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: */
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_extract(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
;
481 /* Taps are constant, so we can load them without holding r->lock. */
482 tap1
= r
->poolinfo
->tap1
;
483 tap2
= r
->poolinfo
->tap2
;
484 tap3
= r
->poolinfo
->tap3
;
485 tap4
= r
->poolinfo
->tap4
;
486 tap5
= r
->poolinfo
->tap5
;
488 spin_lock_irqsave(&r
->lock
, flags
);
489 input_rotate
= r
->input_rotate
;
492 /* mix one byte at a time to simplify size handling and churn faster */
494 w
= rol32(*bytes
++, input_rotate
& 31);
495 i
= (i
- 1) & wordmask
;
497 /* XOR in the various taps */
499 w
^= r
->pool
[(i
+ tap1
) & wordmask
];
500 w
^= r
->pool
[(i
+ tap2
) & wordmask
];
501 w
^= r
->pool
[(i
+ tap3
) & wordmask
];
502 w
^= r
->pool
[(i
+ tap4
) & wordmask
];
503 w
^= r
->pool
[(i
+ tap5
) & wordmask
];
505 /* Mix the result back in with a twist */
506 r
->pool
[i
] = (w
>> 3) ^ twist_table
[w
& 7];
509 * Normally, we add 7 bits of rotation to the pool.
510 * At the beginning of the pool, add an extra 7 bits
511 * rotation, so that successive passes spread the
512 * input bits across the pool evenly.
514 input_rotate
+= i
? 7 : 14;
517 r
->input_rotate
= input_rotate
;
521 for (j
= 0; j
< 16; j
++)
522 ((__u32
*)out
)[j
] = r
->pool
[(i
- j
) & wordmask
];
524 spin_unlock_irqrestore(&r
->lock
, flags
);
527 static void mix_pool_bytes(struct entropy_store
*r
, const void *in
, int bytes
)
529 mix_pool_bytes_extract(r
, in
, bytes
, NULL
);
535 unsigned short count
;
536 unsigned char rotate
;
537 unsigned char last_timer_intr
;
541 * This is a fast mixing routine used by the interrupt randomness
542 * collector. It's hardcoded for an 128 bit pool and assumes that any
543 * locks that might be needed are taken by the caller.
545 static void fast_mix(struct fast_pool
*f
, const void *in
, int nbytes
)
547 const char *bytes
= in
;
549 unsigned i
= f
->count
;
550 unsigned input_rotate
= f
->rotate
;
553 w
= rol32(*bytes
++, input_rotate
& 31) ^ f
->pool
[i
& 3] ^
554 f
->pool
[(i
+ 1) & 3];
555 f
->pool
[i
& 3] = (w
>> 3) ^ twist_table
[w
& 7];
556 input_rotate
+= (i
++ & 3) ? 7 : 14;
559 f
->rotate
= input_rotate
;
563 * Credit (or debit) the entropy store with n bits of entropy
565 static void credit_entropy_bits(struct entropy_store
*r
, int nbits
)
573 spin_lock_irqsave(&r
->lock
, flags
);
575 DEBUG_ENT("added %d entropy credits to %s\n", nbits
, r
->name
);
576 entropy_count
= 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 r
->entropy_count
= entropy_count
;
585 if (!r
->initialized
&& nbits
> 0) {
586 r
->entropy_total
+= nbits
;
587 if (r
->entropy_total
> 128)
591 /* should we wake readers? */
592 if (r
== &input_pool
&& entropy_count
>= random_read_wakeup_thresh
) {
593 wake_up_interruptible(&random_read_wait
);
594 kill_fasync(&fasync
, SIGIO
, POLL_IN
);
596 spin_unlock_irqrestore(&r
->lock
, flags
);
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
));
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
));
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
);
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
];
894 /* Generate a hash across the pool, 16 words (512 bits) at a time */
896 for (i
= 0; i
< r
->poolinfo
->poolwords
; i
+= 16)
897 sha_transform(hash
, (__u8
*)(r
->pool
+ i
), workspace
);
900 * We mix the hash back into the pool to prevent backtracking
901 * attacks (where the attacker knows the state of the pool
902 * plus the current outputs, and attempts to find previous
903 * ouputs), unless the hash function can be inverted. By
904 * mixing at least a SHA1 worth of hash data back, we make
905 * brute-forcing the feedback as hard as brute-forcing the
908 mix_pool_bytes_extract(r
, hash
, sizeof(hash
), extract
);
911 * To avoid duplicates, we atomically extract a portion of the
912 * pool while mixing, and hash one final time.
914 sha_transform(hash
, extract
, workspace
);
915 memset(extract
, 0, sizeof(extract
));
916 memset(workspace
, 0, sizeof(workspace
));
919 * In case the hash function has some recognizable output
920 * pattern, we fold it in half. Thus, we always feed back
921 * twice as much data as we output.
925 hash
[2] ^= rol32(hash
[2], 16);
926 memcpy(out
, hash
, EXTRACT_SIZE
);
927 memset(hash
, 0, sizeof(hash
));
930 static ssize_t
extract_entropy(struct entropy_store
*r
, void *buf
,
931 size_t nbytes
, int min
, int reserved
)
934 __u8 tmp
[EXTRACT_SIZE
];
937 xfer_secondary_pool(r
, nbytes
);
938 nbytes
= account(r
, nbytes
, min
, reserved
);
944 spin_lock_irqsave(&r
->lock
, flags
);
945 if (!memcmp(tmp
, r
->last_data
, EXTRACT_SIZE
))
946 panic("Hardware RNG duplicated output!\n");
947 memcpy(r
->last_data
, tmp
, EXTRACT_SIZE
);
948 spin_unlock_irqrestore(&r
->lock
, flags
);
950 i
= min_t(int, nbytes
, EXTRACT_SIZE
);
957 /* Wipe data just returned from memory */
958 memset(tmp
, 0, sizeof(tmp
));
963 static ssize_t
extract_entropy_user(struct entropy_store
*r
, void __user
*buf
,
967 __u8 tmp
[EXTRACT_SIZE
];
969 xfer_secondary_pool(r
, nbytes
);
970 nbytes
= account(r
, nbytes
, 0, 0);
973 if (need_resched()) {
974 if (signal_pending(current
)) {
983 i
= min_t(int, nbytes
, EXTRACT_SIZE
);
984 if (copy_to_user(buf
, tmp
, i
)) {
994 /* Wipe data just returned from memory */
995 memset(tmp
, 0, sizeof(tmp
));
1001 * This function is the exported kernel interface. It returns some
1002 * number of good random numbers, suitable for seeding TCP sequence
1005 void get_random_bytes(void *buf
, int nbytes
)
1011 int chunk
= min(nbytes
, (int)sizeof(unsigned long));
1013 if (!arch_get_random_long(&v
))
1016 memcpy(p
, &v
, chunk
);
1021 extract_entropy(&nonblocking_pool
, p
, nbytes
, 0, 0);
1023 EXPORT_SYMBOL(get_random_bytes
);
1026 * init_std_data - initialize pool with system data
1028 * @r: pool to initialize
1030 * This function clears the pool's entropy count and mixes some system
1031 * data into the pool to prepare it for use. The pool is not cleared
1032 * as that can only decrease the entropy in the pool.
1034 static void init_std_data(struct entropy_store
*r
)
1038 unsigned long flags
;
1040 spin_lock_irqsave(&r
->lock
, flags
);
1041 r
->entropy_count
= 0;
1042 r
->entropy_total
= 0;
1043 spin_unlock_irqrestore(&r
->lock
, flags
);
1045 now
= ktime_get_real();
1046 mix_pool_bytes(r
, &now
, sizeof(now
));
1047 for (i
= r
->poolinfo
->POOLBYTES
; i
> 0; i
-= sizeof flags
) {
1048 if (!arch_get_random_long(&flags
))
1050 mix_pool_bytes(r
, &flags
, sizeof(flags
));
1052 mix_pool_bytes(r
, utsname(), sizeof(*(utsname())));
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
);
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 extern ctl_table random_table
[];
1352 ctl_table random_table
[] = {
1354 .procname
= "poolsize",
1355 .data
= &sysctl_poolsize
,
1356 .maxlen
= sizeof(int),
1358 .proc_handler
= proc_dointvec
,
1361 .procname
= "entropy_avail",
1362 .maxlen
= sizeof(int),
1364 .proc_handler
= proc_dointvec
,
1365 .data
= &input_pool
.entropy_count
,
1368 .procname
= "read_wakeup_threshold",
1369 .data
= &random_read_wakeup_thresh
,
1370 .maxlen
= sizeof(int),
1372 .proc_handler
= proc_dointvec_minmax
,
1373 .extra1
= &min_read_thresh
,
1374 .extra2
= &max_read_thresh
,
1377 .procname
= "write_wakeup_threshold",
1378 .data
= &random_write_wakeup_thresh
,
1379 .maxlen
= sizeof(int),
1381 .proc_handler
= proc_dointvec_minmax
,
1382 .extra1
= &min_write_thresh
,
1383 .extra2
= &max_write_thresh
,
1386 .procname
= "boot_id",
1387 .data
= &sysctl_bootid
,
1390 .proc_handler
= proc_do_uuid
,
1396 .proc_handler
= proc_do_uuid
,
1400 #endif /* CONFIG_SYSCTL */
1402 static u32 random_int_secret
[MD5_MESSAGE_BYTES
/ 4] ____cacheline_aligned
;
1404 static int __init
random_int_secret_init(void)
1406 get_random_bytes(random_int_secret
, sizeof(random_int_secret
));
1409 late_initcall(random_int_secret_init
);
1412 * Get a random word for internal kernel use only. Similar to urandom but
1413 * with the goal of minimal entropy pool depletion. As a result, the random
1414 * value is not cryptographically secure but for several uses the cost of
1415 * depleting entropy is too high
1417 static DEFINE_PER_CPU(__u32
[MD5_DIGEST_WORDS
], get_random_int_hash
);
1418 unsigned int get_random_int(void)
1423 if (arch_get_random_int(&ret
))
1426 hash
= get_cpu_var(get_random_int_hash
);
1428 hash
[0] += current
->pid
+ jiffies
+ get_cycles();
1429 md5_transform(hash
, random_int_secret
);
1431 put_cpu_var(get_random_int_hash
);
1437 * randomize_range() returns a start address such that
1439 * [...... <range> .....]
1442 * a <range> with size "len" starting at the return value is inside in the
1443 * area defined by [start, end], but is otherwise randomized.
1446 randomize_range(unsigned long start
, unsigned long end
, unsigned long len
)
1448 unsigned long range
= end
- len
- start
;
1450 if (end
<= start
+ len
)
1452 return PAGE_ALIGN(get_random_int() % range
+ start
);