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Linux/drivers/char/random.c

  1 /*
  2  * random.c -- A strong random number generator
  3  *
  4  * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
  5  *
  6  * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999.  All
  7  * rights reserved.
  8  *
  9  * Redistribution and use in source and binary forms, with or without
 10  * modification, are permitted provided that the following conditions
 11  * are met:
 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
 20  *    written permission.
 21  *
 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.)
 27  *
 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
 39  * DAMAGE.
 40  */
 41 
 42 /*
 43  * (now, with legal B.S. out of the way.....)
 44  *
 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.
 51  *
 52  * Theory of operation
 53  * ===================
 54  *
 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.
 65  *
 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.
 77  *
 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.
 89  *
 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
 96  * of purposes.
 97  *
 98  * Exported interfaces ---- output
 99  * ===============================
100  *
101  * There are three exported interfaces; the first is one designed to
102  * be used from within the kernel:
103  *
104  *      void get_random_bytes(void *buf, int nbytes);
105  *
106  * This interface will return the requested number of random bytes,
107  * and place it in the requested buffer.
108  *
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.
115  *
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.
121  *
122  * Exported interfaces ---- input
123  * ==============================
124  *
125  * The current exported interfaces for gathering environmental noise
126  * from the devices are:
127  *
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);
133  *
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).
141  *
142  * add_input_randomness() uses the input layer interrupt timing, as well as
143  * the event type information from the hardware.
144  *
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.
148  *
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.
154  *
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.
158  *
159  * Ensuring unpredictability at system startup
160  * ============================================
161  *
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
170  * sequence:
171  *
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
178  *      else
179  *              touch $random_seed
180  *      fi
181  *      chmod 600 $random_seed
182  *      dd if=/dev/urandom of=$random_seed count=1 bs=512
183  *
184  * and the following lines in an appropriate script which is run as
185  * the system is shutdown:
186  *
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
191  *      touch $random_seed
192  *      chmod 600 $random_seed
193  *      dd if=/dev/urandom of=$random_seed count=1 bs=512
194  *
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.
199  *
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
207  * the system.
208  *
209  * Configuring the /dev/random driver under Linux
210  * ==============================================
211  *
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:
216  *
217  *      mknod /dev/random c 1 8
218  *      mknod /dev/urandom c 1 9
219  *
220  * Acknowledgements:
221  * =================
222  *
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.
229  *
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.
232  *
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.
236  */
237 
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/workqueue.h>
259 #include <linux/irq.h>
260 
261 #include <asm/processor.h>
262 #include <asm/uaccess.h>
263 #include <asm/irq.h>
264 #include <asm/irq_regs.h>
265 #include <asm/io.h>
266 
267 #define CREATE_TRACE_POINTS
268 #include <trace/events/random.h>
269 
270 /*
271  * Configuration information
272  */
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
279 
280 #define DEBUG_RANDOM_BOOT 0
281 
282 #define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))
283 
284 /*
285  * To allow fractional bits to be tracked, the entropy_count field is
286  * denominated in units of 1/8th bits.
287  *
288  * 2*(ENTROPY_SHIFT + log2(poolbits)) must <= 31, or the multiply in
289  * credit_entropy_bits() needs to be 64 bits wide.
290  */
291 #define ENTROPY_SHIFT 3
292 #define ENTROPY_BITS(r) ((r)->entropy_count >> ENTROPY_SHIFT)
293 
294 /*
295  * The minimum number of bits of entropy before we wake up a read on
296  * /dev/random.  Should be enough to do a significant reseed.
297  */
298 static int random_read_wakeup_bits = 64;
299 
300 /*
301  * If the entropy count falls under this number of bits, then we
302  * should wake up processes which are selecting or polling on write
303  * access to /dev/random.
304  */
305 static int random_write_wakeup_bits = 28 * OUTPUT_POOL_WORDS;
306 
307 /*
308  * The minimum number of seconds between urandom pool reseeding.  We
309  * do this to limit the amount of entropy that can be drained from the
310  * input pool even if there are heavy demands on /dev/urandom.
311  */
312 static int random_min_urandom_seed = 60;
313 
314 /*
315  * Originally, we used a primitive polynomial of degree .poolwords
316  * over GF(2).  The taps for various sizes are defined below.  They
317  * were chosen to be evenly spaced except for the last tap, which is 1
318  * to get the twisting happening as fast as possible.
319  *
320  * For the purposes of better mixing, we use the CRC-32 polynomial as
321  * well to make a (modified) twisted Generalized Feedback Shift
322  * Register.  (See M. Matsumoto & Y. Kurita, 1992.  Twisted GFSR
323  * generators.  ACM Transactions on Modeling and Computer Simulation
324  * 2(3):179-194.  Also see M. Matsumoto & Y. Kurita, 1994.  Twisted
325  * GFSR generators II.  ACM Transactions on Modeling and Computer
326  * Simulation 4:254-266)
327  *
328  * Thanks to Colin Plumb for suggesting this.
329  *
330  * The mixing operation is much less sensitive than the output hash,
331  * where we use SHA-1.  All that we want of mixing operation is that
332  * it be a good non-cryptographic hash; i.e. it not produce collisions
333  * when fed "random" data of the sort we expect to see.  As long as
334  * the pool state differs for different inputs, we have preserved the
335  * input entropy and done a good job.  The fact that an intelligent
336  * attacker can construct inputs that will produce controlled
337  * alterations to the pool's state is not important because we don't
338  * consider such inputs to contribute any randomness.  The only
339  * property we need with respect to them is that the attacker can't
340  * increase his/her knowledge of the pool's state.  Since all
341  * additions are reversible (knowing the final state and the input,
342  * you can reconstruct the initial state), if an attacker has any
343  * uncertainty about the initial state, he/she can only shuffle that
344  * uncertainty about, but never cause any collisions (which would
345  * decrease the uncertainty).
346  *
347  * Our mixing functions were analyzed by Lacharme, Roeck, Strubel, and
348  * Videau in their paper, "The Linux Pseudorandom Number Generator
349  * Revisited" (see: http://eprint.iacr.org/2012/251.pdf).  In their
350  * paper, they point out that we are not using a true Twisted GFSR,
351  * since Matsumoto & Kurita used a trinomial feedback polynomial (that
352  * is, with only three taps, instead of the six that we are using).
353  * As a result, the resulting polynomial is neither primitive nor
354  * irreducible, and hence does not have a maximal period over
355  * GF(2**32).  They suggest a slight change to the generator
356  * polynomial which improves the resulting TGFSR polynomial to be
357  * irreducible, which we have made here.
358  */
359 static struct poolinfo {
360         int poolbitshift, poolwords, poolbytes, poolbits, poolfracbits;
361 #define S(x) ilog2(x)+5, (x), (x)*4, (x)*32, (x) << (ENTROPY_SHIFT+5)
362         int tap1, tap2, tap3, tap4, tap5;
363 } poolinfo_table[] = {
364         /* was: x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 */
365         /* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */
366         { S(128),       104,    76,     51,     25,     1 },
367         /* was: x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 */
368         /* x^32 + x^26 + x^19 + x^14 + x^7 + x + 1 */
369         { S(32),        26,     19,     14,     7,      1 },
370 #if 0
371         /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1  -- 115 */
372         { S(2048),      1638,   1231,   819,    411,    1 },
373 
374         /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
375         { S(1024),      817,    615,    412,    204,    1 },
376 
377         /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
378         { S(1024),      819,    616,    410,    207,    2 },
379 
380         /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
381         { S(512),       411,    308,    208,    104,    1 },
382 
383         /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
384         { S(512),       409,    307,    206,    102,    2 },
385         /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
386         { S(512),       409,    309,    205,    103,    2 },
387 
388         /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
389         { S(256),       205,    155,    101,    52,     1 },
390 
391         /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
392         { S(128),       103,    78,     51,     27,     2 },
393 
394         /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
395         { S(64),        52,     39,     26,     14,     1 },
396 #endif
397 };
398 
399 /*
400  * Static global variables
401  */
402 static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
403 static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
404 static struct fasync_struct *fasync;
405 
406 /**********************************************************************
407  *
408  * OS independent entropy store.   Here are the functions which handle
409  * storing entropy in an entropy pool.
410  *
411  **********************************************************************/
412 
413 struct entropy_store;
414 struct entropy_store {
415         /* read-only data: */
416         const struct poolinfo *poolinfo;
417         __u32 *pool;
418         const char *name;
419         struct entropy_store *pull;
420         struct work_struct push_work;
421 
422         /* read-write data: */
423         unsigned long last_pulled;
424         spinlock_t lock;
425         unsigned short add_ptr;
426         unsigned short input_rotate;
427         int entropy_count;
428         int entropy_total;
429         unsigned int initialized:1;
430         unsigned int limit:1;
431         unsigned int last_data_init:1;
432         __u8 last_data[EXTRACT_SIZE];
433 };
434 
435 static void push_to_pool(struct work_struct *work);
436 static __u32 input_pool_data[INPUT_POOL_WORDS];
437 static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
438 static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
439 
440 static struct entropy_store input_pool = {
441         .poolinfo = &poolinfo_table[0],
442         .name = "input",
443         .limit = 1,
444         .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
445         .pool = input_pool_data
446 };
447 
448 static struct entropy_store blocking_pool = {
449         .poolinfo = &poolinfo_table[1],
450         .name = "blocking",
451         .limit = 1,
452         .pull = &input_pool,
453         .lock = __SPIN_LOCK_UNLOCKED(blocking_pool.lock),
454         .pool = blocking_pool_data,
455         .push_work = __WORK_INITIALIZER(blocking_pool.push_work,
456                                         push_to_pool),
457 };
458 
459 static struct entropy_store nonblocking_pool = {
460         .poolinfo = &poolinfo_table[1],
461         .name = "nonblocking",
462         .pull = &input_pool,
463         .lock = __SPIN_LOCK_UNLOCKED(nonblocking_pool.lock),
464         .pool = nonblocking_pool_data,
465         .push_work = __WORK_INITIALIZER(nonblocking_pool.push_work,
466                                         push_to_pool),
467 };
468 
469 static __u32 const twist_table[8] = {
470         0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
471         0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
472 
473 /*
474  * This function adds bytes into the entropy "pool".  It does not
475  * update the entropy estimate.  The caller should call
476  * credit_entropy_bits if this is appropriate.
477  *
478  * The pool is stirred with a primitive polynomial of the appropriate
479  * degree, and then twisted.  We twist by three bits at a time because
480  * it's cheap to do so and helps slightly in the expected case where
481  * the entropy is concentrated in the low-order bits.
482  */
483 static void _mix_pool_bytes(struct entropy_store *r, const void *in,
484                             int nbytes, __u8 out[64])
485 {
486         unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
487         int input_rotate;
488         int wordmask = r->poolinfo->poolwords - 1;
489         const char *bytes = in;
490         __u32 w;
491 
492         tap1 = r->poolinfo->tap1;
493         tap2 = r->poolinfo->tap2;
494         tap3 = r->poolinfo->tap3;
495         tap4 = r->poolinfo->tap4;
496         tap5 = r->poolinfo->tap5;
497 
498         smp_rmb();
499         input_rotate = ACCESS_ONCE(r->input_rotate);
500         i = ACCESS_ONCE(r->add_ptr);
501 
502         /* mix one byte at a time to simplify size handling and churn faster */
503         while (nbytes--) {
504                 w = rol32(*bytes++, input_rotate);
505                 i = (i - 1) & wordmask;
506 
507                 /* XOR in the various taps */
508                 w ^= r->pool[i];
509                 w ^= r->pool[(i + tap1) & wordmask];
510                 w ^= r->pool[(i + tap2) & wordmask];
511                 w ^= r->pool[(i + tap3) & wordmask];
512                 w ^= r->pool[(i + tap4) & wordmask];
513                 w ^= r->pool[(i + tap5) & wordmask];
514 
515                 /* Mix the result back in with a twist */
516                 r->pool[i] = (w >> 3) ^ twist_table[w & 7];
517 
518                 /*
519                  * Normally, we add 7 bits of rotation to the pool.
520                  * At the beginning of the pool, add an extra 7 bits
521                  * rotation, so that successive passes spread the
522                  * input bits across the pool evenly.
523                  */
524                 input_rotate = (input_rotate + (i ? 7 : 14)) & 31;
525         }
526 
527         ACCESS_ONCE(r->input_rotate) = input_rotate;
528         ACCESS_ONCE(r->add_ptr) = i;
529         smp_wmb();
530 
531         if (out)
532                 for (j = 0; j < 16; j++)
533                         ((__u32 *)out)[j] = r->pool[(i - j) & wordmask];
534 }
535 
536 static void __mix_pool_bytes(struct entropy_store *r, const void *in,
537                              int nbytes, __u8 out[64])
538 {
539         trace_mix_pool_bytes_nolock(r->name, nbytes, _RET_IP_);
540         _mix_pool_bytes(r, in, nbytes, out);
541 }
542 
543 static void mix_pool_bytes(struct entropy_store *r, const void *in,
544                            int nbytes, __u8 out[64])
545 {
546         unsigned long flags;
547 
548         trace_mix_pool_bytes(r->name, nbytes, _RET_IP_);
549         spin_lock_irqsave(&r->lock, flags);
550         _mix_pool_bytes(r, in, nbytes, out);
551         spin_unlock_irqrestore(&r->lock, flags);
552 }
553 
554 struct fast_pool {
555         __u32           pool[4];
556         unsigned long   last;
557         unsigned short  count;
558         unsigned char   rotate;
559         unsigned char   last_timer_intr;
560 };
561 
562 /*
563  * This is a fast mixing routine used by the interrupt randomness
564  * collector.  It's hardcoded for an 128 bit pool and assumes that any
565  * locks that might be needed are taken by the caller.
566  */
567 static void fast_mix(struct fast_pool *f, __u32 input[4])
568 {
569         __u32           w;
570         unsigned        input_rotate = f->rotate;
571 
572         w = rol32(input[0], input_rotate) ^ f->pool[0] ^ f->pool[3];
573         f->pool[0] = (w >> 3) ^ twist_table[w & 7];
574         input_rotate = (input_rotate + 14) & 31;
575         w = rol32(input[1], input_rotate) ^ f->pool[1] ^ f->pool[0];
576         f->pool[1] = (w >> 3) ^ twist_table[w & 7];
577         input_rotate = (input_rotate + 7) & 31;
578         w = rol32(input[2], input_rotate) ^ f->pool[2] ^ f->pool[1];
579         f->pool[2] = (w >> 3) ^ twist_table[w & 7];
580         input_rotate = (input_rotate + 7) & 31;
581         w = rol32(input[3], input_rotate) ^ f->pool[3] ^ f->pool[2];
582         f->pool[3] = (w >> 3) ^ twist_table[w & 7];
583         input_rotate = (input_rotate + 7) & 31;
584 
585         f->rotate = input_rotate;
586         f->count++;
587 }
588 
589 /*
590  * Credit (or debit) the entropy store with n bits of entropy.
591  * Use credit_entropy_bits_safe() if the value comes from userspace
592  * or otherwise should be checked for extreme values.
593  */
594 static void credit_entropy_bits(struct entropy_store *r, int nbits)
595 {
596         int entropy_count, orig;
597         const int pool_size = r->poolinfo->poolfracbits;
598         int nfrac = nbits << ENTROPY_SHIFT;
599 
600         if (!nbits)
601                 return;
602 
603 retry:
604         entropy_count = orig = ACCESS_ONCE(r->entropy_count);
605         if (nfrac < 0) {
606                 /* Debit */
607                 entropy_count += nfrac;
608         } else {
609                 /*
610                  * Credit: we have to account for the possibility of
611                  * overwriting already present entropy.  Even in the
612                  * ideal case of pure Shannon entropy, new contributions
613                  * approach the full value asymptotically:
614                  *
615                  * entropy <- entropy + (pool_size - entropy) *
616                  *      (1 - exp(-add_entropy/pool_size))
617                  *
618                  * For add_entropy <= pool_size/2 then
619                  * (1 - exp(-add_entropy/pool_size)) >=
620                  *    (add_entropy/pool_size)*0.7869...
621                  * so we can approximate the exponential with
622                  * 3/4*add_entropy/pool_size and still be on the
623                  * safe side by adding at most pool_size/2 at a time.
624                  *
625                  * The use of pool_size-2 in the while statement is to
626                  * prevent rounding artifacts from making the loop
627                  * arbitrarily long; this limits the loop to log2(pool_size)*2
628                  * turns no matter how large nbits is.
629                  */
630                 int pnfrac = nfrac;
631                 const int s = r->poolinfo->poolbitshift + ENTROPY_SHIFT + 2;
632                 /* The +2 corresponds to the /4 in the denominator */
633 
634                 do {
635                         unsigned int anfrac = min(pnfrac, pool_size/2);
636                         unsigned int add =
637                                 ((pool_size - entropy_count)*anfrac*3) >> s;
638 
639                         entropy_count += add;
640                         pnfrac -= anfrac;
641                 } while (unlikely(entropy_count < pool_size-2 && pnfrac));
642         }
643 
644         if (unlikely(entropy_count < 0)) {
645                 pr_warn("random: negative entropy/overflow: pool %s count %d\n",
646                         r->name, entropy_count);
647                 WARN_ON(1);
648                 entropy_count = 0;
649         } else if (entropy_count > pool_size)
650                 entropy_count = pool_size;
651         if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
652                 goto retry;
653 
654         r->entropy_total += nbits;
655         if (!r->initialized && r->entropy_total > 128) {
656                 r->initialized = 1;
657                 r->entropy_total = 0;
658                 if (r == &nonblocking_pool) {
659                         prandom_reseed_late();
660                         pr_notice("random: %s pool is initialized\n", r->name);
661                 }
662         }
663 
664         trace_credit_entropy_bits(r->name, nbits,
665                                   entropy_count >> ENTROPY_SHIFT,
666                                   r->entropy_total, _RET_IP_);
667 
668         if (r == &input_pool) {
669                 int entropy_bits = entropy_count >> ENTROPY_SHIFT;
670 
671                 /* should we wake readers? */
672                 if (entropy_bits >= random_read_wakeup_bits) {
673                         wake_up_interruptible(&random_read_wait);
674                         kill_fasync(&fasync, SIGIO, POLL_IN);
675                 }
676                 /* If the input pool is getting full, send some
677                  * entropy to the two output pools, flipping back and
678                  * forth between them, until the output pools are 75%
679                  * full.
680                  */
681                 if (entropy_bits > random_write_wakeup_bits &&
682                     r->initialized &&
683                     r->entropy_total >= 2*random_read_wakeup_bits) {
684                         static struct entropy_store *last = &blocking_pool;
685                         struct entropy_store *other = &blocking_pool;
686 
687                         if (last == &blocking_pool)
688                                 other = &nonblocking_pool;
689                         if (other->entropy_count <=
690                             3 * other->poolinfo->poolfracbits / 4)
691                                 last = other;
692                         if (last->entropy_count <=
693                             3 * last->poolinfo->poolfracbits / 4) {
694                                 schedule_work(&last->push_work);
695                                 r->entropy_total = 0;
696                         }
697                 }
698         }
699 }
700 
701 static void credit_entropy_bits_safe(struct entropy_store *r, int nbits)
702 {
703         const int nbits_max = (int)(~0U >> (ENTROPY_SHIFT + 1));
704 
705         /* Cap the value to avoid overflows */
706         nbits = min(nbits,  nbits_max);
707         nbits = max(nbits, -nbits_max);
708 
709         credit_entropy_bits(r, nbits);
710 }
711 
712 /*********************************************************************
713  *
714  * Entropy input management
715  *
716  *********************************************************************/
717 
718 /* There is one of these per entropy source */
719 struct timer_rand_state {
720         cycles_t last_time;
721         long last_delta, last_delta2;
722         unsigned dont_count_entropy:1;
723 };
724 
725 #define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, };
726 
727 /*
728  * Add device- or boot-specific data to the input and nonblocking
729  * pools to help initialize them to unique values.
730  *
731  * None of this adds any entropy, it is meant to avoid the
732  * problem of the nonblocking pool having similar initial state
733  * across largely identical devices.
734  */
735 void add_device_randomness(const void *buf, unsigned int size)
736 {
737         unsigned long time = random_get_entropy() ^ jiffies;
738         unsigned long flags;
739 
740         trace_add_device_randomness(size, _RET_IP_);
741         spin_lock_irqsave(&input_pool.lock, flags);
742         _mix_pool_bytes(&input_pool, buf, size, NULL);
743         _mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
744         spin_unlock_irqrestore(&input_pool.lock, flags);
745 
746         spin_lock_irqsave(&nonblocking_pool.lock, flags);
747         _mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
748         _mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
749         spin_unlock_irqrestore(&nonblocking_pool.lock, flags);
750 }
751 EXPORT_SYMBOL(add_device_randomness);
752 
753 static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE;
754 
755 /*
756  * This function adds entropy to the entropy "pool" by using timing
757  * delays.  It uses the timer_rand_state structure to make an estimate
758  * of how many bits of entropy this call has added to the pool.
759  *
760  * The number "num" is also added to the pool - it should somehow describe
761  * the type of event which just happened.  This is currently 0-255 for
762  * keyboard scan codes, and 256 upwards for interrupts.
763  *
764  */
765 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
766 {
767         struct entropy_store    *r;
768         struct {
769                 long jiffies;
770                 unsigned cycles;
771                 unsigned num;
772         } sample;
773         long delta, delta2, delta3;
774 
775         preempt_disable();
776 
777         sample.jiffies = jiffies;
778         sample.cycles = random_get_entropy();
779         sample.num = num;
780         r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
781         mix_pool_bytes(r, &sample, sizeof(sample), NULL);
782 
783         /*
784          * Calculate number of bits of randomness we probably added.
785          * We take into account the first, second and third-order deltas
786          * in order to make our estimate.
787          */
788 
789         if (!state->dont_count_entropy) {
790                 delta = sample.jiffies - state->last_time;
791                 state->last_time = sample.jiffies;
792 
793                 delta2 = delta - state->last_delta;
794                 state->last_delta = delta;
795 
796                 delta3 = delta2 - state->last_delta2;
797                 state->last_delta2 = delta2;
798 
799                 if (delta < 0)
800                         delta = -delta;
801                 if (delta2 < 0)
802                         delta2 = -delta2;
803                 if (delta3 < 0)
804                         delta3 = -delta3;
805                 if (delta > delta2)
806                         delta = delta2;
807                 if (delta > delta3)
808                         delta = delta3;
809 
810                 /*
811                  * delta is now minimum absolute delta.
812                  * Round down by 1 bit on general principles,
813                  * and limit entropy entimate to 12 bits.
814                  */
815                 credit_entropy_bits(r, min_t(int, fls(delta>>1), 11));
816         }
817         preempt_enable();
818 }
819 
820 void add_input_randomness(unsigned int type, unsigned int code,
821                                  unsigned int value)
822 {
823         static unsigned char last_value;
824 
825         /* ignore autorepeat and the like */
826         if (value == last_value)
827                 return;
828 
829         last_value = value;
830         add_timer_randomness(&input_timer_state,
831                              (type << 4) ^ code ^ (code >> 4) ^ value);
832         trace_add_input_randomness(ENTROPY_BITS(&input_pool));
833 }
834 EXPORT_SYMBOL_GPL(add_input_randomness);
835 
836 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
837 
838 void add_interrupt_randomness(int irq, int irq_flags)
839 {
840         struct entropy_store    *r;
841         struct fast_pool        *fast_pool = &__get_cpu_var(irq_randomness);
842         struct pt_regs          *regs = get_irq_regs();
843         unsigned long           now = jiffies;
844         cycles_t                cycles = random_get_entropy();
845         __u32                   input[4], c_high, j_high;
846         __u64                   ip;
847         unsigned long           seed;
848         int                     credit;
849 
850         c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;
851         j_high = (sizeof(now) > 4) ? now >> 32 : 0;
852         input[0] = cycles ^ j_high ^ irq;
853         input[1] = now ^ c_high;
854         ip = regs ? instruction_pointer(regs) : _RET_IP_;
855         input[2] = ip;
856         input[3] = ip >> 32;
857 
858         fast_mix(fast_pool, input);
859 
860         if ((fast_pool->count & 63) && !time_after(now, fast_pool->last + HZ))
861                 return;
862 
863         fast_pool->last = now;
864 
865         r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
866         __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
867 
868         /*
869          * If we don't have a valid cycle counter, and we see
870          * back-to-back timer interrupts, then skip giving credit for
871          * any entropy, otherwise credit 1 bit.
872          */
873         credit = 1;
874         if (cycles == 0) {
875                 if (irq_flags & __IRQF_TIMER) {
876                         if (fast_pool->last_timer_intr)
877                                 credit = 0;
878                         fast_pool->last_timer_intr = 1;
879                 } else
880                         fast_pool->last_timer_intr = 0;
881         }
882 
883         /*
884          * If we have architectural seed generator, produce a seed and
885          * add it to the pool.  For the sake of paranoia count it as
886          * 50% entropic.
887          */
888         if (arch_get_random_seed_long(&seed)) {
889                 __mix_pool_bytes(r, &seed, sizeof(seed), NULL);
890                 credit += sizeof(seed) * 4;
891         }
892 
893         credit_entropy_bits(r, credit);
894 }
895 
896 #ifdef CONFIG_BLOCK
897 void add_disk_randomness(struct gendisk *disk)
898 {
899         if (!disk || !disk->random)
900                 return;
901         /* first major is 1, so we get >= 0x200 here */
902         add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
903         trace_add_disk_randomness(disk_devt(disk), ENTROPY_BITS(&input_pool));
904 }
905 EXPORT_SYMBOL_GPL(add_disk_randomness);
906 #endif
907 
908 /*********************************************************************
909  *
910  * Entropy extraction routines
911  *
912  *********************************************************************/
913 
914 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
915                                size_t nbytes, int min, int rsvd);
916 
917 /*
918  * This utility inline function is responsible for transferring entropy
919  * from the primary pool to the secondary extraction pool. We make
920  * sure we pull enough for a 'catastrophic reseed'.
921  */
922 static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes);
923 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
924 {
925         if (r->limit == 0 && random_min_urandom_seed) {
926                 unsigned long now = jiffies;
927 
928                 if (time_before(now,
929                                 r->last_pulled + random_min_urandom_seed * HZ))
930                         return;
931                 r->last_pulled = now;
932         }
933         if (r->pull &&
934             r->entropy_count < (nbytes << (ENTROPY_SHIFT + 3)) &&
935             r->entropy_count < r->poolinfo->poolfracbits)
936                 _xfer_secondary_pool(r, nbytes);
937 }
938 
939 static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
940 {
941         __u32   tmp[OUTPUT_POOL_WORDS];
942 
943         /* For /dev/random's pool, always leave two wakeups' worth */
944         int rsvd_bytes = r->limit ? 0 : random_read_wakeup_bits / 4;
945         int bytes = nbytes;
946 
947         /* pull at least as much as a wakeup */
948         bytes = max_t(int, bytes, random_read_wakeup_bits / 8);
949         /* but never more than the buffer size */
950         bytes = min_t(int, bytes, sizeof(tmp));
951 
952         trace_xfer_secondary_pool(r->name, bytes * 8, nbytes * 8,
953                                   ENTROPY_BITS(r), ENTROPY_BITS(r->pull));
954         bytes = extract_entropy(r->pull, tmp, bytes,
955                                 random_read_wakeup_bits / 8, rsvd_bytes);
956         mix_pool_bytes(r, tmp, bytes, NULL);
957         credit_entropy_bits(r, bytes*8);
958 }
959 
960 /*
961  * Used as a workqueue function so that when the input pool is getting
962  * full, we can "spill over" some entropy to the output pools.  That
963  * way the output pools can store some of the excess entropy instead
964  * of letting it go to waste.
965  */
966 static void push_to_pool(struct work_struct *work)
967 {
968         struct entropy_store *r = container_of(work, struct entropy_store,
969                                               push_work);
970         BUG_ON(!r);
971         _xfer_secondary_pool(r, random_read_wakeup_bits/8);
972         trace_push_to_pool(r->name, r->entropy_count >> ENTROPY_SHIFT,
973                            r->pull->entropy_count >> ENTROPY_SHIFT);
974 }
975 
976 /*
977  * This function decides how many bytes to actually take from the
978  * given pool, and also debits the entropy count accordingly.
979  */
980 static size_t account(struct entropy_store *r, size_t nbytes, int min,
981                       int reserved)
982 {
983         int entropy_count, orig;
984         size_t ibytes, nfrac;
985 
986         BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
987 
988         /* Can we pull enough? */
989 retry:
990         entropy_count = orig = ACCESS_ONCE(r->entropy_count);
991         ibytes = nbytes;
992         /* If limited, never pull more than available */
993         if (r->limit) {
994                 int have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);
995 
996                 if ((have_bytes -= reserved) < 0)
997                         have_bytes = 0;
998                 ibytes = min_t(size_t, ibytes, have_bytes);
999         }
1000         if (ibytes < min)
1001                 ibytes = 0;
1002 
1003         if (unlikely(entropy_count < 0)) {
1004                 pr_warn("random: negative entropy count: pool %s count %d\n",
1005                         r->name, entropy_count);
1006                 WARN_ON(1);
1007                 entropy_count = 0;
1008         }
1009         nfrac = ibytes << (ENTROPY_SHIFT + 3);
1010         if ((size_t) entropy_count > nfrac)
1011                 entropy_count -= nfrac;
1012         else
1013                 entropy_count = 0;
1014 
1015         if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
1016                 goto retry;
1017 
1018         trace_debit_entropy(r->name, 8 * ibytes);
1019         if (ibytes &&
1020             (r->entropy_count >> ENTROPY_SHIFT) < random_write_wakeup_bits) {
1021                 wake_up_interruptible(&random_write_wait);
1022                 kill_fasync(&fasync, SIGIO, POLL_OUT);
1023         }
1024 
1025         return ibytes;
1026 }
1027 
1028 /*
1029  * This function does the actual extraction for extract_entropy and
1030  * extract_entropy_user.
1031  *
1032  * Note: we assume that .poolwords is a multiple of 16 words.
1033  */
1034 static void extract_buf(struct entropy_store *r, __u8 *out)
1035 {
1036         int i;
1037         union {
1038                 __u32 w[5];
1039                 unsigned long l[LONGS(20)];
1040         } hash;
1041         __u32 workspace[SHA_WORKSPACE_WORDS];
1042         __u8 extract[64];
1043         unsigned long flags;
1044 
1045         /*
1046          * If we have an architectural hardware random number
1047          * generator, use it for SHA's initial vector
1048          */
1049         sha_init(hash.w);
1050         for (i = 0; i < LONGS(20); i++) {
1051                 unsigned long v;
1052                 if (!arch_get_random_long(&v))
1053                         break;
1054                 hash.l[i] = v;
1055         }
1056 
1057         /* Generate a hash across the pool, 16 words (512 bits) at a time */
1058         spin_lock_irqsave(&r->lock, flags);
1059         for (i = 0; i < r->poolinfo->poolwords; i += 16)
1060                 sha_transform(hash.w, (__u8 *)(r->pool + i), workspace);
1061 
1062         /*
1063          * We mix the hash back into the pool to prevent backtracking
1064          * attacks (where the attacker knows the state of the pool
1065          * plus the current outputs, and attempts to find previous
1066          * ouputs), unless the hash function can be inverted. By
1067          * mixing at least a SHA1 worth of hash data back, we make
1068          * brute-forcing the feedback as hard as brute-forcing the
1069          * hash.
1070          */
1071         __mix_pool_bytes(r, hash.w, sizeof(hash.w), extract);
1072         spin_unlock_irqrestore(&r->lock, flags);
1073 
1074         /*
1075          * To avoid duplicates, we atomically extract a portion of the
1076          * pool while mixing, and hash one final time.
1077          */
1078         sha_transform(hash.w, extract, workspace);
1079         memset(extract, 0, sizeof(extract));
1080         memset(workspace, 0, sizeof(workspace));
1081 
1082         /*
1083          * In case the hash function has some recognizable output
1084          * pattern, we fold it in half. Thus, we always feed back
1085          * twice as much data as we output.
1086          */
1087         hash.w[0] ^= hash.w[3];
1088         hash.w[1] ^= hash.w[4];
1089         hash.w[2] ^= rol32(hash.w[2], 16);
1090 
1091         memcpy(out, &hash, EXTRACT_SIZE);
1092         memset(&hash, 0, sizeof(hash));
1093 }
1094 
1095 /*
1096  * This function extracts randomness from the "entropy pool", and
1097  * returns it in a buffer.
1098  *
1099  * The min parameter specifies the minimum amount we can pull before
1100  * failing to avoid races that defeat catastrophic reseeding while the
1101  * reserved parameter indicates how much entropy we must leave in the
1102  * pool after each pull to avoid starving other readers.
1103  */
1104 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
1105                                  size_t nbytes, int min, int reserved)
1106 {
1107         ssize_t ret = 0, i;
1108         __u8 tmp[EXTRACT_SIZE];
1109         unsigned long flags;
1110 
1111         /* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */
1112         if (fips_enabled) {
1113                 spin_lock_irqsave(&r->lock, flags);
1114                 if (!r->last_data_init) {
1115                         r->last_data_init = 1;
1116                         spin_unlock_irqrestore(&r->lock, flags);
1117                         trace_extract_entropy(r->name, EXTRACT_SIZE,
1118                                               ENTROPY_BITS(r), _RET_IP_);
1119                         xfer_secondary_pool(r, EXTRACT_SIZE);
1120                         extract_buf(r, tmp);
1121                         spin_lock_irqsave(&r->lock, flags);
1122                         memcpy(r->last_data, tmp, EXTRACT_SIZE);
1123                 }
1124                 spin_unlock_irqrestore(&r->lock, flags);
1125         }
1126 
1127         trace_extract_entropy(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
1128         xfer_secondary_pool(r, nbytes);
1129         nbytes = account(r, nbytes, min, reserved);
1130 
1131         while (nbytes) {
1132                 extract_buf(r, tmp);
1133 
1134                 if (fips_enabled) {
1135                         spin_lock_irqsave(&r->lock, flags);
1136                         if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
1137                                 panic("Hardware RNG duplicated output!\n");
1138                         memcpy(r->last_data, tmp, EXTRACT_SIZE);
1139                         spin_unlock_irqrestore(&r->lock, flags);
1140                 }
1141                 i = min_t(int, nbytes, EXTRACT_SIZE);
1142                 memcpy(buf, tmp, i);
1143                 nbytes -= i;
1144                 buf += i;
1145                 ret += i;
1146         }
1147 
1148         /* Wipe data just returned from memory */
1149         memset(tmp, 0, sizeof(tmp));
1150 
1151         return ret;
1152 }
1153 
1154 /*
1155  * This function extracts randomness from the "entropy pool", and
1156  * returns it in a userspace buffer.
1157  */
1158 static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
1159                                     size_t nbytes)
1160 {
1161         ssize_t ret = 0, i;
1162         __u8 tmp[EXTRACT_SIZE];
1163 
1164         trace_extract_entropy_user(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
1165         xfer_secondary_pool(r, nbytes);
1166         nbytes = account(r, nbytes, 0, 0);
1167 
1168         while (nbytes) {
1169                 if (need_resched()) {
1170                         if (signal_pending(current)) {
1171                                 if (ret == 0)
1172                                         ret = -ERESTARTSYS;
1173                                 break;
1174                         }
1175                         schedule();
1176                 }
1177 
1178                 extract_buf(r, tmp);
1179                 i = min_t(int, nbytes, EXTRACT_SIZE);
1180                 if (copy_to_user(buf, tmp, i)) {
1181                         ret = -EFAULT;
1182                         break;
1183                 }
1184 
1185                 nbytes -= i;
1186                 buf += i;
1187                 ret += i;
1188         }
1189 
1190         /* Wipe data just returned from memory */
1191         memset(tmp, 0, sizeof(tmp));
1192 
1193         return ret;
1194 }
1195 
1196 /*
1197  * This function is the exported kernel interface.  It returns some
1198  * number of good random numbers, suitable for key generation, seeding
1199  * TCP sequence numbers, etc.  It does not rely on the hardware random
1200  * number generator.  For random bytes direct from the hardware RNG
1201  * (when available), use get_random_bytes_arch().
1202  */
1203 void get_random_bytes(void *buf, int nbytes)
1204 {
1205 #if DEBUG_RANDOM_BOOT > 0
1206         if (unlikely(nonblocking_pool.initialized == 0))
1207                 printk(KERN_NOTICE "random: %pF get_random_bytes called "
1208                        "with %d bits of entropy available\n",
1209                        (void *) _RET_IP_,
1210                        nonblocking_pool.entropy_total);
1211 #endif
1212         trace_get_random_bytes(nbytes, _RET_IP_);
1213         extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
1214 }
1215 EXPORT_SYMBOL(get_random_bytes);
1216 
1217 /*
1218  * This function will use the architecture-specific hardware random
1219  * number generator if it is available.  The arch-specific hw RNG will
1220  * almost certainly be faster than what we can do in software, but it
1221  * is impossible to verify that it is implemented securely (as
1222  * opposed, to, say, the AES encryption of a sequence number using a
1223  * key known by the NSA).  So it's useful if we need the speed, but
1224  * only if we're willing to trust the hardware manufacturer not to
1225  * have put in a back door.
1226  */
1227 void get_random_bytes_arch(void *buf, int nbytes)
1228 {
1229         char *p = buf;
1230 
1231         trace_get_random_bytes_arch(nbytes, _RET_IP_);
1232         while (nbytes) {
1233                 unsigned long v;
1234                 int chunk = min(nbytes, (int)sizeof(unsigned long));
1235 
1236                 if (!arch_get_random_long(&v))
1237                         break;
1238                 
1239                 memcpy(p, &v, chunk);
1240                 p += chunk;
1241                 nbytes -= chunk;
1242         }
1243 
1244         if (nbytes)
1245                 extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
1246 }
1247 EXPORT_SYMBOL(get_random_bytes_arch);
1248 
1249 
1250 /*
1251  * init_std_data - initialize pool with system data
1252  *
1253  * @r: pool to initialize
1254  *
1255  * This function clears the pool's entropy count and mixes some system
1256  * data into the pool to prepare it for use. The pool is not cleared
1257  * as that can only decrease the entropy in the pool.
1258  */
1259 static void init_std_data(struct entropy_store *r)
1260 {
1261         int i;
1262         ktime_t now = ktime_get_real();
1263         unsigned long rv;
1264 
1265         r->last_pulled = jiffies;
1266         mix_pool_bytes(r, &now, sizeof(now), NULL);
1267         for (i = r->poolinfo->poolbytes; i > 0; i -= sizeof(rv)) {
1268                 if (!arch_get_random_seed_long(&rv) &&
1269                     !arch_get_random_long(&rv))
1270                         rv = random_get_entropy();
1271                 mix_pool_bytes(r, &rv, sizeof(rv), NULL);
1272         }
1273         mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
1274 }
1275 
1276 /*
1277  * Note that setup_arch() may call add_device_randomness()
1278  * long before we get here. This allows seeding of the pools
1279  * with some platform dependent data very early in the boot
1280  * process. But it limits our options here. We must use
1281  * statically allocated structures that already have all
1282  * initializations complete at compile time. We should also
1283  * take care not to overwrite the precious per platform data
1284  * we were given.
1285  */
1286 static int rand_initialize(void)
1287 {
1288         init_std_data(&input_pool);
1289         init_std_data(&blocking_pool);
1290         init_std_data(&nonblocking_pool);
1291         return 0;
1292 }
1293 early_initcall(rand_initialize);
1294 
1295 #ifdef CONFIG_BLOCK
1296 void rand_initialize_disk(struct gendisk *disk)
1297 {
1298         struct timer_rand_state *state;
1299 
1300         /*
1301          * If kzalloc returns null, we just won't use that entropy
1302          * source.
1303          */
1304         state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1305         if (state) {
1306                 state->last_time = INITIAL_JIFFIES;
1307                 disk->random = state;
1308         }
1309 }
1310 #endif
1311 
1312 /*
1313  * Attempt an emergency refill using arch_get_random_seed_long().
1314  *
1315  * As with add_interrupt_randomness() be paranoid and only
1316  * credit the output as 50% entropic.
1317  */
1318 static int arch_random_refill(void)
1319 {
1320         const unsigned int nlongs = 64; /* Arbitrary number */
1321         unsigned int n = 0;
1322         unsigned int i;
1323         unsigned long buf[nlongs];
1324 
1325         if (!arch_has_random_seed())
1326                 return 0;
1327 
1328         for (i = 0; i < nlongs; i++) {
1329                 if (arch_get_random_seed_long(&buf[n]))
1330                         n++;
1331         }
1332 
1333         if (n) {
1334                 unsigned int rand_bytes = n * sizeof(unsigned long);
1335 
1336                 mix_pool_bytes(&input_pool, buf, rand_bytes, NULL);
1337                 credit_entropy_bits(&input_pool, rand_bytes*4);
1338         }
1339 
1340         return n;
1341 }
1342 
1343 static ssize_t
1344 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1345 {
1346         ssize_t n;
1347 
1348         if (nbytes == 0)
1349                 return 0;
1350 
1351         nbytes = min_t(size_t, nbytes, SEC_XFER_SIZE);
1352         while (1) {
1353                 n = extract_entropy_user(&blocking_pool, buf, nbytes);
1354                 if (n < 0)
1355                         return n;
1356                 trace_random_read(n*8, (nbytes-n)*8,
1357                                   ENTROPY_BITS(&blocking_pool),
1358                                   ENTROPY_BITS(&input_pool));
1359                 if (n > 0)
1360                         return n;
1361 
1362                 /* Pool is (near) empty.  Maybe wait and retry. */
1363 
1364                 /* First try an emergency refill */
1365                 if (arch_random_refill())
1366                         continue;
1367 
1368                 if (file->f_flags & O_NONBLOCK)
1369                         return -EAGAIN;
1370 
1371                 wait_event_interruptible(random_read_wait,
1372                         ENTROPY_BITS(&input_pool) >=
1373                         random_read_wakeup_bits);
1374                 if (signal_pending(current))
1375                         return -ERESTARTSYS;
1376         }
1377 }
1378 
1379 static ssize_t
1380 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1381 {
1382         int ret;
1383 
1384         if (unlikely(nonblocking_pool.initialized == 0))
1385                 printk_once(KERN_NOTICE "random: %s urandom read "
1386                             "with %d bits of entropy available\n",
1387                             current->comm, nonblocking_pool.entropy_total);
1388 
1389         nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3));
1390         ret = extract_entropy_user(&nonblocking_pool, buf, nbytes);
1391 
1392         trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool),
1393                            ENTROPY_BITS(&input_pool));
1394         return ret;
1395 }
1396 
1397 static unsigned int
1398 random_poll(struct file *file, poll_table * wait)
1399 {
1400         unsigned int mask;
1401 
1402         poll_wait(file, &random_read_wait, wait);
1403         poll_wait(file, &random_write_wait, wait);
1404         mask = 0;
1405         if (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits)
1406                 mask |= POLLIN | POLLRDNORM;
1407         if (ENTROPY_BITS(&input_pool) < random_write_wakeup_bits)
1408                 mask |= POLLOUT | POLLWRNORM;
1409         return mask;
1410 }
1411 
1412 static int
1413 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1414 {
1415         size_t bytes;
1416         __u32 buf[16];
1417         const char __user *p = buffer;
1418 
1419         while (count > 0) {
1420                 bytes = min(count, sizeof(buf));
1421                 if (copy_from_user(&buf, p, bytes))
1422                         return -EFAULT;
1423 
1424                 count -= bytes;
1425                 p += bytes;
1426 
1427                 mix_pool_bytes(r, buf, bytes, NULL);
1428                 cond_resched();
1429         }
1430 
1431         return 0;
1432 }
1433 
1434 static ssize_t random_write(struct file *file, const char __user *buffer,
1435                             size_t count, loff_t *ppos)
1436 {
1437         size_t ret;
1438 
1439         ret = write_pool(&blocking_pool, buffer, count);
1440         if (ret)
1441                 return ret;
1442         ret = write_pool(&nonblocking_pool, buffer, count);
1443         if (ret)
1444                 return ret;
1445 
1446         return (ssize_t)count;
1447 }
1448 
1449 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1450 {
1451         int size, ent_count;
1452         int __user *p = (int __user *)arg;
1453         int retval;
1454 
1455         switch (cmd) {
1456         case RNDGETENTCNT:
1457                 /* inherently racy, no point locking */
1458                 ent_count = ENTROPY_BITS(&input_pool);
1459                 if (put_user(ent_count, p))
1460                         return -EFAULT;
1461                 return 0;
1462         case RNDADDTOENTCNT:
1463                 if (!capable(CAP_SYS_ADMIN))
1464                         return -EPERM;
1465                 if (get_user(ent_count, p))
1466                         return -EFAULT;
1467                 credit_entropy_bits_safe(&input_pool, ent_count);
1468                 return 0;
1469         case RNDADDENTROPY:
1470                 if (!capable(CAP_SYS_ADMIN))
1471                         return -EPERM;
1472                 if (get_user(ent_count, p++))
1473                         return -EFAULT;
1474                 if (ent_count < 0)
1475                         return -EINVAL;
1476                 if (get_user(size, p++))
1477                         return -EFAULT;
1478                 retval = write_pool(&input_pool, (const char __user *)p,
1479                                     size);
1480                 if (retval < 0)
1481                         return retval;
1482                 credit_entropy_bits_safe(&input_pool, ent_count);
1483                 return 0;
1484         case RNDZAPENTCNT:
1485         case RNDCLEARPOOL:
1486                 /*
1487                  * Clear the entropy pool counters. We no longer clear
1488                  * the entropy pool, as that's silly.
1489                  */
1490                 if (!capable(CAP_SYS_ADMIN))
1491                         return -EPERM;
1492                 input_pool.entropy_count = 0;
1493                 nonblocking_pool.entropy_count = 0;
1494                 blocking_pool.entropy_count = 0;
1495                 return 0;
1496         default:
1497                 return -EINVAL;
1498         }
1499 }
1500 
1501 static int random_fasync(int fd, struct file *filp, int on)
1502 {
1503         return fasync_helper(fd, filp, on, &fasync);
1504 }
1505 
1506 const struct file_operations random_fops = {
1507         .read  = random_read,
1508         .write = random_write,
1509         .poll  = random_poll,
1510         .unlocked_ioctl = random_ioctl,
1511         .fasync = random_fasync,
1512         .llseek = noop_llseek,
1513 };
1514 
1515 const struct file_operations urandom_fops = {
1516         .read  = urandom_read,
1517         .write = random_write,
1518         .unlocked_ioctl = random_ioctl,
1519         .fasync = random_fasync,
1520         .llseek = noop_llseek,
1521 };
1522 
1523 /***************************************************************
1524  * Random UUID interface
1525  *
1526  * Used here for a Boot ID, but can be useful for other kernel
1527  * drivers.
1528  ***************************************************************/
1529 
1530 /*
1531  * Generate random UUID
1532  */
1533 void generate_random_uuid(unsigned char uuid_out[16])
1534 {
1535         get_random_bytes(uuid_out, 16);
1536         /* Set UUID version to 4 --- truly random generation */
1537         uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1538         /* Set the UUID variant to DCE */
1539         uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1540 }
1541 EXPORT_SYMBOL(generate_random_uuid);
1542 
1543 /********************************************************************
1544  *
1545  * Sysctl interface
1546  *
1547  ********************************************************************/
1548 
1549 #ifdef CONFIG_SYSCTL
1550 
1551 #include <linux/sysctl.h>
1552 
1553 static int min_read_thresh = 8, min_write_thresh;
1554 static int max_read_thresh = OUTPUT_POOL_WORDS * 32;
1555 static int max_write_thresh = INPUT_POOL_WORDS * 32;
1556 static char sysctl_bootid[16];
1557 
1558 /*
1559  * This function is used to return both the bootid UUID, and random
1560  * UUID.  The difference is in whether table->data is NULL; if it is,
1561  * then a new UUID is generated and returned to the user.
1562  *
1563  * If the user accesses this via the proc interface, the UUID will be
1564  * returned as an ASCII string in the standard UUID format; if via the
1565  * sysctl system call, as 16 bytes of binary data.
1566  */
1567 static int proc_do_uuid(struct ctl_table *table, int write,
1568                         void __user *buffer, size_t *lenp, loff_t *ppos)
1569 {
1570         struct ctl_table fake_table;
1571         unsigned char buf[64], tmp_uuid[16], *uuid;
1572 
1573         uuid = table->data;
1574         if (!uuid) {
1575                 uuid = tmp_uuid;
1576                 generate_random_uuid(uuid);
1577         } else {
1578                 static DEFINE_SPINLOCK(bootid_spinlock);
1579 
1580                 spin_lock(&bootid_spinlock);
1581                 if (!uuid[8])
1582                         generate_random_uuid(uuid);
1583                 spin_unlock(&bootid_spinlock);
1584         }
1585 
1586         sprintf(buf, "%pU", uuid);
1587 
1588         fake_table.data = buf;
1589         fake_table.maxlen = sizeof(buf);
1590 
1591         return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1592 }
1593 
1594 /*
1595  * Return entropy available scaled to integral bits
1596  */
1597 static int proc_do_entropy(struct ctl_table *table, int write,
1598                            void __user *buffer, size_t *lenp, loff_t *ppos)
1599 {
1600         struct ctl_table fake_table;
1601         int entropy_count;
1602 
1603         entropy_count = *(int *)table->data >> ENTROPY_SHIFT;
1604 
1605         fake_table.data = &entropy_count;
1606         fake_table.maxlen = sizeof(entropy_count);
1607 
1608         return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
1609 }
1610 
1611 static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1612 extern struct ctl_table random_table[];
1613 struct ctl_table random_table[] = {
1614         {
1615                 .procname       = "poolsize",
1616                 .data           = &sysctl_poolsize,
1617                 .maxlen         = sizeof(int),
1618                 .mode           = 0444,
1619                 .proc_handler   = proc_dointvec,
1620         },
1621         {
1622                 .procname       = "entropy_avail",
1623                 .maxlen         = sizeof(int),
1624                 .mode           = 0444,
1625                 .proc_handler   = proc_do_entropy,
1626                 .data           = &input_pool.entropy_count,
1627         },
1628         {
1629                 .procname       = "read_wakeup_threshold",
1630                 .data           = &random_read_wakeup_bits,
1631                 .maxlen         = sizeof(int),
1632                 .mode           = 0644,
1633                 .proc_handler   = proc_dointvec_minmax,
1634                 .extra1         = &min_read_thresh,
1635                 .extra2         = &max_read_thresh,
1636         },
1637         {
1638                 .procname       = "write_wakeup_threshold",
1639                 .data           = &random_write_wakeup_bits,
1640                 .maxlen         = sizeof(int),
1641                 .mode           = 0644,
1642                 .proc_handler   = proc_dointvec_minmax,
1643                 .extra1         = &min_write_thresh,
1644                 .extra2         = &max_write_thresh,
1645         },
1646         {
1647                 .procname       = "urandom_min_reseed_secs",
1648                 .data           = &random_min_urandom_seed,
1649                 .maxlen         = sizeof(int),
1650                 .mode           = 0644,
1651                 .proc_handler   = proc_dointvec,
1652         },
1653         {
1654                 .procname       = "boot_id",
1655                 .data           = &sysctl_bootid,
1656                 .maxlen         = 16,
1657                 .mode           = 0444,
1658                 .proc_handler   = proc_do_uuid,
1659         },
1660         {
1661                 .procname       = "uuid",
1662                 .maxlen         = 16,
1663                 .mode           = 0444,
1664                 .proc_handler   = proc_do_uuid,
1665         },
1666         { }
1667 };
1668 #endif  /* CONFIG_SYSCTL */
1669 
1670 static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1671 
1672 int random_int_secret_init(void)
1673 {
1674         get_random_bytes(random_int_secret, sizeof(random_int_secret));
1675         return 0;
1676 }
1677 
1678 /*
1679  * Get a random word for internal kernel use only. Similar to urandom but
1680  * with the goal of minimal entropy pool depletion. As a result, the random
1681  * value is not cryptographically secure but for several uses the cost of
1682  * depleting entropy is too high
1683  */
1684 static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1685 unsigned int get_random_int(void)
1686 {
1687         __u32 *hash;
1688         unsigned int ret;
1689 
1690         if (arch_get_random_int(&ret))
1691                 return ret;
1692 
1693         hash = get_cpu_var(get_random_int_hash);
1694 
1695         hash[0] += current->pid + jiffies + random_get_entropy();
1696         md5_transform(hash, random_int_secret);
1697         ret = hash[0];
1698         put_cpu_var(get_random_int_hash);
1699 
1700         return ret;
1701 }
1702 EXPORT_SYMBOL(get_random_int);
1703 
1704 /*
1705  * randomize_range() returns a start address such that
1706  *
1707  *    [...... <range> .....]
1708  *  start                  end
1709  *
1710  * a <range> with size "len" starting at the return value is inside in the
1711  * area defined by [start, end], but is otherwise randomized.
1712  */
1713 unsigned long
1714 randomize_range(unsigned long start, unsigned long end, unsigned long len)
1715 {
1716         unsigned long range = end - len - start;
1717 
1718         if (end <= start + len)
1719                 return 0;
1720         return PAGE_ALIGN(get_random_int() % range + start);
1721 }
1722 

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