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 bool 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                long jiffies;
 628                unsigned cycles;
 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
 641        /* Use arch random value, fall back to cycles */
 642        if (!arch_get_random_int(&sample.cycles))
 643                sample.cycles = get_cycles();
 644
 645        sample.num = num;
 646        mix_pool_bytes(&input_pool, &sample, sizeof(sample));
 647
 648        /*
 649         * Calculate number of bits of randomness we probably added.
 650         * We take into account the first, second and third-order deltas
 651         * in order to make our estimate.
 652         */
 653
 654        if (!state->dont_count_entropy) {
 655                delta = sample.jiffies - state->last_time;
 656                state->last_time = sample.jiffies;
 657
 658                delta2 = delta - state->last_delta;
 659                state->last_delta = delta;
 660
 661                delta3 = delta2 - state->last_delta2;
 662                state->last_delta2 = delta2;
 663
 664                if (delta < 0)
 665                        delta = -delta;
 666                if (delta2 < 0)
 667                        delta2 = -delta2;
 668                if (delta3 < 0)
 669                        delta3 = -delta3;
 670                if (delta > delta2)
 671                        delta = delta2;
 672                if (delta > delta3)
 673                        delta = delta3;
 674
 675                /*
 676                 * delta is now minimum absolute delta.
 677                 * Round down by 1 bit on general principles,
 678                 * and limit entropy entimate to 12 bits.
 679                 */
 680                credit_entropy_bits(&input_pool,
 681                                    min_t(int, fls(delta>>1), 11));
 682        }
 683out:
 684        preempt_enable();
 685}
 686
 687void add_input_randomness(unsigned int type, unsigned int code,
 688                                 unsigned int value)
 689{
 690        static unsigned char last_value;
 691
 692        /* ignore autorepeat and the like */
 693        if (value == last_value)
 694                return;
 695
 696        DEBUG_ENT("input event\n");
 697        last_value = value;
 698        add_timer_randomness(&input_timer_state,
 699                             (type << 4) ^ code ^ (code >> 4) ^ value);
 700}
 701EXPORT_SYMBOL_GPL(add_input_randomness);
 702
 703void add_interrupt_randomness(int irq)
 704{
 705        struct timer_rand_state *state;
 706
 707        state = get_timer_rand_state(irq);
 708
 709        if (state == NULL)
 710                return;
 711
 712        DEBUG_ENT("irq event %d\n", irq);
 713        add_timer_randomness(state, 0x100 + irq);
 714}
 715
 716#ifdef CONFIG_BLOCK
 717void add_disk_randomness(struct gendisk *disk)
 718{
 719        if (!disk || !disk->random)
 720                return;
 721        /* first major is 1, so we get >= 0x200 here */
 722        DEBUG_ENT("disk event %d:%d\n",
 723                  MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));
 724
 725        add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
 726}
 727#endif
 728
 729/*********************************************************************
 730 *
 731 * Entropy extraction routines
 732 *
 733 *********************************************************************/
 734
 735static ssize_t extract_entropy(struct entropy_store *r, void *buf,
 736                               size_t nbytes, int min, int rsvd);
 737
 738/*
 739 * This utility inline function is responsible for transferring entropy
 740 * from the primary pool to the secondary extraction pool. We make
 741 * sure we pull enough for a 'catastrophic reseed'.
 742 */
 743static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
 744{
 745        __u32 tmp[OUTPUT_POOL_WORDS];
 746
 747        if (r->pull && r->entropy_count < nbytes * 8 &&
 748            r->entropy_count < r->poolinfo->POOLBITS) {
 749                /* If we're limited, always leave two wakeup worth's BITS */
 750                int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
 751                int bytes = nbytes;
 752
 753                /* pull at least as many as BYTES as wakeup BITS */
 754                bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
 755                /* but never more than the buffer size */
 756                bytes = min_t(int, bytes, sizeof(tmp));
 757
 758                DEBUG_ENT("going to reseed %s with %d bits "
 759                          "(%d of %d requested)\n",
 760                          r->name, bytes * 8, nbytes * 8, r->entropy_count);
 761
 762                bytes = extract_entropy(r->pull, tmp, bytes,
 763                                        random_read_wakeup_thresh / 8, rsvd);
 764                mix_pool_bytes(r, tmp, bytes);
 765                credit_entropy_bits(r, bytes*8);
 766        }
 767}
 768
 769/*
 770 * These functions extracts randomness from the "entropy pool", and
 771 * returns it in a buffer.
 772 *
 773 * The min parameter specifies the minimum amount we can pull before
 774 * failing to avoid races that defeat catastrophic reseeding while the
 775 * reserved parameter indicates how much entropy we must leave in the
 776 * pool after each pull to avoid starving other readers.
 777 *
 778 * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
 779 */
 780
 781static size_t account(struct entropy_store *r, size_t nbytes, int min,
 782                      int reserved)
 783{
 784        unsigned long flags;
 785
 786        /* Hold lock while accounting */
 787        spin_lock_irqsave(&r->lock, flags);
 788
 789        BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
 790        DEBUG_ENT("trying to extract %d bits from %s\n",
 791                  nbytes * 8, r->name);
 792
 793        /* Can we pull enough? */
 794        if (r->entropy_count / 8 < min + reserved) {
 795                nbytes = 0;
 796        } else {
 797                /* If limited, never pull more than available */
 798                if (r->limit && nbytes + reserved >= r->entropy_count / 8)
 799                        nbytes = r->entropy_count/8 - reserved;
 800
 801                if (r->entropy_count / 8 >= nbytes + reserved)
 802                        r->entropy_count -= nbytes*8;
 803                else
 804                        r->entropy_count = reserved;
 805
 806                if (r->entropy_count < random_write_wakeup_thresh) {
 807                        wake_up_interruptible(&random_write_wait);
 808                        kill_fasync(&fasync, SIGIO, POLL_OUT);
 809                }
 810        }
 811
 812        DEBUG_ENT("debiting %d entropy credits from %s%s\n",
 813                  nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
 814
 815        spin_unlock_irqrestore(&r->lock, flags);
 816
 817        return nbytes;
 818}
 819
 820static void extract_buf(struct entropy_store *r, __u8 *out)
 821{
 822        int i;
 823        __u32 hash[5], workspace[SHA_WORKSPACE_WORDS];
 824        __u8 extract[64];
 825
 826        /* Generate a hash across the pool, 16 words (512 bits) at a time */
 827        sha_init(hash);
 828        for (i = 0; i < r->poolinfo->poolwords; i += 16)
 829                sha_transform(hash, (__u8 *)(r->pool + i), workspace);
 830
 831        /*
 832         * We mix the hash back into the pool to prevent backtracking
 833         * attacks (where the attacker knows the state of the pool
 834         * plus the current outputs, and attempts to find previous
 835         * ouputs), unless the hash function can be inverted. By
 836         * mixing at least a SHA1 worth of hash data back, we make
 837         * brute-forcing the feedback as hard as brute-forcing the
 838         * hash.
 839         */
 840        mix_pool_bytes_extract(r, hash, sizeof(hash), extract);
 841
 842        /*
 843         * To avoid duplicates, we atomically extract a portion of the
 844         * pool while mixing, and hash one final time.
 845         */
 846        sha_transform(hash, extract, workspace);
 847        memset(extract, 0, sizeof(extract));
 848        memset(workspace, 0, sizeof(workspace));
 849
 850        /*
 851         * In case the hash function has some recognizable output
 852         * pattern, we fold it in half. Thus, we always feed back
 853         * twice as much data as we output.
 854         */
 855        hash[0] ^= hash[3];
 856        hash[1] ^= hash[4];
 857        hash[2] ^= rol32(hash[2], 16);
 858        memcpy(out, hash, EXTRACT_SIZE);
 859        memset(hash, 0, sizeof(hash));
 860}
 861
 862static ssize_t extract_entropy(struct entropy_store *r, void *buf,
 863                               size_t nbytes, int min, int reserved)
 864{
 865        ssize_t ret = 0, i;
 866        __u8 tmp[EXTRACT_SIZE];
 867        unsigned long flags;
 868
 869        xfer_secondary_pool(r, nbytes);
 870        nbytes = account(r, nbytes, min, reserved);
 871
 872        while (nbytes) {
 873                extract_buf(r, tmp);
 874
 875                if (fips_enabled) {
 876                        spin_lock_irqsave(&r->lock, flags);
 877                        if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
 878                                panic("Hardware RNG duplicated output!\n");
 879                        memcpy(r->last_data, tmp, EXTRACT_SIZE);
 880                        spin_unlock_irqrestore(&r->lock, flags);
 881                }
 882                i = min_t(int, nbytes, EXTRACT_SIZE);
 883                memcpy(buf, tmp, i);
 884                nbytes -= i;
 885                buf += i;
 886                ret += i;
 887        }
 888
 889        /* Wipe data just returned from memory */
 890        memset(tmp, 0, sizeof(tmp));
 891
 892        return ret;
 893}
 894
 895static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
 896                                    size_t nbytes)
 897{
 898        ssize_t ret = 0, i;
 899        __u8 tmp[EXTRACT_SIZE];
 900
 901        xfer_secondary_pool(r, nbytes);
 902        nbytes = account(r, nbytes, 0, 0);
 903
 904        while (nbytes) {
 905                if (need_resched()) {
 906                        if (signal_pending(current)) {
 907                                if (ret == 0)
 908                                        ret = -ERESTARTSYS;
 909                                break;
 910                        }
 911                        schedule();
 912                }
 913
 914                extract_buf(r, tmp);
 915                i = min_t(int, nbytes, EXTRACT_SIZE);
 916                if (copy_to_user(buf, tmp, i)) {
 917                        ret = -EFAULT;
 918                        break;
 919                }
 920
 921                nbytes -= i;
 922                buf += i;
 923                ret += i;
 924        }
 925
 926        /* Wipe data just returned from memory */
 927        memset(tmp, 0, sizeof(tmp));
 928
 929        return ret;
 930}
 931
 932/*
 933 * This function is the exported kernel interface.  It returns some
 934 * number of good random numbers, suitable for seeding TCP sequence
 935 * numbers, etc.
 936 */
 937void get_random_bytes(void *buf, int nbytes)
 938{
 939        char *p = buf;
 940
 941        while (nbytes) {
 942                unsigned long v;
 943                int chunk = min(nbytes, (int)sizeof(unsigned long));
 944                
 945                if (!arch_get_random_long(&v))
 946                        break;
 947                
 948                memcpy(p, &v, chunk);
 949                p += chunk;
 950                nbytes -= chunk;
 951        }
 952
 953        extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
 954}
 955EXPORT_SYMBOL(get_random_bytes);
 956
 957/*
 958 * init_std_data - initialize pool with system data
 959 *
 960 * @r: pool to initialize
 961 *
 962 * This function clears the pool's entropy count and mixes some system
 963 * data into the pool to prepare it for use. The pool is not cleared
 964 * as that can only decrease the entropy in the pool.
 965 */
 966static void init_std_data(struct entropy_store *r)
 967{
 968        int i;
 969        ktime_t now;
 970        unsigned long flags;
 971
 972        spin_lock_irqsave(&r->lock, flags);
 973        r->entropy_count = 0;
 974        spin_unlock_irqrestore(&r->lock, flags);
 975
 976        now = ktime_get_real();
 977        mix_pool_bytes(r, &now, sizeof(now));
 978        for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof flags) {
 979                if (!arch_get_random_long(&flags))
 980                        break;
 981                mix_pool_bytes(r, &flags, sizeof(flags));
 982        }
 983        mix_pool_bytes(r, utsname(), sizeof(*(utsname())));
 984}
 985
 986static int rand_initialize(void)
 987{
 988        init_std_data(&input_pool);
 989        init_std_data(&blocking_pool);
 990        init_std_data(&nonblocking_pool);
 991        return 0;
 992}
 993module_init(rand_initialize);
 994
 995void rand_initialize_irq(int irq)
 996{
 997        struct timer_rand_state *state;
 998
 999        state = get_timer_rand_state(irq);
1000
1001        if (state)
1002                return;
1003
1004        /*
1005         * If kzalloc returns null, we just won't use that entropy
1006         * source.
1007         */
1008        state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1009        if (state)
1010                set_timer_rand_state(irq, state);
1011}
1012
1013#ifdef CONFIG_BLOCK
1014void rand_initialize_disk(struct gendisk *disk)
1015{
1016        struct timer_rand_state *state;
1017
1018        /*
1019         * If kzalloc returns null, we just won't use that entropy
1020         * source.
1021         */
1022        state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
1023        if (state)
1024                disk->random = state;
1025}
1026#endif
1027
1028static ssize_t
1029random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1030{
1031        ssize_t n, retval = 0, count = 0;
1032
1033        if (nbytes == 0)
1034                return 0;
1035
1036        while (nbytes > 0) {
1037                n = nbytes;
1038                if (n > SEC_XFER_SIZE)
1039                        n = SEC_XFER_SIZE;
1040
1041                DEBUG_ENT("reading %d bits\n", n*8);
1042
1043                n = extract_entropy_user(&blocking_pool, buf, n);
1044
1045                DEBUG_ENT("read got %d bits (%d still needed)\n",
1046                          n*8, (nbytes-n)*8);
1047
1048                if (n == 0) {
1049                        if (file->f_flags & O_NONBLOCK) {
1050                                retval = -EAGAIN;
1051                                break;
1052                        }
1053
1054                        DEBUG_ENT("sleeping?\n");
1055
1056                        wait_event_interruptible(random_read_wait,
1057                                input_pool.entropy_count >=
1058                                                 random_read_wakeup_thresh);
1059
1060                        DEBUG_ENT("awake\n");
1061
1062                        if (signal_pending(current)) {
1063                                retval = -ERESTARTSYS;
1064                                break;
1065                        }
1066
1067                        continue;
1068                }
1069
1070                if (n < 0) {
1071                        retval = n;
1072                        break;
1073                }
1074                count += n;
1075                buf += n;
1076                nbytes -= n;
1077                break;          /* This break makes the device work */
1078                                /* like a named pipe */
1079        }
1080
1081        return (count ? count : retval);
1082}
1083
1084static ssize_t
1085urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1086{
1087        return extract_entropy_user(&nonblocking_pool, buf, nbytes);
1088}
1089
1090static unsigned int
1091random_poll(struct file *file, poll_table * wait)
1092{
1093        unsigned int mask;
1094
1095        poll_wait(file, &random_read_wait, wait);
1096        poll_wait(file, &random_write_wait, wait);
1097        mask = 0;
1098        if (input_pool.entropy_count >= random_read_wakeup_thresh)
1099                mask |= POLLIN | POLLRDNORM;
1100        if (input_pool.entropy_count < random_write_wakeup_thresh)
1101                mask |= POLLOUT | POLLWRNORM;
1102        return mask;
1103}
1104
1105static int
1106write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1107{
1108        size_t bytes;
1109        __u32 buf[16];
1110        const char __user *p = buffer;
1111
1112        while (count > 0) {
1113                bytes = min(count, sizeof(buf));
1114                if (copy_from_user(&buf, p, bytes))
1115                        return -EFAULT;
1116
1117                count -= bytes;
1118                p += bytes;
1119
1120                mix_pool_bytes(r, buf, bytes);
1121                cond_resched();
1122        }
1123
1124        return 0;
1125}
1126
1127static ssize_t random_write(struct file *file, const char __user *buffer,
1128                            size_t count, loff_t *ppos)
1129{
1130        size_t ret;
1131
1132        ret = write_pool(&blocking_pool, buffer, count);
1133        if (ret)
1134                return ret;
1135        ret = write_pool(&nonblocking_pool, buffer, count);
1136        if (ret)
1137                return ret;
1138
1139        return (ssize_t)count;
1140}
1141
1142static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1143{
1144        int size, ent_count;
1145        int __user *p = (int __user *)arg;
1146        int retval;
1147
1148        switch (cmd) {
1149        case RNDGETENTCNT:
1150                /* inherently racy, no point locking */
1151                if (put_user(input_pool.entropy_count, p))
1152                        return -EFAULT;
1153                return 0;
1154        case RNDADDTOENTCNT:
1155                if (!capable(CAP_SYS_ADMIN))
1156                        return -EPERM;
1157                if (get_user(ent_count, p))
1158                        return -EFAULT;
1159                credit_entropy_bits(&input_pool, ent_count);
1160                return 0;
1161        case RNDADDENTROPY:
1162                if (!capable(CAP_SYS_ADMIN))
1163                        return -EPERM;
1164                if (get_user(ent_count, p++))
1165                        return -EFAULT;
1166                if (ent_count < 0)
1167                        return -EINVAL;
1168                if (get_user(size, p++))
1169                        return -EFAULT;
1170                retval = write_pool(&input_pool, (const char __user *)p,
1171                                    size);
1172                if (retval < 0)
1173                        return retval;
1174                credit_entropy_bits(&input_pool, ent_count);
1175                return 0;
1176        case RNDZAPENTCNT:
1177        case RNDCLEARPOOL:
1178                /* Clear the entropy pool counters. */
1179                if (!capable(CAP_SYS_ADMIN))
1180                        return -EPERM;
1181                rand_initialize();
1182                return 0;
1183        default:
1184                return -EINVAL;
1185        }
1186}
1187
1188static int random_fasync(int fd, struct file *filp, int on)
1189{
1190        return fasync_helper(fd, filp, on, &fasync);
1191}
1192
1193const struct file_operations random_fops = {
1194        .read  = random_read,
1195        .write = random_write,
1196        .poll  = random_poll,
1197        .unlocked_ioctl = random_ioctl,
1198        .fasync = random_fasync,
1199        .llseek = noop_llseek,
1200};
1201
1202const struct file_operations urandom_fops = {
1203        .read  = urandom_read,
1204        .write = random_write,
1205        .unlocked_ioctl = random_ioctl,
1206        .fasync = random_fasync,
1207        .llseek = noop_llseek,
1208};
1209
1210/***************************************************************
1211 * Random UUID interface
1212 *
1213 * Used here for a Boot ID, but can be useful for other kernel
1214 * drivers.
1215 ***************************************************************/
1216
1217/*
1218 * Generate random UUID
1219 */
1220void generate_random_uuid(unsigned char uuid_out[16])
1221{
1222        get_random_bytes(uuid_out, 16);
1223        /* Set UUID version to 4 --- truly random generation */
1224        uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1225        /* Set the UUID variant to DCE */
1226        uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1227}
1228EXPORT_SYMBOL(generate_random_uuid);
1229
1230/********************************************************************
1231 *
1232 * Sysctl interface
1233 *
1234 ********************************************************************/
1235
1236#ifdef CONFIG_SYSCTL
1237
1238#include <linux/sysctl.h>
1239
1240static int min_read_thresh = 8, min_write_thresh;
1241static int max_read_thresh = INPUT_POOL_WORDS * 32;
1242static int max_write_thresh = INPUT_POOL_WORDS * 32;
1243static char sysctl_bootid[16];
1244
1245/*
1246 * These functions is used to return both the bootid UUID, and random
1247 * UUID.  The difference is in whether table->data is NULL; if it is,
1248 * then a new UUID is generated and returned to the user.
1249 *
1250 * If the user accesses this via the proc interface, it will be returned
1251 * as an ASCII string in the standard UUID format.  If accesses via the
1252 * sysctl system call, it is returned as 16 bytes of binary data.
1253 */
1254static int proc_do_uuid(ctl_table *table, int write,
1255                        void __user *buffer, size_t *lenp, loff_t *ppos)
1256{
1257        ctl_table fake_table;
1258        unsigned char buf[64], tmp_uuid[16], *uuid;
1259
1260        uuid = table->data;
1261        if (!uuid) {
1262                uuid = tmp_uuid;
1263                uuid[8] = 0;
1264        }
1265        if (uuid[8] == 0)
1266                generate_random_uuid(uuid);
1267
1268        sprintf(buf, "%pU", uuid);
1269
1270        fake_table.data = buf;
1271        fake_table.maxlen = sizeof(buf);
1272
1273        return proc_dostring(&fake_table, write, buffer, lenp, ppos);
1274}
1275
1276static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1277ctl_table random_table[] = {
1278        {
1279                .procname       = "poolsize",
1280                .data           = &sysctl_poolsize,
1281                .maxlen         = sizeof(int),
1282                .mode           = 0444,
1283                .proc_handler   = proc_dointvec,
1284        },
1285        {
1286                .procname       = "entropy_avail",
1287                .maxlen         = sizeof(int),
1288                .mode           = 0444,
1289                .proc_handler   = proc_dointvec,
1290                .data           = &input_pool.entropy_count,
1291        },
1292        {
1293                .procname       = "read_wakeup_threshold",
1294                .data           = &random_read_wakeup_thresh,
1295                .maxlen         = sizeof(int),
1296                .mode           = 0644,
1297                .proc_handler   = proc_dointvec_minmax,
1298                .extra1         = &min_read_thresh,
1299                .extra2         = &max_read_thresh,
1300        },
1301        {
1302                .procname       = "write_wakeup_threshold",
1303                .data           = &random_write_wakeup_thresh,
1304                .maxlen         = sizeof(int),
1305                .mode           = 0644,
1306                .proc_handler   = proc_dointvec_minmax,
1307                .extra1         = &min_write_thresh,
1308                .extra2         = &max_write_thresh,
1309        },
1310        {
1311                .procname       = "boot_id",
1312                .data           = &sysctl_bootid,
1313                .maxlen         = 16,
1314                .mode           = 0444,
1315                .proc_handler   = proc_do_uuid,
1316        },
1317        {
1318                .procname       = "uuid",
1319                .maxlen         = 16,
1320                .mode           = 0444,
1321                .proc_handler   = proc_do_uuid,
1322        },
1323        { }
1324};
1325#endif  /* CONFIG_SYSCTL */
1326
1327static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
1328
1329static int __init random_int_secret_init(void)
1330{
1331        get_random_bytes(random_int_secret, sizeof(random_int_secret));
1332        return 0;
1333}
1334late_initcall(random_int_secret_init);
1335
1336/*
1337 * Get a random word for internal kernel use only. Similar to urandom but
1338 * with the goal of minimal entropy pool depletion. As a result, the random
1339 * value is not cryptographically secure but for several uses the cost of
1340 * depleting entropy is too high
1341 */
1342DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);
1343unsigned int get_random_int(void)
1344{
1345        __u32 *hash;
1346        unsigned int ret;
1347
1348        if (arch_get_random_int(&ret))
1349                return ret;
1350
1351        hash = get_cpu_var(get_random_int_hash);
1352
1353        hash[0] += current->pid + jiffies + get_cycles();
1354        md5_transform(hash, random_int_secret);
1355        ret = hash[0];
1356        put_cpu_var(get_random_int_hash);
1357
1358        return ret;
1359}
1360
1361/*
1362 * randomize_range() returns a start address such that
1363 *
1364 *    [...... <range> .....]
1365 *  start                  end
1366 *
1367 * a <range> with size "len" starting at the return value is inside in the
1368 * area defined by [start, end], but is otherwise randomized.
1369 */
1370unsigned long
1371randomize_range(unsigned long start, unsigned long end, unsigned long len)
1372{
1373        unsigned long range = end - len - start;
1374
1375        if (end <= start + len)
1376                return 0;
1377        return PAGE_ALIGN(get_random_int() % range + start);
1378}
1379
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