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_input_randomness(unsigned int type, unsigned int code,
129 * unsigned int value);
130 * void add_interrupt_randomness(int irq, int irq_flags);
131 * void add_disk_randomness(struct gendisk *disk);
133 * add_input_randomness() uses the input layer interrupt timing, as well as
134 * the event type information from the hardware.
136 * add_interrupt_randomness() uses the interrupt timing as random
137 * inputs to the entropy pool. Using the cycle counters and the irq source
138 * as inputs, it feeds the randomness roughly once a second.
140 * add_disk_randomness() uses what amounts to the seek time of block
141 * layer request events, on a per-disk_devt basis, as input to the
142 * entropy pool. Note that high-speed solid state drives with very low
143 * seek times do not make for good sources of entropy, as their seek
144 * times are usually fairly consistent.
146 * All of these routines try to estimate how many bits of randomness a
147 * particular randomness source. They do this by keeping track of the
148 * first and second order deltas of the event timings.
150 * Ensuring unpredictability at system startup
151 * ============================================
153 * When any operating system starts up, it will go through a sequence
154 * of actions that are fairly predictable by an adversary, especially
155 * if the start-up does not involve interaction with a human operator.
156 * This reduces the actual number of bits of unpredictability in the
157 * entropy pool below the value in entropy_count. In order to
158 * counteract this effect, it helps to carry information in the
159 * entropy pool across shut-downs and start-ups. To do this, put the
160 * following lines an appropriate script which is run during the boot
163 * echo "Initializing random number generator..."
164 * random_seed=/var/run/random-seed
165 * # Carry a random seed from start-up to start-up
166 * # Load and then save the whole entropy pool
167 * if [ -f $random_seed ]; then
168 * cat $random_seed >/dev/urandom
172 * chmod 600 $random_seed
173 * dd if=/dev/urandom of=$random_seed count=1 bs=512
175 * and the following lines in an appropriate script which is run as
176 * the system is shutdown:
178 * # Carry a random seed from shut-down to start-up
179 * # Save the whole entropy pool
180 * echo "Saving random seed..."
181 * random_seed=/var/run/random-seed
183 * chmod 600 $random_seed
184 * dd if=/dev/urandom of=$random_seed count=1 bs=512
186 * For example, on most modern systems using the System V init
187 * scripts, such code fragments would be found in
188 * /etc/rc.d/init.d/random. On older Linux systems, the correct script
189 * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0.
191 * Effectively, these commands cause the contents of the entropy pool
192 * to be saved at shut-down time and reloaded into the entropy pool at
193 * start-up. (The 'dd' in the addition to the bootup script is to
194 * make sure that /etc/random-seed is different for every start-up,
195 * even if the system crashes without executing rc.0.) Even with
196 * complete knowledge of the start-up activities, predicting the state
197 * of the entropy pool requires knowledge of the previous history of
200 * Configuring the /dev/random driver under Linux
201 * ==============================================
203 * The /dev/random driver under Linux uses minor numbers 8 and 9 of
204 * the /dev/mem major number (#1). So if your system does not have
205 * /dev/random and /dev/urandom created already, they can be created
206 * by using the commands:
208 * mknod /dev/random c 1 8
209 * mknod /dev/urandom c 1 9
214 * Ideas for constructing this random number generator were derived
215 * from Pretty Good Privacy's random number generator, and from private
216 * discussions with Phil Karn. Colin Plumb provided a faster random
217 * number generator, which speed up the mixing function of the entropy
218 * pool, taken from PGPfone. Dale Worley has also contributed many
219 * useful ideas and suggestions to improve this driver.
221 * Any flaws in the design are solely my responsibility, and should
222 * not be attributed to the Phil, Colin, or any of authors of PGP.
224 * Further background information on this topic may be obtained from
225 * RFC 1750, "Randomness Recommendations for Security", by Donald
226 * Eastlake, Steve Crocker, and Jeff Schiller.
229 #include <linux/utsname.h>
230 #include <linux/module.h>
231 #include <linux/kernel.h>
232 #include <linux/major.h>
233 #include <linux/string.h>
234 #include <linux/fcntl.h>
235 #include <linux/slab.h>
236 #include <linux/random.h>
237 #include <linux/poll.h>
238 #include <linux/init.h>
239 #include <linux/fs.h>
240 #include <linux/genhd.h>
241 #include <linux/interrupt.h>
242 #include <linux/mm.h>
243 #include <linux/spinlock.h>
244 #include <linux/percpu.h>
245 #include <linux/cryptohash.h>
246 #include <linux/fips.h>
247 #include <linux/ptrace.h>
249 #ifdef CONFIG_GENERIC_HARDIRQS
250 # include <linux/irq.h>
253 #include <asm/processor.h>
254 #include <asm/uaccess.h>
256 #include <asm/irq_regs.h>
260 * Configuration information
262 #define INPUT_POOL_WORDS 128
263 #define OUTPUT_POOL_WORDS 32
264 #define SEC_XFER_SIZE 512
265 #define EXTRACT_SIZE 10
268 * The minimum number of bits of entropy before we wake up a read on
269 * /dev/random. Should be enough to do a significant reseed.
271 static int random_read_wakeup_thresh = 64;
274 * If the entropy count falls under this number of bits, then we
275 * should wake up processes which are selecting or polling on write
276 * access to /dev/random.
278 static int random_write_wakeup_thresh = 128;
281 * When the input pool goes over trickle_thresh, start dropping most
282 * samples to avoid wasting CPU time and reduce lock contention.
285 static int trickle_thresh __read_mostly = INPUT_POOL_WORDS * 28;
287 static DEFINE_PER_CPU(int, trickle_count);
290 * A pool of size .poolwords is stirred with a primitive polynomial
291 * of degree .poolwords over GF(2). The taps for various sizes are
292 * defined below. They are chosen to be evenly spaced (minimum RMS
293 * distance from evenly spaced; the numbers in the comments are a
294 * scaled squared error sum) except for the last tap, which is 1 to
295 * get the twisting happening as fast as possible.
297 static struct poolinfo {
299 int tap1, tap2, tap3, tap4, tap5;
300 } poolinfo_table[] = {
301 /* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */
302 { 128, 103, 76, 51, 25, 1 },
303 /* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */
304 { 32, 26, 20, 14, 7, 1 },
306 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */
307 { 2048, 1638, 1231, 819, 411, 1 },
309 /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
310 { 1024, 817, 615, 412, 204, 1 },
312 /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
313 { 1024, 819, 616, 410, 207, 2 },
315 /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
316 { 512, 411, 308, 208, 104, 1 },
318 /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
319 { 512, 409, 307, 206, 102, 2 },
320 /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
321 { 512, 409, 309, 205, 103, 2 },
323 /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
324 { 256, 205, 155, 101, 52, 1 },
326 /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
327 { 128, 103, 78, 51, 27, 2 },
329 /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
330 { 64, 52, 39, 26, 14, 1 },
334 #define POOLBITS poolwords*32
335 #define POOLBYTES poolwords*4
338 * For the purposes of better mixing, we use the CRC-32 polynomial as
339 * well to make a twisted Generalized Feedback Shift Reigster
341 * (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR generators. ACM
342 * Transactions on Modeling and Computer Simulation 2(3):179-194.
343 * Also see M. Matsumoto & Y. Kurita, 1994. Twisted GFSR generators
344 * II. ACM Transactions on Mdeling and Computer Simulation 4:254-266)
346 * Thanks to Colin Plumb for suggesting this.
348 * We have not analyzed the resultant polynomial to prove it primitive;
349 * in fact it almost certainly isn't. Nonetheless, the irreducible factors
350 * of a random large-degree polynomial over GF(2) are more than large enough
351 * that periodicity is not a concern.
353 * The input hash is much less sensitive than the output hash. All
354 * that we want of it is that it be a good non-cryptographic hash;
355 * i.e. it not produce collisions when fed "random" data of the sort
356 * we expect to see. As long as the pool state differs for different
357 * inputs, we have preserved the input entropy and done a good job.
358 * The fact that an intelligent attacker can construct inputs that
359 * will produce controlled alterations to the pool's state is not
360 * important because we don't consider such inputs to contribute any
361 * randomness. The only property we need with respect to them is that
362 * the attacker can't increase his/her knowledge of the pool's state.
363 * Since all additions are reversible (knowing the final state and the
364 * input, you can reconstruct the initial state), if an attacker has
365 * any uncertainty about the initial state, he/she can only shuffle
366 * that uncertainty about, but never cause any collisions (which would
367 * decrease the uncertainty).
369 * The chosen system lets the state of the pool be (essentially) the input
370 * modulo the generator polymnomial. Now, for random primitive polynomials,
371 * this is a universal class of hash functions, meaning that the chance
372 * of a collision is limited by the attacker's knowledge of the generator
373 * polynomail, so if it is chosen at random, an attacker can never force
374 * a collision. Here, we use a fixed polynomial, but we *can* assume that
375 * ###--> it is unknown to the processes generating the input entropy. <-###
376 * Because of this important property, this is a good, collision-resistant
377 * hash; hash collisions will occur no more often than chance.
381 * Static global variables
383 static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
384 static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
385 static struct fasync_struct *fasync;
389 module_param(debug, bool, 0644);
390 #define DEBUG_ENT(fmt, arg...) do { \
392 printk(KERN_DEBUG "random %04d %04d %04d: " \
394 input_pool.entropy_count,\
395 blocking_pool.entropy_count,\
396 nonblocking_pool.entropy_count,\
399 #define DEBUG_ENT(fmt, arg...) do {} while (0)
402 /**********************************************************************
404 * OS independent entropy store. Here are the functions which handle
405 * storing entropy in an entropy pool.
407 **********************************************************************/
409 struct entropy_store;
410 struct entropy_store {
411 /* read-only data: */
412 struct poolinfo *poolinfo;
415 struct entropy_store *pull;
418 /* read-write data: */
421 unsigned input_rotate;
424 unsigned int initialized:1;
425 __u8 last_data[EXTRACT_SIZE];
428 static __u32 input_pool_data[INPUT_POOL_WORDS];
429 static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
430 static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
432 static struct entropy_store input_pool = {
433 .poolinfo = &poolinfo_table[0],
436 .lock = __SPIN_LOCK_UNLOCKED(&input_pool.lock),
437 .pool = input_pool_data
440 static struct entropy_store blocking_pool = {
441 .poolinfo = &poolinfo_table[1],
445 .lock = __SPIN_LOCK_UNLOCKED(&blocking_pool.lock),
446 .pool = blocking_pool_data
449 static struct entropy_store nonblocking_pool = {
450 .poolinfo = &poolinfo_table[1],
451 .name = "nonblocking",
453 .lock = __SPIN_LOCK_UNLOCKED(&nonblocking_pool.lock),
454 .pool = nonblocking_pool_data
457 static __u32 const twist_table[8] = {
458 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
459 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
462 * This function adds bytes into the entropy "pool". It does not
463 * update the entropy estimate. The caller should call
464 * credit_entropy_bits if this is appropriate.
466 * The pool is stirred with a primitive polynomial of the appropriate
467 * degree, and then twisted. We twist by three bits at a time because
468 * it's cheap to do so and helps slightly in the expected case where
469 * the entropy is concentrated in the low-order bits.
471 static void __mix_pool_bytes(struct entropy_store *r, const void *in,
472 int nbytes, __u8 out[64])
474 unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
476 int wordmask = r->poolinfo->poolwords - 1;
477 const char *bytes = in;
480 tap1 = r->poolinfo->tap1;
481 tap2 = r->poolinfo->tap2;
482 tap3 = r->poolinfo->tap3;
483 tap4 = r->poolinfo->tap4;
484 tap5 = r->poolinfo->tap5;
487 input_rotate = ACCESS_ONCE(r->input_rotate);
488 i = ACCESS_ONCE(r->add_ptr);
490 /* mix one byte at a time to simplify size handling and churn faster */
492 w = rol32(*bytes++, input_rotate & 31);
493 i = (i - 1) & wordmask;
495 /* XOR in the various taps */
497 w ^= r->pool[(i + tap1) & wordmask];
498 w ^= r->pool[(i + tap2) & wordmask];
499 w ^= r->pool[(i + tap3) & wordmask];
500 w ^= r->pool[(i + tap4) & wordmask];
501 w ^= r->pool[(i + tap5) & wordmask];
503 /* Mix the result back in with a twist */
504 r->pool[i] = (w >> 3) ^ twist_table[w & 7];
507 * Normally, we add 7 bits of rotation to the pool.
508 * At the beginning of the pool, add an extra 7 bits
509 * rotation, so that successive passes spread the
510 * input bits across the pool evenly.
512 input_rotate += i ? 7 : 14;
515 ACCESS_ONCE(r->input_rotate) = input_rotate;
516 ACCESS_ONCE(r->add_ptr) = i;
520 for (j = 0; j < 16; j++)
521 ((__u32 *)out)[j] = r->pool[(i - j) & wordmask];
524 static void mix_pool_bytes(struct entropy_store *r, const void *in,
525 int nbytes, __u8 out[64])
529 spin_lock_irqsave(&r->lock, flags);
530 __mix_pool_bytes(r, in, nbytes, out);
531 spin_unlock_irqrestore(&r->lock, flags);
537 unsigned short count;
538 unsigned char rotate;
539 unsigned char last_timer_intr;
543 * This is a fast mixing routine used by the interrupt randomness
544 * collector. It's hardcoded for an 128 bit pool and assumes that any
545 * locks that might be needed are taken by the caller.
547 static void fast_mix(struct fast_pool *f, const void *in, int nbytes)
549 const char *bytes = in;
551 unsigned i = f->count;
552 unsigned input_rotate = f->rotate;
555 w = rol32(*bytes++, input_rotate & 31) ^ f->pool[i & 3] ^
556 f->pool[(i + 1) & 3];
557 f->pool[i & 3] = (w >> 3) ^ twist_table[w & 7];
558 input_rotate += (i++ & 3) ? 7 : 14;
561 f->rotate = input_rotate;
565 * Credit (or debit) the entropy store with n bits of entropy
567 static void credit_entropy_bits(struct entropy_store *r, int nbits)
569 int entropy_count, orig;
574 DEBUG_ENT("added %d entropy credits to %s\n", nbits, r->name);
576 entropy_count = orig = ACCESS_ONCE(r->entropy_count);
577 entropy_count += nbits;
578 if (entropy_count < 0) {
579 DEBUG_ENT("negative entropy/overflow\n");
581 } else if (entropy_count > r->poolinfo->POOLBITS)
582 entropy_count = r->poolinfo->POOLBITS;
583 if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
586 if (!r->initialized && nbits > 0) {
587 r->entropy_total += nbits;
588 if (r->entropy_total > 128)
592 /* should we wake readers? */
593 if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {
594 wake_up_interruptible(&random_read_wait);
595 kill_fasync(&fasync, SIGIO, POLL_IN);
599 /*********************************************************************
601 * Entropy input management
603 *********************************************************************/
605 /* There is one of these per entropy source */
606 struct timer_rand_state {
608 long last_delta, last_delta2;
609 unsigned dont_count_entropy:1;
612 #ifndef CONFIG_GENERIC_HARDIRQS
614 static struct timer_rand_state *irq_timer_state[NR_IRQS];
616 static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
618 return irq_timer_state[irq];
621 static void set_timer_rand_state(unsigned int irq,
622 struct timer_rand_state *state)
624 irq_timer_state[irq] = state;
629 static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
631 struct irq_desc *desc;
633 desc = irq_to_desc(irq);
635 return desc->timer_rand_state;
638 static void set_timer_rand_state(unsigned int irq,
639 struct timer_rand_state *state)
641 struct irq_desc *desc;
643 desc = irq_to_desc(irq);
645 desc->timer_rand_state = state;
649 static struct timer_rand_state input_timer_state;
652 * This function adds entropy to the entropy "pool" by using timing
653 * delays. It uses the timer_rand_state structure to make an estimate
654 * of how many bits of entropy this call has added to the pool.
656 * The number "num" is also added to the pool - it should somehow describe
657 * the type of event which just happened. This is currently 0-255 for
658 * keyboard scan codes, and 256 upwards for interrupts.
661 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
668 long delta, delta2, delta3;
671 /* if over the trickle threshold, use only 1 in 4096 samples */
672 if (input_pool.entropy_count > trickle_thresh &&
673 ((__this_cpu_inc_return(trickle_count) - 1) & 0xfff))
676 sample.jiffies = jiffies;
678 /* Use arch random value, fall back to cycles */
679 if (!arch_get_random_int(&sample.cycles))
680 sample.cycles = get_cycles();
683 mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
686 * Calculate number of bits of randomness we probably added.
687 * We take into account the first, second and third-order deltas
688 * in order to make our estimate.
691 if (!state->dont_count_entropy) {
692 delta = sample.jiffies - state->last_time;
693 state->last_time = sample.jiffies;
695 delta2 = delta - state->last_delta;
696 state->last_delta = delta;
698 delta3 = delta2 - state->last_delta2;
699 state->last_delta2 = delta2;
713 * delta is now minimum absolute delta.
714 * Round down by 1 bit on general principles,
715 * and limit entropy entimate to 12 bits.
717 credit_entropy_bits(&input_pool,
718 min_t(int, fls(delta>>1), 11));
724 void add_input_randomness(unsigned int type, unsigned int code,
727 static unsigned char last_value;
729 /* ignore autorepeat and the like */
730 if (value == last_value)
733 DEBUG_ENT("input event\n");
735 add_timer_randomness(&input_timer_state,
736 (type << 4) ^ code ^ (code >> 4) ^ value);
738 EXPORT_SYMBOL_GPL(add_input_randomness);
740 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
742 void add_interrupt_randomness(int irq, int irq_flags)
744 struct entropy_store *r;
745 struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
746 struct pt_regs *regs = get_irq_regs();
747 unsigned long now = jiffies;
748 __u32 input[4], cycles = get_cycles();
750 input[0] = cycles ^ jiffies;
753 __u64 ip = instruction_pointer(regs);
758 fast_mix(fast_pool, input, sizeof(input));
760 if ((fast_pool->count & 1023) &&
761 !time_after(now, fast_pool->last + HZ))
764 fast_pool->last = now;
766 r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
767 __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
769 * If we don't have a valid cycle counter, and we see
770 * back-to-back timer interrupts, then skip giving credit for
774 if (irq_flags & __IRQF_TIMER) {
775 if (fast_pool->last_timer_intr)
777 fast_pool->last_timer_intr = 1;
779 fast_pool->last_timer_intr = 0;
781 credit_entropy_bits(r, 1);
785 void add_disk_randomness(struct gendisk *disk)
787 if (!disk || !disk->random)
789 /* first major is 1, so we get >= 0x200 here */
790 DEBUG_ENT("disk event %d:%d\n",
791 MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));
793 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
797 /*********************************************************************
799 * Entropy extraction routines
801 *********************************************************************/
803 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
804 size_t nbytes, int min, int rsvd);
807 * This utility inline function is responsible for transferring entropy
808 * from the primary pool to the secondary extraction pool. We make
809 * sure we pull enough for a 'catastrophic reseed'.
811 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
813 __u32 tmp[OUTPUT_POOL_WORDS];
815 if (r->pull && r->entropy_count < nbytes * 8 &&
816 r->entropy_count < r->poolinfo->POOLBITS) {
817 /* If we're limited, always leave two wakeup worth's BITS */
818 int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
821 /* pull at least as many as BYTES as wakeup BITS */
822 bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
823 /* but never more than the buffer size */
824 bytes = min_t(int, bytes, sizeof(tmp));
826 DEBUG_ENT("going to reseed %s with %d bits "
827 "(%d of %d requested)\n",
828 r->name, bytes * 8, nbytes * 8, r->entropy_count);
830 bytes = extract_entropy(r->pull, tmp, bytes,
831 random_read_wakeup_thresh / 8, rsvd);
832 mix_pool_bytes(r, tmp, bytes, NULL);
833 credit_entropy_bits(r, bytes*8);
838 * These functions extracts randomness from the "entropy pool", and
839 * returns it in a buffer.
841 * The min parameter specifies the minimum amount we can pull before
842 * failing to avoid races that defeat catastrophic reseeding while the
843 * reserved parameter indicates how much entropy we must leave in the
844 * pool after each pull to avoid starving other readers.
846 * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
849 static size_t account(struct entropy_store *r, size_t nbytes, int min,
854 /* Hold lock while accounting */
855 spin_lock_irqsave(&r->lock, flags);
857 BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
858 DEBUG_ENT("trying to extract %d bits from %s\n",
859 nbytes * 8, r->name);
861 /* Can we pull enough? */
862 if (r->entropy_count / 8 < min + reserved) {
865 /* If limited, never pull more than available */
866 if (r->limit && nbytes + reserved >= r->entropy_count / 8)
867 nbytes = r->entropy_count/8 - reserved;
869 if (r->entropy_count / 8 >= nbytes + reserved)
870 r->entropy_count -= nbytes*8;
872 r->entropy_count = reserved;
874 if (r->entropy_count < random_write_wakeup_thresh) {
875 wake_up_interruptible(&random_write_wait);
876 kill_fasync(&fasync, SIGIO, POLL_OUT);
880 DEBUG_ENT("debiting %d entropy credits from %s%s\n",
881 nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
883 spin_unlock_irqrestore(&r->lock, flags);
888 static void extract_buf(struct entropy_store *r, __u8 *out)
891 __u32 hash[5], workspace[SHA_WORKSPACE_WORDS];
895 /* Generate a hash across the pool, 16 words (512 bits) at a time */
897 spin_lock_irqsave(&r->lock, flags);
898 for (i = 0; i < r->poolinfo->poolwords; i += 16)
899 sha_transform(hash, (__u8 *)(r->pool + i), workspace);
902 * We mix the hash back into the pool to prevent backtracking
903 * attacks (where the attacker knows the state of the pool
904 * plus the current outputs, and attempts to find previous
905 * ouputs), unless the hash function can be inverted. By
906 * mixing at least a SHA1 worth of hash data back, we make
907 * brute-forcing the feedback as hard as brute-forcing the
910 __mix_pool_bytes(r, hash, sizeof(hash), extract);
911 spin_unlock_irqrestore(&r->lock, flags);
914 * To avoid duplicates, we atomically extract a portion of the
915 * pool while mixing, and hash one final time.
917 sha_transform(hash, extract, workspace);
918 memset(extract, 0, sizeof(extract));
919 memset(workspace, 0, sizeof(workspace));
922 * In case the hash function has some recognizable output
923 * pattern, we fold it in half. Thus, we always feed back
924 * twice as much data as we output.
928 hash[2] ^= rol32(hash[2], 16);
929 memcpy(out, hash, EXTRACT_SIZE);
930 memset(hash, 0, sizeof(hash));
933 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
934 size_t nbytes, int min, int reserved)
937 __u8 tmp[EXTRACT_SIZE];
939 xfer_secondary_pool(r, nbytes);
940 nbytes = account(r, nbytes, min, reserved);
948 spin_lock_irqsave(&r->lock, flags);
949 if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
950 panic("Hardware RNG duplicated output!\n");
951 memcpy(r->last_data, tmp, EXTRACT_SIZE);
952 spin_unlock_irqrestore(&r->lock, flags);
954 i = min_t(int, nbytes, EXTRACT_SIZE);
961 /* Wipe data just returned from memory */
962 memset(tmp, 0, sizeof(tmp));
967 static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
971 __u8 tmp[EXTRACT_SIZE];
973 xfer_secondary_pool(r, nbytes);
974 nbytes = account(r, nbytes, 0, 0);
977 if (need_resched()) {
978 if (signal_pending(current)) {
987 i = min_t(int, nbytes, EXTRACT_SIZE);
988 if (copy_to_user(buf, tmp, i)) {
998 /* Wipe data just returned from memory */
999 memset(tmp, 0, sizeof(tmp));
1005 * This function is the exported kernel interface. It returns some
1006 * number of good random numbers, suitable for seeding TCP sequence
1009 void get_random_bytes(void *buf, int nbytes)
1015 int chunk = min(nbytes, (int)sizeof(unsigned long));
1017 if (!arch_get_random_long(&v))
1020 memcpy(p, &v, chunk);
1025 extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
1027 EXPORT_SYMBOL(get_random_bytes);
1030 * init_std_data - initialize pool with system data
1032 * @r: pool to initialize
1034 * This function clears the pool's entropy count and mixes some system
1035 * data into the pool to prepare it for use. The pool is not cleared
1036 * as that can only decrease the entropy in the pool.
1038 static void init_std_data(struct entropy_store *r)
1041 ktime_t now = ktime_get_real();
1044 r->entropy_count = 0;
1045 r->entropy_total = 0;
1046 mix_pool_bytes(r, &now, sizeof(now), NULL);
1047 for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof(rv)) {
1048 if (!arch_get_random_long(&rv))
1050 mix_pool_bytes(r, &rv, sizeof(rv), NULL);
1052 mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
1055 static int rand_initialize(void)
1057 init_std_data(&input_pool);
1058 init_std_data(&blocking_pool);
1059 init_std_data(&nonblocking_pool);
1062 module_init(rand_initialize);
1064 void rand_initialize_irq(int irq)
1066 struct timer_rand_state *state;
1068 state = get_timer_rand_state(irq);
1074 * If kzalloc returns null, we just won't use that entropy
1077 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1079 set_timer_rand_state(irq, state);
1083 void rand_initialize_disk(struct gendisk *disk)
1085 struct timer_rand_state *state;
1088 * If kzalloc returns null, we just won't use that entropy
1091 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1093 disk->random = state;
1098 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1100 ssize_t n, retval = 0, count = 0;
1105 while (nbytes > 0) {
1107 if (n > SEC_XFER_SIZE)
1110 DEBUG_ENT("reading %d bits\n", n*8);
1112 n = extract_entropy_user(&blocking_pool, buf, n);
1114 DEBUG_ENT("read got %d bits (%d still needed)\n",
1118 if (file->f_flags & O_NONBLOCK) {
1123 DEBUG_ENT("sleeping?\n");
1125 wait_event_interruptible(random_read_wait,
1126 input_pool.entropy_count >=
1127 random_read_wakeup_thresh);
1129 DEBUG_ENT("awake\n");
1131 if (signal_pending(current)) {
1132 retval = -ERESTARTSYS;
1146 break; /* This break makes the device work */
1147 /* like a named pipe */
1150 return (count ? count : retval);
1154 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1156 return extract_entropy_user(&nonblocking_pool, buf, nbytes);
1160 random_poll(struct file *file, poll_table * wait)
1164 poll_wait(file, &random_read_wait, wait);
1165 poll_wait(file, &random_write_wait, wait);
1167 if (input_pool.entropy_count >= random_read_wakeup_thresh)
1168 mask |= POLLIN | POLLRDNORM;
1169 if (input_pool.entropy_count < random_write_wakeup_thresh)
1170 mask |= POLLOUT | POLLWRNORM;
1175 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1179 const char __user *p = buffer;
1182 bytes = min(count, sizeof(buf));
1183 if (copy_from_user(&buf, p, bytes))
1189 mix_pool_bytes(r, buf, bytes, NULL);
1196 static ssize_t random_write(struct file *file, const char __user *buffer,
1197 size_t count, loff_t *ppos)
1201 ret = write_pool(&blocking_pool, buffer, count);
1204 ret = write_pool(&nonblocking_pool, buffer, count);
1208 return (ssize_t)count;
1211 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1213 int size, ent_count;
1214 int __user *p = (int __user *)arg;
1219 /* inherently racy, no point locking */
1220 if (put_user(input_pool.entropy_count, p))
1223 case RNDADDTOENTCNT:
1224 if (!capable(CAP_SYS_ADMIN))
1226 if (get_user(ent_count, p))
1228 credit_entropy_bits(&input_pool, ent_count);
1231 if (!capable(CAP_SYS_ADMIN))
1233 if (get_user(ent_count, p++))
1237 if (get_user(size, p++))
1239 retval = write_pool(&input_pool, (const char __user *)p,
1243 credit_entropy_bits(&input_pool, ent_count);
1247 /* Clear the entropy pool counters. */
1248 if (!capable(CAP_SYS_ADMIN))
1257 static int random_fasync(int fd, struct file *filp, int on)
1259 return fasync_helper(fd, filp, on, &fasync);
1262 const struct file_operations random_fops = {
1263 .read = random_read,
1264 .write = random_write,
1265 .poll = random_poll,
1266 .unlocked_ioctl = random_ioctl,
1267 .fasync = random_fasync,
1268 .llseek = noop_llseek,
1271 const struct file_operations urandom_fops = {
1272 .read = urandom_read,
1273 .write = random_write,
1274 .unlocked_ioctl = random_ioctl,
1275 .fasync = random_fasync,
1276 .llseek = noop_llseek,
1279 /***************************************************************
1280 * Random UUID interface
1282 * Used here for a Boot ID, but can be useful for other kernel
1284 ***************************************************************/
1287 * Generate random UUID
1289 void generate_random_uuid(unsigned char uuid_out[16])
1291 get_random_bytes(uuid_out, 16);
1292 /* Set UUID version to 4 --- truly random generation */
1293 uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1294 /* Set the UUID variant to DCE */
1295 uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1297 EXPORT_SYMBOL(generate_random_uuid);
1299 /********************************************************************
1303 ********************************************************************/
1305 #ifdef CONFIG_SYSCTL
1307 #include <linux/sysctl.h>
1309 static int min_read_thresh = 8, min_write_thresh;
1310 static int max_read_thresh = INPUT_POOL_WORDS * 32;
1311 static int max_write_thresh = INPUT_POOL_WORDS * 32;
1312 static char sysctl_bootid[16];
1315 * These functions is used to return both the bootid UUID, and random
1316 * UUID. The difference is in whether table->data is NULL; if it is,
1317 * then a new UUID is generated and returned to the user.
1319 * If the user accesses this via the proc interface, it will be returned
1320 * as an ASCII string in the standard UUID format. If accesses via the
1321 * sysctl system call, it is returned as 16 bytes of binary data.
1323 static int proc_do_uuid(ctl_table *table, int write,
1324 void __user *buffer, size_t *lenp, loff_t *ppos)
1326 ctl_table fake_table;
1327 unsigned char buf[64], tmp_uuid[16], *uuid;
1332 generate_random_uuid(uuid);
1334 static DEFINE_SPINLOCK(bootid_spinlock);
1336 spin_lock(&bootid_spinlock);
1338 generate_random_uuid(uuid);
1339 spin_unlock(&bootid_spinlock);
1342 sprintf(buf, "%pU", uuid);
1344 fake_table.data = buf;
1345 fake_table.maxlen = sizeof(buf);
1347 return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1350 static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1351 ctl_table random_table[] = {
1353 .procname = "poolsize",
1354 .data = &sysctl_poolsize,
1355 .maxlen = sizeof(int),
1357 .proc_handler = proc_dointvec,
1360 .procname = "entropy_avail",
1361 .maxlen = sizeof(int),
1363 .proc_handler = proc_dointvec,
1364 .data = &input_pool.entropy_count,
1367 .procname = "read_wakeup_threshold",
1368 .data = &random_read_wakeup_thresh,
1369 .maxlen = sizeof(int),
1371 .proc_handler = proc_dointvec_minmax,
1372 .extra1 = &min_read_thresh,
1373 .extra2 = &max_read_thresh,
1376 .procname = "write_wakeup_threshold",
1377 .data = &random_write_wakeup_thresh,
1378 .maxlen = sizeof(int),
1380 .proc_handler = proc_dointvec_minmax,
1381 .extra1 = &min_write_thresh,
1382 .extra2 = &max_write_thresh,
1385 .procname = "boot_id",
1386 .data = &sysctl_bootid,
1389 .proc_handler = proc_do_uuid,
1395 .proc_handler = proc_do_uuid,
1399 #endif /* CONFIG_SYSCTL */
1401 static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1403 static int __init random_int_secret_init(void)
1405 get_random_bytes(random_int_secret, sizeof(random_int_secret));
1408 late_initcall(random_int_secret_init);
1411 * Get a random word for internal kernel use only. Similar to urandom but
1412 * with the goal of minimal entropy pool depletion. As a result, the random
1413 * value is not cryptographically secure but for several uses the cost of
1414 * depleting entropy is too high
1416 DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1417 unsigned int get_random_int(void)
1422 if (arch_get_random_int(&ret))
1425 hash = get_cpu_var(get_random_int_hash);
1427 hash[0] += current->pid + jiffies + get_cycles();
1428 md5_transform(hash, random_int_secret);
1430 put_cpu_var(get_random_int_hash);
1436 * randomize_range() returns a start address such that
1438 * [...... <range> .....]
1441 * a <range> with size "len" starting at the return value is inside in the
1442 * area defined by [start, end], but is otherwise randomized.
1445 randomize_range(unsigned long start, unsigned long end, unsigned long len)
1447 unsigned long range = end - len - start;
1449 if (end <= start + len)
1451 return PAGE_ALIGN(get_random_int() % range + start);