int() % range + start);