vfs: do bulk POLL* -> EPOLL* replacement

[linux-2.6-microblaze.git] / drivers / char / random.c

/*
 * random.c -- A strong random number generator
 *
 * Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All
 * Rights Reserved.
 *
 * 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_device_randomness(const void *buf, unsigned int size);
 *      void add_input_randomness(unsigned int type, unsigned int code,
 *                                unsigned int value);
 *      void add_interrupt_randomness(int irq, int irq_flags);
 *      void add_disk_randomness(struct gendisk *disk);
 *
 * add_device_randomness() is for adding data to the random pool that
 * is likely to differ between two devices (or possibly even per boot).
 * This would be things like MAC addresses or serial numbers, or the
 * read-out of the RTC. This does *not* add any actual entropy to the
 * pool, but it initializes the pool to different values for devices
 * that might otherwise be identical and have very little entropy
 * available to them (particularly common in the embedded world).
 *
 * add_input_randomness() uses the input layer interrupt timing, as well as
 * the event type information from the hardware.
 *
 * add_interrupt_randomness() uses the interrupt timing as random
 * inputs to the entropy pool. Using the cycle counters and the irq source
 * as inputs, it feeds the randomness roughly once a second.
 *
 * 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/nodemask.h>
#include <linux/spinlock.h>
#include <linux/kthread.h>
#include <linux/percpu.h>
#include <linux/cryptohash.h>
#include <linux/fips.h>
#include <linux/ptrace.h>
#include <linux/workqueue.h>
#include <linux/irq.h>
#include <linux/syscalls.h>
#include <linux/completion.h>
#include <linux/uuid.h>
#include <crypto/chacha20.h>

#include <asm/processor.h>
#include <linux/uaccess.h>
#include <asm/irq.h>
#include <asm/irq_regs.h>
#include <asm/io.h>

#define CREATE_TRACE_POINTS
#include <trace/events/random.h>

/* #define ADD_INTERRUPT_BENCH */

/*
 * Configuration information
 */
#define INPUT_POOL_SHIFT        12
#define INPUT_POOL_WORDS        (1 << (INPUT_POOL_SHIFT-5))
#define OUTPUT_POOL_SHIFT       10
#define OUTPUT_POOL_WORDS       (1 << (OUTPUT_POOL_SHIFT-5))
#define SEC_XFER_SIZE           512
#define EXTRACT_SIZE            10


#define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))

/*
 * To allow fractional bits to be tracked, the entropy_count field is
 * denominated in units of 1/8th bits.
 *
 * 2*(ENTROPY_SHIFT + log2(poolbits)) must <= 31, or the multiply in
 * credit_entropy_bits() needs to be 64 bits wide.
 */
#define ENTROPY_SHIFT 3
#define ENTROPY_BITS(r) ((r)->entropy_count >> ENTROPY_SHIFT)

/*
 * 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_bits = 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_bits = 28 * OUTPUT_POOL_WORDS;

/*
 * Originally, we used a primitive polynomial of degree .poolwords
 * over GF(2).  The taps for various sizes are defined below.  They
 * were chosen to be evenly spaced except for the last tap, which is 1
 * to get the twisting happening as fast as possible.
 *
 * For the purposes of better mixing, we use the CRC-32 polynomial as
 * well to make a (modified) twisted Generalized Feedback Shift
 * Register.  (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 Modeling and Computer
 * Simulation 4:254-266)
 *
 * Thanks to Colin Plumb for suggesting this.
 *
 * The mixing operation is much less sensitive than the output hash,
 * where we use SHA-1.  All that we want of mixing operation 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).
 *
 * Our mixing functions were analyzed by Lacharme, Roeck, Strubel, and
 * Videau in their paper, "The Linux Pseudorandom Number Generator
 * Revisited" (see: http://eprint.iacr.org/2012/251.pdf).  In their
 * paper, they point out that we are not using a true Twisted GFSR,
 * since Matsumoto & Kurita used a trinomial feedback polynomial (that
 * is, with only three taps, instead of the six that we are using).
 * As a result, the resulting polynomial is neither primitive nor
 * irreducible, and hence does not have a maximal period over
 * GF(2**32).  They suggest a slight change to the generator
 * polynomial which improves the resulting TGFSR polynomial to be
 * irreducible, which we have made here.
 */
static struct poolinfo {
        int poolbitshift, poolwords, poolbytes, poolbits, poolfracbits;
#define S(x) ilog2(x)+5, (x), (x)*4, (x)*32, (x) << (ENTROPY_SHIFT+5)
        int tap1, tap2, tap3, tap4, tap5;
} poolinfo_table[] = {
        /* was: x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 */
        /* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */
        { S(128),       104,    76,     51,     25,     1 },
        /* was: x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 */
        /* x^32 + x^26 + x^19 + x^14 + x^7 + x + 1 */
        { S(32),        26,     19,     14,     7,      1 },
#if 0
        /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1  -- 115 */
        { S(2048),      1638,   1231,   819,    411,    1 },

        /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
        { S(1024),      817,    615,    412,    204,    1 },

        /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
        { S(1024),      819,    616,    410,    207,    2 },

        /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
        { S(512),       411,    308,    208,    104,    1 },

        /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
        { S(512),       409,    307,    206,    102,    2 },
        /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
        { S(512),       409,    309,    205,    103,    2 },

        /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
        { S(256),       205,    155,    101,    52,     1 },

        /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
        { S(128),       103,    78,     51,     27,     2 },

        /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
        { S(64),        52,     39,     26,     14,     1 },
#endif
};

/*
 * Static global variables
 */
static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
static struct fasync_struct *fasync;

static DEFINE_SPINLOCK(random_ready_list_lock);
static LIST_HEAD(random_ready_list);

struct crng_state {
        __u32           state[16];
        unsigned long   init_time;
        spinlock_t      lock;
};

struct crng_state primary_crng = {
        .lock = __SPIN_LOCK_UNLOCKED(primary_crng.lock),
};

/*
 * crng_init =  0 --> Uninitialized
 *              1 --> Initialized
 *              2 --> Initialized from input_pool
 *
 * crng_init is protected by primary_crng->lock, and only increases
 * its value (from 0->1->2).
 */
static int crng_init = 0;
#define crng_ready() (likely(crng_init > 0))
static int crng_init_cnt = 0;
#define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE)
static void _extract_crng(struct crng_state *crng,
                          __u32 out[CHACHA20_BLOCK_WORDS]);
static void _crng_backtrack_protect(struct crng_state *crng,
                                    __u32 tmp[CHACHA20_BLOCK_WORDS], int used);
static void process_random_ready_list(void);
static void _get_random_bytes(void *buf, int nbytes);

/**********************************************************************
 *
 * 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: */
        const struct poolinfo *poolinfo;
        __u32 *pool;
        const char *name;
        struct entropy_store *pull;
        struct work_struct push_work;

        /* read-write data: */
        unsigned long last_pulled;
        spinlock_t lock;
        unsigned short add_ptr;
        unsigned short input_rotate;
        int entropy_count;
        int entropy_total;
        unsigned int initialized:1;
        unsigned int last_data_init:1;
        __u8 last_data[EXTRACT_SIZE];
};

static ssize_t extract_entropy(struct entropy_store *r, void *buf,
                               size_t nbytes, int min, int rsvd);
static ssize_t _extract_entropy(struct entropy_store *r, void *buf,
                                size_t nbytes, int fips);

static void crng_reseed(struct crng_state *crng, struct entropy_store *r);
static void push_to_pool(struct work_struct *work);
static __u32 input_pool_data[INPUT_POOL_WORDS] __latent_entropy;
static __u32 blocking_pool_data[OUTPUT_POOL_WORDS] __latent_entropy;

static struct entropy_store input_pool = {
        .poolinfo = &poolinfo_table[0],
        .name = "input",
        .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
        .pool = input_pool_data
};

static struct entropy_store blocking_pool = {
        .poolinfo = &poolinfo_table[1],
        .name = "blocking",
        .pull = &input_pool,
        .lock = __SPIN_LOCK_UNLOCKED(blocking_pool.lock),
        .pool = blocking_pool_data,
        .push_work = __WORK_INITIALIZER(blocking_pool.push_work,
                                        push_to_pool),
};

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

/*
 * 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(struct entropy_store *r, const void *in,
                            int nbytes)
{
        unsigned long i, tap1, tap2, tap3, tap4, tap5;
        int input_rotate;
        int wordmask = r->poolinfo->poolwords - 1;
        const char *bytes = in;
        __u32 w;

        tap1 = r->poolinfo->tap1;
        tap2 = r->poolinfo->tap2;
        tap3 = r->poolinfo->tap3;
        tap4 = r->poolinfo->tap4;
        tap5 = r->poolinfo->tap5;

        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);
                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 = (input_rotate + (i ? 7 : 14)) & 31;
        }

        r->input_rotate = input_rotate;
        r->add_ptr = i;
}

static void __mix_pool_bytes(struct entropy_store *r, const void *in,
                             int nbytes)
{
        trace_mix_pool_bytes_nolock(r->name, nbytes, _RET_IP_);
        _mix_pool_bytes(r, in, nbytes);
}

static void mix_pool_bytes(struct entropy_store *r, const void *in,
                           int nbytes)
{
        unsigned long flags;

        trace_mix_pool_bytes(r->name, nbytes, _RET_IP_);
        spin_lock_irqsave(&r->lock, flags);
        _mix_pool_bytes(r, in, nbytes);
        spin_unlock_irqrestore(&r->lock, flags);
}

struct fast_pool {
        __u32           pool[4];
        unsigned long   last;
        unsigned short  reg_idx;
        unsigned char   count;
};

/*
 * This is a fast mixing routine used by the interrupt randomness
 * collector.  It's hardcoded for an 128 bit pool and assumes that any
 * locks that might be needed are taken by the caller.
 */
static void fast_mix(struct fast_pool *f)
{
        __u32 a = f->pool[0],   b = f->pool[1];
        __u32 c = f->pool[2],   d = f->pool[3];

        a += b;                 c += d;
        b = rol32(b, 6);        d = rol32(d, 27);
        d ^= a;                 b ^= c;

        a += b;                 c += d;
        b = rol32(b, 16);       d = rol32(d, 14);
        d ^= a;                 b ^= c;

        a += b;                 c += d;
        b = rol32(b, 6);        d = rol32(d, 27);
        d ^= a;                 b ^= c;

        a += b;                 c += d;
        b = rol32(b, 16);       d = rol32(d, 14);
        d ^= a;                 b ^= c;

        f->pool[0] = a;  f->pool[1] = b;
        f->pool[2] = c;  f->pool[3] = d;
        f->count++;
}

static void process_random_ready_list(void)
{
        unsigned long flags;
        struct random_ready_callback *rdy, *tmp;

        spin_lock_irqsave(&random_ready_list_lock, flags);
        list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) {
                struct module *owner = rdy->owner;

                list_del_init(&rdy->list);
                rdy->func(rdy);
                module_put(owner);
        }
        spin_unlock_irqrestore(&random_ready_list_lock, flags);
}

/*
 * Credit (or debit) the entropy store with n bits of entropy.
 * Use credit_entropy_bits_safe() if the value comes from userspace
 * or otherwise should be checked for extreme values.
 */
static void credit_entropy_bits(struct entropy_store *r, int nbits)
{
        int entropy_count, orig;
        const int pool_size = r->poolinfo->poolfracbits;
        int nfrac = nbits << ENTROPY_SHIFT;

        if (!nbits)
                return;

retry:
        entropy_count = orig = READ_ONCE(r->entropy_count);
        if (nfrac < 0) {
                /* Debit */
                entropy_count += nfrac;
        } else {
                /*
                 * Credit: we have to account for the possibility of
                 * overwriting already present entropy.  Even in the
                 * ideal case of pure Shannon entropy, new contributions
                 * approach the full value asymptotically:
                 *
                 * entropy <- entropy + (pool_size - entropy) *
                 *      (1 - exp(-add_entropy/pool_size))
                 *
                 * For add_entropy <= pool_size/2 then
                 * (1 - exp(-add_entropy/pool_size)) >=
                 *    (add_entropy/pool_size)*0.7869...
                 * so we can approximate the exponential with
                 * 3/4*add_entropy/pool_size and still be on the
                 * safe side by adding at most pool_size/2 at a time.
                 *
                 * The use of pool_size-2 in the while statement is to
                 * prevent rounding artifacts from making the loop
                 * arbitrarily long; this limits the loop to log2(pool_size)*2
                 * turns no matter how large nbits is.
                 */
                int pnfrac = nfrac;
                const int s = r->poolinfo->poolbitshift + ENTROPY_SHIFT + 2;
                /* The +2 corresponds to the /4 in the denominator */

                do {
                        unsigned int anfrac = min(pnfrac, pool_size/2);
                        unsigned int add =
                                ((pool_size - entropy_count)*anfrac*3) >> s;

                        entropy_count += add;
                        pnfrac -= anfrac;
                } while (unlikely(entropy_count < pool_size-2 && pnfrac));
        }

        if (unlikely(entropy_count < 0)) {
                pr_warn("random: negative entropy/overflow: pool %s count %d\n",
                        r->name, entropy_count);
                WARN_ON(1);
                entropy_count = 0;
        } else if (entropy_count > pool_size)
                entropy_count = pool_size;
        if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
                goto retry;

        r->entropy_total += nbits;
        if (!r->initialized && r->entropy_total > 128) {
                r->initialized = 1;
                r->entropy_total = 0;
        }

        trace_credit_entropy_bits(r->name, nbits,
                                  entropy_count >> ENTROPY_SHIFT,
                                  r->entropy_total, _RET_IP_);

        if (r == &input_pool) {
                int entropy_bits = entropy_count >> ENTROPY_SHIFT;

                if (crng_init < 2 && entropy_bits >= 128) {
                        crng_reseed(&primary_crng, r);
                        entropy_bits = r->entropy_count >> ENTROPY_SHIFT;
                }

                /* should we wake readers? */
                if (entropy_bits >= random_read_wakeup_bits) {
                        wake_up_interruptible(&random_read_wait);
                        kill_fasync(&fasync, SIGIO, POLL_IN);
                }
                /* If the input pool is getting full, send some
                 * entropy to the blocking pool until it is 75% full.
                 */
                if (entropy_bits > random_write_wakeup_bits &&
                    r->initialized &&
                    r->entropy_total >= 2*random_read_wakeup_bits) {
                        struct entropy_store *other = &blocking_pool;

                        if (other->entropy_count <=
                            3 * other->poolinfo->poolfracbits / 4) {
                                schedule_work(&other->push_work);
                                r->entropy_total = 0;
                        }
                }
        }
}

static int credit_entropy_bits_safe(struct entropy_store *r, int nbits)
{
        const int nbits_max = (int)(~0U >> (ENTROPY_SHIFT + 1));

        if (nbits < 0)
                return -EINVAL;

        /* Cap the value to avoid overflows */
        nbits = min(nbits,  nbits_max);

        credit_entropy_bits(r, nbits);
        return 0;
}

/*********************************************************************
 *
 * CRNG using CHACHA20
 *
 *********************************************************************/

#define CRNG_RESEED_INTERVAL (300*HZ)

static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);

#ifdef CONFIG_NUMA
/*
 * Hack to deal with crazy userspace progams when they are all trying
 * to access /dev/urandom in parallel.  The programs are almost
 * certainly doing something terribly wrong, but we'll work around
 * their brain damage.
 */
static struct crng_state **crng_node_pool __read_mostly;
#endif

static void invalidate_batched_entropy(void);

static void crng_initialize(struct crng_state *crng)
{
        int             i;
        unsigned long   rv;

        memcpy(&crng->state[0], "expand 32-byte k", 16);
        if (crng == &primary_crng)
                _extract_entropy(&input_pool, &crng->state[4],
                                 sizeof(__u32) * 12, 0);
        else
                _get_random_bytes(&crng->state[4], sizeof(__u32) * 12);
        for (i = 4; i < 16; i++) {
                if (!arch_get_random_seed_long(&rv) &&
                    !arch_get_random_long(&rv))
                        rv = random_get_entropy();
                crng->state[i] ^= rv;
        }
        crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
}

static int crng_fast_load(const char *cp, size_t len)
{
        unsigned long flags;
        char *p;

        if (!spin_trylock_irqsave(&primary_crng.lock, flags))
                return 0;
        if (crng_ready()) {
                spin_unlock_irqrestore(&primary_crng.lock, flags);
                return 0;
        }
        p = (unsigned char *) &primary_crng.state[4];
        while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) {
                p[crng_init_cnt % CHACHA20_KEY_SIZE] ^= *cp;
                cp++; crng_init_cnt++; len--;
        }
        spin_unlock_irqrestore(&primary_crng.lock, flags);
        if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
                invalidate_batched_entropy();
                crng_init = 1;
                wake_up_interruptible(&crng_init_wait);
                pr_notice("random: fast init done\n");
        }
        return 1;
}

static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
{
        unsigned long   flags;
        int             i, num;
        union {
                __u32   block[CHACHA20_BLOCK_WORDS];
                __u32   key[8];
        } buf;

        if (r) {
                num = extract_entropy(r, &buf, 32, 16, 0);
                if (num == 0)
                        return;
        } else {
                _extract_crng(&primary_crng, buf.block);
                _crng_backtrack_protect(&primary_crng, buf.block,
                                        CHACHA20_KEY_SIZE);
        }
        spin_lock_irqsave(&primary_crng.lock, flags);
        for (i = 0; i < 8; i++) {
                unsigned long   rv;
                if (!arch_get_random_seed_long(&rv) &&
                    !arch_get_random_long(&rv))
                        rv = random_get_entropy();
                crng->state[i+4] ^= buf.key[i] ^ rv;
        }
        memzero_explicit(&buf, sizeof(buf));
        crng->init_time = jiffies;
        spin_unlock_irqrestore(&primary_crng.lock, flags);
        if (crng == &primary_crng && crng_init < 2) {
                invalidate_batched_entropy();
                crng_init = 2;
                process_random_ready_list();
                wake_up_interruptible(&crng_init_wait);
                pr_notice("random: crng init done\n");
        }
}

static void _extract_crng(struct crng_state *crng,
                          __u32 out[CHACHA20_BLOCK_WORDS])
{
        unsigned long v, flags;

        if (crng_init > 1 &&
            time_after(jiffies, crng->init_time + CRNG_RESEED_INTERVAL))
                crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL);
        spin_lock_irqsave(&crng->lock, flags);
        if (arch_get_random_long(&v))
                crng->state[14] ^= v;
        chacha20_block(&crng->state[0], out);
        if (crng->state[12] == 0)
                crng->state[13]++;
        spin_unlock_irqrestore(&crng->lock, flags);
}

static void extract_crng(__u32 out[CHACHA20_BLOCK_WORDS])
{
        struct crng_state *crng = NULL;

#ifdef CONFIG_NUMA
        if (crng_node_pool)
                crng = crng_node_pool[numa_node_id()];
        if (crng == NULL)
#endif
                crng = &primary_crng;
        _extract_crng(crng, out);
}

/*
 * Use the leftover bytes from the CRNG block output (if there is
 * enough) to mutate the CRNG key to provide backtracking protection.
 */
static void _crng_backtrack_protect(struct crng_state *crng,
                                    __u32 tmp[CHACHA20_BLOCK_WORDS], int used)
{
        unsigned long   flags;
        __u32           *s, *d;
        int             i;

        used = round_up(used, sizeof(__u32));
        if (used + CHACHA20_KEY_SIZE > CHACHA20_BLOCK_SIZE) {
                extract_crng(tmp);
                used = 0;
        }
        spin_lock_irqsave(&crng->lock, flags);
        s = &tmp[used / sizeof(__u32)];
        d = &crng->state[4];
        for (i=0; i < 8; i++)
                *d++ ^= *s++;
        spin_unlock_irqrestore(&crng->lock, flags);
}

static void crng_backtrack_protect(__u32 tmp[CHACHA20_BLOCK_WORDS], int used)
{
        struct crng_state *crng = NULL;

#ifdef CONFIG_NUMA
        if (crng_node_pool)
                crng = crng_node_pool[numa_node_id()];
        if (crng == NULL)
#endif
                crng = &primary_crng;
        _crng_backtrack_protect(crng, tmp, used);
}

static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
{
        ssize_t ret = 0, i = CHACHA20_BLOCK_SIZE;
        __u32 tmp[CHACHA20_BLOCK_WORDS];
        int large_request = (nbytes > 256);

        while (nbytes) {
                if (large_request && need_resched()) {
                        if (signal_pending(current)) {
                                if (ret == 0)
                                        ret = -ERESTARTSYS;
                                break;
                        }
                        schedule();
                }

                extract_crng(tmp);
                i = min_t(int, nbytes, CHACHA20_BLOCK_SIZE);
                if (copy_to_user(buf, tmp, i)) {
                        ret = -EFAULT;
                        break;
                }

                nbytes -= i;
                buf += i;
                ret += i;
        }
        crng_backtrack_protect(tmp, i);

        /* Wipe data just written to memory */
        memzero_explicit(tmp, sizeof(tmp));

        return ret;
}


/*********************************************************************
 *
 * 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;
};

#define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, };

/*
 * Add device- or boot-specific data to the input pool to help
 * initialize it.
 *
 * None of this adds any entropy; it is meant to avoid the problem of
 * the entropy pool having similar initial state across largely
 * identical devices.
 */
void add_device_randomness(const void *buf, unsigned int size)
{
        unsigned long time = random_get_entropy() ^ jiffies;
        unsigned long flags;

        if (!crng_ready()) {
                crng_fast_load(buf, size);
                return;
        }

        trace_add_device_randomness(size, _RET_IP_);
        spin_lock_irqsave(&input_pool.lock, flags);
        _mix_pool_bytes(&input_pool, buf, size);
        _mix_pool_bytes(&input_pool, &time, sizeof(time));
        spin_unlock_irqrestore(&input_pool.lock, flags);
}
EXPORT_SYMBOL(add_device_randomness);

static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_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 entropy_store    *r;
        struct {
                long jiffies;
                unsigned cycles;
                unsigned num;
        } sample;
        long delta, delta2, delta3;

        preempt_disable();

        sample.jiffies = jiffies;
        sample.cycles = random_get_entropy();
        sample.num = num;
        r = &input_pool;
        mix_pool_bytes(r, &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(r, min_t(int, fls(delta>>1), 11));
        }
        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;

        last_value = value;
        add_timer_randomness(&input_timer_state,
                             (type << 4) ^ code ^ (code >> 4) ^ value);
        trace_add_input_randomness(ENTROPY_BITS(&input_pool));
}
EXPORT_SYMBOL_GPL(add_input_randomness);

static DEFINE_PER_CPU(struct fast_pool, irq_randomness);

#ifdef ADD_INTERRUPT_BENCH
static unsigned long avg_cycles, avg_deviation;

#define AVG_SHIFT 8     /* Exponential average factor k=1/256 */
#define FIXED_1_2 (1 << (AVG_SHIFT-1))

static void add_interrupt_bench(cycles_t start)
{
        long delta = random_get_entropy() - start;

        /* Use a weighted moving average */
        delta = delta - ((avg_cycles + FIXED_1_2) >> AVG_SHIFT);
        avg_cycles += delta;
        /* And average deviation */
        delta = abs(delta) - ((avg_deviation + FIXED_1_2) >> AVG_SHIFT);
        avg_deviation += delta;
}
#else
#define add_interrupt_bench(x)
#endif

static __u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
{
        __u32 *ptr = (__u32 *) regs;
        unsigned int idx;

        if (regs == NULL)
                return 0;
        idx = READ_ONCE(f->reg_idx);
        if (idx >= sizeof(struct pt_regs) / sizeof(__u32))
                idx = 0;
        ptr += idx++;
        WRITE_ONCE(f->reg_idx, idx);
        return *ptr;
}

void add_interrupt_randomness(int irq, int irq_flags)
{
        struct entropy_store    *r;
        struct fast_pool        *fast_pool = this_cpu_ptr(&irq_randomness);
        struct pt_regs          *regs = get_irq_regs();
        unsigned long           now = jiffies;
        cycles_t                cycles = random_get_entropy();
        __u32                   c_high, j_high;
        __u64                   ip;
        unsigned long           seed;
        int                     credit = 0;

        if (cycles == 0)
                cycles = get_reg(fast_pool, regs);
        c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;
        j_high = (sizeof(now) > 4) ? now >> 32 : 0;
        fast_pool->pool[0] ^= cycles ^ j_high ^ irq;
        fast_pool->pool[1] ^= now ^ c_high;
        ip = regs ? instruction_pointer(regs) : _RET_IP_;
        fast_pool->pool[2] ^= ip;
        fast_pool->pool[3] ^= (sizeof(ip) > 4) ? ip >> 32 :
                get_reg(fast_pool, regs);

        fast_mix(fast_pool);
        add_interrupt_bench(cycles);

        if (!crng_ready()) {
                if ((fast_pool->count >= 64) &&
                    crng_fast_load((char *) fast_pool->pool,
                                   sizeof(fast_pool->pool))) {
                        fast_pool->count = 0;
                        fast_pool->last = now;
                }
                return;
        }

        if ((fast_pool->count < 64) &&
            !time_after(now, fast_pool->last + HZ))
                return;

        r = &input_pool;
        if (!spin_trylock(&r->lock))
                return;

        fast_pool->last = now;
        __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool));

        /*
         * If we have architectural seed generator, produce a seed and
         * add it to the pool.  For the sake of paranoia don't let the
         * architectural seed generator dominate the input from the
         * interrupt noise.
         */
        if (arch_get_random_seed_long(&seed)) {
                __mix_pool_bytes(r, &seed, sizeof(seed));
                credit = 1;
        }
        spin_unlock(&r->lock);

        fast_pool->count = 0;

        /* award one bit for the contents of the fast pool */
        credit_entropy_bits(r, credit + 1);
}
EXPORT_SYMBOL_GPL(add_interrupt_randomness);

#ifdef CONFIG_BLOCK
void add_disk_randomness(struct gendisk *disk)
{
        if (!disk || !disk->random)
                return;
        /* first major is 1, so we get >= 0x200 here */
        add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
        trace_add_disk_randomness(disk_devt(disk), ENTROPY_BITS(&input_pool));
}
EXPORT_SYMBOL_GPL(add_disk_randomness);
#endif

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

/*
 * 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);
static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
{
        if (!r->pull ||
            r->entropy_count >= (nbytes << (ENTROPY_SHIFT + 3)) ||
            r->entropy_count > r->poolinfo->poolfracbits)
                return;

        _xfer_secondary_pool(r, nbytes);
}

static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
{
        __u32   tmp[OUTPUT_POOL_WORDS];

        int bytes = nbytes;

        /* pull at least as much as a wakeup */
        bytes = max_t(int, bytes, random_read_wakeup_bits / 8);
        /* but never more than the buffer size */
        bytes = min_t(int, bytes, sizeof(tmp));

        trace_xfer_secondary_pool(r->name, bytes * 8, nbytes * 8,
                                  ENTROPY_BITS(r), ENTROPY_BITS(r->pull));
        bytes = extract_entropy(r->pull, tmp, bytes,
                                random_read_wakeup_bits / 8, 0);
        mix_pool_bytes(r, tmp, bytes);
        credit_entropy_bits(r, bytes*8);
}

/*
 * Used as a workqueue function so that when the input pool is getting
 * full, we can "spill over" some entropy to the output pools.  That
 * way the output pools can store some of the excess entropy instead
 * of letting it go to waste.
 */
static void push_to_pool(struct work_struct *work)
{
        struct entropy_store *r = container_of(work, struct entropy_store,
                                              push_work);
        BUG_ON(!r);
        _xfer_secondary_pool(r, random_read_wakeup_bits/8);
        trace_push_to_pool(r->name, r->entropy_count >> ENTROPY_SHIFT,
                           r->pull->entropy_count >> ENTROPY_SHIFT);
}

/*
 * This function decides how many bytes to actually take from the
 * given pool, and also debits the entropy count accordingly.
 */
static size_t account(struct entropy_store *r, size_t nbytes, int min,
                      int reserved)
{
        int entropy_count, orig, have_bytes;
        size_t ibytes, nfrac;

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

        /* Can we pull enough? */
retry:
        entropy_count = orig = READ_ONCE(r->entropy_count);
        ibytes = nbytes;
        /* never pull more than available */
        have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);

        if ((have_bytes -= reserved) < 0)
                have_bytes = 0;
        ibytes = min_t(size_t, ibytes, have_bytes);
        if (ibytes < min)
                ibytes = 0;

        if (unlikely(entropy_count < 0)) {
                pr_warn("random: negative entropy count: pool %s count %d\n",
                        r->name, entropy_count);
                WARN_ON(1);
                entropy_count = 0;
        }
        nfrac = ibytes << (ENTROPY_SHIFT + 3);
        if ((size_t) entropy_count > nfrac)
                entropy_count -= nfrac;
        else
                entropy_count = 0;

        if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
                goto retry;

        trace_debit_entropy(r->name, 8 * ibytes);
        if (ibytes &&
            (r->entropy_count >> ENTROPY_SHIFT) < random_write_wakeup_bits) {
                wake_up_interruptible(&random_write_wait);
                kill_fasync(&fasync, SIGIO, POLL_OUT);
        }

        return ibytes;
}

/*
 * This function does the actual extraction for extract_entropy and
 * extract_entropy_user.
 *
 * Note: we assume that .poolwords is a multiple of 16 words.
 */
static void extract_buf(struct entropy_store *r, __u8 *out)
{
        int i;
        union {
                __u32 w[5];
                unsigned long l[LONGS(20)];
        } hash;
        __u32 workspace[SHA_WORKSPACE_WORDS];
        unsigned long flags;

        /*
         * If we have an architectural hardware random number
         * generator, use it for SHA's initial vector
         */
        sha_init(hash.w);
        for (i = 0; i < LONGS(20); i++) {
                unsigned long v;
                if (!arch_get_random_long(&v))
                        break;
                hash.l[i] = v;
        }

        /* Generate a hash across the pool, 16 words (512 bits) at a time */
        spin_lock_irqsave(&r->lock, flags);
        for (i = 0; i < r->poolinfo->poolwords; i += 16)
                sha_transform(hash.w, (__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(r, hash.w, sizeof(hash.w));
        spin_unlock_irqrestore(&r->lock, flags);

        memzero_explicit(workspace, 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.w[0] ^= hash.w[3];
        hash.w[1] ^= hash.w[4];
        hash.w[2] ^= rol32(hash.w[2], 16);

        memcpy(out, &hash, EXTRACT_SIZE);
        memzero_explicit(&hash, sizeof(hash));
}

static ssize_t _extract_entropy(struct entropy_store *r, void *buf,
                                size_t nbytes, int fips)
{
        ssize_t ret = 0, i;
        __u8 tmp[EXTRACT_SIZE];
        unsigned long flags;

        while (nbytes) {
                extract_buf(r, tmp);

                if (fips) {
                        spin_lock_irqsave(&r->lock, flags);
                        if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
                                panic("Hardware RNG duplicated output!\n");
                        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 */
        memzero_explicit(tmp, sizeof(tmp));

        return ret;
}

/*
 * This function 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.
 */
static ssize_t extract_entropy(struct entropy_store *r, void *buf,
                                 size_t nbytes, int min, int reserved)
{
        __u8 tmp[EXTRACT_SIZE];
        unsigned long flags;

        /* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */
        if (fips_enabled) {
                spin_lock_irqsave(&r->lock, flags);
                if (!r->last_data_init) {
                        r->last_data_init = 1;
                        spin_unlock_irqrestore(&r->lock, flags);
                        trace_extract_entropy(r->name, EXTRACT_SIZE,
                                              ENTROPY_BITS(r), _RET_IP_);
                        xfer_secondary_pool(r, EXTRACT_SIZE);
                        extract_buf(r, tmp);
                        spin_lock_irqsave(&r->lock, flags);
                        memcpy(r->last_data, tmp, EXTRACT_SIZE);
                }
                spin_unlock_irqrestore(&r->lock, flags);
        }

        trace_extract_entropy(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
        xfer_secondary_pool(r, nbytes);
        nbytes = account(r, nbytes, min, reserved);

        return _extract_entropy(r, buf, nbytes, fips_enabled);
}

/*
 * This function extracts randomness from the "entropy pool", and
 * returns it in a userspace buffer.
 */
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];
        int large_request = (nbytes > 256);

        trace_extract_entropy_user(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
        xfer_secondary_pool(r, nbytes);
        nbytes = account(r, nbytes, 0, 0);

        while (nbytes) {
                if (large_request && 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 */
        memzero_explicit(tmp, sizeof(tmp));

        return ret;
}

#define warn_unseeded_randomness(previous) \
        _warn_unseeded_randomness(__func__, (void *) _RET_IP_, (previous))

static void _warn_unseeded_randomness(const char *func_name, void *caller,
                                      void **previous)
{
#ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM
        const bool print_once = false;
#else
        static bool print_once __read_mostly;
#endif

        if (print_once ||
            crng_ready() ||
            (previous && (caller == READ_ONCE(*previous))))
                return;
        WRITE_ONCE(*previous, caller);
#ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM
        print_once = true;
#endif
        pr_notice("random: %s called from %pS with crng_init=%d\n",
                  func_name, caller, crng_init);
}

/*
 * This function is the exported kernel interface.  It returns some
 * number of good random numbers, suitable for key generation, seeding
 * TCP sequence numbers, etc.  It does not rely on the hardware random
 * number generator.  For random bytes direct from the hardware RNG
 * (when available), use get_random_bytes_arch(). In order to ensure
 * that the randomness provided by this function is okay, the function
 * wait_for_random_bytes() should be called and return 0 at least once
 * at any point prior.
 */
static void _get_random_bytes(void *buf, int nbytes)
{
        __u32 tmp[CHACHA20_BLOCK_WORDS];

        trace_get_random_bytes(nbytes, _RET_IP_);

        while (nbytes >= CHACHA20_BLOCK_SIZE) {
                extract_crng(buf);
                buf += CHACHA20_BLOCK_SIZE;
                nbytes -= CHACHA20_BLOCK_SIZE;
        }

        if (nbytes > 0) {
                extract_crng(tmp);
                memcpy(buf, tmp, nbytes);
                crng_backtrack_protect(tmp, nbytes);
        } else
                crng_backtrack_protect(tmp, CHACHA20_BLOCK_SIZE);
        memzero_explicit(tmp, sizeof(tmp));
}

void get_random_bytes(void *buf, int nbytes)
{
        static void *previous;

        warn_unseeded_randomness(&previous);
        _get_random_bytes(buf, nbytes);
}
EXPORT_SYMBOL(get_random_bytes);

/*
 * Wait for the urandom pool to be seeded and thus guaranteed to supply
 * cryptographically secure random numbers. This applies to: the /dev/urandom
 * device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
 * family of functions. Using any of these functions without first calling
 * this function forfeits the guarantee of security.
 *
 * Returns: 0 if the urandom pool has been seeded.
 *          -ERESTARTSYS if the function was interrupted by a signal.
 */
int wait_for_random_bytes(void)
{
        if (likely(crng_ready()))
                return 0;
        return wait_event_interruptible(crng_init_wait, crng_ready());
}
EXPORT_SYMBOL(wait_for_random_bytes);

/*
 * Add a callback function that will be invoked when the nonblocking
 * pool is initialised.
 *
 * returns: 0 if callback is successfully added
 *          -EALREADY if pool is already initialised (callback not called)
 *          -ENOENT if module for callback is not alive
 */
int add_random_ready_callback(struct random_ready_callback *rdy)
{
        struct module *owner;
        unsigned long flags;
        int err = -EALREADY;

        if (crng_ready())
                return err;

        owner = rdy->owner;
        if (!try_module_get(owner))
                return -ENOENT;

        spin_lock_irqsave(&random_ready_list_lock, flags);
        if (crng_ready())
                goto out;

        owner = NULL;

        list_add(&rdy->list, &random_ready_list);
        err = 0;

out:
        spin_unlock_irqrestore(&random_ready_list_lock, flags);

        module_put(owner);

        return err;
}
EXPORT_SYMBOL(add_random_ready_callback);

/*
 * Delete a previously registered readiness callback function.
 */
void del_random_ready_callback(struct random_ready_callback *rdy)
{
        unsigned long flags;
        struct module *owner = NULL;

        spin_lock_irqsave(&random_ready_list_lock, flags);
        if (!list_empty(&rdy->list)) {
                list_del_init(&rdy->list);
                owner = rdy->owner;
        }
        spin_unlock_irqrestore(&random_ready_list_lock, flags);

        module_put(owner);
}
EXPORT_SYMBOL(del_random_ready_callback);

/*
 * This function will use the architecture-specific hardware random
 * number generator if it is available.  The arch-specific hw RNG will
 * almost certainly be faster than what we can do in software, but it
 * is impossible to verify that it is implemented securely (as
 * opposed, to, say, the AES encryption of a sequence number using a
 * key known by the NSA).  So it's useful if we need the speed, but
 * only if we're willing to trust the hardware manufacturer not to
 * have put in a back door.
 */
void get_random_bytes_arch(void *buf, int nbytes)
{
        char *p = buf;

        trace_get_random_bytes_arch(nbytes, _RET_IP_);
        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;
        }

        if (nbytes)
                get_random_bytes(p, nbytes);
}
EXPORT_SYMBOL(get_random_bytes_arch);


/*
 * 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 = ktime_get_real();
        unsigned long rv;

        r->last_pulled = jiffies;
        mix_pool_bytes(r, &now, sizeof(now));
        for (i = r->poolinfo->poolbytes; i > 0; i -= sizeof(rv)) {
                if (!arch_get_random_seed_long(&rv) &&
                    !arch_get_random_long(&rv))
                        rv = random_get_entropy();
                mix_pool_bytes(r, &rv, sizeof(rv));
        }
        mix_pool_bytes(r, utsname(), sizeof(*(utsname())));
}

/*
 * Note that setup_arch() may call add_device_randomness()
 * long before we get here. This allows seeding of the pools
 * with some platform dependent data very early in the boot
 * process. But it limits our options here. We must use
 * statically allocated structures that already have all
 * initializations complete at compile time. We should also
 * take care not to overwrite the precious per platform data
 * we were given.
 */
static int rand_initialize(void)
{
#ifdef CONFIG_NUMA
        int i;
        struct crng_state *crng;
        struct crng_state **pool;
#endif

        init_std_data(&input_pool);
        init_std_data(&blocking_pool);
        crng_initialize(&primary_crng);

#ifdef CONFIG_NUMA
        pool = kcalloc(nr_node_ids, sizeof(*pool), GFP_KERNEL|__GFP_NOFAIL);
        for_each_online_node(i) {
                crng = kmalloc_node(sizeof(struct crng_state),
                                    GFP_KERNEL | __GFP_NOFAIL, i);
                spin_lock_init(&crng->lock);
                crng_initialize(crng);
                pool[i] = crng;
        }
        mb();
        crng_node_pool = pool;
#endif
        return 0;
}
early_initcall(rand_initialize);

#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) {
                state->last_time = INITIAL_JIFFIES;
                disk->random = state;
        }
}
#endif

static ssize_t
_random_read(int nonblock, char __user *buf, size_t nbytes)
{
        ssize_t n;

        if (nbytes == 0)
                return 0;

        nbytes = min_t(size_t, nbytes, SEC_XFER_SIZE);
        while (1) {
                n = extract_entropy_user(&blocking_pool, buf, nbytes);
                if (n < 0)
                        return n;
                trace_random_read(n*8, (nbytes-n)*8,
                                  ENTROPY_BITS(&blocking_pool),
                                  ENTROPY_BITS(&input_pool));
                if (n > 0)
                        return n;

                /* Pool is (near) empty.  Maybe wait and retry. */
                if (nonblock)
                        return -EAGAIN;

                wait_event_interruptible(random_read_wait,
                        ENTROPY_BITS(&input_pool) >=
                        random_read_wakeup_bits);
                if (signal_pending(current))
                        return -ERESTARTSYS;
        }
}

static ssize_t
random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
        return _random_read(file->f_flags & O_NONBLOCK, buf, nbytes);
}

static ssize_t
urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
        unsigned long flags;
        static int maxwarn = 10;
        int ret;

        if (!crng_ready() && maxwarn > 0) {
                maxwarn--;
                printk(KERN_NOTICE "random: %s: uninitialized urandom read "
                       "(%zd bytes read)\n",
                       current->comm, nbytes);
                spin_lock_irqsave(&primary_crng.lock, flags);
                crng_init_cnt = 0;
                spin_unlock_irqrestore(&primary_crng.lock, flags);
        }
        nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3));
        ret = extract_crng_user(buf, nbytes);
        trace_urandom_read(8 * nbytes, 0, ENTROPY_BITS(&input_pool));
        return ret;
}

static __poll_t
random_poll(struct file *file, poll_table * wait)
{
        __poll_t mask;

        poll_wait(file, &random_read_wait, wait);
        poll_wait(file, &random_write_wait, wait);
        mask = 0;
        if (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits)
                mask |= EPOLLIN | EPOLLRDNORM;
        if (ENTROPY_BITS(&input_pool) < random_write_wakeup_bits)
                mask |= EPOLLOUT | EPOLLWRNORM;
        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(&input_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 */
                ent_count = ENTROPY_BITS(&input_pool);
                if (put_user(ent_count, p))
                        return -EFAULT;
                return 0;
        case RNDADDTOENTCNT:
                if (!capable(CAP_SYS_ADMIN))
                        return -EPERM;
                if (get_user(ent_count, p))
                        return -EFAULT;
                return credit_entropy_bits_safe(&input_pool, ent_count);
        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;
                return credit_entropy_bits_safe(&input_pool, ent_count);
        case RNDZAPENTCNT:
        case RNDCLEARPOOL:
                /*
                 * Clear the entropy pool counters. We no longer clear
                 * the entropy pool, as that's silly.
                 */
                if (!capable(CAP_SYS_ADMIN))
                        return -EPERM;
                input_pool.entropy_count = 0;
                blocking_pool.entropy_count = 0;
                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,
};

SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
                unsigned int, flags)
{
        int ret;

        if (flags & ~(GRND_NONBLOCK|GRND_RANDOM))
                return -EINVAL;

        if (count > INT_MAX)
                count = INT_MAX;

        if (flags & GRND_RANDOM)
                return _random_read(flags & GRND_NONBLOCK, buf, count);

        if (!crng_ready()) {
                if (flags & GRND_NONBLOCK)
                        return -EAGAIN;
                ret = wait_for_random_bytes();
                if (unlikely(ret))
                        return ret;
        }
        return urandom_read(NULL, buf, count, NULL);
}

/********************************************************************
 *
 * Sysctl interface
 *
 ********************************************************************/

#ifdef CONFIG_SYSCTL

#include <linux/sysctl.h>

static int min_read_thresh = 8, min_write_thresh;
static int max_read_thresh = OUTPUT_POOL_WORDS * 32;
static int max_write_thresh = INPUT_POOL_WORDS * 32;
static int random_min_urandom_seed = 60;
static char sysctl_bootid[16];

/*
 * This function 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, the UUID will be
 * returned as an ASCII string in the standard UUID format; if via the
 * sysctl system call, as 16 bytes of binary data.
 */
static int proc_do_uuid(struct ctl_table *table, int write,
                        void __user *buffer, size_t *lenp, loff_t *ppos)
{
        struct ctl_table fake_table;
        unsigned char buf[64], tmp_uuid[16], *uuid;

        uuid = table->data;
        if (!uuid) {
                uuid = tmp_uuid;
                generate_random_uuid(uuid);
        } else {
                static DEFINE_SPINLOCK(bootid_spinlock);

                spin_lock(&bootid_spinlock);
                if (!uuid[8])
                        generate_random_uuid(uuid);
                spin_unlock(&bootid_spinlock);
        }

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

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

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

/*
 * Return entropy available scaled to integral bits
 */
static int proc_do_entropy(struct ctl_table *table, int write,
                           void __user *buffer, size_t *lenp, loff_t *ppos)
{
        struct ctl_table fake_table;
        int entropy_count;

        entropy_count = *(int *)table->data >> ENTROPY_SHIFT;

        fake_table.data = &entropy_count;
        fake_table.maxlen = sizeof(entropy_count);

        return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
}

static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
extern struct ctl_table random_table[];
struct 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_do_entropy,
                .data           = &input_pool.entropy_count,
        },
        {
                .procname       = "read_wakeup_threshold",
                .data           = &random_read_wakeup_bits,
                .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_bits,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &min_write_thresh,
                .extra2         = &max_write_thresh,
        },
        {
                .procname       = "urandom_min_reseed_secs",
                .data           = &random_min_urandom_seed,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec,
        },
        {
                .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,
        },
#ifdef ADD_INTERRUPT_BENCH
        {
                .procname       = "add_interrupt_avg_cycles",
                .data           = &avg_cycles,
                .maxlen         = sizeof(avg_cycles),
                .mode           = 0444,
                .proc_handler   = proc_doulongvec_minmax,
        },
        {
                .procname       = "add_interrupt_avg_deviation",
                .data           = &avg_deviation,
                .maxlen         = sizeof(avg_deviation),
                .mode           = 0444,
                .proc_handler   = proc_doulongvec_minmax,
        },
#endif
        { }
};
#endif  /* CONFIG_SYSCTL */

struct batched_entropy {
        union {
                u64 entropy_u64[CHACHA20_BLOCK_SIZE / sizeof(u64)];
                u32 entropy_u32[CHACHA20_BLOCK_SIZE / sizeof(u32)];
        };
        unsigned int position;
};
static rwlock_t batched_entropy_reset_lock = __RW_LOCK_UNLOCKED(batched_entropy_reset_lock);

/*
 * Get a random word for internal kernel use only. The quality of the random
 * number is either as good as RDRAND or as good as /dev/urandom, with the
 * goal of being quite fast and not depleting entropy. In order to ensure
 * that the randomness provided by this function is okay, the function
 * wait_for_random_bytes() should be called and return 0 at least once
 * at any point prior.
 */
static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64);
u64 get_random_u64(void)
{
        u64 ret;
        bool use_lock;
        unsigned long flags = 0;
        struct batched_entropy *batch;
        static void *previous;

#if BITS_PER_LONG == 64
        if (arch_get_random_long((unsigned long *)&ret))
                return ret;
#else
        if (arch_get_random_long((unsigned long *)&ret) &&
            arch_get_random_long((unsigned long *)&ret + 1))
            return ret;
#endif

        warn_unseeded_randomness(&previous);

        use_lock = READ_ONCE(crng_init) < 2;
        batch = &get_cpu_var(batched_entropy_u64);
        if (use_lock)
                read_lock_irqsave(&batched_entropy_reset_lock, flags);
        if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
                extract_crng((__u32 *)batch->entropy_u64);
                batch->position = 0;
        }
        ret = batch->entropy_u64[batch->position++];
        if (use_lock)
                read_unlock_irqrestore(&batched_entropy_reset_lock, flags);
        put_cpu_var(batched_entropy_u64);
        return ret;
}
EXPORT_SYMBOL(get_random_u64);

static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32);
u32 get_random_u32(void)
{
        u32 ret;
        bool use_lock;
        unsigned long flags = 0;
        struct batched_entropy *batch;
        static void *previous;

        if (arch_get_random_int(&ret))
                return ret;

        warn_unseeded_randomness(&previous);

        use_lock = READ_ONCE(crng_init) < 2;
        batch = &get_cpu_var(batched_entropy_u32);
        if (use_lock)
                read_lock_irqsave(&batched_entropy_reset_lock, flags);
        if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) {
                extract_crng(batch->entropy_u32);
                batch->position = 0;
        }
        ret = batch->entropy_u32[batch->position++];
        if (use_lock)
                read_unlock_irqrestore(&batched_entropy_reset_lock, flags);
        put_cpu_var(batched_entropy_u32);
        return ret;
}
EXPORT_SYMBOL(get_random_u32);

/* It's important to invalidate all potential batched entropy that might
 * be stored before the crng is initialized, which we can do lazily by
 * simply resetting the counter to zero so that it's re-extracted on the
 * next usage. */
static void invalidate_batched_entropy(void)
{
        int cpu;
        unsigned long flags;

        write_lock_irqsave(&batched_entropy_reset_lock, flags);
        for_each_possible_cpu (cpu) {
                per_cpu_ptr(&batched_entropy_u32, cpu)->position = 0;
                per_cpu_ptr(&batched_entropy_u64, cpu)->position = 0;
        }
        write_unlock_irqrestore(&batched_entropy_reset_lock, flags);
}

/**
 * randomize_page - Generate a random, page aligned address
 * @start:      The smallest acceptable address the caller will take.
 * @range:      The size of the area, starting at @start, within which the
 *              random address must fall.
 *
 * If @start + @range would overflow, @range is capped.
 *
 * NOTE: Historical use of randomize_range, which this replaces, presumed that
 * @start was already page aligned.  We now align it regardless.
 *
 * Return: A page aligned address within [start, start + range).  On error,
 * @start is returned.
 */
unsigned long
randomize_page(unsigned long start, unsigned long range)
{
        if (!PAGE_ALIGNED(start)) {
                range -= PAGE_ALIGN(start) - start;
                start = PAGE_ALIGN(start);
        }

        if (start > ULONG_MAX - range)
                range = ULONG_MAX - start;

        range >>= PAGE_SHIFT;

        if (range == 0)
                return start;

        return start + (get_random_long() % range << PAGE_SHIFT);
}

/* Interface for in-kernel drivers of true hardware RNGs.
 * Those devices may produce endless random bits and will be throttled
 * when our pool is full.
 */
void add_hwgenerator_randomness(const char *buffer, size_t count,
                                size_t entropy)
{
        struct entropy_store *poolp = &input_pool;

        if (!crng_ready()) {
                crng_fast_load(buffer, count);
                return;
        }

        /* Suspend writing if we're above the trickle threshold.
         * We'll be woken up again once below random_write_wakeup_thresh,
         * or when the calling thread is about to terminate.
         */
        wait_event_interruptible(random_write_wait, kthread_should_stop() ||
                        ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
        mix_pool_bytes(poolp, buffer, count);
        credit_entropy_bits(poolp, entropy);
}
EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);