/*
   * random.c -- A strong random number generator
   *

   * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005

   *
   * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999.  All
   * rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, and the entire permission notice in its entirety,
   *    including the disclaimer of warranties.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. The name of the author may not be used to endorse or promote
   *    products derived from this software without specific prior
   *    written permission.
   *
   * ALTERNATIVELY, this product may be distributed under the terms of
   * the GNU General Public License, in which case the provisions of the GPL are
   * required INSTEAD OF the above restrictions.  (This clause is
   * necessary due to a potential bad interaction between the GPL and
   * the restrictions contained in a BSD-style copyright.)
   *
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
   * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
   * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
   * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
   * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
   * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
   * DAMAGE.
   */
  
  /*
   * (now, with legal B.S. out of the way.....)
   *
   * This routine gathers environmental noise from device drivers, etc.,
   * and returns good random numbers, suitable for cryptographic use.
   * Besides the obvious cryptographic uses, these numbers are also good
   * for seeding TCP sequence numbers, and other places where it is
   * desirable to have numbers which are not only random, but hard to
   * predict by an attacker.
   *
   * Theory of operation
   * ===================
   *
   * Computers are very predictable devices.  Hence it is extremely hard
   * to produce truly random numbers on a computer --- as opposed to
   * pseudo-random numbers, which can easily generated by using a
   * algorithm.  Unfortunately, it is very easy for attackers to guess
   * the sequence of pseudo-random number generators, and for some
   * applications this is not acceptable.  So instead, we must try to
   * gather "environmental noise" from the computer's environment, which
   * must be hard for outside attackers to observe, and use that to
   * generate random numbers.  In a Unix environment, this is best done
   * from inside the kernel.
   *
   * Sources of randomness from the environment include inter-keyboard
   * timings, inter-interrupt timings from some interrupts, and other
   * events which are both (a) non-deterministic and (b) hard for an
   * outside observer to measure.  Randomness from these sources are
   * added to an "entropy pool", which is mixed using a CRC-like function.
   * This is not cryptographically strong, but it is adequate assuming
   * the randomness is not chosen maliciously, and it is fast enough that
   * the overhead of doing it on every interrupt is very reasonable.
   * As random bytes are mixed into the entropy pool, the routines keep
   * an *estimate* of how many bits of randomness have been stored into
   * the random number generator's internal state.
   *
   * When random bytes are desired, they are obtained by taking the SHA
   * hash of the contents of the "entropy pool".  The SHA hash avoids
   * exposing the internal state of the entropy pool.  It is believed to
   * be computationally infeasible to derive any useful information
   * about the input of SHA from its output.  Even if it is possible to
   * analyze SHA in some clever way, as long as the amount of data
   * returned from the generator is less than the inherent entropy in
   * the pool, the output data is totally unpredictable.  For this
   * reason, the routine decreases its internal estimate of how many
   * bits of "true randomness" are contained in the entropy pool as it
   * outputs random numbers.
   *
   * If this estimate goes to zero, the routine can still generate
   * random numbers; however, an attacker may (at least in theory) be
   * able to infer the future output of the generator from prior
   * outputs.  This requires successful cryptanalysis of SHA, which is
   * not believed to be feasible, but there is a remote possibility.
   * Nonetheless, these numbers should be useful for the vast majority
   * of purposes.
   *
   * Exported interfaces ---- output
   * ===============================
   *
   * There are three exported interfaces; the first is one designed to
   * be used from within the kernel:
   *
   * 	void get_random_bytes(void *buf, int nbytes);
   *
   * This interface will return the requested number of random bytes,
   * and place it in the requested buffer.
   *
   * The two other interfaces are two character devices /dev/random and
   * /dev/urandom.  /dev/random is suitable for use when very high
   * quality randomness is desired (for example, for key generation or
   * one-time pads), as it will only return a maximum of the number of
   * bits of randomness (as estimated by the random number generator)
   * contained in the entropy pool.
   *
   * The /dev/urandom device does not have this limit, and will return
   * as many bytes as are requested.  As more and more random bytes are
   * requested without giving time for the entropy pool to recharge,
   * this will result in random numbers that are merely cryptographically
   * strong.  For many applications, however, this is acceptable.
   *
   * Exported interfaces ---- input
   * ==============================
   *
   * The current exported interfaces for gathering environmental noise
   * from the devices are:
   *
   * 	void add_input_randomness(unsigned int type, unsigned int code,
   *                                unsigned int value);
   * 	void add_interrupt_randomness(int irq);

   * 	void add_disk_randomness(struct gendisk *disk);

   *
   * add_input_randomness() uses the input layer interrupt timing, as well as
   * the event type information from the hardware.
   *
   * add_interrupt_randomness() uses the inter-interrupt timing as random
   * inputs to the entropy pool.  Note that not all interrupts are good
   * sources of randomness!  For example, the timer interrupts is not a
   * good choice, because the periodicity of the interrupts is too

   * regular, and hence predictable to an attacker.  Network Interface
   * Controller interrupts are a better measure, since the timing of the
   * NIC interrupts are more unpredictable.
   *
   * add_disk_randomness() uses what amounts to the seek time of block
   * layer request events, on a per-disk_devt basis, as input to the
   * entropy pool. Note that high-speed solid state drives with very low
   * seek times do not make for good sources of entropy, as their seek
   * times are usually fairly consistent.

   *
   * All of these routines try to estimate how many bits of randomness a
   * particular randomness source.  They do this by keeping track of the
   * first and second order deltas of the event timings.
   *
   * Ensuring unpredictability at system startup
   * ============================================
   *
   * When any operating system starts up, it will go through a sequence
   * of actions that are fairly predictable by an adversary, especially
   * if the start-up does not involve interaction with a human operator.
   * This reduces the actual number of bits of unpredictability in the
   * entropy pool below the value in entropy_count.  In order to
   * counteract this effect, it helps to carry information in the
   * entropy pool across shut-downs and start-ups.  To do this, put the
   * following lines an appropriate script which is run during the boot
   * sequence:
   *
   *	echo "Initializing random number generator..."
   *	random_seed=/var/run/random-seed
   *	# Carry a random seed from start-up to start-up
   *	# Load and then save the whole entropy pool
   *	if [ -f $random_seed ]; then
   *		cat $random_seed >/dev/urandom
   *	else
   *		touch $random_seed
   *	fi
   *	chmod 600 $random_seed
   *	dd if=/dev/urandom of=$random_seed count=1 bs=512
   *
   * and the following lines in an appropriate script which is run as
   * the system is shutdown:
   *
   *	# Carry a random seed from shut-down to start-up
   *	# Save the whole entropy pool
   *	echo "Saving random seed..."
   *	random_seed=/var/run/random-seed
   *	touch $random_seed
   *	chmod 600 $random_seed
   *	dd if=/dev/urandom of=$random_seed count=1 bs=512
   *
   * For example, on most modern systems using the System V init
   * scripts, such code fragments would be found in
   * /etc/rc.d/init.d/random.  On older Linux systems, the correct script
   * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0.
   *
   * Effectively, these commands cause the contents of the entropy pool
   * to be saved at shut-down time and reloaded into the entropy pool at
   * start-up.  (The 'dd' in the addition to the bootup script is to
   * make sure that /etc/random-seed is different for every start-up,
   * even if the system crashes without executing rc.0.)  Even with
   * complete knowledge of the start-up activities, predicting the state
   * of the entropy pool requires knowledge of the previous history of
   * the system.
   *
   * Configuring the /dev/random driver under Linux
   * ==============================================
   *
   * The /dev/random driver under Linux uses minor numbers 8 and 9 of
   * the /dev/mem major number (#1).  So if your system does not have
   * /dev/random and /dev/urandom created already, they can be created
   * by using the commands:
   *
   * 	mknod /dev/random c 1 8
   * 	mknod /dev/urandom c 1 9
   *
   * Acknowledgements:
   * =================
   *
   * Ideas for constructing this random number generator were derived
   * from Pretty Good Privacy's random number generator, and from private
   * discussions with Phil Karn.  Colin Plumb provided a faster random
   * number generator, which speed up the mixing function of the entropy
   * pool, taken from PGPfone.  Dale Worley has also contributed many
   * useful ideas and suggestions to improve this driver.
   *
   * Any flaws in the design are solely my responsibility, and should
   * not be attributed to the Phil, Colin, or any of authors of PGP.
   *
   * Further background information on this topic may be obtained from
   * RFC 1750, "Randomness Recommendations for Security", by Donald
   * Eastlake, Steve Crocker, and Jeff Schiller.
   */
  
  #include <linux/utsname.h>

  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/major.h>
  #include <linux/string.h>
  #include <linux/fcntl.h>
  #include <linux/slab.h>
  #include <linux/random.h>
  #include <linux/poll.h>
  #include <linux/init.h>
  #include <linux/fs.h>
  #include <linux/genhd.h>
  #include <linux/interrupt.h>

  #include <linux/mm.h>

  #include <linux/spinlock.h>
  #include <linux/percpu.h>
  #include <linux/cryptohash.h>

  #include <linux/fips.h>

  #ifdef CONFIG_GENERIC_HARDIRQS
  # include <linux/irq.h>
  #endif

  #include <asm/processor.h>
  #include <asm/uaccess.h>
  #include <asm/irq.h>
  #include <asm/io.h>
  
  /*
   * Configuration information
   */
  #define INPUT_POOL_WORDS 128
  #define OUTPUT_POOL_WORDS 32
  #define SEC_XFER_SIZE 512

  #define EXTRACT_SIZE 10

  
  /*
   * The minimum number of bits of entropy before we wake up a read on
   * /dev/random.  Should be enough to do a significant reseed.
   */
  static int random_read_wakeup_thresh = 64;
  
  /*
   * If the entropy count falls under this number of bits, then we
   * should wake up processes which are selecting or polling on write
   * access to /dev/random.
   */
  static int random_write_wakeup_thresh = 128;
  
  /*
   * When the input pool goes over trickle_thresh, start dropping most
   * samples to avoid wasting CPU time and reduce lock contention.
   */

  static int trickle_thresh __read_mostly = INPUT_POOL_WORDS * 28;

  static DEFINE_PER_CPU(int, trickle_count);

  
  /*
   * A pool of size .poolwords is stirred with a primitive polynomial
   * of degree .poolwords over GF(2).  The taps for various sizes are
   * defined below.  They are chosen to be evenly spaced (minimum RMS
   * distance from evenly spaced; the numbers in the comments are a
   * scaled squared error sum) except for the last tap, which is 1 to
   * get the twisting happening as fast as possible.
   */
  static struct poolinfo {
  	int poolwords;
  	int tap1, tap2, tap3, tap4, tap5;
  } poolinfo_table[] = {
  	/* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */
  	{ 128,	103,	76,	51,	25,	1 },
  	/* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */
  	{ 32,	26,	20,	14,	7,	1 },
  #if 0
  	/* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1  -- 115 */
  	{ 2048,	1638,	1231,	819,	411,	1 },
  
  	/* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
  	{ 1024,	817,	615,	412,	204,	1 },
  
  	/* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
  	{ 1024,	819,	616,	410,	207,	2 },
  
  	/* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
  	{ 512,	411,	308,	208,	104,	1 },
  
  	/* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
  	{ 512,	409,	307,	206,	102,	2 },
  	/* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
  	{ 512,	409,	309,	205,	103,	2 },
  
  	/* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
  	{ 256,	205,	155,	101,	52,	1 },
  
  	/* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
  	{ 128,	103,	78,	51,	27,	2 },
  
  	/* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
  	{ 64,	52,	39,	26,	14,	1 },
  #endif
  };
  
  #define POOLBITS	poolwords*32
  #define POOLBYTES	poolwords*4
  
  /*
   * For the purposes of better mixing, we use the CRC-32 polynomial as
   * well to make a twisted Generalized Feedback Shift Reigster
   *
   * (See M. Matsumoto & Y. Kurita, 1992.  Twisted GFSR generators.  ACM
   * Transactions on Modeling and Computer Simulation 2(3):179-194.
   * Also see M. Matsumoto & Y. Kurita, 1994.  Twisted GFSR generators
   * II.  ACM Transactions on Mdeling and Computer Simulation 4:254-266)
   *
   * Thanks to Colin Plumb for suggesting this.
   *
   * We have not analyzed the resultant polynomial to prove it primitive;
   * in fact it almost certainly isn't.  Nonetheless, the irreducible factors
   * of a random large-degree polynomial over GF(2) are more than large enough
   * that periodicity is not a concern.
   *
   * The input hash is much less sensitive than the output hash.  All
   * that we want of it is that it be a good non-cryptographic hash;
   * i.e. it not produce collisions when fed "random" data of the sort
   * we expect to see.  As long as the pool state differs for different
   * inputs, we have preserved the input entropy and done a good job.
   * The fact that an intelligent attacker can construct inputs that
   * will produce controlled alterations to the pool's state is not
   * important because we don't consider such inputs to contribute any
   * randomness.  The only property we need with respect to them is that
   * the attacker can't increase his/her knowledge of the pool's state.
   * Since all additions are reversible (knowing the final state and the
   * input, you can reconstruct the initial state), if an attacker has
   * any uncertainty about the initial state, he/she can only shuffle
   * that uncertainty about, but never cause any collisions (which would
   * decrease the uncertainty).
   *
   * The chosen system lets the state of the pool be (essentially) the input
   * modulo the generator polymnomial.  Now, for random primitive polynomials,
   * this is a universal class of hash functions, meaning that the chance
   * of a collision is limited by the attacker's knowledge of the generator
   * polynomail, so if it is chosen at random, an attacker can never force
   * a collision.  Here, we use a fixed polynomial, but we *can* assume that
   * ###--> it is unknown to the processes generating the input entropy. <-###
   * Because of this important property, this is a good, collision-resistant
   * hash; hash collisions will occur no more often than chance.
   */
  
  /*
   * Static global variables
   */
  static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
  static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);

  static struct fasync_struct *fasync;

  
  #if 0

  static int debug;

  module_param(debug, bool, 0644);

  #define DEBUG_ENT(fmt, arg...) do { \
  	if (debug) \
  		printk(KERN_DEBUG "random %04d %04d %04d: " \
  		fmt,\
  		input_pool.entropy_count,\
  		blocking_pool.entropy_count,\
  		nonblocking_pool.entropy_count,\
  		## arg); } while (0)

  #else
  #define DEBUG_ENT(fmt, arg...) do {} while (0)
  #endif
  
  /**********************************************************************
   *
   * OS independent entropy store.   Here are the functions which handle
   * storing entropy in an entropy pool.
   *
   **********************************************************************/
  
  struct entropy_store;
  struct entropy_store {

  	/* read-only data: */

  	struct poolinfo *poolinfo;
  	__u32 *pool;
  	const char *name;

  	struct entropy_store *pull;

  	int limit;

  
  	/* read-write data: */

  	spinlock_t lock;

  	unsigned add_ptr;

  	int entropy_count;

  	int input_rotate;

  	__u8 last_data[EXTRACT_SIZE];

  };
  
  static __u32 input_pool_data[INPUT_POOL_WORDS];
  static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
  static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
  
  static struct entropy_store input_pool = {
  	.poolinfo = &poolinfo_table[0],
  	.name = "input",
  	.limit = 1,

  	.lock = __SPIN_LOCK_UNLOCKED(&input_pool.lock),

  	.pool = input_pool_data
  };
  
  static struct entropy_store blocking_pool = {
  	.poolinfo = &poolinfo_table[1],
  	.name = "blocking",
  	.limit = 1,
  	.pull = &input_pool,

  	.lock = __SPIN_LOCK_UNLOCKED(&blocking_pool.lock),

  	.pool = blocking_pool_data
  };
  
  static struct entropy_store nonblocking_pool = {
  	.poolinfo = &poolinfo_table[1],
  	.name = "nonblocking",
  	.pull = &input_pool,

  	.lock = __SPIN_LOCK_UNLOCKED(&nonblocking_pool.lock),

  	.pool = nonblocking_pool_data
  };
  
  /*

   * This function adds bytes into the entropy "pool".  It does not

   * update the entropy estimate.  The caller should call

   * credit_entropy_bits if this is appropriate.

   *
   * The pool is stirred with a primitive polynomial of the appropriate
   * degree, and then twisted.  We twist by three bits at a time because
   * it's cheap to do so and helps slightly in the expected case where
   * the entropy is concentrated in the low-order bits.
   */

  static void mix_pool_bytes_extract(struct entropy_store *r, const void *in,
  				   int nbytes, __u8 out[64])

  {
  	static __u32 const twist_table[8] = {
  		0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
  		0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };

  	unsigned long i, j, tap1, tap2, tap3, tap4, tap5;

  	int input_rotate;

  	int wordmask = r->poolinfo->poolwords - 1;

  	const char *bytes = in;

  	__u32 w;

  	unsigned long flags;
  
  	/* Taps are constant, so we can load them without holding r->lock.  */
  	tap1 = r->poolinfo->tap1;
  	tap2 = r->poolinfo->tap2;
  	tap3 = r->poolinfo->tap3;
  	tap4 = r->poolinfo->tap4;
  	tap5 = r->poolinfo->tap5;

  
  	spin_lock_irqsave(&r->lock, flags);

  	input_rotate = r->input_rotate;

  	i = r->add_ptr;

  	/* mix one byte at a time to simplify size handling and churn faster */
  	while (nbytes--) {
  		w = rol32(*bytes++, input_rotate & 31);

  		i = (i - 1) & wordmask;

  
  		/* XOR in the various taps */

  		w ^= r->pool[i];

  		w ^= r->pool[(i + tap1) & wordmask];
  		w ^= r->pool[(i + tap2) & wordmask];
  		w ^= r->pool[(i + tap3) & wordmask];
  		w ^= r->pool[(i + tap4) & wordmask];
  		w ^= r->pool[(i + tap5) & wordmask];

  
  		/* Mix the result back in with a twist */

  		r->pool[i] = (w >> 3) ^ twist_table[w & 7];

  
  		/*
  		 * Normally, we add 7 bits of rotation to the pool.
  		 * At the beginning of the pool, add an extra 7 bits
  		 * rotation, so that successive passes spread the
  		 * input bits across the pool evenly.
  		 */
  		input_rotate += i ? 7 : 14;

  	}
  
  	r->input_rotate = input_rotate;

  	r->add_ptr = i;

  	if (out)
  		for (j = 0; j < 16; j++)

  			((__u32 *)out)[j] = r->pool[(i - j) & wordmask];

  
  	spin_unlock_irqrestore(&r->lock, flags);
  }

  static void mix_pool_bytes(struct entropy_store *r, const void *in, int bytes)

  {

         mix_pool_bytes_extract(r, in, bytes, NULL);

  }
  
  /*
   * Credit (or debit) the entropy store with n bits of entropy
   */

  static void credit_entropy_bits(struct entropy_store *r, int nbits)

  {
  	unsigned long flags;

  	int entropy_count;

  	if (!nbits)
  		return;

  	spin_lock_irqsave(&r->lock, flags);

  	DEBUG_ENT("added %d entropy credits to %s
  ", nbits, r->name);

  	entropy_count = r->entropy_count;
  	entropy_count += nbits;
  	if (entropy_count < 0) {

  		DEBUG_ENT("negative entropy/overflow
  ");

  		entropy_count = 0;
  	} else if (entropy_count > r->poolinfo->POOLBITS)
  		entropy_count = r->poolinfo->POOLBITS;
  	r->entropy_count = entropy_count;

  	/* should we wake readers? */

  	if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {

  		wake_up_interruptible(&random_read_wait);

  		kill_fasync(&fasync, SIGIO, POLL_IN);
  	}

  	spin_unlock_irqrestore(&r->lock, flags);
  }
  
  /*********************************************************************
   *
   * Entropy input management
   *
   *********************************************************************/
  
  /* There is one of these per entropy source */
  struct timer_rand_state {
  	cycles_t last_time;

  	long last_delta, last_delta2;

  	unsigned dont_count_entropy:1;
  };

  #ifndef CONFIG_GENERIC_HARDIRQS

  
  static struct timer_rand_state *irq_timer_state[NR_IRQS];
  
  static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
  {
  	return irq_timer_state[irq];
  }
  
  static void set_timer_rand_state(unsigned int irq,
  				 struct timer_rand_state *state)
  {
  	irq_timer_state[irq] = state;
  }
  
  #else
  
  static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
  {
  	struct irq_desc *desc;
  
  	desc = irq_to_desc(irq);
  
  	return desc->timer_rand_state;
  }
  
  static void set_timer_rand_state(unsigned int irq,
  				 struct timer_rand_state *state)
  {
  	struct irq_desc *desc;
  
  	desc = irq_to_desc(irq);
  
  	desc->timer_rand_state = state;
  }

  #endif

  static struct timer_rand_state input_timer_state;

  /*
   * This function adds entropy to the entropy "pool" by using timing
   * delays.  It uses the timer_rand_state structure to make an estimate
   * of how many bits of entropy this call has added to the pool.
   *
   * The number "num" is also added to the pool - it should somehow describe
   * the type of event which just happened.  This is currently 0-255 for
   * keyboard scan codes, and 256 upwards for interrupts.
   *
   */
  static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
  {
  	struct {

  		long jiffies;

  		unsigned cycles;

  		unsigned num;
  	} sample;
  	long delta, delta2, delta3;
  
  	preempt_disable();
  	/* if over the trickle threshold, use only 1 in 4096 samples */
  	if (input_pool.entropy_count > trickle_thresh &&

  	    ((__this_cpu_inc_return(trickle_count) - 1) & 0xfff))

  		goto out;
  
  	sample.jiffies = jiffies;

  
  	/* Use arch random value, fall back to cycles */
  	if (!arch_get_random_int(&sample.cycles))
  		sample.cycles = get_cycles();

  	sample.num = num;

  	mix_pool_bytes(&input_pool, &sample, sizeof(sample));

  
  	/*
  	 * Calculate number of bits of randomness we probably added.
  	 * We take into account the first, second and third-order deltas
  	 * in order to make our estimate.
  	 */
  
  	if (!state->dont_count_entropy) {
  		delta = sample.jiffies - state->last_time;
  		state->last_time = sample.jiffies;
  
  		delta2 = delta - state->last_delta;
  		state->last_delta = delta;
  
  		delta3 = delta2 - state->last_delta2;
  		state->last_delta2 = delta2;
  
  		if (delta < 0)
  			delta = -delta;
  		if (delta2 < 0)
  			delta2 = -delta2;
  		if (delta3 < 0)
  			delta3 = -delta3;
  		if (delta > delta2)
  			delta = delta2;
  		if (delta > delta3)
  			delta = delta3;
  
  		/*
  		 * delta is now minimum absolute delta.
  		 * Round down by 1 bit on general principles,
  		 * and limit entropy entimate to 12 bits.
  		 */

  		credit_entropy_bits(&input_pool,
  				    min_t(int, fls(delta>>1), 11));

  	}

  out:
  	preempt_enable();
  }

  void add_input_randomness(unsigned int type, unsigned int code,

  				 unsigned int value)
  {
  	static unsigned char last_value;
  
  	/* ignore autorepeat and the like */
  	if (value == last_value)
  		return;
  
  	DEBUG_ENT("input event
  ");
  	last_value = value;
  	add_timer_randomness(&input_timer_state,
  			     (type << 4) ^ code ^ (code >> 4) ^ value);
  }

  EXPORT_SYMBOL_GPL(add_input_randomness);

  
  void add_interrupt_randomness(int irq)
  {

  	struct timer_rand_state *state;
  
  	state = get_timer_rand_state(irq);
  
  	if (state == NULL)

  		return;
  
  	DEBUG_ENT("irq event %d
  ", irq);

  	add_timer_randomness(state, 0x100 + irq);

  }

  #ifdef CONFIG_BLOCK

  void add_disk_randomness(struct gendisk *disk)
  {
  	if (!disk || !disk->random)
  		return;
  	/* first major is 1, so we get >= 0x200 here */

  	DEBUG_ENT("disk event %d:%d
  ",
  		  MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));

  	add_timer_randomness(disk->random, 0x100 + disk_devt(disk));

  }

  #endif

  /*********************************************************************
   *
   * Entropy extraction routines
   *
   *********************************************************************/

  static ssize_t extract_entropy(struct entropy_store *r, void *buf,

  			       size_t nbytes, int min, int rsvd);
  
  /*

   * This utility inline function is responsible for transferring entropy

   * from the primary pool to the secondary extraction pool. We make
   * sure we pull enough for a 'catastrophic reseed'.
   */
  static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
  {
  	__u32 tmp[OUTPUT_POOL_WORDS];
  
  	if (r->pull && r->entropy_count < nbytes * 8 &&
  	    r->entropy_count < r->poolinfo->POOLBITS) {

  		/* If we're limited, always leave two wakeup worth's BITS */

  		int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;

  		int bytes = nbytes;
  
  		/* pull at least as many as BYTES as wakeup BITS */
  		bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
  		/* but never more than the buffer size */
  		bytes = min_t(int, bytes, sizeof(tmp));

  
  		DEBUG_ENT("going to reseed %s with %d bits "
  			  "(%d of %d requested)
  ",
  			  r->name, bytes * 8, nbytes * 8, r->entropy_count);

  		bytes = extract_entropy(r->pull, tmp, bytes,
  					random_read_wakeup_thresh / 8, rsvd);

  		mix_pool_bytes(r, tmp, bytes);

  		credit_entropy_bits(r, bytes*8);

  	}
  }
  
  /*
   * These functions extracts randomness from the "entropy pool", and
   * returns it in a buffer.
   *
   * The min parameter specifies the minimum amount we can pull before
   * failing to avoid races that defeat catastrophic reseeding while the
   * reserved parameter indicates how much entropy we must leave in the
   * pool after each pull to avoid starving other readers.
   *
   * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
   */
  
  static size_t account(struct entropy_store *r, size_t nbytes, int min,
  		      int reserved)
  {
  	unsigned long flags;

  	/* Hold lock while accounting */
  	spin_lock_irqsave(&r->lock, flags);

  	BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);

  	DEBUG_ENT("trying to extract %d bits from %s
  ",
  		  nbytes * 8, r->name);
  
  	/* Can we pull enough? */
  	if (r->entropy_count / 8 < min + reserved) {
  		nbytes = 0;
  	} else {
  		/* If limited, never pull more than available */
  		if (r->limit && nbytes + reserved >= r->entropy_count / 8)
  			nbytes = r->entropy_count/8 - reserved;

  		if (r->entropy_count / 8 >= nbytes + reserved)

  			r->entropy_count -= nbytes*8;
  		else
  			r->entropy_count = reserved;

  		if (r->entropy_count < random_write_wakeup_thresh) {

  			wake_up_interruptible(&random_write_wait);

  			kill_fasync(&fasync, SIGIO, POLL_OUT);
  		}

  	}
  
  	DEBUG_ENT("debiting %d entropy credits from %s%s
  ",
  		  nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
  
  	spin_unlock_irqrestore(&r->lock, flags);
  
  	return nbytes;
  }
  
  static void extract_buf(struct entropy_store *r, __u8 *out)
  {

  	int i;

  	__u32 hash[5], workspace[SHA_WORKSPACE_WORDS];
  	__u8 extract[64];

  	/* Generate a hash across the pool, 16 words (512 bits) at a time */

  	sha_init(hash);

  	for (i = 0; i < r->poolinfo->poolwords; i += 16)
  		sha_transform(hash, (__u8 *)(r->pool + i), workspace);

  	/*

  	 * We mix the hash back into the pool to prevent backtracking
  	 * attacks (where the attacker knows the state of the pool
  	 * plus the current outputs, and attempts to find previous
  	 * ouputs), unless the hash function can be inverted. By
  	 * mixing at least a SHA1 worth of hash data back, we make
  	 * brute-forcing the feedback as hard as brute-forcing the
  	 * hash.

  	 */

  	mix_pool_bytes_extract(r, hash, sizeof(hash), extract);

  
  	/*

  	 * To avoid duplicates, we atomically extract a portion of the
  	 * pool while mixing, and hash one final time.

  	 */

  	sha_transform(hash, extract, workspace);

  	memset(extract, 0, sizeof(extract));
  	memset(workspace, 0, sizeof(workspace));

  
  	/*

  	 * In case the hash function has some recognizable output
  	 * pattern, we fold it in half. Thus, we always feed back
  	 * twice as much data as we output.

  	 */

  	hash[0] ^= hash[3];
  	hash[1] ^= hash[4];
  	hash[2] ^= rol32(hash[2], 16);
  	memcpy(out, hash, EXTRACT_SIZE);
  	memset(hash, 0, sizeof(hash));

  }

  static ssize_t extract_entropy(struct entropy_store *r, void *buf,

  			       size_t nbytes, int min, int reserved)
  {
  	ssize_t ret = 0, i;
  	__u8 tmp[EXTRACT_SIZE];

  	unsigned long flags;

  
  	xfer_secondary_pool(r, nbytes);
  	nbytes = account(r, nbytes, min, reserved);
  
  	while (nbytes) {
  		extract_buf(r, tmp);

  		if (fips_enabled) {

  			spin_lock_irqsave(&r->lock, flags);
  			if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
  				panic("Hardware RNG duplicated output!
  ");
  			memcpy(r->last_data, tmp, EXTRACT_SIZE);
  			spin_unlock_irqrestore(&r->lock, flags);
  		}

  		i = min_t(int, nbytes, EXTRACT_SIZE);
  		memcpy(buf, tmp, i);
  		nbytes -= i;
  		buf += i;
  		ret += i;
  	}
  
  	/* Wipe data just returned from memory */
  	memset(tmp, 0, sizeof(tmp));
  
  	return ret;
  }
  
  static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
  				    size_t nbytes)
  {
  	ssize_t ret = 0, i;
  	__u8 tmp[EXTRACT_SIZE];
  
  	xfer_secondary_pool(r, nbytes);
  	nbytes = account(r, nbytes, 0, 0);
  
  	while (nbytes) {
  		if (need_resched()) {
  			if (signal_pending(current)) {
  				if (ret == 0)
  					ret = -ERESTARTSYS;
  				break;
  			}
  			schedule();
  		}
  
  		extract_buf(r, tmp);
  		i = min_t(int, nbytes, EXTRACT_SIZE);
  		if (copy_to_user(buf, tmp, i)) {
  			ret = -EFAULT;
  			break;
  		}
  
  		nbytes -= i;
  		buf += i;
  		ret += i;
  	}
  
  	/* Wipe data just returned from memory */
  	memset(tmp, 0, sizeof(tmp));
  
  	return ret;
  }
  
  /*
   * This function is the exported kernel interface.  It returns some
   * number of good random numbers, suitable for seeding TCP sequence
   * numbers, etc.
   */
  void get_random_bytes(void *buf, int nbytes)
  {

  	char *p = buf;
  
  	while (nbytes) {
  		unsigned long v;
  		int chunk = min(nbytes, (int)sizeof(unsigned long));
  		
  		if (!arch_get_random_long(&v))
  			break;
  		

  		memcpy(p, &v, chunk);

  		p += chunk;
  		nbytes -= chunk;
  	}
  
  	extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);

  }

  EXPORT_SYMBOL(get_random_bytes);
  
  /*
   * init_std_data - initialize pool with system data
   *
   * @r: pool to initialize
   *
   * This function clears the pool's entropy count and mixes some system
   * data into the pool to prepare it for use. The pool is not cleared
   * as that can only decrease the entropy in the pool.
   */
  static void init_std_data(struct entropy_store *r)
  {

  	int i;

  	ktime_t now;

  	unsigned long flags;
  
  	spin_lock_irqsave(&r->lock, flags);
  	r->entropy_count = 0;
  	spin_unlock_irqrestore(&r->lock, flags);

  	now = ktime_get_real();

  	mix_pool_bytes(r, &now, sizeof(now));

  	for (i = r->poolinfo->poolwords; i; i--) {
  		if (!arch_get_random_long(&flags))
  			break;
  		mix_pool_bytes(r, &flags, sizeof(flags));
  	}

  	mix_pool_bytes(r, utsname(), sizeof(*(utsname())));

  }

  static int rand_initialize(void)

  {
  	init_std_data(&input_pool);
  	init_std_data(&blocking_pool);
  	init_std_data(&nonblocking_pool);
  	return 0;
  }
  module_init(rand_initialize);
  
  void rand_initialize_irq(int irq)
  {
  	struct timer_rand_state *state;

  	state = get_timer_rand_state(irq);
  
  	if (state)

  		return;
  
  	/*

  	 * If kzalloc returns null, we just won't use that entropy

  	 * source.
  	 */

  	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
  	if (state)

  		set_timer_rand_state(irq, state);

  }

  #ifdef CONFIG_BLOCK

  void rand_initialize_disk(struct gendisk *disk)
  {
  	struct timer_rand_state *state;
  
  	/*

  	 * If kzalloc returns null, we just won't use that entropy

  	 * source.
  	 */

  	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
  	if (state)

  		disk->random = state;

  }

  #endif

  
  static ssize_t

  random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)

  {
  	ssize_t n, retval = 0, count = 0;
  
  	if (nbytes == 0)
  		return 0;
  
  	while (nbytes > 0) {
  		n = nbytes;
  		if (n > SEC_XFER_SIZE)
  			n = SEC_XFER_SIZE;
  
  		DEBUG_ENT("reading %d bits
  ", n*8);
  
  		n = extract_entropy_user(&blocking_pool, buf, n);
  
  		DEBUG_ENT("read got %d bits (%d still needed)
  ",
  			  n*8, (nbytes-n)*8);
  
  		if (n == 0) {
  			if (file->f_flags & O_NONBLOCK) {
  				retval = -EAGAIN;
  				break;
  			}
  
  			DEBUG_ENT("sleeping?
  ");
  
  			wait_event_interruptible(random_read_wait,
  				input_pool.entropy_count >=
  						 random_read_wakeup_thresh);
  
  			DEBUG_ENT("awake
  ");
  
  			if (signal_pending(current)) {
  				retval = -ERESTARTSYS;
  				break;
  			}
  
  			continue;
  		}
  
  		if (n < 0) {
  			retval = n;
  			break;
  		}
  		count += n;
  		buf += n;
  		nbytes -= n;
  		break;		/* This break makes the device work */
  				/* like a named pipe */
  	}

  	return (count ? count : retval);
  }
  
  static ssize_t

  urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)

  {
  	return extract_entropy_user(&nonblocking_pool, buf, nbytes);
  }
  
  static unsigned int
  random_poll(struct file *file, poll_table * wait)
  {
  	unsigned int mask;
  
  	poll_wait(file, &random_read_wait, wait);
  	poll_wait(file, &random_write_wait, wait);
  	mask = 0;
  	if (input_pool.entropy_count >= random_read_wakeup_thresh)
  		mask |= POLLIN | POLLRDNORM;
  	if (input_pool.entropy_count < random_write_wakeup_thresh)
  		mask |= POLLOUT | POLLWRNORM;
  	return mask;
  }

  static int
  write_pool(struct entropy_store *r, const char __user *buffer, size_t count)

  {

  	size_t bytes;
  	__u32 buf[16];
  	const char __user *p = buffer;

  	while (count > 0) {
  		bytes = min(count, sizeof(buf));
  		if (copy_from_user(&buf, p, bytes))
  			return -EFAULT;

  		count -= bytes;

  		p += bytes;

  		mix_pool_bytes(r, buf, bytes);

  		cond_resched();

  	}

  
  	return 0;
  }

  static ssize_t random_write(struct file *file, const char __user *buffer,
  			    size_t count, loff_t *ppos)

  {
  	size_t ret;

  
  	ret = write_pool(&blocking_pool, buffer, count);
  	if (ret)
  		return ret;
  	ret = write_pool(&nonblocking_pool, buffer, count);
  	if (ret)
  		return ret;

  	return (ssize_t)count;

  }

  static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)

  {
  	int size, ent_count;
  	int __user *p = (int __user *)arg;
  	int retval;
  
  	switch (cmd) {
  	case RNDGETENTCNT:

  		/* inherently racy, no point locking */
  		if (put_user(input_pool.entropy_count, p))

  			return -EFAULT;
  		return 0;
  	case RNDADDTOENTCNT:
  		if (!capable(CAP_SYS_ADMIN))
  			return -EPERM;
  		if (get_user(ent_count, p))
  			return -EFAULT;

  		credit_entropy_bits(&input_pool, ent_count);

  		return 0;
  	case RNDADDENTROPY:
  		if (!capable(CAP_SYS_ADMIN))
  			return -EPERM;
  		if (get_user(ent_count, p++))
  			return -EFAULT;
  		if (ent_count < 0)
  			return -EINVAL;
  		if (get_user(size, p++))
  			return -EFAULT;

  		retval = write_pool(&input_pool, (const char __user *)p,
  				    size);

  		if (retval < 0)
  			return retval;

  		credit_entropy_bits(&input_pool, ent_count);

  		return 0;
  	case RNDZAPENTCNT:
  	case RNDCLEARPOOL:
  		/* Clear the entropy pool counters. */
  		if (!capable(CAP_SYS_ADMIN))
  			return -EPERM;

  		rand_initialize();

  		return 0;
  	default:
  		return -EINVAL;
  	}
  }

  static int random_fasync(int fd, struct file *filp, int on)
  {
  	return fasync_helper(fd, filp, on, &fasync);
  }

  const struct file_operations random_fops = {

  	.read  = random_read,
  	.write = random_write,
  	.poll  = random_poll,

  	.unlocked_ioctl = random_ioctl,

  	.fasync = random_fasync,

  	.llseek = noop_llseek,

  };

  const struct file_operations urandom_fops = {

  	.read  = urandom_read,
  	.write = random_write,

  	.unlocked_ioctl = random_ioctl,

  	.fasync = random_fasync,

  	.llseek = noop_llseek,

  };
  
  /***************************************************************
   * Random UUID interface
   *
   * Used here for a Boot ID, but can be useful for other kernel
   * drivers.
   ***************************************************************/
  
  /*
   * Generate random UUID
   */
  void generate_random_uuid(unsigned char uuid_out[16])
  {
  	get_random_bytes(uuid_out, 16);

  	/* Set UUID version to 4 --- truly random generation */

  	uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
  	/* Set the UUID variant to DCE */
  	uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
  }

  EXPORT_SYMBOL(generate_random_uuid);
  
  /********************************************************************
   *
   * Sysctl interface
   *
   ********************************************************************/
  
  #ifdef CONFIG_SYSCTL
  
  #include <linux/sysctl.h>
  
  static int min_read_thresh = 8, min_write_thresh;
  static int max_read_thresh = INPUT_POOL_WORDS * 32;
  static int max_write_thresh = INPUT_POOL_WORDS * 32;
  static char sysctl_bootid[16];
  
  /*
   * These functions is used to return both the bootid UUID, and random
   * UUID.  The difference is in whether table->data is NULL; if it is,
   * then a new UUID is generated and returned to the user.
   *
   * If the user accesses this via the proc interface, it will be returned
   * as an ASCII string in the standard UUID format.  If accesses via the
   * sysctl system call, it is returned as 16 bytes of binary data.
   */

  static int proc_do_uuid(ctl_table *table, int write,

  			void __user *buffer, size_t *lenp, loff_t *ppos)
  {
  	ctl_table fake_table;
  	unsigned char buf[64], tmp_uuid[16], *uuid;
  
  	uuid = table->data;
  	if (!uuid) {
  		uuid = tmp_uuid;
  		uuid[8] = 0;
  	}
  	if (uuid[8] == 0)
  		generate_random_uuid(uuid);

  	sprintf(buf, "%pU", uuid);

  	fake_table.data = buf;
  	fake_table.maxlen = sizeof(buf);

  	return proc_dostring(&fake_table, write, buffer, lenp, ppos);

  }

  static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
  ctl_table random_table[] = {
  	{

  		.procname	= "poolsize",
  		.data		= &sysctl_poolsize,
  		.maxlen		= sizeof(int),
  		.mode		= 0444,

  		.proc_handler	= proc_dointvec,

  	},
  	{

  		.procname	= "entropy_avail",
  		.maxlen		= sizeof(int),
  		.mode		= 0444,

  		.proc_handler	= proc_dointvec,

  		.data		= &input_pool.entropy_count,
  	},
  	{

  		.procname	= "read_wakeup_threshold",
  		.data		= &random_read_wakeup_thresh,
  		.maxlen		= sizeof(int),
  		.mode		= 0644,

  		.proc_handler	= proc_dointvec_minmax,

  		.extra1		= &min_read_thresh,
  		.extra2		= &max_read_thresh,
  	},
  	{

  		.procname	= "write_wakeup_threshold",
  		.data		= &random_write_wakeup_thresh,
  		.maxlen		= sizeof(int),
  		.mode		= 0644,

  		.proc_handler	= proc_dointvec_minmax,

  		.extra1		= &min_write_thresh,
  		.extra2		= &max_write_thresh,
  	},
  	{

  		.procname	= "boot_id",
  		.data		= &sysctl_bootid,
  		.maxlen		= 16,
  		.mode		= 0444,

  		.proc_handler	= proc_do_uuid,

  	},
  	{

  		.procname	= "uuid",
  		.maxlen		= 16,
  		.mode		= 0444,

  		.proc_handler	= proc_do_uuid,

  	},

  	{ }

  };
  #endif 	/* CONFIG_SYSCTL */

  static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;

  static int __init random_int_secret_init(void)

  {

  	get_random_bytes(random_int_secret, sizeof(random_int_secret));

  	return 0;
  }

  late_initcall(random_int_secret_init);

  
  /*
   * Get a random word for internal kernel use only. Similar to urandom but
   * with the goal of minimal entropy pool depletion. As a result, the random
   * value is not cryptographically secure but for several uses the cost of
   * depleting entropy is too high
   */

  DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);

  unsigned int get_random_int(void)
  {

  	__u32 *hash;

  	unsigned int ret;

  	if (arch_get_random_int(&ret))
  		return ret;
  
  	hash = get_cpu_var(get_random_int_hash);

  	hash[0] += current->pid + jiffies + get_cycles();

  	md5_transform(hash, random_int_secret);
  	ret = hash[0];

  	put_cpu_var(get_random_int_hash);
  
  	return ret;

  }
  
  /*
   * randomize_range() returns a start address such that
   *
   *    [...... <range> .....]
   *  start                  end
   *
   * a <range> with size "len" starting at the return value is inside in the
   * area defined by [start, end], but is otherwise randomized.
   */
  unsigned long
  randomize_range(unsigned long start, unsigned long end, unsigned long len)
  {
  	unsigned long range = end - len - start;
  
  	if (end <= start + len)
  		return 0;
  	return PAGE_ALIGN(get_random_int() % range + start);
  }