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>
258 #include <linux/irq.h>
259 #include <linux/workqueue.h>
261 #include <asm/processor.h>
262 #include <asm/uaccess.h>
264 #include <asm/irq_regs.h>
267 #define CREATE_TRACE_POINTS
268 #include <trace/events/random.h>
271 * Configuration information
273 #define INPUT_POOL_SHIFT 12
274 #define INPUT_POOL_WORDS (1 << (INPUT_POOL_SHIFT-5))
275 #define OUTPUT_POOL_SHIFT 10
276 #define OUTPUT_POOL_WORDS (1 << (OUTPUT_POOL_SHIFT-5))
277 #define SEC_XFER_SIZE 512
278 #define EXTRACT_SIZE 10
280 #define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))
283 * To allow fractional bits to be tracked, the entropy_count field is
284 * denominated in units of 1/8th bits.
286 * 2*(ENTROPY_SHIFT + log2(poolbits)) must <= 31, or the multiply in
287 * credit_entropy_bits() needs to be 64 bits wide.
289 #define ENTROPY_SHIFT 3
290 #define ENTROPY_BITS(r) ((r)->entropy_count >> ENTROPY_SHIFT)
293 * The minimum number of bits of entropy before we wake up a read on
294 * /dev/random. Should be enough to do a significant reseed.
296 static int random_read_wakeup_thresh = 64;
299 * If the entropy count falls under this number of bits, then we
300 * should wake up processes which are selecting or polling on write
301 * access to /dev/random.
303 static int random_write_wakeup_thresh = 28 * OUTPUT_POOL_WORDS;
306 * The minimum number of seconds between urandom pool resending. We
307 * do this to limit the amount of entropy that can be drained from the
308 * input pool even if there are heavy demands on /dev/urandom.
310 static int random_min_urandom_seed = 60;
313 * Originally, we used a primitive polynomial of degree .poolwords
314 * over GF(2). The taps for various sizes are defined below. They
315 * were chosen to be evenly spaced except for the last tap, which is 1
316 * to get the twisting happening as fast as possible.
318 * For the purposes of better mixing, we use the CRC-32 polynomial as
319 * well to make a (modified) twisted Generalized Feedback Shift
320 * Register. (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR
321 * generators. ACM Transactions on Modeling and Computer Simulation
322 * 2(3):179-194. Also see M. Matsumoto & Y. Kurita, 1994. Twisted
323 * GFSR generators II. ACM Transactions on Mdeling and Computer
324 * Simulation 4:254-266)
326 * Thanks to Colin Plumb for suggesting this.
328 * The mixing operation is much less sensitive than the output hash,
329 * where we use SHA-1. All that we want of mixing operation is that
330 * it be a good non-cryptographic hash; i.e. it not produce collisions
331 * when fed "random" data of the sort we expect to see. As long as
332 * the pool state differs for different inputs, we have preserved the
333 * input entropy and done a good job. The fact that an intelligent
334 * attacker can construct inputs that will produce controlled
335 * alterations to the pool's state is not important because we don't
336 * consider such inputs to contribute any randomness. The only
337 * property we need with respect to them is that the attacker can't
338 * increase his/her knowledge of the pool's state. Since all
339 * additions are reversible (knowing the final state and the input,
340 * you can reconstruct the initial state), if an attacker has any
341 * uncertainty about the initial state, he/she can only shuffle that
342 * uncertainty about, but never cause any collisions (which would
343 * decrease the uncertainty).
345 * Our mixing functions were analyzed by Lacharme, Roeck, Strubel, and
346 * Videau in their paper, "The Linux Pseudorandom Number Generator
347 * Revisited" (see: http://eprint.iacr.org/2012/251.pdf). In their
348 * paper, they point out that we are not using a true Twisted GFSR,
349 * since Matsumoto & Kurita used a trinomial feedback polynomial (that
350 * is, with only three taps, instead of the six that we are using).
351 * As a result, the resulting polynomial is neither primitive nor
352 * irreducible, and hence does not have a maximal period over
353 * GF(2**32). They suggest a slight change to the generator
354 * polynomial which improves the resulting TGFSR polynomial to be
355 * irreducible, which we have made here.
357 static struct poolinfo {
358 int poolbitshift, poolwords, poolbytes, poolbits, poolfracbits;
359 #define S(x) ilog2(x)+5, (x), (x)*4, (x)*32, (x) << (ENTROPY_SHIFT+5)
360 int tap1, tap2, tap3, tap4, tap5;
361 } poolinfo_table[] = {
362 /* was: x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 */
363 /* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */
364 { S(128), 104, 76, 51, 25, 1 },
365 /* was: x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 */
366 /* x^32 + x^26 + x^19 + x^14 + x^7 + x + 1 */
367 { S(32), 26, 19, 14, 7, 1 },
369 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */
370 { S(2048), 1638, 1231, 819, 411, 1 },
372 /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
373 { S(1024), 817, 615, 412, 204, 1 },
375 /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
376 { S(1024), 819, 616, 410, 207, 2 },
378 /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
379 { S(512), 411, 308, 208, 104, 1 },
381 /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
382 { S(512), 409, 307, 206, 102, 2 },
383 /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
384 { S(512), 409, 309, 205, 103, 2 },
386 /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
387 { S(256), 205, 155, 101, 52, 1 },
389 /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
390 { S(128), 103, 78, 51, 27, 2 },
392 /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
393 { S(64), 52, 39, 26, 14, 1 },
398 * Static global variables
400 static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
401 static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
402 static struct fasync_struct *fasync;
404 /**********************************************************************
406 * OS independent entropy store. Here are the functions which handle
407 * storing entropy in an entropy pool.
409 **********************************************************************/
411 struct entropy_store;
412 struct entropy_store {
413 /* read-only data: */
414 const struct poolinfo *poolinfo;
417 struct entropy_store *pull;
418 struct work_struct push_work;
420 /* read-write data: */
421 unsigned long last_pulled;
423 unsigned short add_ptr;
424 unsigned short input_rotate;
427 unsigned int initialized:1;
428 unsigned int limit:1;
429 unsigned int last_data_init:1;
430 __u8 last_data[EXTRACT_SIZE];
433 static void push_to_pool(struct work_struct *work);
434 static __u32 input_pool_data[INPUT_POOL_WORDS];
435 static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
436 static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
438 static struct entropy_store input_pool = {
439 .poolinfo = &poolinfo_table[0],
442 .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
443 .pool = input_pool_data
446 static struct entropy_store blocking_pool = {
447 .poolinfo = &poolinfo_table[1],
451 .lock = __SPIN_LOCK_UNLOCKED(blocking_pool.lock),
452 .pool = blocking_pool_data,
453 .push_work = __WORK_INITIALIZER(blocking_pool.push_work,
457 static struct entropy_store nonblocking_pool = {
458 .poolinfo = &poolinfo_table[1],
459 .name = "nonblocking",
461 .lock = __SPIN_LOCK_UNLOCKED(nonblocking_pool.lock),
462 .pool = nonblocking_pool_data,
463 .push_work = __WORK_INITIALIZER(nonblocking_pool.push_work,
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);
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 = (input_rotate + (i ? 7 : 14)) & 31;
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])
537 trace_mix_pool_bytes_nolock(r->name, nbytes, _RET_IP_);
538 _mix_pool_bytes(r, in, nbytes, out);
541 static void mix_pool_bytes(struct entropy_store *r, const void *in,
542 int nbytes, __u8 out[64])
546 trace_mix_pool_bytes(r->name, nbytes, _RET_IP_);
547 spin_lock_irqsave(&r->lock, flags);
548 _mix_pool_bytes(r, in, nbytes, out);
549 spin_unlock_irqrestore(&r->lock, flags);
555 unsigned short count;
556 unsigned char rotate;
557 unsigned char last_timer_intr;
561 * This is a fast mixing routine used by the interrupt randomness
562 * collector. It's hardcoded for an 128 bit pool and assumes that any
563 * locks that might be needed are taken by the caller.
565 static void fast_mix(struct fast_pool *f, __u32 input[4])
568 unsigned input_rotate = f->rotate;
570 w = rol32(input[0], input_rotate) ^ f->pool[0] ^ f->pool[3];
571 f->pool[0] = (w >> 3) ^ twist_table[w & 7];
572 input_rotate = (input_rotate + 14) & 31;
573 w = rol32(input[1], input_rotate) ^ f->pool[1] ^ f->pool[0];
574 f->pool[1] = (w >> 3) ^ twist_table[w & 7];
575 input_rotate = (input_rotate + 7) & 31;
576 w = rol32(input[2], input_rotate) ^ f->pool[2] ^ f->pool[1];
577 f->pool[2] = (w >> 3) ^ twist_table[w & 7];
578 input_rotate = (input_rotate + 7) & 31;
579 w = rol32(input[3], input_rotate) ^ f->pool[3] ^ f->pool[2];
580 f->pool[3] = (w >> 3) ^ twist_table[w & 7];
581 input_rotate = (input_rotate + 7) & 31;
583 f->rotate = input_rotate;
588 * Credit (or debit) the entropy store with n bits of entropy.
589 * Use credit_entropy_bits_safe() if the value comes from userspace
590 * or otherwise should be checked for extreme values.
592 static void credit_entropy_bits(struct entropy_store *r, int nbits)
594 int entropy_count, orig;
595 const int pool_size = r->poolinfo->poolfracbits;
596 int nfrac = nbits << ENTROPY_SHIFT;
602 entropy_count = orig = ACCESS_ONCE(r->entropy_count);
605 entropy_count += nfrac;
608 * Credit: we have to account for the possibility of
609 * overwriting already present entropy. Even in the
610 * ideal case of pure Shannon entropy, new contributions
611 * approach the full value asymptotically:
613 * entropy <- entropy + (pool_size - entropy) *
614 * (1 - exp(-add_entropy/pool_size))
616 * For add_entropy <= pool_size/2 then
617 * (1 - exp(-add_entropy/pool_size)) >=
618 * (add_entropy/pool_size)*0.7869...
619 * so we can approximate the exponential with
620 * 3/4*add_entropy/pool_size and still be on the
621 * safe side by adding at most pool_size/2 at a time.
623 * The use of pool_size-2 in the while statement is to
624 * prevent rounding artifacts from making the loop
625 * arbitrarily long; this limits the loop to log2(pool_size)*2
626 * turns no matter how large nbits is.
629 const int s = r->poolinfo->poolbitshift + ENTROPY_SHIFT + 2;
630 /* The +2 corresponds to the /4 in the denominator */
633 unsigned int anfrac = min(pnfrac, pool_size/2);
635 ((pool_size - entropy_count)*anfrac*3) >> s;
637 entropy_count += add;
639 } while (unlikely(entropy_count < pool_size-2 && pnfrac));
642 if (entropy_count < 0) {
643 pr_warn("random: negative entropy/overflow: pool %s count %d\n",
644 r->name, entropy_count);
647 } else if (entropy_count > pool_size)
648 entropy_count = pool_size;
649 if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
652 r->entropy_total += nbits;
653 if (!r->initialized && nbits > 0) {
654 if (r->entropy_total > 128) {
656 r->entropy_total = 0;
660 trace_credit_entropy_bits(r->name, nbits,
661 entropy_count >> ENTROPY_SHIFT,
662 r->entropy_total, _RET_IP_);
664 if (r == &input_pool) {
665 int entropy_bytes = entropy_count >> ENTROPY_SHIFT;
667 /* should we wake readers? */
668 if (entropy_bytes >= random_read_wakeup_thresh) {
669 wake_up_interruptible(&random_read_wait);
670 kill_fasync(&fasync, SIGIO, POLL_IN);
672 /* If the input pool is getting full, send some
673 * entropy to the two output pools, flipping back and
674 * forth between them, until the output pools are 75%
677 if (entropy_bytes > random_write_wakeup_thresh &&
679 r->entropy_total >= 2*random_read_wakeup_thresh) {
680 static struct entropy_store *last = &blocking_pool;
681 struct entropy_store *other = &blocking_pool;
683 if (last == &blocking_pool)
684 other = &nonblocking_pool;
685 if (other->entropy_count <=
686 3 * other->poolinfo->poolfracbits / 4)
688 if (last->entropy_count <=
689 3 * last->poolinfo->poolfracbits / 4) {
690 schedule_work(&last->push_work);
691 r->entropy_total = 0;
697 static void credit_entropy_bits_safe(struct entropy_store *r, int nbits)
699 const int nbits_max = (int)(~0U >> (ENTROPY_SHIFT + 1));
701 /* Cap the value to avoid overflows */
702 nbits = min(nbits, nbits_max);
703 nbits = max(nbits, -nbits_max);
705 credit_entropy_bits(r, nbits);
708 /*********************************************************************
710 * Entropy input management
712 *********************************************************************/
714 /* There is one of these per entropy source */
715 struct timer_rand_state {
717 long last_delta, last_delta2;
718 unsigned dont_count_entropy:1;
722 * Add device- or boot-specific data to the input and nonblocking
723 * pools to help initialize them to unique values.
725 * None of this adds any entropy, it is meant to avoid the
726 * problem of the nonblocking pool having similar initial state
727 * across largely identical devices.
729 void add_device_randomness(const void *buf, unsigned int size)
731 unsigned long time = random_get_entropy() ^ jiffies;
734 trace_add_device_randomness(size, _RET_IP_);
735 spin_lock_irqsave(&input_pool.lock, flags);
736 _mix_pool_bytes(&input_pool, buf, size, NULL);
737 _mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
738 spin_unlock_irqrestore(&input_pool.lock, flags);
740 spin_lock_irqsave(&nonblocking_pool.lock, flags);
741 _mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
742 _mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
743 spin_unlock_irqrestore(&nonblocking_pool.lock, flags);
745 EXPORT_SYMBOL(add_device_randomness);
747 static struct timer_rand_state input_timer_state;
750 * This function adds entropy to the entropy "pool" by using timing
751 * delays. It uses the timer_rand_state structure to make an estimate
752 * of how many bits of entropy this call has added to the pool.
754 * The number "num" is also added to the pool - it should somehow describe
755 * the type of event which just happened. This is currently 0-255 for
756 * keyboard scan codes, and 256 upwards for interrupts.
759 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
766 long delta, delta2, delta3;
770 sample.jiffies = jiffies;
771 sample.cycles = random_get_entropy();
773 mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
776 * Calculate number of bits of randomness we probably added.
777 * We take into account the first, second and third-order deltas
778 * in order to make our estimate.
781 if (!state->dont_count_entropy) {
782 delta = sample.jiffies - state->last_time;
783 state->last_time = sample.jiffies;
785 delta2 = delta - state->last_delta;
786 state->last_delta = delta;
788 delta3 = delta2 - state->last_delta2;
789 state->last_delta2 = delta2;
803 * delta is now minimum absolute delta.
804 * Round down by 1 bit on general principles,
805 * and limit entropy entimate to 12 bits.
807 credit_entropy_bits(&input_pool,
808 min_t(int, fls(delta>>1), 11));
813 void add_input_randomness(unsigned int type, unsigned int code,
816 static unsigned char last_value;
818 /* ignore autorepeat and the like */
819 if (value == last_value)
823 add_timer_randomness(&input_timer_state,
824 (type << 4) ^ code ^ (code >> 4) ^ value);
825 trace_add_input_randomness(ENTROPY_BITS(&input_pool));
827 EXPORT_SYMBOL_GPL(add_input_randomness);
829 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
831 void add_interrupt_randomness(int irq, int irq_flags)
833 struct entropy_store *r;
834 struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
835 struct pt_regs *regs = get_irq_regs();
836 unsigned long now = jiffies;
837 cycles_t cycles = random_get_entropy();
838 __u32 input[4], c_high, j_high;
841 c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;
842 j_high = (sizeof(now) > 4) ? now >> 32 : 0;
843 input[0] = cycles ^ j_high ^ irq;
844 input[1] = now ^ c_high;
845 ip = regs ? instruction_pointer(regs) : _RET_IP_;
849 fast_mix(fast_pool, input);
851 if ((fast_pool->count & 63) && !time_after(now, fast_pool->last + HZ))
854 fast_pool->last = now;
856 r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
857 __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
859 * If we don't have a valid cycle counter, and we see
860 * back-to-back timer interrupts, then skip giving credit for
864 if (irq_flags & __IRQF_TIMER) {
865 if (fast_pool->last_timer_intr)
867 fast_pool->last_timer_intr = 1;
869 fast_pool->last_timer_intr = 0;
871 credit_entropy_bits(r, 1);
875 void add_disk_randomness(struct gendisk *disk)
877 if (!disk || !disk->random)
879 /* first major is 1, so we get >= 0x200 here */
880 add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
881 trace_add_disk_randomness(disk_devt(disk), ENTROPY_BITS(&input_pool));
885 /*********************************************************************
887 * Entropy extraction routines
889 *********************************************************************/
891 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
892 size_t nbytes, int min, int rsvd);
895 * This utility inline function is responsible for transferring entropy
896 * from the primary pool to the secondary extraction pool. We make
897 * sure we pull enough for a 'catastrophic reseed'.
899 static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes);
900 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
902 if (r->limit == 0 && random_min_urandom_seed) {
903 unsigned long now = jiffies;
906 r->last_pulled + random_min_urandom_seed * HZ))
908 r->last_pulled = now;
911 r->entropy_count < (nbytes << (ENTROPY_SHIFT + 3)) &&
912 r->entropy_count < r->poolinfo->poolfracbits)
913 _xfer_secondary_pool(r, nbytes);
916 static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
918 __u32 tmp[OUTPUT_POOL_WORDS];
920 /* For /dev/random's pool, always leave two wakeup worth's BITS */
921 int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
924 /* pull at least as many as BYTES as wakeup BITS */
925 bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
926 /* but never more than the buffer size */
927 bytes = min_t(int, bytes, sizeof(tmp));
929 trace_xfer_secondary_pool(r->name, bytes * 8, nbytes * 8,
930 ENTROPY_BITS(r), ENTROPY_BITS(r->pull));
931 bytes = extract_entropy(r->pull, tmp, bytes,
932 random_read_wakeup_thresh / 8, rsvd);
933 mix_pool_bytes(r, tmp, bytes, NULL);
934 credit_entropy_bits(r, bytes*8);
938 * Used as a workqueue function so that when the input pool is getting
939 * full, we can "spill over" some entropy to the output pools. That
940 * way the output pools can store some of the excess entropy instead
941 * of letting it go to waste.
943 static void push_to_pool(struct work_struct *work)
945 struct entropy_store *r = container_of(work, struct entropy_store,
948 _xfer_secondary_pool(r, random_read_wakeup_thresh/8);
949 trace_push_to_pool(r->name, r->entropy_count >> ENTROPY_SHIFT,
950 r->pull->entropy_count >> ENTROPY_SHIFT);
954 * These functions extracts randomness from the "entropy pool", and
955 * returns it in a buffer.
957 * The min parameter specifies the minimum amount we can pull before
958 * failing to avoid races that defeat catastrophic reseeding while the
959 * reserved parameter indicates how much entropy we must leave in the
960 * pool after each pull to avoid starving other readers.
962 * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
965 static size_t account(struct entropy_store *r, size_t nbytes, int min,
969 int wakeup_write = 0;
971 int entropy_count, orig;
974 /* Hold lock while accounting */
975 spin_lock_irqsave(&r->lock, flags);
977 BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
979 /* Can we pull enough? */
981 entropy_count = orig = ACCESS_ONCE(r->entropy_count);
982 have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);
984 if (have_bytes < min + reserved) {
987 /* If limited, never pull more than available */
988 if (r->limit && ibytes + reserved >= have_bytes)
989 ibytes = have_bytes - reserved;
991 if (have_bytes >= ibytes + reserved)
992 entropy_count -= ibytes << (ENTROPY_SHIFT + 3);
994 entropy_count = reserved << (ENTROPY_SHIFT + 3);
996 if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
999 if ((r->entropy_count >> ENTROPY_SHIFT)
1000 < random_write_wakeup_thresh)
1003 spin_unlock_irqrestore(&r->lock, flags);
1005 trace_debit_entropy(r->name, 8 * ibytes);
1007 wake_up_interruptible(&random_write_wait);
1008 kill_fasync(&fasync, SIGIO, POLL_OUT);
1014 static void extract_buf(struct entropy_store *r, __u8 *out)
1019 unsigned long l[LONGS(20)];
1021 __u32 workspace[SHA_WORKSPACE_WORDS];
1023 unsigned long flags;
1025 /* Generate a hash across the pool, 16 words (512 bits) at a time */
1027 spin_lock_irqsave(&r->lock, flags);
1028 for (i = 0; i < r->poolinfo->poolwords; i += 16)
1029 sha_transform(hash.w, (__u8 *)(r->pool + i), workspace);
1032 * If we have a architectural hardware random number
1033 * generator, mix that in, too.
1035 for (i = 0; i < LONGS(20); i++) {
1037 if (!arch_get_random_long(&v))
1043 * We mix the hash back into the pool to prevent backtracking
1044 * attacks (where the attacker knows the state of the pool
1045 * plus the current outputs, and attempts to find previous
1046 * ouputs), unless the hash function can be inverted. By
1047 * mixing at least a SHA1 worth of hash data back, we make
1048 * brute-forcing the feedback as hard as brute-forcing the
1051 __mix_pool_bytes(r, hash.w, sizeof(hash.w), extract);
1052 spin_unlock_irqrestore(&r->lock, flags);
1055 * To avoid duplicates, we atomically extract a portion of the
1056 * pool while mixing, and hash one final time.
1058 sha_transform(hash.w, extract, workspace);
1059 memset(extract, 0, sizeof(extract));
1060 memset(workspace, 0, sizeof(workspace));
1063 * In case the hash function has some recognizable output
1064 * pattern, we fold it in half. Thus, we always feed back
1065 * twice as much data as we output.
1067 hash.w[0] ^= hash.w[3];
1068 hash.w[1] ^= hash.w[4];
1069 hash.w[2] ^= rol32(hash.w[2], 16);
1071 memcpy(out, &hash, EXTRACT_SIZE);
1072 memset(&hash, 0, sizeof(hash));
1075 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
1076 size_t nbytes, int min, int reserved)
1079 __u8 tmp[EXTRACT_SIZE];
1080 unsigned long flags;
1082 /* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */
1084 spin_lock_irqsave(&r->lock, flags);
1085 if (!r->last_data_init) {
1086 r->last_data_init = 1;
1087 spin_unlock_irqrestore(&r->lock, flags);
1088 trace_extract_entropy(r->name, EXTRACT_SIZE,
1089 ENTROPY_BITS(r), _RET_IP_);
1090 xfer_secondary_pool(r, EXTRACT_SIZE);
1091 extract_buf(r, tmp);
1092 spin_lock_irqsave(&r->lock, flags);
1093 memcpy(r->last_data, tmp, EXTRACT_SIZE);
1095 spin_unlock_irqrestore(&r->lock, flags);
1098 trace_extract_entropy(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
1099 xfer_secondary_pool(r, nbytes);
1100 nbytes = account(r, nbytes, min, reserved);
1103 extract_buf(r, tmp);
1106 spin_lock_irqsave(&r->lock, flags);
1107 if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
1108 panic("Hardware RNG duplicated output!\n");
1109 memcpy(r->last_data, tmp, EXTRACT_SIZE);
1110 spin_unlock_irqrestore(&r->lock, flags);
1112 i = min_t(int, nbytes, EXTRACT_SIZE);
1113 memcpy(buf, tmp, i);
1119 /* Wipe data just returned from memory */
1120 memset(tmp, 0, sizeof(tmp));
1125 static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
1129 __u8 tmp[EXTRACT_SIZE];
1131 trace_extract_entropy_user(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
1132 xfer_secondary_pool(r, nbytes);
1133 nbytes = account(r, nbytes, 0, 0);
1136 if (need_resched()) {
1137 if (signal_pending(current)) {
1145 extract_buf(r, tmp);
1146 i = min_t(int, nbytes, EXTRACT_SIZE);
1147 if (copy_to_user(buf, tmp, i)) {
1157 /* Wipe data just returned from memory */
1158 memset(tmp, 0, sizeof(tmp));
1164 * This function is the exported kernel interface. It returns some
1165 * number of good random numbers, suitable for key generation, seeding
1166 * TCP sequence numbers, etc. It does not use the hw random number
1167 * generator, if available; use get_random_bytes_arch() for that.
1169 void get_random_bytes(void *buf, int nbytes)
1171 trace_get_random_bytes(nbytes, _RET_IP_);
1172 extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
1174 EXPORT_SYMBOL(get_random_bytes);
1177 * This function will use the architecture-specific hardware random
1178 * number generator if it is available. The arch-specific hw RNG will
1179 * almost certainly be faster than what we can do in software, but it
1180 * is impossible to verify that it is implemented securely (as
1181 * opposed, to, say, the AES encryption of a sequence number using a
1182 * key known by the NSA). So it's useful if we need the speed, but
1183 * only if we're willing to trust the hardware manufacturer not to
1184 * have put in a back door.
1186 void get_random_bytes_arch(void *buf, int nbytes)
1190 trace_get_random_bytes_arch(nbytes, _RET_IP_);
1193 int chunk = min(nbytes, (int)sizeof(unsigned long));
1195 if (!arch_get_random_long(&v))
1198 memcpy(p, &v, chunk);
1204 extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
1206 EXPORT_SYMBOL(get_random_bytes_arch);
1210 * init_std_data - initialize pool with system data
1212 * @r: pool to initialize
1214 * This function clears the pool's entropy count and mixes some system
1215 * data into the pool to prepare it for use. The pool is not cleared
1216 * as that can only decrease the entropy in the pool.
1218 static void init_std_data(struct entropy_store *r)
1221 ktime_t now = ktime_get_real();
1224 r->entropy_count = 0;
1225 r->entropy_total = 0;
1226 r->last_data_init = 0;
1227 r->last_pulled = jiffies;
1228 mix_pool_bytes(r, &now, sizeof(now), NULL);
1229 for (i = r->poolinfo->poolbytes; i > 0; i -= sizeof(rv)) {
1230 if (!arch_get_random_long(&rv))
1232 mix_pool_bytes(r, &rv, sizeof(rv), NULL);
1234 mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
1238 * Note that setup_arch() may call add_device_randomness()
1239 * long before we get here. This allows seeding of the pools
1240 * with some platform dependent data very early in the boot
1241 * process. But it limits our options here. We must use
1242 * statically allocated structures that already have all
1243 * initializations complete at compile time. We should also
1244 * take care not to overwrite the precious per platform data
1247 static int rand_initialize(void)
1249 init_std_data(&input_pool);
1250 init_std_data(&blocking_pool);
1251 init_std_data(&nonblocking_pool);
1254 module_init(rand_initialize);
1257 void rand_initialize_disk(struct gendisk *disk)
1259 struct timer_rand_state *state;
1262 * If kzalloc returns null, we just won't use that entropy
1265 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1267 disk->random = state;
1272 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1274 ssize_t n, retval = 0, count = 0;
1279 while (nbytes > 0) {
1281 if (n > SEC_XFER_SIZE)
1284 n = extract_entropy_user(&blocking_pool, buf, n);
1291 trace_random_read(n*8, (nbytes-n)*8,
1292 ENTROPY_BITS(&blocking_pool),
1293 ENTROPY_BITS(&input_pool));
1296 if (file->f_flags & O_NONBLOCK) {
1301 wait_event_interruptible(random_read_wait,
1302 ENTROPY_BITS(&input_pool) >=
1303 random_read_wakeup_thresh);
1305 if (signal_pending(current)) {
1306 retval = -ERESTARTSYS;
1316 break; /* This break makes the device work */
1317 /* like a named pipe */
1320 return (count ? count : retval);
1324 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1326 int ret = extract_entropy_user(&nonblocking_pool, buf, nbytes);
1328 trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool),
1329 ENTROPY_BITS(&input_pool));
1334 random_poll(struct file *file, poll_table * wait)
1338 poll_wait(file, &random_read_wait, wait);
1339 poll_wait(file, &random_write_wait, wait);
1341 if (ENTROPY_BITS(&input_pool) >= random_read_wakeup_thresh)
1342 mask |= POLLIN | POLLRDNORM;
1343 if (ENTROPY_BITS(&input_pool) < random_write_wakeup_thresh)
1344 mask |= POLLOUT | POLLWRNORM;
1349 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1353 const char __user *p = buffer;
1356 bytes = min(count, sizeof(buf));
1357 if (copy_from_user(&buf, p, bytes))
1363 mix_pool_bytes(r, buf, bytes, NULL);
1370 static ssize_t random_write(struct file *file, const char __user *buffer,
1371 size_t count, loff_t *ppos)
1375 ret = write_pool(&blocking_pool, buffer, count);
1378 ret = write_pool(&nonblocking_pool, buffer, count);
1382 return (ssize_t)count;
1385 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1387 int size, ent_count;
1388 int __user *p = (int __user *)arg;
1393 /* inherently racy, no point locking */
1394 ent_count = ENTROPY_BITS(&input_pool);
1395 if (put_user(ent_count, p))
1398 case RNDADDTOENTCNT:
1399 if (!capable(CAP_SYS_ADMIN))
1401 if (get_user(ent_count, p))
1403 credit_entropy_bits_safe(&input_pool, ent_count);
1406 if (!capable(CAP_SYS_ADMIN))
1408 if (get_user(ent_count, p++))
1412 if (get_user(size, p++))
1414 retval = write_pool(&input_pool, (const char __user *)p,
1418 credit_entropy_bits_safe(&input_pool, ent_count);
1422 /* Clear the entropy pool counters. */
1423 if (!capable(CAP_SYS_ADMIN))
1432 static int random_fasync(int fd, struct file *filp, int on)
1434 return fasync_helper(fd, filp, on, &fasync);
1437 const struct file_operations random_fops = {
1438 .read = random_read,
1439 .write = random_write,
1440 .poll = random_poll,
1441 .unlocked_ioctl = random_ioctl,
1442 .fasync = random_fasync,
1443 .llseek = noop_llseek,
1446 const struct file_operations urandom_fops = {
1447 .read = urandom_read,
1448 .write = random_write,
1449 .unlocked_ioctl = random_ioctl,
1450 .fasync = random_fasync,
1451 .llseek = noop_llseek,
1454 /***************************************************************
1455 * Random UUID interface
1457 * Used here for a Boot ID, but can be useful for other kernel
1459 ***************************************************************/
1462 * Generate random UUID
1464 void generate_random_uuid(unsigned char uuid_out[16])
1466 get_random_bytes(uuid_out, 16);
1467 /* Set UUID version to 4 --- truly random generation */
1468 uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1469 /* Set the UUID variant to DCE */
1470 uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1472 EXPORT_SYMBOL(generate_random_uuid);
1474 /********************************************************************
1478 ********************************************************************/
1480 #ifdef CONFIG_SYSCTL
1482 #include <linux/sysctl.h>
1484 static int min_read_thresh = 8, min_write_thresh;
1485 static int max_read_thresh = INPUT_POOL_WORDS * 32;
1486 static int max_write_thresh = INPUT_POOL_WORDS * 32;
1487 static char sysctl_bootid[16];
1490 * These functions is used to return both the bootid UUID, and random
1491 * UUID. The difference is in whether table->data is NULL; if it is,
1492 * then a new UUID is generated and returned to the user.
1494 * If the user accesses this via the proc interface, it will be returned
1495 * as an ASCII string in the standard UUID format. If accesses via the
1496 * sysctl system call, it is returned as 16 bytes of binary data.
1498 static int proc_do_uuid(struct ctl_table *table, int write,
1499 void __user *buffer, size_t *lenp, loff_t *ppos)
1501 struct ctl_table fake_table;
1502 unsigned char buf[64], tmp_uuid[16], *uuid;
1507 generate_random_uuid(uuid);
1509 static DEFINE_SPINLOCK(bootid_spinlock);
1511 spin_lock(&bootid_spinlock);
1513 generate_random_uuid(uuid);
1514 spin_unlock(&bootid_spinlock);
1517 sprintf(buf, "%pU", uuid);
1519 fake_table.data = buf;
1520 fake_table.maxlen = sizeof(buf);
1522 return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1526 * Return entropy available scaled to integral bits
1528 static int proc_do_entropy(ctl_table *table, int write,
1529 void __user *buffer, size_t *lenp, loff_t *ppos)
1531 ctl_table fake_table;
1534 entropy_count = *(int *)table->data >> ENTROPY_SHIFT;
1536 fake_table.data = &entropy_count;
1537 fake_table.maxlen = sizeof(entropy_count);
1539 return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
1542 static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1543 extern struct ctl_table random_table[];
1544 struct ctl_table random_table[] = {
1546 .procname = "poolsize",
1547 .data = &sysctl_poolsize,
1548 .maxlen = sizeof(int),
1550 .proc_handler = proc_dointvec,
1553 .procname = "entropy_avail",
1554 .maxlen = sizeof(int),
1556 .proc_handler = proc_do_entropy,
1557 .data = &input_pool.entropy_count,
1560 .procname = "read_wakeup_threshold",
1561 .data = &random_read_wakeup_thresh,
1562 .maxlen = sizeof(int),
1564 .proc_handler = proc_dointvec_minmax,
1565 .extra1 = &min_read_thresh,
1566 .extra2 = &max_read_thresh,
1569 .procname = "write_wakeup_threshold",
1570 .data = &random_write_wakeup_thresh,
1571 .maxlen = sizeof(int),
1573 .proc_handler = proc_dointvec_minmax,
1574 .extra1 = &min_write_thresh,
1575 .extra2 = &max_write_thresh,
1578 .procname = "urandom_min_reseed_secs",
1579 .data = &random_min_urandom_seed,
1580 .maxlen = sizeof(int),
1582 .proc_handler = proc_dointvec,
1585 .procname = "boot_id",
1586 .data = &sysctl_bootid,
1589 .proc_handler = proc_do_uuid,
1595 .proc_handler = proc_do_uuid,
1599 #endif /* CONFIG_SYSCTL */
1601 static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1603 int random_int_secret_init(void)
1605 get_random_bytes(random_int_secret, sizeof(random_int_secret));
1610 * Get a random word for internal kernel use only. Similar to urandom but
1611 * with the goal of minimal entropy pool depletion. As a result, the random
1612 * value is not cryptographically secure but for several uses the cost of
1613 * depleting entropy is too high
1615 static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1616 unsigned int get_random_int(void)
1621 if (arch_get_random_int(&ret))
1624 hash = get_cpu_var(get_random_int_hash);
1626 hash[0] += current->pid + jiffies + random_get_entropy();
1627 md5_transform(hash, random_int_secret);
1629 put_cpu_var(get_random_int_hash);
1633 EXPORT_SYMBOL(get_random_int);
1636 * randomize_range() returns a start address such that
1638 * [...... <range> .....]
1641 * a <range> with size "len" starting at the return value is inside in the
1642 * area defined by [start, end], but is otherwise randomized.
1645 randomize_range(unsigned long start, unsigned long end, unsigned long len)
1647 unsigned long range = end - len - start;
1649 if (end <= start + len)
1651 return PAGE_ALIGN(get_random_int() % range + start);