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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_thresh = 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_thresh = 28 * OUTPUT_POOL_WORDS;
306 
307 /*
308  * The minimum number of seconds between urandom pool resending.  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 Mdeling 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 (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_bytes = entropy_count >> ENTROPY_SHIFT;
670 
671                 /* should we wake readers? */
672                 if (entropy_bytes >= random_read_wakeup_thresh) {
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_bytes > random_write_wakeup_thresh &&
682                     r->initialized &&
683                     r->entropy_total >= 2*random_read_wakeup_thresh) {
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 
848         c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;
849         j_high = (sizeof(now) > 4) ? now >> 32 : 0;
850         input[0] = cycles ^ j_high ^ irq;
851         input[1] = now ^ c_high;
852         ip = regs ? instruction_pointer(regs) : _RET_IP_;
853         input[2] = ip;
854         input[3] = ip >> 32;
855 
856         fast_mix(fast_pool, input);
857 
858         if ((fast_pool->count & 63) && !time_after(now, fast_pool->last + HZ))
859                 return;
860 
861         fast_pool->last = now;
862 
863         r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
864         __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
865         /*
866          * If we don't have a valid cycle counter, and we see
867          * back-to-back timer interrupts, then skip giving credit for
868          * any entropy.
869          */
870         if (cycles == 0) {
871                 if (irq_flags & __IRQF_TIMER) {
872                         if (fast_pool->last_timer_intr)
873                                 return;
874                         fast_pool->last_timer_intr = 1;
875                 } else
876                         fast_pool->last_timer_intr = 0;
877         }
878         credit_entropy_bits(r, 1);
879 }
880 
881 #ifdef CONFIG_BLOCK
882 void add_disk_randomness(struct gendisk *disk)
883 {
884         if (!disk || !disk->random)
885                 return;
886         /* first major is 1, so we get >= 0x200 here */
887         add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
888         trace_add_disk_randomness(disk_devt(disk), ENTROPY_BITS(&input_pool));
889 }
890 #endif
891 
892 /*********************************************************************
893  *
894  * Entropy extraction routines
895  *
896  *********************************************************************/
897 
898 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
899                                size_t nbytes, int min, int rsvd);
900 
901 /*
902  * This utility inline function is responsible for transferring entropy
903  * from the primary pool to the secondary extraction pool. We make
904  * sure we pull enough for a 'catastrophic reseed'.
905  */
906 static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes);
907 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
908 {
909         if (r->limit == 0 && random_min_urandom_seed) {
910                 unsigned long now = jiffies;
911 
912                 if (time_before(now,
913                                 r->last_pulled + random_min_urandom_seed * HZ))
914                         return;
915                 r->last_pulled = now;
916         }
917         if (r->pull &&
918             r->entropy_count < (nbytes << (ENTROPY_SHIFT + 3)) &&
919             r->entropy_count < r->poolinfo->poolfracbits)
920                 _xfer_secondary_pool(r, nbytes);
921 }
922 
923 static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
924 {
925         __u32   tmp[OUTPUT_POOL_WORDS];
926 
927         /* For /dev/random's pool, always leave two wakeup worth's BITS */
928         int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
929         int bytes = nbytes;
930 
931         /* pull at least as many as BYTES as wakeup BITS */
932         bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
933         /* but never more than the buffer size */
934         bytes = min_t(int, bytes, sizeof(tmp));
935 
936         trace_xfer_secondary_pool(r->name, bytes * 8, nbytes * 8,
937                                   ENTROPY_BITS(r), ENTROPY_BITS(r->pull));
938         bytes = extract_entropy(r->pull, tmp, bytes,
939                                 random_read_wakeup_thresh / 8, rsvd);
940         mix_pool_bytes(r, tmp, bytes, NULL);
941         credit_entropy_bits(r, bytes*8);
942 }
943 
944 /*
945  * Used as a workqueue function so that when the input pool is getting
946  * full, we can "spill over" some entropy to the output pools.  That
947  * way the output pools can store some of the excess entropy instead
948  * of letting it go to waste.
949  */
950 static void push_to_pool(struct work_struct *work)
951 {
952         struct entropy_store *r = container_of(work, struct entropy_store,
953                                               push_work);
954         BUG_ON(!r);
955         _xfer_secondary_pool(r, random_read_wakeup_thresh/8);
956         trace_push_to_pool(r->name, r->entropy_count >> ENTROPY_SHIFT,
957                            r->pull->entropy_count >> ENTROPY_SHIFT);
958 }
959 
960 /*
961  * These functions extracts randomness from the "entropy pool", and
962  * returns it in a buffer.
963  *
964  * The min parameter specifies the minimum amount we can pull before
965  * failing to avoid races that defeat catastrophic reseeding while the
966  * reserved parameter indicates how much entropy we must leave in the
967  * pool after each pull to avoid starving other readers.
968  *
969  * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
970  */
971 
972 static size_t account(struct entropy_store *r, size_t nbytes, int min,
973                       int reserved)
974 {
975         unsigned long flags;
976         int wakeup_write = 0;
977         int have_bytes;
978         int entropy_count, orig;
979         size_t ibytes;
980 
981         /* Hold lock while accounting */
982         spin_lock_irqsave(&r->lock, flags);
983 
984         BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
985 
986         /* Can we pull enough? */
987 retry:
988         entropy_count = orig = ACCESS_ONCE(r->entropy_count);
989         have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);
990         ibytes = nbytes;
991         if (have_bytes < min + reserved) {
992                 ibytes = 0;
993         } else {
994                 /* If limited, never pull more than available */
995                 if (r->limit && ibytes + reserved >= have_bytes)
996                         ibytes = have_bytes - reserved;
997 
998                 if (have_bytes >= ibytes + reserved)
999                         entropy_count -= ibytes << (ENTROPY_SHIFT + 3);
1000                 else
1001                         entropy_count = reserved << (ENTROPY_SHIFT + 3);
1002 
1003                 if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
1004                         goto retry;
1005 
1006                 if ((r->entropy_count >> ENTROPY_SHIFT)
1007                     < random_write_wakeup_thresh)
1008                         wakeup_write = 1;
1009         }
1010         spin_unlock_irqrestore(&r->lock, flags);
1011 
1012         trace_debit_entropy(r->name, 8 * ibytes);
1013         if (wakeup_write) {
1014                 wake_up_interruptible(&random_write_wait);
1015                 kill_fasync(&fasync, SIGIO, POLL_OUT);
1016         }
1017 
1018         return ibytes;
1019 }
1020 
1021 static void extract_buf(struct entropy_store *r, __u8 *out)
1022 {
1023         int i;
1024         union {
1025                 __u32 w[5];
1026                 unsigned long l[LONGS(20)];
1027         } hash;
1028         __u32 workspace[SHA_WORKSPACE_WORDS];
1029         __u8 extract[64];
1030         unsigned long flags;
1031 
1032         /* Generate a hash across the pool, 16 words (512 bits) at a time */
1033         sha_init(hash.w);
1034         spin_lock_irqsave(&r->lock, flags);
1035         for (i = 0; i < r->poolinfo->poolwords; i += 16)
1036                 sha_transform(hash.w, (__u8 *)(r->pool + i), workspace);
1037 
1038         /*
1039          * If we have a architectural hardware random number
1040          * generator, mix that in, too.
1041          */
1042         for (i = 0; i < LONGS(20); i++) {
1043                 unsigned long v;
1044                 if (!arch_get_random_long(&v))
1045                         break;
1046                 hash.l[i] ^= v;
1047         }
1048 
1049         /*
1050          * We mix the hash back into the pool to prevent backtracking
1051          * attacks (where the attacker knows the state of the pool
1052          * plus the current outputs, and attempts to find previous
1053          * ouputs), unless the hash function can be inverted. By
1054          * mixing at least a SHA1 worth of hash data back, we make
1055          * brute-forcing the feedback as hard as brute-forcing the
1056          * hash.
1057          */
1058         __mix_pool_bytes(r, hash.w, sizeof(hash.w), extract);
1059         spin_unlock_irqrestore(&r->lock, flags);
1060 
1061         /*
1062          * To avoid duplicates, we atomically extract a portion of the
1063          * pool while mixing, and hash one final time.
1064          */
1065         sha_transform(hash.w, extract, workspace);
1066         memset(extract, 0, sizeof(extract));
1067         memset(workspace, 0, sizeof(workspace));
1068 
1069         /*
1070          * In case the hash function has some recognizable output
1071          * pattern, we fold it in half. Thus, we always feed back
1072          * twice as much data as we output.
1073          */
1074         hash.w[0] ^= hash.w[3];
1075         hash.w[1] ^= hash.w[4];
1076         hash.w[2] ^= rol32(hash.w[2], 16);
1077 
1078         memcpy(out, &hash, EXTRACT_SIZE);
1079         memset(&hash, 0, sizeof(hash));
1080 }
1081 
1082 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
1083                                  size_t nbytes, int min, int reserved)
1084 {
1085         ssize_t ret = 0, i;
1086         __u8 tmp[EXTRACT_SIZE];
1087         unsigned long flags;
1088 
1089         /* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */
1090         if (fips_enabled) {
1091                 spin_lock_irqsave(&r->lock, flags);
1092                 if (!r->last_data_init) {
1093                         r->last_data_init = 1;
1094                         spin_unlock_irqrestore(&r->lock, flags);
1095                         trace_extract_entropy(r->name, EXTRACT_SIZE,
1096                                               ENTROPY_BITS(r), _RET_IP_);
1097                         xfer_secondary_pool(r, EXTRACT_SIZE);
1098                         extract_buf(r, tmp);
1099                         spin_lock_irqsave(&r->lock, flags);
1100                         memcpy(r->last_data, tmp, EXTRACT_SIZE);
1101                 }
1102                 spin_unlock_irqrestore(&r->lock, flags);
1103         }
1104 
1105         trace_extract_entropy(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
1106         xfer_secondary_pool(r, nbytes);
1107         nbytes = account(r, nbytes, min, reserved);
1108 
1109         while (nbytes) {
1110                 extract_buf(r, tmp);
1111 
1112                 if (fips_enabled) {
1113                         spin_lock_irqsave(&r->lock, flags);
1114                         if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
1115                                 panic("Hardware RNG duplicated output!\n");
1116                         memcpy(r->last_data, tmp, EXTRACT_SIZE);
1117                         spin_unlock_irqrestore(&r->lock, flags);
1118                 }
1119                 i = min_t(int, nbytes, EXTRACT_SIZE);
1120                 memcpy(buf, tmp, i);
1121                 nbytes -= i;
1122                 buf += i;
1123                 ret += i;
1124         }
1125 
1126         /* Wipe data just returned from memory */
1127         memset(tmp, 0, sizeof(tmp));
1128 
1129         return ret;
1130 }
1131 
1132 static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
1133                                     size_t nbytes)
1134 {
1135         ssize_t ret = 0, i;
1136         __u8 tmp[EXTRACT_SIZE];
1137 
1138         trace_extract_entropy_user(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
1139         xfer_secondary_pool(r, nbytes);
1140         nbytes = account(r, nbytes, 0, 0);
1141 
1142         while (nbytes) {
1143                 if (need_resched()) {
1144                         if (signal_pending(current)) {
1145                                 if (ret == 0)
1146                                         ret = -ERESTARTSYS;
1147                                 break;
1148                         }
1149                         schedule();
1150                 }
1151 
1152                 extract_buf(r, tmp);
1153                 i = min_t(int, nbytes, EXTRACT_SIZE);
1154                 if (copy_to_user(buf, tmp, i)) {
1155                         ret = -EFAULT;
1156                         break;
1157                 }
1158 
1159                 nbytes -= i;
1160                 buf += i;
1161                 ret += i;
1162         }
1163 
1164         /* Wipe data just returned from memory */
1165         memset(tmp, 0, sizeof(tmp));
1166 
1167         return ret;
1168 }
1169 
1170 /*
1171  * This function is the exported kernel interface.  It returns some
1172  * number of good random numbers, suitable for key generation, seeding
1173  * TCP sequence numbers, etc.  It does not use the hw random number
1174  * generator, if available; use get_random_bytes_arch() for that.
1175  */
1176 void get_random_bytes(void *buf, int nbytes)
1177 {
1178 #if DEBUG_RANDOM_BOOT > 0
1179         if (unlikely(nonblocking_pool.initialized == 0))
1180                 printk(KERN_NOTICE "random: %pF get_random_bytes called "
1181                        "with %d bits of entropy available\n",
1182                        (void *) _RET_IP_,
1183                        nonblocking_pool.entropy_total);
1184 #endif
1185         trace_get_random_bytes(nbytes, _RET_IP_);
1186         extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
1187 }
1188 EXPORT_SYMBOL(get_random_bytes);
1189 
1190 /*
1191  * This function will use the architecture-specific hardware random
1192  * number generator if it is available.  The arch-specific hw RNG will
1193  * almost certainly be faster than what we can do in software, but it
1194  * is impossible to verify that it is implemented securely (as
1195  * opposed, to, say, the AES encryption of a sequence number using a
1196  * key known by the NSA).  So it's useful if we need the speed, but
1197  * only if we're willing to trust the hardware manufacturer not to
1198  * have put in a back door.
1199  */
1200 void get_random_bytes_arch(void *buf, int nbytes)
1201 {
1202         char *p = buf;
1203 
1204         trace_get_random_bytes_arch(nbytes, _RET_IP_);
1205         while (nbytes) {
1206                 unsigned long v;
1207                 int chunk = min(nbytes, (int)sizeof(unsigned long));
1208 
1209                 if (!arch_get_random_long(&v))
1210                         break;
1211                 
1212                 memcpy(p, &v, chunk);
1213                 p += chunk;
1214                 nbytes -= chunk;
1215         }
1216 
1217         if (nbytes)
1218                 extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
1219 }
1220 EXPORT_SYMBOL(get_random_bytes_arch);
1221 
1222 
1223 /*
1224  * init_std_data - initialize pool with system data
1225  *
1226  * @r: pool to initialize
1227  *
1228  * This function clears the pool's entropy count and mixes some system
1229  * data into the pool to prepare it for use. The pool is not cleared
1230  * as that can only decrease the entropy in the pool.
1231  */
1232 static void init_std_data(struct entropy_store *r)
1233 {
1234         int i;
1235         ktime_t now = ktime_get_real();
1236         unsigned long rv;
1237 
1238         r->last_pulled = jiffies;
1239         mix_pool_bytes(r, &now, sizeof(now), NULL);
1240         for (i = r->poolinfo->poolbytes; i > 0; i -= sizeof(rv)) {
1241                 if (!arch_get_random_long(&rv))
1242                         rv = random_get_entropy();
1243                 mix_pool_bytes(r, &rv, sizeof(rv), NULL);
1244         }
1245         mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
1246 }
1247 
1248 /*
1249  * Note that setup_arch() may call add_device_randomness()
1250  * long before we get here. This allows seeding of the pools
1251  * with some platform dependent data very early in the boot
1252  * process. But it limits our options here. We must use
1253  * statically allocated structures that already have all
1254  * initializations complete at compile time. We should also
1255  * take care not to overwrite the precious per platform data
1256  * we were given.
1257  */
1258 static int rand_initialize(void)
1259 {
1260         init_std_data(&input_pool);
1261         init_std_data(&blocking_pool);
1262         init_std_data(&nonblocking_pool);
1263         return 0;
1264 }
1265 early_initcall(rand_initialize);
1266 
1267 #ifdef CONFIG_BLOCK
1268 void rand_initialize_disk(struct gendisk *disk)
1269 {
1270         struct timer_rand_state *state;
1271 
1272         /*
1273          * If kzalloc returns null, we just won't use that entropy
1274          * source.
1275          */
1276         state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1277         if (state) {
1278                 state->last_time = INITIAL_JIFFIES;
1279                 disk->random = state;
1280         }
1281 }
1282 #endif
1283 
1284 static ssize_t
1285 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1286 {
1287         ssize_t n, retval = 0, count = 0;
1288 
1289         if (nbytes == 0)
1290                 return 0;
1291 
1292         while (nbytes > 0) {
1293                 n = nbytes;
1294                 if (n > SEC_XFER_SIZE)
1295                         n = SEC_XFER_SIZE;
1296 
1297                 n = extract_entropy_user(&blocking_pool, buf, n);
1298 
1299                 if (n < 0) {
1300                         retval = n;
1301                         break;
1302                 }
1303 
1304                 trace_random_read(n*8, (nbytes-n)*8,
1305                                   ENTROPY_BITS(&blocking_pool),
1306                                   ENTROPY_BITS(&input_pool));
1307 
1308                 if (n == 0) {
1309                         if (file->f_flags & O_NONBLOCK) {
1310                                 retval = -EAGAIN;
1311                                 break;
1312                         }
1313 
1314                         wait_event_interruptible(random_read_wait,
1315                                 ENTROPY_BITS(&input_pool) >=
1316                                 random_read_wakeup_thresh);
1317 
1318                         if (signal_pending(current)) {
1319                                 retval = -ERESTARTSYS;
1320                                 break;
1321                         }
1322 
1323                         continue;
1324                 }
1325 
1326                 count += n;
1327                 buf += n;
1328                 nbytes -= n;
1329                 break;          /* This break makes the device work */
1330                                 /* like a named pipe */
1331         }
1332 
1333         return (count ? count : retval);
1334 }
1335 
1336 static ssize_t
1337 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1338 {
1339         int ret;
1340 
1341         if (unlikely(nonblocking_pool.initialized == 0))
1342                 printk_once(KERN_NOTICE "random: %s urandom read "
1343                             "with %d bits of entropy available\n",
1344                             current->comm, nonblocking_pool.entropy_total);
1345 
1346         ret = extract_entropy_user(&nonblocking_pool, buf, nbytes);
1347 
1348         trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool),
1349                            ENTROPY_BITS(&input_pool));
1350         return ret;
1351 }
1352 
1353 static unsigned int
1354 random_poll(struct file *file, poll_table * wait)
1355 {
1356         unsigned int mask;
1357 
1358         poll_wait(file, &random_read_wait, wait);
1359         poll_wait(file, &random_write_wait, wait);
1360         mask = 0;
1361         if (ENTROPY_BITS(&input_pool) >= random_read_wakeup_thresh)
1362                 mask |= POLLIN | POLLRDNORM;
1363         if (ENTROPY_BITS(&input_pool) < random_write_wakeup_thresh)
1364                 mask |= POLLOUT | POLLWRNORM;
1365         return mask;
1366 }
1367 
1368 static int
1369 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1370 {
1371         size_t bytes;
1372         __u32 buf[16];
1373         const char __user *p = buffer;
1374 
1375         while (count > 0) {
1376                 bytes = min(count, sizeof(buf));
1377                 if (copy_from_user(&buf, p, bytes))
1378                         return -EFAULT;
1379 
1380                 count -= bytes;
1381                 p += bytes;
1382 
1383                 mix_pool_bytes(r, buf, bytes, NULL);
1384                 cond_resched();
1385         }
1386 
1387         return 0;
1388 }
1389 
1390 static ssize_t random_write(struct file *file, const char __user *buffer,
1391                             size_t count, loff_t *ppos)
1392 {
1393         size_t ret;
1394 
1395         ret = write_pool(&blocking_pool, buffer, count);
1396         if (ret)
1397                 return ret;
1398         ret = write_pool(&nonblocking_pool, buffer, count);
1399         if (ret)
1400                 return ret;
1401 
1402         return (ssize_t)count;
1403 }
1404 
1405 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1406 {
1407         int size, ent_count;
1408         int __user *p = (int __user *)arg;
1409         int retval;
1410 
1411         switch (cmd) {
1412         case RNDGETENTCNT:
1413                 /* inherently racy, no point locking */
1414                 ent_count = ENTROPY_BITS(&input_pool);
1415                 if (put_user(ent_count, p))
1416                         return -EFAULT;
1417                 return 0;
1418         case RNDADDTOENTCNT:
1419                 if (!capable(CAP_SYS_ADMIN))
1420                         return -EPERM;
1421                 if (get_user(ent_count, p))
1422                         return -EFAULT;
1423                 credit_entropy_bits_safe(&input_pool, ent_count);
1424                 return 0;
1425         case RNDADDENTROPY:
1426                 if (!capable(CAP_SYS_ADMIN))
1427                         return -EPERM;
1428                 if (get_user(ent_count, p++))
1429                         return -EFAULT;
1430                 if (ent_count < 0)
1431                         return -EINVAL;
1432                 if (get_user(size, p++))
1433                         return -EFAULT;
1434                 retval = write_pool(&input_pool, (const char __user *)p,
1435                                     size);
1436                 if (retval < 0)
1437                         return retval;
1438                 credit_entropy_bits_safe(&input_pool, ent_count);
1439                 return 0;
1440         case RNDZAPENTCNT:
1441         case RNDCLEARPOOL:
1442                 /*
1443                  * Clear the entropy pool counters. We no longer clear
1444                  * the entropy pool, as that's silly.
1445                  */
1446                 if (!capable(CAP_SYS_ADMIN))
1447                         return -EPERM;
1448                 input_pool.entropy_count = 0;
1449                 nonblocking_pool.entropy_count = 0;
1450                 blocking_pool.entropy_count = 0;
1451                 return 0;
1452         default:
1453                 return -EINVAL;
1454         }
1455 }
1456 
1457 static int random_fasync(int fd, struct file *filp, int on)
1458 {
1459         return fasync_helper(fd, filp, on, &fasync);
1460 }
1461 
1462 const struct file_operations random_fops = {
1463         .read  = random_read,
1464         .write = random_write,
1465         .poll  = random_poll,
1466         .unlocked_ioctl = random_ioctl,
1467         .fasync = random_fasync,
1468         .llseek = noop_llseek,
1469 };
1470 
1471 const struct file_operations urandom_fops = {
1472         .read  = urandom_read,
1473         .write = random_write,
1474         .unlocked_ioctl = random_ioctl,
1475         .fasync = random_fasync,
1476         .llseek = noop_llseek,
1477 };
1478 
1479 /***************************************************************
1480  * Random UUID interface
1481  *
1482  * Used here for a Boot ID, but can be useful for other kernel
1483  * drivers.
1484  ***************************************************************/
1485 
1486 /*
1487  * Generate random UUID
1488  */
1489 void generate_random_uuid(unsigned char uuid_out[16])
1490 {
1491         get_random_bytes(uuid_out, 16);
1492         /* Set UUID version to 4 --- truly random generation */
1493         uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1494         /* Set the UUID variant to DCE */
1495         uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1496 }
1497 EXPORT_SYMBOL(generate_random_uuid);
1498 
1499 /********************************************************************
1500  *
1501  * Sysctl interface
1502  *
1503  ********************************************************************/
1504 
1505 #ifdef CONFIG_SYSCTL
1506 
1507 #include <linux/sysctl.h>
1508 
1509 static int min_read_thresh = 8, min_write_thresh;
1510 static int max_read_thresh = INPUT_POOL_WORDS * 32;
1511 static int max_write_thresh = INPUT_POOL_WORDS * 32;
1512 static char sysctl_bootid[16];
1513 
1514 /*
1515  * These functions is used to return both the bootid UUID, and random
1516  * UUID.  The difference is in whether table->data is NULL; if it is,
1517  * then a new UUID is generated and returned to the user.
1518  *
1519  * If the user accesses this via the proc interface, it will be returned
1520  * as an ASCII string in the standard UUID format.  If accesses via the
1521  * sysctl system call, it is returned as 16 bytes of binary data.
1522  */
1523 static int proc_do_uuid(struct ctl_table *table, int write,
1524                         void __user *buffer, size_t *lenp, loff_t *ppos)
1525 {
1526         struct ctl_table fake_table;
1527         unsigned char buf[64], tmp_uuid[16], *uuid;
1528 
1529         uuid = table->data;
1530         if (!uuid) {
1531                 uuid = tmp_uuid;
1532                 generate_random_uuid(uuid);
1533         } else {
1534                 static DEFINE_SPINLOCK(bootid_spinlock);
1535 
1536                 spin_lock(&bootid_spinlock);
1537                 if (!uuid[8])
1538                         generate_random_uuid(uuid);
1539                 spin_unlock(&bootid_spinlock);
1540         }
1541 
1542         sprintf(buf, "%pU", uuid);
1543 
1544         fake_table.data = buf;
1545         fake_table.maxlen = sizeof(buf);
1546 
1547         return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1548 }
1549 
1550 /*
1551  * Return entropy available scaled to integral bits
1552  */
1553 static int proc_do_entropy(ctl_table *table, int write,
1554                            void __user *buffer, size_t *lenp, loff_t *ppos)
1555 {
1556         ctl_table fake_table;
1557         int entropy_count;
1558 
1559         entropy_count = *(int *)table->data >> ENTROPY_SHIFT;
1560 
1561         fake_table.data = &entropy_count;
1562         fake_table.maxlen = sizeof(entropy_count);
1563 
1564         return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
1565 }
1566 
1567 static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1568 extern struct ctl_table random_table[];
1569 struct ctl_table random_table[] = {
1570         {
1571                 .procname       = "poolsize",
1572                 .data           = &sysctl_poolsize,
1573                 .maxlen         = sizeof(int),
1574                 .mode           = 0444,
1575                 .proc_handler   = proc_dointvec,
1576         },
1577         {
1578                 .procname       = "entropy_avail",
1579                 .maxlen         = sizeof(int),
1580                 .mode           = 0444,
1581                 .proc_handler   = proc_do_entropy,
1582                 .data           = &input_pool.entropy_count,
1583         },
1584         {
1585                 .procname       = "read_wakeup_threshold",
1586                 .data           = &random_read_wakeup_thresh,
1587                 .maxlen         = sizeof(int),
1588                 .mode           = 0644,
1589                 .proc_handler   = proc_dointvec_minmax,
1590                 .extra1         = &min_read_thresh,
1591                 .extra2         = &max_read_thresh,
1592         },
1593         {
1594                 .procname       = "write_wakeup_threshold",
1595                 .data           = &random_write_wakeup_thresh,
1596                 .maxlen         = sizeof(int),
1597                 .mode           = 0644,
1598                 .proc_handler   = proc_dointvec_minmax,
1599                 .extra1         = &min_write_thresh,
1600                 .extra2         = &max_write_thresh,
1601         },
1602         {
1603                 .procname       = "urandom_min_reseed_secs",
1604                 .data           = &random_min_urandom_seed,
1605                 .maxlen         = sizeof(int),
1606                 .mode           = 0644,
1607                 .proc_handler   = proc_dointvec,
1608         },
1609         {
1610                 .procname       = "boot_id",
1611                 .data           = &sysctl_bootid,
1612                 .maxlen         = 16,
1613                 .mode           = 0444,
1614                 .proc_handler   = proc_do_uuid,
1615         },
1616         {
1617                 .procname       = "uuid",
1618                 .maxlen         = 16,
1619                 .mode           = 0444,
1620                 .proc_handler   = proc_do_uuid,
1621         },
1622         { }
1623 };
1624 #endif  /* CONFIG_SYSCTL */
1625 
1626 static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1627 
1628 int random_int_secret_init(void)
1629 {
1630         get_random_bytes(random_int_secret, sizeof(random_int_secret));
1631         return 0;
1632 }
1633 
1634 /*
1635  * Get a random word for internal kernel use only. Similar to urandom but
1636  * with the goal of minimal entropy pool depletion. As a result, the random
1637  * value is not cryptographically secure but for several uses the cost of
1638  * depleting entropy is too high
1639  */
1640 static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1641 unsigned int get_random_int(void)
1642 {
1643         __u32 *hash;
1644         unsigned int ret;
1645 
1646         if (arch_get_random_int(&ret))
1647                 return ret;
1648 
1649         hash = get_cpu_var(get_random_int_hash);
1650 
1651         hash[0] += current->pid + jiffies + random_get_entropy();
1652         md5_transform(hash, random_int_secret);
1653         ret = hash[0];
1654         put_cpu_var(get_random_int_hash);
1655 
1656         return ret;
1657 }
1658 EXPORT_SYMBOL(get_random_int);
1659 
1660 /*
1661  * randomize_range() returns a start address such that
1662  *
1663  *    [...... <range> .....]
1664  *  start                  end
1665  *
1666  * a <range> with size "len" starting at the return value is inside in the
1667  * area defined by [start, end], but is otherwise randomized.
1668  */
1669 unsigned long
1670 randomize_range(unsigned long start, unsigned long end, unsigned long len)
1671 {
1672         unsigned long range = end - len - start;
1673 
1674         if (end <= start + len)
1675                 return 0;
1676         return PAGE_ALIGN(get_random_int() % range + start);
1677 }
1678 

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