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>
269 #define CREATE_TRACE_POINTS
270 #include <trace/events/random.h>
273 * Configuration information
275 #define INPUT_POOL_WORDS 128
276 #define OUTPUT_POOL_WORDS 32
277 #define SEC_XFER_SIZE 512
278 #define EXTRACT_SIZE 10
280 #define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))
283 * The minimum number of bits of entropy before we wake up a read on
284 * /dev/random. Should be enough to do a significant reseed.
286 static int random_read_wakeup_thresh = 64;
289 * If the entropy count falls under this number of bits, then we
290 * should wake up processes which are selecting or polling on write
291 * access to /dev/random.
293 static int random_write_wakeup_thresh = 128;
296 * When the input pool goes over trickle_thresh, start dropping most
297 * samples to avoid wasting CPU time and reduce lock contention.
300 static int trickle_thresh __read_mostly = INPUT_POOL_WORDS * 28;
302 static DEFINE_PER_CPU(int, trickle_count);
305 * A pool of size .poolwords is stirred with a primitive polynomial
306 * of degree .poolwords over GF(2). The taps for various sizes are
307 * defined below. They are chosen to be evenly spaced (minimum RMS
308 * distance from evenly spaced; the numbers in the comments are a
309 * scaled squared error sum) except for the last tap, which is 1 to
310 * get the twisting happening as fast as possible.
312 static struct poolinfo {
314 int tap1, tap2, tap3, tap4, tap5;
315 } poolinfo_table[] = {
316 /* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */
317 { 128, 103, 76, 51, 25, 1 },
318 /* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */
319 { 32, 26, 20, 14, 7, 1 },
321 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */
322 { 2048, 1638, 1231, 819, 411, 1 },
324 /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
325 { 1024, 817, 615, 412, 204, 1 },
327 /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
328 { 1024, 819, 616, 410, 207, 2 },
330 /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
331 { 512, 411, 308, 208, 104, 1 },
333 /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
334 { 512, 409, 307, 206, 102, 2 },
335 /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
336 { 512, 409, 309, 205, 103, 2 },
338 /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
339 { 256, 205, 155, 101, 52, 1 },
341 /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
342 { 128, 103, 78, 51, 27, 2 },
344 /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
345 { 64, 52, 39, 26, 14, 1 },
349 #define POOLBITS poolwords*32
350 #define POOLBYTES poolwords*4
353 * For the purposes of better mixing, we use the CRC-32 polynomial as
354 * well to make a twisted Generalized Feedback Shift Reigster
356 * (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR generators. ACM
357 * Transactions on Modeling and Computer Simulation 2(3):179-194.
358 * Also see M. Matsumoto & Y. Kurita, 1994. Twisted GFSR generators
359 * II. ACM Transactions on Mdeling and Computer Simulation 4:254-266)
361 * Thanks to Colin Plumb for suggesting this.
363 * We have not analyzed the resultant polynomial to prove it primitive;
364 * in fact it almost certainly isn't. Nonetheless, the irreducible factors
365 * of a random large-degree polynomial over GF(2) are more than large enough
366 * that periodicity is not a concern.
368 * The input hash is much less sensitive than the output hash. All
369 * that we want of it is that it be a good non-cryptographic hash;
370 * i.e. it not produce collisions when fed "random" data of the sort
371 * we expect to see. As long as the pool state differs for different
372 * inputs, we have preserved the input entropy and done a good job.
373 * The fact that an intelligent attacker can construct inputs that
374 * will produce controlled alterations to the pool's state is not
375 * important because we don't consider such inputs to contribute any
376 * randomness. The only property we need with respect to them is that
377 * the attacker can't increase his/her knowledge of the pool's state.
378 * Since all additions are reversible (knowing the final state and the
379 * input, you can reconstruct the initial state), if an attacker has
380 * any uncertainty about the initial state, he/she can only shuffle
381 * that uncertainty about, but never cause any collisions (which would
382 * decrease the uncertainty).
384 * The chosen system lets the state of the pool be (essentially) the input
385 * modulo the generator polymnomial. Now, for random primitive polynomials,
386 * this is a universal class of hash functions, meaning that the chance
387 * of a collision is limited by the attacker's knowledge of the generator
388 * polynomail, so if it is chosen at random, an attacker can never force
389 * a collision. Here, we use a fixed polynomial, but we *can* assume that
390 * ###--> it is unknown to the processes generating the input entropy. <-###
391 * Because of this important property, this is a good, collision-resistant
392 * hash; hash collisions will occur no more often than chance.
396 * Static global variables
398 static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
399 static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
400 static struct fasync_struct *fasync;
403 module_param(debug, bool, 0644);
404 #define DEBUG_ENT(fmt, arg...) do { \
406 printk(KERN_DEBUG "random %04d %04d %04d: " \
408 input_pool.entropy_count,\
409 blocking_pool.entropy_count,\
410 nonblocking_pool.entropy_count,\
413 /**********************************************************************
415 * OS independent entropy store. Here are the functions which handle
416 * storing entropy in an entropy pool.
418 **********************************************************************/
420 struct entropy_store;
421 struct entropy_store {
422 /* read-only data: */
423 struct poolinfo *poolinfo;
426 struct entropy_store *pull;
429 /* read-write data: */
432 unsigned input_rotate;
435 unsigned int initialized:1;
436 __u8 last_data[EXTRACT_SIZE];
439 static __u32 input_pool_data[INPUT_POOL_WORDS];
440 static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
441 static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
443 static struct entropy_store input_pool = {
444 .poolinfo = &poolinfo_table[0],
447 .lock = __SPIN_LOCK_UNLOCKED(&input_pool.lock),
448 .pool = input_pool_data
451 static struct entropy_store blocking_pool = {
452 .poolinfo = &poolinfo_table[1],
456 .lock = __SPIN_LOCK_UNLOCKED(&blocking_pool.lock),
457 .pool = blocking_pool_data
460 static struct entropy_store nonblocking_pool = {
461 .poolinfo = &poolinfo_table[1],
462 .name = "nonblocking",
464 .lock = __SPIN_LOCK_UNLOCKED(&nonblocking_pool.lock),
465 .pool = nonblocking_pool_data
468 static __u32 const twist_table[8] = {
469 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
470 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
473 * This function adds bytes into the entropy "pool". It does not
474 * update the entropy estimate. The caller should call
475 * credit_entropy_bits if this is appropriate.
477 * The pool is stirred with a primitive polynomial of the appropriate
478 * degree, and then twisted. We twist by three bits at a time because
479 * it's cheap to do so and helps slightly in the expected case where
480 * the entropy is concentrated in the low-order bits.
482 static void _mix_pool_bytes(struct entropy_store *r, const void *in,
483 int nbytes, __u8 out[64])
485 unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
487 int wordmask = r->poolinfo->poolwords - 1;
488 const char *bytes = in;
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;
498 input_rotate = ACCESS_ONCE(r->input_rotate);
499 i = ACCESS_ONCE(r->add_ptr);
501 /* mix one byte at a time to simplify size handling and churn faster */
503 w = rol32(*bytes++, input_rotate & 31);
504 i = (i - 1) & wordmask;
506 /* XOR in the various taps */
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];
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.
523 input_rotate += i ? 7 : 14;
526 ACCESS_ONCE(r->input_rotate) = input_rotate;
527 ACCESS_ONCE(r->add_ptr) = i;
531 for (j = 0; j < 16; j++)
532 ((__u32 *)out)[j] = r->pool[(i - j) & wordmask];
535 static void __mix_pool_bytes(struct entropy_store *r, const void *in,
536 int nbytes, __u8 out[64])
538 trace_mix_pool_bytes_nolock(r->name, nbytes, _RET_IP_);
539 _mix_pool_bytes(r, in, nbytes, out);
542 static void mix_pool_bytes(struct entropy_store *r, const void *in,
543 int nbytes, __u8 out[64])
547 trace_mix_pool_bytes(r->name, nbytes, _RET_IP_);
548 spin_lock_irqsave(&r->lock, flags);
549 _mix_pool_bytes(r, in, nbytes, out);
550 spin_unlock_irqrestore(&r->lock, flags);
556 unsigned short count;
557 unsigned char rotate;
558 unsigned char last_timer_intr;
562 * This is a fast mixing routine used by the interrupt randomness
563 * collector. It's hardcoded for an 128 bit pool and assumes that any
564 * locks that might be needed are taken by the caller.
566 static void fast_mix(struct fast_pool *f, const void *in, int nbytes)
568 const char *bytes = in;
570 unsigned i = f->count;
571 unsigned input_rotate = f->rotate;
574 w = rol32(*bytes++, input_rotate & 31) ^ f->pool[i & 3] ^
575 f->pool[(i + 1) & 3];
576 f->pool[i & 3] = (w >> 3) ^ twist_table[w & 7];
577 input_rotate += (i++ & 3) ? 7 : 14;
580 f->rotate = input_rotate;
584 * Credit (or debit) the entropy store with n bits of entropy
586 static void credit_entropy_bits(struct entropy_store *r, int nbits)
588 int entropy_count, orig;
593 DEBUG_ENT("added %d entropy credits to %s\n", nbits, r->name);
595 entropy_count = orig = ACCESS_ONCE(r->entropy_count);
596 entropy_count += nbits;
598 if (entropy_count < 0) {
599 DEBUG_ENT("negative entropy/overflow\n");
601 } else if (entropy_count > r->poolinfo->POOLBITS)
602 entropy_count = r->poolinfo->POOLBITS;
603 if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
606 if (!r->initialized && nbits > 0) {
607 r->entropy_total += nbits;
608 if (r->entropy_total > 128)
612 trace_credit_entropy_bits(r->name, nbits, entropy_count,
613 r->entropy_total, _RET_IP_);
615 /* should we wake readers? */
616 if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {
617 wake_up_interruptible(&random_read_wait);
618 kill_fasync(&fasync, SIGIO, POLL_IN);
622 /*********************************************************************
624 * Entropy input management
626 *********************************************************************/
628 /* There is one of these per entropy source */
629 struct timer_rand_state {
631 long last_delta, last_delta2;
632 unsigned dont_count_entropy:1;
636 * Add device- or boot-specific data to the input and nonblocking
637 * pools to help initialize them to unique values.
639 * None of this adds any entropy, it is meant to avoid the
640 * problem of the nonblocking pool having similar initial state
641 * across largely identical devices.
643 void add_device_randomness(const void *buf, unsigned int size)
645 unsigned long time = get_cycles() ^ jiffies;
647 mix_pool_bytes(&input_pool, buf, size, NULL);
648 mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
649 mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
650 mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
652 EXPORT_SYMBOL(add_device_randomness);
654 static struct timer_rand_state input_timer_state;
657 * This function adds entropy to the entropy "pool" by using timing
658 * delays. It uses the timer_rand_state structure to make an estimate
659 * of how many bits of entropy this call has added to the pool.
661 * The number "num" is also added to the pool - it should somehow describe
662 * the type of event which just happened. This is currently 0-255 for
663 * keyboard scan codes, and 256 upwards for interrupts.
666 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
673 long delta, delta2, delta3;
676 /* if over the trickle threshold, use only 1 in 4096 samples */
677 if (input_pool.entropy_count > trickle_thresh &&
678 ((__this_cpu_inc_return(trickle_count) - 1) & 0xfff))
681 sample.jiffies = jiffies;
682 sample.cycles = get_cycles();
684 mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
687 * Calculate number of bits of randomness we probably added.
688 * We take into account the first, second and third-order deltas
689 * in order to make our estimate.
692 if (!state->dont_count_entropy) {
693 delta = sample.jiffies - state->last_time;
694 state->last_time = sample.jiffies;
696 delta2 = delta - state->last_delta;
697 state->last_delta = delta;
699 delta3 = delta2 - state->last_delta2;
700 state->last_delta2 = delta2;
714 * delta is now minimum absolute delta.
715 * Round down by 1 bit on general principles,
716 * and limit entropy entimate to 12 bits.
718 credit_entropy_bits(&input_pool,
719 min_t(int, fls(delta>>1), 11));
725 void add_input_randomness(unsigned int type, unsigned int code,
728 static unsigned char last_value;
730 /* ignore autorepeat and the like */
731 if (value == last_value)
734 DEBUG_ENT("input event\n");
736 add_timer_randomness(&input_timer_state,
737 (type << 4) ^ code ^ (code >> 4) ^ value);
739 EXPORT_SYMBOL_GPL(add_input_randomness);
741 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
743 void add_interrupt_randomness(int irq, int irq_flags)
745 struct entropy_store *r;
746 struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
747 struct pt_regs *regs = get_irq_regs();
748 unsigned long now = jiffies;
749 __u32 input[4], cycles = get_cycles();
751 input[0] = cycles ^ jiffies;
754 __u64 ip = instruction_pointer(regs);
759 fast_mix(fast_pool, input, sizeof(input));
761 if ((fast_pool->count & 1023) &&
762 !time_after(now, fast_pool->last + HZ))
765 fast_pool->last = now;
767 r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
768 __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
770 * If we don't have a valid cycle counter, and we see
771 * back-to-back timer interrupts, then skip giving credit for
775 if (irq_flags & __IRQF_TIMER) {
776 if (fast_pool->last_timer_intr)
778 fast_pool->last_timer_intr = 1;
780 fast_pool->last_timer_intr = 0;
782 credit_entropy_bits(r, 1);
786 void add_disk_randomness(struct gendisk *disk)
788 if (!disk || !disk->random)
790 /* first major is 1, so we get >= 0x200 here */
791 DEBUG_ENT("disk event %d:%d\n",
792 MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));
794 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
798 /*********************************************************************
800 * Entropy extraction routines
802 *********************************************************************/
804 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
805 size_t nbytes, int min, int rsvd);
808 * This utility inline function is responsible for transferring entropy
809 * from the primary pool to the secondary extraction pool. We make
810 * sure we pull enough for a 'catastrophic reseed'.
812 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
814 __u32 tmp[OUTPUT_POOL_WORDS];
816 if (r->pull && r->entropy_count < nbytes * 8 &&
817 r->entropy_count < r->poolinfo->POOLBITS) {
818 /* If we're limited, always leave two wakeup worth's BITS */
819 int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
822 /* pull at least as many as BYTES as wakeup BITS */
823 bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
824 /* but never more than the buffer size */
825 bytes = min_t(int, bytes, sizeof(tmp));
827 DEBUG_ENT("going to reseed %s with %d bits "
828 "(%zu of %d requested)\n",
829 r->name, bytes * 8, nbytes * 8, r->entropy_count);
831 bytes = extract_entropy(r->pull, tmp, bytes,
832 random_read_wakeup_thresh / 8, rsvd);
833 mix_pool_bytes(r, tmp, bytes, NULL);
834 credit_entropy_bits(r, bytes*8);
839 * These functions extracts randomness from the "entropy pool", and
840 * returns it in a buffer.
842 * The min parameter specifies the minimum amount we can pull before
843 * failing to avoid races that defeat catastrophic reseeding while the
844 * reserved parameter indicates how much entropy we must leave in the
845 * pool after each pull to avoid starving other readers.
847 * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
850 static size_t account(struct entropy_store *r, size_t nbytes, int min,
855 /* Hold lock while accounting */
856 spin_lock_irqsave(&r->lock, flags);
858 BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
859 DEBUG_ENT("trying to extract %zu bits from %s\n",
860 nbytes * 8, r->name);
862 /* Can we pull enough? */
863 if (r->entropy_count / 8 < min + reserved) {
866 /* If limited, never pull more than available */
867 if (r->limit && nbytes + reserved >= r->entropy_count / 8)
868 nbytes = r->entropy_count/8 - reserved;
870 if (r->entropy_count / 8 >= nbytes + reserved)
871 r->entropy_count -= nbytes*8;
873 r->entropy_count = reserved;
875 if (r->entropy_count < random_write_wakeup_thresh) {
876 wake_up_interruptible(&random_write_wait);
877 kill_fasync(&fasync, SIGIO, POLL_OUT);
881 DEBUG_ENT("debiting %zu entropy credits from %s%s\n",
882 nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
884 spin_unlock_irqrestore(&r->lock, flags);
889 static void extract_buf(struct entropy_store *r, __u8 *out)
894 unsigned long l[LONGS(EXTRACT_SIZE)];
896 __u32 workspace[SHA_WORKSPACE_WORDS];
900 /* Generate a hash across the pool, 16 words (512 bits) at a time */
902 spin_lock_irqsave(&r->lock, flags);
903 for (i = 0; i < r->poolinfo->poolwords; i += 16)
904 sha_transform(hash.w, (__u8 *)(r->pool + i), workspace);
907 * We mix the hash back into the pool to prevent backtracking
908 * attacks (where the attacker knows the state of the pool
909 * plus the current outputs, and attempts to find previous
910 * ouputs), unless the hash function can be inverted. By
911 * mixing at least a SHA1 worth of hash data back, we make
912 * brute-forcing the feedback as hard as brute-forcing the
915 __mix_pool_bytes(r, hash.w, sizeof(hash.w), extract);
916 spin_unlock_irqrestore(&r->lock, flags);
919 * To avoid duplicates, we atomically extract a portion of the
920 * pool while mixing, and hash one final time.
922 sha_transform(hash.w, extract, workspace);
923 memset(extract, 0, sizeof(extract));
924 memset(workspace, 0, sizeof(workspace));
927 * In case the hash function has some recognizable output
928 * pattern, we fold it in half. Thus, we always feed back
929 * twice as much data as we output.
931 hash.w[0] ^= hash.w[3];
932 hash.w[1] ^= hash.w[4];
933 hash.w[2] ^= rol32(hash.w[2], 16);
936 * If we have a architectural hardware random number
937 * generator, mix that in, too.
939 for (i = 0; i < LONGS(EXTRACT_SIZE); i++) {
941 if (!arch_get_random_long(&v))
946 memcpy(out, &hash, EXTRACT_SIZE);
947 memset(&hash, 0, sizeof(hash));
950 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
951 size_t nbytes, int min, int reserved)
954 __u8 tmp[EXTRACT_SIZE];
956 trace_extract_entropy(r->name, nbytes, r->entropy_count, _RET_IP_);
957 xfer_secondary_pool(r, nbytes);
958 nbytes = account(r, nbytes, min, reserved);
966 spin_lock_irqsave(&r->lock, flags);
967 if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
968 panic("Hardware RNG duplicated output!\n");
969 memcpy(r->last_data, tmp, EXTRACT_SIZE);
970 spin_unlock_irqrestore(&r->lock, flags);
972 i = min_t(int, nbytes, EXTRACT_SIZE);
979 /* Wipe data just returned from memory */
980 memset(tmp, 0, sizeof(tmp));
985 static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
989 __u8 tmp[EXTRACT_SIZE];
991 trace_extract_entropy_user(r->name, nbytes, r->entropy_count, _RET_IP_);
992 xfer_secondary_pool(r, nbytes);
993 nbytes = account(r, nbytes, 0, 0);
996 if (need_resched()) {
997 if (signal_pending(current)) {
1005 extract_buf(r, tmp);
1006 i = min_t(int, nbytes, EXTRACT_SIZE);
1007 if (copy_to_user(buf, tmp, i)) {
1017 /* Wipe data just returned from memory */
1018 memset(tmp, 0, sizeof(tmp));
1024 * This function is the exported kernel interface. It returns some
1025 * number of good random numbers, suitable for key generation, seeding
1026 * TCP sequence numbers, etc. It does not use the hw random number
1027 * generator, if available; use get_random_bytes_arch() for that.
1029 void get_random_bytes(void *buf, int nbytes)
1031 extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
1033 EXPORT_SYMBOL(get_random_bytes);
1036 * This function will use the architecture-specific hardware random
1037 * number generator if it is available. The arch-specific hw RNG will
1038 * almost certainly be faster than what we can do in software, but it
1039 * is impossible to verify that it is implemented securely (as
1040 * opposed, to, say, the AES encryption of a sequence number using a
1041 * key known by the NSA). So it's useful if we need the speed, but
1042 * only if we're willing to trust the hardware manufacturer not to
1043 * have put in a back door.
1045 void get_random_bytes_arch(void *buf, int nbytes)
1049 trace_get_random_bytes(nbytes, _RET_IP_);
1052 int chunk = min(nbytes, (int)sizeof(unsigned long));
1054 if (!arch_get_random_long(&v))
1057 memcpy(p, &v, chunk);
1063 extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
1065 EXPORT_SYMBOL(get_random_bytes_arch);
1069 * init_std_data - initialize pool with system data
1071 * @r: pool to initialize
1073 * This function clears the pool's entropy count and mixes some system
1074 * data into the pool to prepare it for use. The pool is not cleared
1075 * as that can only decrease the entropy in the pool.
1077 static void init_std_data(struct entropy_store *r)
1080 ktime_t now = ktime_get_real();
1083 r->entropy_count = 0;
1084 r->entropy_total = 0;
1085 mix_pool_bytes(r, &now, sizeof(now), NULL);
1086 for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof(rv)) {
1087 if (!arch_get_random_long(&rv))
1089 mix_pool_bytes(r, &rv, sizeof(rv), NULL);
1091 mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
1095 * Note that setup_arch() may call add_device_randomness()
1096 * long before we get here. This allows seeding of the pools
1097 * with some platform dependent data very early in the boot
1098 * process. But it limits our options here. We must use
1099 * statically allocated structures that already have all
1100 * initializations complete at compile time. We should also
1101 * take care not to overwrite the precious per platform data
1104 static int rand_initialize(void)
1106 init_std_data(&input_pool);
1107 init_std_data(&blocking_pool);
1108 init_std_data(&nonblocking_pool);
1111 module_init(rand_initialize);
1114 void rand_initialize_disk(struct gendisk *disk)
1116 struct timer_rand_state *state;
1119 * If kzalloc returns null, we just won't use that entropy
1122 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1124 disk->random = state;
1129 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1131 ssize_t n, retval = 0, count = 0;
1136 while (nbytes > 0) {
1138 if (n > SEC_XFER_SIZE)
1141 DEBUG_ENT("reading %zu bits\n", n*8);
1143 n = extract_entropy_user(&blocking_pool, buf, n);
1150 DEBUG_ENT("read got %zd bits (%zd still needed)\n",
1154 if (file->f_flags & O_NONBLOCK) {
1159 DEBUG_ENT("sleeping?\n");
1161 wait_event_interruptible(random_read_wait,
1162 input_pool.entropy_count >=
1163 random_read_wakeup_thresh);
1165 DEBUG_ENT("awake\n");
1167 if (signal_pending(current)) {
1168 retval = -ERESTARTSYS;
1178 break; /* This break makes the device work */
1179 /* like a named pipe */
1182 return (count ? count : retval);
1186 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1188 return extract_entropy_user(&nonblocking_pool, buf, nbytes);
1192 random_poll(struct file *file, poll_table * wait)
1196 poll_wait(file, &random_read_wait, wait);
1197 poll_wait(file, &random_write_wait, wait);
1199 if (input_pool.entropy_count >= random_read_wakeup_thresh)
1200 mask |= POLLIN | POLLRDNORM;
1201 if (input_pool.entropy_count < random_write_wakeup_thresh)
1202 mask |= POLLOUT | POLLWRNORM;
1207 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1211 const char __user *p = buffer;
1214 bytes = min(count, sizeof(buf));
1215 if (copy_from_user(&buf, p, bytes))
1221 mix_pool_bytes(r, buf, bytes, NULL);
1228 static ssize_t random_write(struct file *file, const char __user *buffer,
1229 size_t count, loff_t *ppos)
1233 ret = write_pool(&blocking_pool, buffer, count);
1236 ret = write_pool(&nonblocking_pool, buffer, count);
1240 return (ssize_t)count;
1243 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1245 int size, ent_count;
1246 int __user *p = (int __user *)arg;
1251 /* inherently racy, no point locking */
1252 if (put_user(input_pool.entropy_count, p))
1255 case RNDADDTOENTCNT:
1256 if (!capable(CAP_SYS_ADMIN))
1258 if (get_user(ent_count, p))
1260 credit_entropy_bits(&input_pool, ent_count);
1263 if (!capable(CAP_SYS_ADMIN))
1265 if (get_user(ent_count, p++))
1269 if (get_user(size, p++))
1271 retval = write_pool(&input_pool, (const char __user *)p,
1275 credit_entropy_bits(&input_pool, ent_count);
1279 /* Clear the entropy pool counters. */
1280 if (!capable(CAP_SYS_ADMIN))
1289 static int random_fasync(int fd, struct file *filp, int on)
1291 return fasync_helper(fd, filp, on, &fasync);
1294 const struct file_operations random_fops = {
1295 .read = random_read,
1296 .write = random_write,
1297 .poll = random_poll,
1298 .unlocked_ioctl = random_ioctl,
1299 .fasync = random_fasync,
1300 .llseek = noop_llseek,
1303 const struct file_operations urandom_fops = {
1304 .read = urandom_read,
1305 .write = random_write,
1306 .unlocked_ioctl = random_ioctl,
1307 .fasync = random_fasync,
1308 .llseek = noop_llseek,
1311 /***************************************************************
1312 * Random UUID interface
1314 * Used here for a Boot ID, but can be useful for other kernel
1316 ***************************************************************/
1319 * Generate random UUID
1321 void generate_random_uuid(unsigned char uuid_out[16])
1323 get_random_bytes(uuid_out, 16);
1324 /* Set UUID version to 4 --- truly random generation */
1325 uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1326 /* Set the UUID variant to DCE */
1327 uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1329 EXPORT_SYMBOL(generate_random_uuid);
1331 /********************************************************************
1335 ********************************************************************/
1337 #ifdef CONFIG_SYSCTL
1339 #include <linux/sysctl.h>
1341 static int min_read_thresh = 8, min_write_thresh;
1342 static int max_read_thresh = INPUT_POOL_WORDS * 32;
1343 static int max_write_thresh = INPUT_POOL_WORDS * 32;
1344 static char sysctl_bootid[16];
1347 * These functions is used to return both the bootid UUID, and random
1348 * UUID. The difference is in whether table->data is NULL; if it is,
1349 * then a new UUID is generated and returned to the user.
1351 * If the user accesses this via the proc interface, it will be returned
1352 * as an ASCII string in the standard UUID format. If accesses via the
1353 * sysctl system call, it is returned as 16 bytes of binary data.
1355 static int proc_do_uuid(ctl_table *table, int write,
1356 void __user *buffer, size_t *lenp, loff_t *ppos)
1358 ctl_table fake_table;
1359 unsigned char buf[64], tmp_uuid[16], *uuid;
1364 generate_random_uuid(uuid);
1366 static DEFINE_SPINLOCK(bootid_spinlock);
1368 spin_lock(&bootid_spinlock);
1370 generate_random_uuid(uuid);
1371 spin_unlock(&bootid_spinlock);
1374 sprintf(buf, "%pU", uuid);
1376 fake_table.data = buf;
1377 fake_table.maxlen = sizeof(buf);
1379 return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1382 static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1383 extern ctl_table random_table[];
1384 ctl_table random_table[] = {
1386 .procname = "poolsize",
1387 .data = &sysctl_poolsize,
1388 .maxlen = sizeof(int),
1390 .proc_handler = proc_dointvec,
1393 .procname = "entropy_avail",
1394 .maxlen = sizeof(int),
1396 .proc_handler = proc_dointvec,
1397 .data = &input_pool.entropy_count,
1400 .procname = "read_wakeup_threshold",
1401 .data = &random_read_wakeup_thresh,
1402 .maxlen = sizeof(int),
1404 .proc_handler = proc_dointvec_minmax,
1405 .extra1 = &min_read_thresh,
1406 .extra2 = &max_read_thresh,
1409 .procname = "write_wakeup_threshold",
1410 .data = &random_write_wakeup_thresh,
1411 .maxlen = sizeof(int),
1413 .proc_handler = proc_dointvec_minmax,
1414 .extra1 = &min_write_thresh,
1415 .extra2 = &max_write_thresh,
1418 .procname = "boot_id",
1419 .data = &sysctl_bootid,
1422 .proc_handler = proc_do_uuid,
1428 .proc_handler = proc_do_uuid,
1432 #endif /* CONFIG_SYSCTL */
1434 static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1436 static int __init random_int_secret_init(void)
1438 get_random_bytes(random_int_secret, sizeof(random_int_secret));
1441 late_initcall(random_int_secret_init);
1444 * Get a random word for internal kernel use only. Similar to urandom but
1445 * with the goal of minimal entropy pool depletion. As a result, the random
1446 * value is not cryptographically secure but for several uses the cost of
1447 * depleting entropy is too high
1449 static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1450 unsigned int get_random_int(void)
1455 if (arch_get_random_int(&ret))
1458 hash = get_cpu_var(get_random_int_hash);
1460 hash[0] += current->pid + jiffies + get_cycles();
1461 md5_transform(hash, random_int_secret);
1463 put_cpu_var(get_random_int_hash);
1469 * randomize_range() returns a start address such that
1471 * [...... <range> .....]
1474 * a <range> with size "len" starting at the return value is inside in the
1475 * area defined by [start, end], but is otherwise randomized.
1478 randomize_range(unsigned long start, unsigned long end, unsigned long len)
1480 unsigned long range = end - len - start;
1482 if (end <= start + len)
1484 return PAGE_ALIGN(get_random_int() % range + start);