linux/drivers/char/random.c
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   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_input_randomness(unsigned int type, unsigned int code,
 129 *                                unsigned int value);
 130 *      void add_interrupt_randomness(int irq);
 131 *      void add_disk_randomness(struct gendisk *disk);
 132 *
 133 * add_input_randomness() uses the input layer interrupt timing, as well as
 134 * the event type information from the hardware.
 135 *
 136 * add_interrupt_randomness() uses the inter-interrupt timing as random
 137 * inputs to the entropy pool.  Note that not all interrupts are good
 138 * sources of randomness!  For example, the timer interrupts is not a
 139 * good choice, because the periodicity of the interrupts is too
 140 * regular, and hence predictable to an attacker.  Network Interface
 141 * Controller interrupts are a better measure, since the timing of the
 142 * NIC interrupts are more unpredictable.
 143 *
 144 * add_disk_randomness() uses what amounts to the seek time of block
 145 * layer request events, on a per-disk_devt basis, as input to the
 146 * entropy pool. Note that high-speed solid state drives with very low
 147 * seek times do not make for good sources of entropy, as their seek
 148 * times are usually fairly consistent.
 149 *
 150 * All of these routines try to estimate how many bits of randomness a
 151 * particular randomness source.  They do this by keeping track of the
 152 * first and second order deltas of the event timings.
 153 *
 154 * Ensuring unpredictability at system startup
 155 * ============================================
 156 *
 157 * When any operating system starts up, it will go through a sequence
 158 * of actions that are fairly predictable by an adversary, especially
 159 * if the start-up does not involve interaction with a human operator.
 160 * This reduces the actual number of bits of unpredictability in the
 161 * entropy pool below the value in entropy_count.  In order to
 162 * counteract this effect, it helps to carry information in the
 163 * entropy pool across shut-downs and start-ups.  To do this, put the
 164 * following lines an appropriate script which is run during the boot
 165 * sequence:
 166 *
 167 *      echo "Initializing random number generator..."
 168 *      random_seed=/var/run/random-seed
 169 *      # Carry a random seed from start-up to start-up
 170 *      # Load and then save the whole entropy pool
 171 *      if [ -f $random_seed ]; then
 172 *              cat $random_seed >/dev/urandom
 173 *      else
 174 *              touch $random_seed
 175 *      fi
 176 *      chmod 600 $random_seed
 177 *      dd if=/dev/urandom of=$random_seed count=1 bs=512
 178 *
 179 * and the following lines in an appropriate script which is run as
 180 * the system is shutdown:
 181 *
 182 *      # Carry a random seed from shut-down to start-up
 183 *      # Save the whole entropy pool
 184 *      echo "Saving random seed..."
 185 *      random_seed=/var/run/random-seed
 186 *      touch $random_seed
 187 *      chmod 600 $random_seed
 188 *      dd if=/dev/urandom of=$random_seed count=1 bs=512
 189 *
 190 * For example, on most modern systems using the System V init
 191 * scripts, such code fragments would be found in
 192 * /etc/rc.d/init.d/random.  On older Linux systems, the correct script
 193 * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0.
 194 *
 195 * Effectively, these commands cause the contents of the entropy pool
 196 * to be saved at shut-down time and reloaded into the entropy pool at
 197 * start-up.  (The 'dd' in the addition to the bootup script is to
 198 * make sure that /etc/random-seed is different for every start-up,
 199 * even if the system crashes without executing rc.0.)  Even with
 200 * complete knowledge of the start-up activities, predicting the state
 201 * of the entropy pool requires knowledge of the previous history of
 202 * the system.
 203 *
 204 * Configuring the /dev/random driver under Linux
 205 * ==============================================
 206 *
 207 * The /dev/random driver under Linux uses minor numbers 8 and 9 of
 208 * the /dev/mem major number (#1).  So if your system does not have
 209 * /dev/random and /dev/urandom created already, they can be created
 210 * by using the commands:
 211 *
 212 *      mknod /dev/random c 1 8
 213 *      mknod /dev/urandom c 1 9
 214 *
 215 * Acknowledgements:
 216 * =================
 217 *
 218 * Ideas for constructing this random number generator were derived
 219 * from Pretty Good Privacy's random number generator, and from private
 220 * discussions with Phil Karn.  Colin Plumb provided a faster random
 221 * number generator, which speed up the mixing function of the entropy
 222 * pool, taken from PGPfone.  Dale Worley has also contributed many
 223 * useful ideas and suggestions to improve this driver.
 224 *
 225 * Any flaws in the design are solely my responsibility, and should
 226 * not be attributed to the Phil, Colin, or any of authors of PGP.
 227 *
 228 * Further background information on this topic may be obtained from
 229 * RFC 1750, "Randomness Recommendations for Security", by Donald
 230 * Eastlake, Steve Crocker, and Jeff Schiller.
 231 */
 232
 233#include <linux/utsname.h>
 234#include <linux/module.h>
 235#include <linux/kernel.h>
 236#include <linux/major.h>
 237#include <linux/string.h>
 238#include <linux/fcntl.h>
 239#include <linux/slab.h>
 240#include <linux/random.h>
 241#include <linux/poll.h>
 242#include <linux/init.h>
 243#include <linux/fs.h>
 244#include <linux/genhd.h>
 245#include <linux/interrupt.h>
 246#include <linux/mm.h>
 247#include <linux/spinlock.h>
 248#include <linux/percpu.h>
 249#include <linux/cryptohash.h>
 250#include <linux/fips.h>
 251
 252#ifdef CONFIG_GENERIC_HARDIRQS
 253# include <linux/irq.h>
 254#endif
 255
 256#include <asm/processor.h>
 257#include <asm/uaccess.h>
 258#include <asm/irq.h>
 259#include <asm/io.h>
 260
 261/*
 262 * Configuration information
 263 */
 264#define INPUT_POOL_WORDS 128
 265#define OUTPUT_POOL_WORDS 32
 266#define SEC_XFER_SIZE 512
 267#define EXTRACT_SIZE 10
 268
 269/*
 270 * The minimum number of bits of entropy before we wake up a read on
 271 * /dev/random.  Should be enough to do a significant reseed.
 272 */
 273static int random_read_wakeup_thresh = 64;
 274
 275/*
 276 * If the entropy count falls under this number of bits, then we
 277 * should wake up processes which are selecting or polling on write
 278 * access to /dev/random.
 279 */
 280static int random_write_wakeup_thresh = 128;
 281
 282/*
 283 * When the input pool goes over trickle_thresh, start dropping most
 284 * samples to avoid wasting CPU time and reduce lock contention.
 285 */
 286
 287static int trickle_thresh __read_mostly = INPUT_POOL_WORDS * 28;
 288
 289static DEFINE_PER_CPU(int, trickle_count);
 290
 291/*
 292 * A pool of size .poolwords is stirred with a primitive polynomial
 293 * of degree .poolwords over GF(2).  The taps for various sizes are
 294 * defined below.  They are chosen to be evenly spaced (minimum RMS
 295 * distance from evenly spaced; the numbers in the comments are a
 296 * scaled squared error sum) except for the last tap, which is 1 to
 297 * get the twisting happening as fast as possible.
 298 */
 299static struct poolinfo {
 300        int poolwords;
 301        int tap1, tap2, tap3, tap4, tap5;
 302} poolinfo_table[] = {
 303        /* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */
 304        { 128,  103,    76,     51,     25,     1 },
 305        /* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */
 306        { 32,   26,     20,     14,     7,      1 },
 307#if 0
 308        /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1  -- 115 */
 309        { 2048, 1638,   1231,   819,    411,    1 },
 310
 311        /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
 312        { 1024, 817,    615,    412,    204,    1 },
 313
 314        /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
 315        { 1024, 819,    616,    410,    207,    2 },
 316
 317        /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
 318        { 512,  411,    308,    208,    104,    1 },
 319
 320        /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
 321        { 512,  409,    307,    206,    102,    2 },
 322        /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
 323        { 512,  409,    309,    205,    103,    2 },
 324
 325        /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
 326        { 256,  205,    155,    101,    52,     1 },
 327
 328        /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
 329        { 128,  103,    78,     51,     27,     2 },
 330
 331        /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
 332        { 64,   52,     39,     26,     14,     1 },
 333#endif
 334};
 335
 336#define POOLBITS        poolwords*32
 337#define POOLBYTES       poolwords*4
 338
 339/*
 340 * For the purposes of better mixing, we use the CRC-32 polynomial as
 341 * well to make a twisted Generalized Feedback Shift Reigster
 342 *
 343 * (See M. Matsumoto & Y. Kurita, 1992.  Twisted GFSR generators.  ACM
 344 * Transactions on Modeling and Computer Simulation 2(3):179-194.
 345 * Also see M. Matsumoto & Y. Kurita, 1994.  Twisted GFSR generators
 346 * II.  ACM Transactions on Mdeling and Computer Simulation 4:254-266)
 347 *
 348 * Thanks to Colin Plumb for suggesting this.
 349 *
 350 * We have not analyzed the resultant polynomial to prove it primitive;
 351 * in fact it almost certainly isn't.  Nonetheless, the irreducible factors
 352 * of a random large-degree polynomial over GF(2) are more than large enough
 353 * that periodicity is not a concern.
 354 *
 355 * The input hash is much less sensitive than the output hash.  All
 356 * that we want of it is that it be a good non-cryptographic hash;
 357 * i.e. it not produce collisions when fed "random" data of the sort
 358 * we expect to see.  As long as the pool state differs for different
 359 * inputs, we have preserved the input entropy and done a good job.
 360 * The fact that an intelligent attacker can construct inputs that
 361 * will produce controlled alterations to the pool's state is not
 362 * important because we don't consider such inputs to contribute any
 363 * randomness.  The only property we need with respect to them is that
 364 * the attacker can't increase his/her knowledge of the pool's state.
 365 * Since all additions are reversible (knowing the final state and the
 366 * input, you can reconstruct the initial state), if an attacker has
 367 * any uncertainty about the initial state, he/she can only shuffle
 368 * that uncertainty about, but never cause any collisions (which would
 369 * decrease the uncertainty).
 370 *
 371 * The chosen system lets the state of the pool be (essentially) the input
 372 * modulo the generator polymnomial.  Now, for random primitive polynomials,
 373 * this is a universal class of hash functions, meaning that the chance
 374 * of a collision is limited by the attacker's knowledge of the generator
 375 * polynomail, so if it is chosen at random, an attacker can never force
 376 * a collision.  Here, we use a fixed polynomial, but we *can* assume that
 377 * ###--> it is unknown to the processes generating the input entropy. <-###
 378 * Because of this important property, this is a good, collision-resistant
 379 * hash; hash collisions will occur no more often than chance.
 380 */
 381
 382/*
 383 * Static global variables
 384 */
 385static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
 386static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
 387static struct fasync_struct *fasync;
 388
 389#if 0
 390static int debug;
 391module_param(debug, bool, 0644);
 392#define DEBUG_ENT(fmt, arg...) do { \
 393        if (debug) \
 394                printk(KERN_DEBUG "random %04d %04d %04d: " \
 395                fmt,\
 396                input_pool.entropy_count,\
 397                blocking_pool.entropy_count,\
 398                nonblocking_pool.entropy_count,\
 399                ## arg); } while (0)
 400#else
 401#define DEBUG_ENT(fmt, arg...) do {} while (0)
 402#endif
 403
 404/**********************************************************************
 405 *
 406 * OS independent entropy store.   Here are the functions which handle
 407 * storing entropy in an entropy pool.
 408 *
 409 **********************************************************************/
 410
 411struct entropy_store;
 412struct entropy_store {
 413        /* read-only data: */
 414        struct poolinfo *poolinfo;
 415        __u32 *pool;
 416        const char *name;
 417        struct entropy_store *pull;
 418        int limit;
 419
 420        /* read-write data: */
 421        spinlock_t lock;
 422        unsigned add_ptr;
 423        int entropy_count;
 424        int input_rotate;
 425        __u8 last_data[EXTRACT_SIZE];
 426};
 427
 428static __u32 input_pool_data[INPUT_POOL_WORDS];
 429static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
 430static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
 431
 432static struct entropy_store input_pool = {
 433        .poolinfo = &poolinfo_table[0],
 434        .name = "input",
 435        .limit = 1,
 436        .lock = __SPIN_LOCK_UNLOCKED(&input_pool.lock),
 437        .pool = input_pool_data
 438};
 439
 440static struct entropy_store blocking_pool = {
 441        .poolinfo = &poolinfo_table[1],
 442        .name = "blocking",
 443        .limit = 1,
 444        .pull = &input_pool,
 445        .lock = __SPIN_LOCK_UNLOCKED(&blocking_pool.lock),
 446        .pool = blocking_pool_data
 447};
 448
 449static struct entropy_store nonblocking_pool = {
 450        .poolinfo = &poolinfo_table[1],
 451        .name = "nonblocking",
 452        .pull = &input_pool,
 453        .lock = __SPIN_LOCK_UNLOCKED(&nonblocking_pool.lock),
 454        .pool = nonblocking_pool_data
 455};
 456
 457/*
 458 * This function adds bytes into the entropy "pool".  It does not
 459 * update the entropy estimate.  The caller should call
 460 * credit_entropy_bits if this is appropriate.
 461 *
 462 * The pool is stirred with a primitive polynomial of the appropriate
 463 * degree, and then twisted.  We twist by three bits at a time because
 464 * it's cheap to do so and helps slightly in the expected case where
 465 * the entropy is concentrated in the low-order bits.
 466 */
 467static void mix_pool_bytes_extract(struct entropy_store *r, const void *in,
 468                                   int nbytes, __u8 out[64])
 469{
 470        static __u32 const twist_table[8] = {
 471                0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
 472                0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
 473        unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
 474        int input_rotate;
 475        int wordmask = r->poolinfo->poolwords - 1;
 476        const char *bytes = in;
 477        __u32 w;
 478        unsigned long flags;
 479
 480        /* Taps are constant, so we can load them without holding r->lock.  */
 481        tap1 = r->poolinfo->tap1;
 482        tap2 = r->poolinfo->tap2;
 483        tap3 = r->poolinfo->tap3;
 484        tap4 = r->poolinfo->tap4;
 485        tap5 = r->poolinfo->tap5;
 486
 487        spin_lock_irqsave(&r->lock, flags);
 488        input_rotate = r->input_rotate;
 489        i = r->add_ptr;
 490
 491        /* mix one byte at a time to simplify size handling and churn faster */
 492        while (nbytes--) {
 493                w = rol32(*bytes++, input_rotate & 31);
 494                i = (i - 1) & wordmask;
 495
 496                /* XOR in the various taps */
 497                w ^= r->pool[i];
 498                w ^= r->pool[(i + tap1) & wordmask];
 499                w ^= r->pool[(i + tap2) & wordmask];
 500                w ^= r->pool[(i + tap3) & wordmask];
 501                w ^= r->pool[(i + tap4) & wordmask];
 502                w ^= r->pool[(i + tap5) & wordmask];
 503
 504                /* Mix the result back in with a twist */
 505                r->pool[i] = (w >> 3) ^ twist_table[w & 7];
 506
 507                /*
 508                 * Normally, we add 7 bits of rotation to the pool.
 509                 * At the beginning of the pool, add an extra 7 bits
 510                 * rotation, so that successive passes spread the
 511                 * input bits across the pool evenly.
 512                 */
 513                input_rotate += i ? 7 : 14;
 514        }
 515
 516        r->input_rotate = input_rotate;
 517        r->add_ptr = i;
 518
 519        if (out)
 520                for (j = 0; j < 16; j++)
 521                        ((__u32 *)out)[j] = r->pool[(i - j) & wordmask];
 522
 523        spin_unlock_irqrestore(&r->lock, flags);
 524}
 525
 526static void mix_pool_bytes(struct entropy_store *r, const void *in, int bytes)
 527{
 528       mix_pool_bytes_extract(r, in, bytes, NULL);
 529}
 530
 531/*
 532 * Credit (or debit) the entropy store with n bits of entropy
 533 */
 534static void credit_entropy_bits(struct entropy_store *r, int nbits)
 535{
 536        unsigned long flags;
 537        int entropy_count;
 538
 539        if (!nbits)
 540                return;
 541
 542        spin_lock_irqsave(&r->lock, flags);
 543
 544        DEBUG_ENT("added %d entropy credits to %s\n", nbits, r->name);
 545        entropy_count = r->entropy_count;
 546        entropy_count += nbits;
 547        if (entropy_count < 0) {
 548                DEBUG_ENT("negative entropy/overflow\n");
 549                entropy_count = 0;
 550        } else if (entropy_count > r->poolinfo->POOLBITS)
 551                entropy_count = r->poolinfo->POOLBITS;
 552        r->entropy_count = entropy_count;
 553
 554        /* should we wake readers? */
 555        if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {
 556                wake_up_interruptible(&random_read_wait);
 557                kill_fasync(&fasync, SIGIO, POLL_IN);
 558        }
 559        spin_unlock_irqrestore(&r->lock, flags);
 560}
 561
 562/*********************************************************************
 563 *
 564 * Entropy input management
 565 *
 566 *********************************************************************/
 567
 568/* There is one of these per entropy source */
 569struct timer_rand_state {
 570        cycles_t last_time;
 571        long last_delta, last_delta2;
 572        unsigned dont_count_entropy:1;
 573};
 574
 575#ifndef CONFIG_GENERIC_HARDIRQS
 576
 577static struct timer_rand_state *irq_timer_state[NR_IRQS];
 578
 579static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
 580{
 581        return irq_timer_state[irq];
 582}
 583
 584static void set_timer_rand_state(unsigned int irq,
 585                                 struct timer_rand_state *state)
 586{
 587        irq_timer_state[irq] = state;
 588}
 589
 590#else
 591
 592static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
 593{
 594        struct irq_desc *desc;
 595
 596        desc = irq_to_desc(irq);
 597
 598        return desc->timer_rand_state;
 599}
 600
 601static void set_timer_rand_state(unsigned int irq,
 602                                 struct timer_rand_state *state)
 603{
 604        struct irq_desc *desc;
 605
 606        desc = irq_to_desc(irq);
 607
 608        desc->timer_rand_state = state;
 609}
 610#endif
 611
 612static struct timer_rand_state input_timer_state;
 613
 614/*
 615 * This function adds entropy to the entropy "pool" by using timing
 616 * delays.  It uses the timer_rand_state structure to make an estimate
 617 * of how many bits of entropy this call has added to the pool.
 618 *
 619 * The number "num" is also added to the pool - it should somehow describe
 620 * the type of event which just happened.  This is currently 0-255 for
 621 * keyboard scan codes, and 256 upwards for interrupts.
 622 *
 623 */
 624static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
 625{
 626        struct {
 627                cycles_t cycles;
 628                long jiffies;
 629                unsigned num;
 630        } sample;
 631        long delta, delta2, delta3;
 632
 633        preempt_disable();
 634        /* if over the trickle threshold, use only 1 in 4096 samples */
 635        if (input_pool.entropy_count > trickle_thresh &&
 636            ((__this_cpu_inc_return(trickle_count) - 1) & 0xfff))
 637                goto out;
 638
 639        sample.jiffies = jiffies;
 640        sample.cycles = get_cycles();
 641        sample.num = num;
 642        mix_pool_bytes(&input_pool, &sample, sizeof(sample));
 643
 644        /*
 645         * Calculate number of bits of randomness we probably added.
 646         * We take into account the first, second and third-order deltas
 647         * in order to make our estimate.
 648         */
 649
 650        if (!state->dont_count_entropy) {
 651                delta = sample.jiffies - state->last_time;
 652                state->last_time = sample.jiffies;
 653
 654                delta2 = delta - state->last_delta;
 655                state->last_delta = delta;
 656
 657                delta3 = delta2 - state->last_delta2;
 658                state->last_delta2 = delta2;
 659
 660                if (delta < 0)
 661                        delta = -delta;
 662                if (delta2 < 0)
 663                        delta2 = -delta2;
 664                if (delta3 < 0)
 665                        delta3 = -delta3;
 666                if (delta > delta2)
 667                        delta = delta2;
 668                if (delta > delta3)
 669                        delta = delta3;
 670
 671                /*
 672                 * delta is now minimum absolute delta.
 673                 * Round down by 1 bit on general principles,
 674                 * and limit entropy entimate to 12 bits.
 675                 */
 676                credit_entropy_bits(&input_pool,
 677                                    min_t(int, fls(delta>>1), 11));
 678        }
 679out:
 680        preempt_enable();
 681}
 682
 683void add_input_randomness(unsigned int type, unsigned int code,
 684                                 unsigned int value)
 685{
 686        static unsigned char last_value;
 687
 688        /* ignore autorepeat and the like */
 689        if (value == last_value)
 690                return;
 691
 692        DEBUG_ENT("input event\n");
 693        last_value = value;
 694        add_timer_randomness(&input_timer_state,
 695                             (type << 4) ^ code ^ (code >> 4) ^ value);
 696}
 697EXPORT_SYMBOL_GPL(add_input_randomness);
 698
 699void add_interrupt_randomness(int irq)
 700{
 701        struct timer_rand_state *state;
 702
 703        state = get_timer_rand_state(irq);
 704
 705        if (state == NULL)
 706                return;
 707
 708        DEBUG_ENT("irq event %d\n", irq);
 709        add_timer_randomness(state, 0x100 + irq);
 710}
 711
 712#ifdef CONFIG_BLOCK
 713void add_disk_randomness(struct gendisk *disk)
 714{
 715        if (!disk || !disk->random)
 716                return;
 717        /* first major is 1, so we get >= 0x200 here */
 718        DEBUG_ENT("disk event %d:%d\n",
 719                  MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));
 720
 721        add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
 722}
 723#endif
 724
 725/*********************************************************************
 726 *
 727 * Entropy extraction routines
 728 *
 729 *********************************************************************/
 730
 731static ssize_t extract_entropy(struct entropy_store *r, void *buf,
 732                               size_t nbytes, int min, int rsvd);
 733
 734/*
 735 * This utility inline function is responsible for transferring entropy
 736 * from the primary pool to the secondary extraction pool. We make
 737 * sure we pull enough for a 'catastrophic reseed'.
 738 */
 739static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
 740{
 741        __u32 tmp[OUTPUT_POOL_WORDS];
 742
 743        if (r->pull && r->entropy_count < nbytes * 8 &&
 744            r->entropy_count < r->poolinfo->POOLBITS) {
 745                /* If we're limited, always leave two wakeup worth's BITS */
 746                int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
 747                int bytes = nbytes;
 748
 749                /* pull at least as many as BYTES as wakeup BITS */
 750                bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
 751                /* but never more than the buffer size */
 752                bytes = min_t(int, bytes, sizeof(tmp));
 753
 754                DEBUG_ENT("going to reseed %s with %d bits "
 755                          "(%d of %d requested)\n",
 756                          r->name, bytes * 8, nbytes * 8, r->entropy_count);
 757
 758                bytes = extract_entropy(r->pull, tmp, bytes,
 759                                        random_read_wakeup_thresh / 8, rsvd);
 760                mix_pool_bytes(r, tmp, bytes);
 761                credit_entropy_bits(r, bytes*8);
 762        }
 763}
 764
 765/*
 766 * These functions extracts randomness from the "entropy pool", and
 767 * returns it in a buffer.
 768 *
 769 * The min parameter specifies the minimum amount we can pull before
 770 * failing to avoid races that defeat catastrophic reseeding while the
 771 * reserved parameter indicates how much entropy we must leave in the
 772 * pool after each pull to avoid starving other readers.
 773 *
 774 * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
 775 */
 776
 777static size_t account(struct entropy_store *r, size_t nbytes, int min,
 778                      int reserved)
 779{
 780        unsigned long flags;
 781
 782        /* Hold lock while accounting */
 783        spin_lock_irqsave(&r->lock, flags);
 784
 785        BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
 786        DEBUG_ENT("trying to extract %d bits from %s\n",
 787                  nbytes * 8, r->name);
 788
 789        /* Can we pull enough? */
 790        if (r->entropy_count / 8 < min + reserved) {
 791                nbytes = 0;
 792        } else {
 793                /* If limited, never pull more than available */
 794                if (r->limit && nbytes + reserved >= r->entropy_count / 8)
 795                        nbytes = r->entropy_count/8 - reserved;
 796
 797                if (r->entropy_count / 8 >= nbytes + reserved)
 798                        r->entropy_count -= nbytes*8;
 799                else
 800                        r->entropy_count = reserved;
 801
 802                if (r->entropy_count < random_write_wakeup_thresh) {
 803                        wake_up_interruptible(&random_write_wait);
 804                        kill_fasync(&fasync, SIGIO, POLL_OUT);
 805                }
 806        }
 807
 808        DEBUG_ENT("debiting %d entropy credits from %s%s\n",
 809                  nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
 810
 811        spin_unlock_irqrestore(&r->lock, flags);
 812
 813        return nbytes;
 814}
 815
 816static void extract_buf(struct entropy_store *r, __u8 *out)
 817{
 818        int i;
 819        __u32 hash[5], workspace[SHA_WORKSPACE_WORDS];
 820        __u8 extract[64];
 821
 822        /* Generate a hash across the pool, 16 words (512 bits) at a time */
 823        sha_init(hash);
 824        for (i = 0; i < r->poolinfo->poolwords; i += 16)
 825                sha_transform(hash, (__u8 *)(r->pool + i), workspace);
 826
 827        /*
 828         * We mix the hash back into the pool to prevent backtracking
 829         * attacks (where the attacker knows the state of the pool
 830         * plus the current outputs, and attempts to find previous
 831         * ouputs), unless the hash function can be inverted. By
 832         * mixing at least a SHA1 worth of hash data back, we make
 833         * brute-forcing the feedback as hard as brute-forcing the
 834         * hash.
 835         */
 836        mix_pool_bytes_extract(r, hash, sizeof(hash), extract);
 837
 838        /*
 839         * To avoid duplicates, we atomically extract a portion of the
 840         * pool while mixing, and hash one final time.
 841         */
 842        sha_transform(hash, extract, workspace);
 843        memset(extract, 0, sizeof(extract));
 844        memset(workspace, 0, sizeof(workspace));
 845
 846        /*
 847         * In case the hash function has some recognizable output
 848         * pattern, we fold it in half. Thus, we always feed back
 849         * twice as much data as we output.
 850         */
 851        hash[0] ^= hash[3];
 852        hash[1] ^= hash[4];
 853        hash[2] ^= rol32(hash[2], 16);
 854        memcpy(out, hash, EXTRACT_SIZE);
 855        memset(hash, 0, sizeof(hash));
 856}
 857
 858static ssize_t extract_entropy(struct entropy_store *r, void *buf,
 859                               size_t nbytes, int min, int reserved)
 860{
 861        ssize_t ret = 0, i;
 862        __u8 tmp[EXTRACT_SIZE];
 863        unsigned long flags;
 864
 865        xfer_secondary_pool(r, nbytes);
 866        nbytes = account(r, nbytes, min, reserved);
 867
 868        while (nbytes) {
 869                extract_buf(r, tmp);
 870
 871                if (fips_enabled) {
 872                        spin_lock_irqsave(&r->lock, flags);
 873                        if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
 874                                panic("Hardware RNG duplicated output!\n");
 875                        memcpy(r->last_data, tmp, EXTRACT_SIZE);
 876                        spin_unlock_irqrestore(&r->lock, flags);
 877                }
 878                i = min_t(int, nbytes, EXTRACT_SIZE);
 879                memcpy(buf, tmp, i);
 880                nbytes -= i;
 881                buf += i;
 882                ret += i;
 883        }
 884
 885        /* Wipe data just returned from memory */
 886        memset(tmp, 0, sizeof(tmp));
 887
 888        return ret;
 889}
 890
 891static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
 892                                    size_t nbytes)
 893{
 894        ssize_t ret = 0, i;
 895        __u8 tmp[EXTRACT_SIZE];
 896
 897        xfer_secondary_pool(r, nbytes);
 898        nbytes = account(r, nbytes, 0, 0);
 899
 900        while (nbytes) {
 901                if (need_resched()) {
 902                        if (signal_pending(current)) {
 903                                if (ret == 0)
 904                                        ret = -ERESTARTSYS;
 905                                break;
 906                        }
 907                        schedule();
 908                }
 909
 910                extract_buf(r, tmp);
 911                i = min_t(int, nbytes, EXTRACT_SIZE);
 912                if (copy_to_user(buf, tmp, i)) {
 913                        ret = -EFAULT;
 914                        break;
 915                }
 916
 917                nbytes -= i;
 918                buf += i;
 919                ret += i;
 920        }
 921
 922        /* Wipe data just returned from memory */
 923        memset(tmp, 0, sizeof(tmp));
 924
 925        return ret;
 926}
 927
 928/*
 929 * This function is the exported kernel interface.  It returns some
 930 * number of good random numbers, suitable for seeding TCP sequence
 931 * numbers, etc.
 932 */
 933void get_random_bytes(void *buf, int nbytes)
 934{
 935        extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
 936}
 937EXPORT_SYMBOL(get_random_bytes);
 938
 939/*
 940 * init_std_data - initialize pool with system data
 941 *
 942 * @r: pool to initialize
 943 *
 944 * This function clears the pool's entropy count and mixes some system
 945 * data into the pool to prepare it for use. The pool is not cleared
 946 * as that can only decrease the entropy in the pool.
 947 */
 948static void init_std_data(struct entropy_store *r)
 949{
 950        ktime_t now;
 951        unsigned long flags;
 952
 953        spin_lock_irqsave(&r->lock, flags);
 954        r->entropy_count = 0;
 955        spin_unlock_irqrestore(&r->lock, flags);
 956
 957        now = ktime_get_real();
 958        mix_pool_bytes(r, &now, sizeof(now));
 959        mix_pool_bytes(r, utsname(), sizeof(*(utsname())));
 960}
 961
 962static int rand_initialize(void)
 963{
 964        init_std_data(&input_pool);
 965        init_std_data(&blocking_pool);
 966        init_std_data(&nonblocking_pool);
 967        return 0;
 968}
 969module_init(rand_initialize);
 970
 971void rand_initialize_irq(int irq)
 972{
 973        struct timer_rand_state *state;
 974
 975        state = get_timer_rand_state(irq);
 976
 977        if (state)
 978                return;
 979
 980        /*
 981         * If kzalloc returns null, we just won't use that entropy
 982         * source.
 983         */
 984        state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
 985        if (state)
 986                set_timer_rand_state(irq, state);
 987}
 988
 989#ifdef CONFIG_BLOCK
 990void rand_initialize_disk(struct gendisk *disk)
 991{
 992        struct timer_rand_state *state;
 993
 994        /*
 995         * If kzalloc returns null, we just won't use that entropy
 996         * source.
 997         */
 998        state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
 999        if (state)
1000                disk->random = state;
1001}
1002#endif
1003
1004static ssize_t
1005random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1006{
1007        ssize_t n, retval = 0, count = 0;
1008
1009        if (nbytes == 0)
1010                return 0;
1011
1012        while (nbytes > 0) {
1013                n = nbytes;
1014                if (n > SEC_XFER_SIZE)
1015                        n = SEC_XFER_SIZE;
1016
1017                DEBUG_ENT("reading %d bits\n", n*8);
1018
1019                n = extract_entropy_user(&blocking_pool, buf, n);
1020
1021                DEBUG_ENT("read got %d bits (%d still needed)\n",
1022                          n*8, (nbytes-n)*8);
1023
1024                if (n == 0) {
1025                        if (file->f_flags & O_NONBLOCK) {
1026                                retval = -EAGAIN;
1027                                break;
1028                        }
1029
1030                        DEBUG_ENT("sleeping?\n");
1031
1032                        wait_event_interruptible(random_read_wait,
1033                                input_pool.entropy_count >=
1034                                                 random_read_wakeup_thresh);
1035
1036                        DEBUG_ENT("awake\n");
1037
1038                        if (signal_pending(current)) {
1039                                retval = -ERESTARTSYS;
1040                                break;
1041                        }
1042
1043                        continue;
1044                }
1045
1046                if (n < 0) {
1047                        retval = n;
1048                        break;
1049                }
1050                count += n;
1051                buf += n;
1052                nbytes -= n;
1053                break;          /* This break makes the device work */
1054                                /* like a named pipe */
1055        }
1056
1057        return (count ? count : retval);
1058}
1059
1060static ssize_t
1061urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1062{
1063        return extract_entropy_user(&nonblocking_pool, buf, nbytes);
1064}
1065
1066static unsigned int
1067random_poll(struct file *file, poll_table * wait)
1068{
1069        unsigned int mask;
1070
1071        poll_wait(file, &random_read_wait, wait);
1072        poll_wait(file, &random_write_wait, wait);
1073        mask = 0;
1074        if (input_pool.entropy_count >= random_read_wakeup_thresh)
1075                mask |= POLLIN | POLLRDNORM;
1076        if (input_pool.entropy_count < random_write_wakeup_thresh)
1077                mask |= POLLOUT | POLLWRNORM;
1078        return mask;
1079}
1080
1081static int
1082write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1083{
1084        size_t bytes;
1085        __u32 buf[16];
1086        const char __user *p = buffer;
1087
1088        while (count > 0) {
1089                bytes = min(count, sizeof(buf));
1090                if (copy_from_user(&buf, p, bytes))
1091                        return -EFAULT;
1092
1093                count -= bytes;
1094                p += bytes;
1095
1096                mix_pool_bytes(r, buf, bytes);
1097                cond_resched();
1098        }
1099
1100        return 0;
1101}
1102
1103static ssize_t random_write(struct file *file, const char __user *buffer,
1104                            size_t count, loff_t *ppos)
1105{
1106        size_t ret;
1107
1108        ret = write_pool(&blocking_pool, buffer, count);
1109        if (ret)
1110                return ret;
1111        ret = write_pool(&nonblocking_pool, buffer, count);
1112        if (ret)
1113                return ret;
1114
1115        return (ssize_t)count;
1116}
1117
1118static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1119{
1120        int size, ent_count;
1121        int __user *p = (int __user *)arg;
1122        int retval;
1123
1124        switch (cmd) {
1125        case RNDGETENTCNT:
1126                /* inherently racy, no point locking */
1127                if (put_user(input_pool.entropy_count, p))
1128                        return -EFAULT;
1129                return 0;
1130        case RNDADDTOENTCNT:
1131                if (!capable(CAP_SYS_ADMIN))
1132                        return -EPERM;
1133                if (get_user(ent_count, p))
1134                        return -EFAULT;
1135                credit_entropy_bits(&input_pool, ent_count);
1136                return 0;
1137        case RNDADDENTROPY:
1138                if (!capable(CAP_SYS_ADMIN))
1139                        return -EPERM;
1140                if (get_user(ent_count, p++))
1141                        return -EFAULT;
1142                if (ent_count < 0)
1143                        return -EINVAL;
1144                if (get_user(size, p++))
1145                        return -EFAULT;
1146                retval = write_pool(&input_pool, (const char __user *)p,
1147                                    size);
1148                if (retval < 0)
1149                        return retval;
1150                credit_entropy_bits(&input_pool, ent_count);
1151                return 0;
1152        case RNDZAPENTCNT:
1153        case RNDCLEARPOOL:
1154                /* Clear the entropy pool counters. */
1155                if (!capable(CAP_SYS_ADMIN))
1156                        return -EPERM;
1157                rand_initialize();
1158                return 0;
1159        default:
1160                return -EINVAL;
1161        }
1162}
1163
1164static int random_fasync(int fd, struct file *filp, int on)
1165{
1166        return fasync_helper(fd, filp, on, &fasync);
1167}
1168
1169const struct file_operations random_fops = {
1170        .read  = random_read,
1171        .write = random_write,
1172        .poll  = random_poll,
1173        .unlocked_ioctl = random_ioctl,
1174        .fasync = random_fasync,
1175        .llseek = noop_llseek,
1176};
1177
1178const struct file_operations urandom_fops = {
1179        .read  = urandom_read,
1180        .write = random_write,
1181        .unlocked_ioctl = random_ioctl,
1182        .fasync = random_fasync,
1183        .llseek = noop_llseek,
1184};
1185
1186/***************************************************************
1187 * Random UUID interface
1188 *
1189 * Used here for a Boot ID, but can be useful for other kernel
1190 * drivers.
1191 ***************************************************************/
1192
1193/*
1194 * Generate random UUID
1195 */
1196void generate_random_uuid(unsigned char uuid_out[16])
1197{
1198        get_random_bytes(uuid_out, 16);
1199        /* Set UUID version to 4 --- truly random generation */
1200        uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1201        /* Set the UUID variant to DCE */
1202        uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1203}
1204EXPORT_SYMBOL(generate_random_uuid);
1205
1206/********************************************************************
1207 *
1208 * Sysctl interface
1209 *
1210 ********************************************************************/
1211
1212#ifdef CONFIG_SYSCTL
1213
1214#include <linux/sysctl.h>
1215
1216static int min_read_thresh = 8, min_write_thresh;
1217static int max_read_thresh = INPUT_POOL_WORDS * 32;
1218static int max_write_thresh = INPUT_POOL_WORDS * 32;
1219static char sysctl_bootid[16];
1220
1221/*
1222 * These functions is used to return both the bootid UUID, and random
1223 * UUID.  The difference is in whether table->data is NULL; if it is,
1224 * then a new UUID is generated and returned to the user.
1225 *
1226 * If the user accesses this via the proc interface, it will be returned
1227 * as an ASCII string in the standard UUID format.  If accesses via the
1228 * sysctl system call, it is returned as 16 bytes of binary data.
1229 */
1230static int proc_do_uuid(ctl_table *table, int write,
1231                        void __user *buffer, size_t *lenp, loff_t *ppos)
1232{
1233        ctl_table fake_table;
1234        unsigned char buf[64], tmp_uuid[16], *uuid;
1235
1236        uuid = table->data;
1237        if (!uuid) {
1238                uuid = tmp_uuid;
1239                uuid[8] = 0;
1240        }
1241        if (uuid[8] == 0)
1242                generate_random_uuid(uuid);
1243
1244        sprintf(buf, "%pU", uuid);
1245
1246        fake_table.data = buf;
1247        fake_table.maxlen = sizeof(buf);
1248
1249        return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1250}
1251
1252static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1253ctl_table random_table[] = {
1254        {
1255                .procname       = "poolsize",
1256                .data           = &sysctl_poolsize,
1257                .maxlen         = sizeof(int),
1258                .mode           = 0444,
1259                .proc_handler   = proc_dointvec,
1260        },
1261        {
1262                .procname       = "entropy_avail",
1263                .maxlen         = sizeof(int),
1264                .mode           = 0444,
1265                .proc_handler   = proc_dointvec,
1266                .data           = &input_pool.entropy_count,
1267        },
1268        {
1269                .procname       = "read_wakeup_threshold",
1270                .data           = &random_read_wakeup_thresh,
1271                .maxlen         = sizeof(int),
1272                .mode           = 0644,
1273                .proc_handler   = proc_dointvec_minmax,
1274                .extra1         = &min_read_thresh,
1275                .extra2         = &max_read_thresh,
1276        },
1277        {
1278                .procname       = "write_wakeup_threshold",
1279                .data           = &random_write_wakeup_thresh,
1280                .maxlen         = sizeof(int),
1281                .mode           = 0644,
1282                .proc_handler   = proc_dointvec_minmax,
1283                .extra1         = &min_write_thresh,
1284                .extra2         = &max_write_thresh,
1285        },
1286        {
1287                .procname       = "boot_id",
1288                .data           = &sysctl_bootid,
1289                .maxlen         = 16,
1290                .mode           = 0444,
1291                .proc_handler   = proc_do_uuid,
1292        },
1293        {
1294                .procname       = "uuid",
1295                .maxlen         = 16,
1296                .mode           = 0444,
1297                .proc_handler   = proc_do_uuid,
1298        },
1299        { }
1300};
1301#endif  /* CONFIG_SYSCTL */
1302
1303static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1304
1305static int __init random_int_secret_init(void)
1306{
1307        get_random_bytes(random_int_secret, sizeof(random_int_secret));
1308        return 0;
1309}
1310late_initcall(random_int_secret_init);
1311
1312/*
1313 * Get a random word for internal kernel use only. Similar to urandom but
1314 * with the goal of minimal entropy pool depletion. As a result, the random
1315 * value is not cryptographically secure but for several uses the cost of
1316 * depleting entropy is too high
1317 */
1318DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1319unsigned int get_random_int(void)
1320{
1321        __u32 *hash = get_cpu_var(get_random_int_hash);
1322        unsigned int ret;
1323
1324        hash[0] += current->pid + jiffies + get_cycles();
1325        md5_transform(hash, random_int_secret);
1326        ret = hash[0];
1327        put_cpu_var(get_random_int_hash);
1328
1329        return ret;
1330}
1331
1332/*
1333 * randomize_range() returns a start address such that
1334 *
1335 *    [...... <range> .....]
1336 *  start                  end
1337 *
1338 * a <range> with size "len" starting at the return value is inside in the
1339 * area defined by [start, end], but is otherwise randomized.
1340 */
1341unsigned long
1342randomize_range(unsigned long start, unsigned long end, unsigned long len)
1343{
1344        unsigned long range = end - len - start;
1345
1346        if (end <= start + len)
1347                return 0;
1348        return PAGE_ALIGN(get_random_int() % range + start);
1349}
1350
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