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32 results

random.c

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  • random.c 67.59 KiB
    /*
     * 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 four exported interfaces; two for use within the kernel,
     * and two or use from userspace.
     *
     * Exported interfaces ---- userspace output
     * -----------------------------------------
     *
     * The userspace 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 ---- kernel output
     * --------------------------------------
     *
     * The primary kernel interface is
     *
     * 	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.  This is equivalent to a
     * read from /dev/urandom.
     *
     * For less critical applications, there are the functions:
     *
     * 	u32 get_random_u32()
     * 	u64 get_random_u64()
     * 	unsigned int get_random_int()
     * 	unsigned long get_random_long()
     *
     * These are produced by a cryptographic RNG seeded from get_random_bytes,
     * and so do not deplete the entropy pool as much.  These are recommended
     * for most in-kernel operations *if the result is going to be stored in
     * the kernel*.
     *
     * Specifically, the get_random_int() family do not attempt to do
     * "anti-backtracking".  If you capture the state of the kernel (e.g.
     * by snapshotting the VM), you can figure out previous get_random_int()
     * return values.  But if the value is stored in the kernel anyway,
     * this is not a problem.
     *
     * It *is* safe to expose get_random_int() output to attackers (e.g. as
     * network cookies); given outputs 1..n, it's not feasible to predict
     * outputs 0 or n+1.  The only concern is an attacker who breaks into
     * the kernel later; the get_random_int() engine is not reseeded as
     * often as the get_random_bytes() one.
     *
     * get_random_bytes() is needed for keys that need to stay secret after
     * they are erased from the kernel.  For example, any key that will
     * be wrapped and stored encrypted.  And session encryption keys: we'd
     * like to know that after the session is closed and the keys erased,
     * the plaintext is unrecoverable to someone who recorded the ciphertext.
     *
     * But for network ports/cookies, stack canaries, PRNG seeds, address
     * space layout randomization, session *authentication* keys, or other
     * applications where the sensitive data is stored in the kernel in
     * plaintext for as long as it's sensitive, the get_random_int() family
     * is just fine.
     *
     * Consider ASLR.  We want to keep the address space secret from an
     * outside attacker while the process is running, but once the address
     * space is torn down, it's of no use to an attacker any more.  And it's
     * stored in kernel data structures as long as it's alive, so worrying
     * about an attacker's ability to extrapolate it from the get_random_int()
     * CRNG is silly.
     *
     * Even some cryptographic keys are safe to generate with get_random_int().
     * In particular, keys for SipHash are generally fine.  Here, knowledge
     * of the key authorizes you to do something to a kernel object (inject
     * packets to a network connection, or flood a hash table), and the
     * key is stored with the object being protected.  Once it goes away,
     * we no longer care if anyone knows the key.
     *
     * prandom_u32()
     * -------------
     *
     * For even weaker applications, see the pseudorandom generator
     * prandom_u32(), prandom_max(), and prandom_bytes().  If the random
     * numbers aren't security-critical at all, these are *far* cheaper.
     * Useful for self-tests, random error simulation, randomized backoffs,
     * and any other application where you trust that nobody is trying to
     * maliciously mess with you by guessing the "random" numbers.
     *
     * 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.
     */
    
    #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
    
    #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/ratelimit.h>
    #include <linux/syscalls.h>
    #include <linux/completion.h>
    #include <linux/uuid.h>
    #include <crypto/chacha.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 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 + poolbitshift) 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)
    
    /*
     * 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 const struct poolinfo {
    	int poolbitshift, poolwords, poolbytes, poolfracbits;
    #define S(x) ilog2(x)+5, (x), (x)*4, (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 },
    };
    
    /*
     * Static global variables
     */
    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;
    };
    
    static 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 > 1))
    static int crng_init_cnt = 0;
    static unsigned long crng_global_init_time = 0;
    #define CRNG_INIT_CNT_THRESH (2*CHACHA_KEY_SIZE)
    static void _extract_crng(struct crng_state *crng, __u8 out[CHACHA_BLOCK_SIZE]);
    static void _crng_backtrack_protect(struct crng_state *crng,
    				    __u8 tmp[CHACHA_BLOCK_SIZE], int used);
    static void process_random_ready_list(void);
    static void _get_random_bytes(void *buf, int nbytes);
    
    static struct ratelimit_state unseeded_warning =
    	RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3);
    static struct ratelimit_state urandom_warning =
    	RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
    
    static int ratelimit_disable __read_mostly;
    
    module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
    MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
    
    /**********************************************************************
     *
     * 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;
    
    	/* read-write data: */
    	spinlock_t lock;
    	unsigned short add_ptr;
    	unsigned short input_rotate;
    	int entropy_count;
    	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 __u32 input_pool_data[INPUT_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 __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, has_initialized = 0;
    	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 (WARN_ON(entropy_count < 0)) {
    		pr_warn("negative entropy/overflow: pool %s count %d\n",
    			r->name, entropy_count);
    		entropy_count = 0;
    	} else if (entropy_count > pool_size)
    		entropy_count = pool_size;
    	if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
    		goto retry;
    
    	if (has_initialized) {
    		r->initialized = 1;
    		kill_fasync(&fasync, SIGIO, POLL_IN);
    	}
    
    	trace_credit_entropy_bits(r->name, nbits,
    				  entropy_count >> ENTROPY_SHIFT, _RET_IP_);
    
    	if (r == &input_pool) {
    		int entropy_bits = entropy_count >> ENTROPY_SHIFT;
    
    		if (crng_init < 2) {
    			if (entropy_bits < 128)
    				return;
    			crng_reseed(&primary_crng, r);
    			entropy_bits = ENTROPY_BITS(r);
    		}
    	}
    }
    
    static int credit_entropy_bits_safe(struct entropy_store *r, int nbits)
    {
    	const int nbits_max = r->poolinfo->poolwords * 32;
    
    	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 numa_crng_init(void);
    
    static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
    static int __init parse_trust_cpu(char *arg)
    {
    	return kstrtobool(arg, &trust_cpu);
    }
    early_param("random.trust_cpu", parse_trust_cpu);
    
    static bool crng_init_try_arch(struct crng_state *crng)
    {
    	int		i;
    	bool		arch_init = true;
    	unsigned long	rv;
    
    	for (i = 4; i < 16; i++) {
    		if (!arch_get_random_seed_long(&rv) &&
    		    !arch_get_random_long(&rv)) {
    			rv = random_get_entropy();
    			arch_init = false;
    		}
    		crng->state[i] ^= rv;
    	}
    
    	return arch_init;
    }
    
    static void crng_initialize_secondary(struct crng_state *crng)
    {
    	memcpy(&crng->state[0], "expand 32-byte k", 16);
    	_get_random_bytes(&crng->state[4], sizeof(__u32) * 12);
    	crng_init_try_arch(crng);
    	crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
    }
    
    static void __init crng_initialize_primary(struct crng_state *crng)
    {
    	memcpy(&crng->state[0], "expand 32-byte k", 16);
    	_extract_entropy(&input_pool, &crng->state[4], sizeof(__u32) * 12, 0);
    	if (crng_init_try_arch(crng) && trust_cpu) {
    		invalidate_batched_entropy();
    		numa_crng_init();
    		crng_init = 2;
    		pr_notice("crng done (trusting CPU's manufacturer)\n");
    	}
    	crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
    }
    
    #ifdef CONFIG_NUMA
    static void do_numa_crng_init(struct work_struct *work)
    {
    	int i;
    	struct crng_state *crng;
    	struct crng_state **pool;
    
    	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_secondary(crng);
    		pool[i] = crng;
    	}
    	mb();
    	if (cmpxchg(&crng_node_pool, NULL, pool)) {
    		for_each_node(i)
    			kfree(pool[i]);
    		kfree(pool);
    	}
    }
    
    static DECLARE_WORK(numa_crng_init_work, do_numa_crng_init);
    
    static void numa_crng_init(void)
    {
    	schedule_work(&numa_crng_init_work);
    }
    #else
    static void numa_crng_init(void) {}
    #endif
    
    /*
     * crng_fast_load() can be called by code in the interrupt service
     * path.  So we can't afford to dilly-dally.
     */
    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_init != 0) {
    		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 % CHACHA_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;
    		pr_notice("fast init done\n");
    	}
    	return 1;
    }
    
    /*
     * crng_slow_load() is called by add_device_randomness, which has two
     * attributes.  (1) We can't trust the buffer passed to it is
     * guaranteed to be unpredictable (so it might not have any entropy at
     * all), and (2) it doesn't have the performance constraints of
     * crng_fast_load().
     *
     * So we do something more comprehensive which is guaranteed to touch
     * all of the primary_crng's state, and which uses a LFSR with a
     * period of 255 as part of the mixing algorithm.  Finally, we do
     * *not* advance crng_init_cnt since buffer we may get may be something
     * like a fixed DMI table (for example), which might very well be
     * unique to the machine, but is otherwise unvarying.
     */
    static int crng_slow_load(const char *cp, size_t len)
    {
    	unsigned long		flags;
    	static unsigned char	lfsr = 1;
    	unsigned char		tmp;
    	unsigned		i, max = CHACHA_KEY_SIZE;
    	const char *		src_buf = cp;
    	char *			dest_buf = (char *) &primary_crng.state[4];
    
    	if (!spin_trylock_irqsave(&primary_crng.lock, flags))
    		return 0;
    	if (crng_init != 0) {
    		spin_unlock_irqrestore(&primary_crng.lock, flags);
    		return 0;
    	}
    	if (len > max)
    		max = len;
    
    	for (i = 0; i < max ; i++) {
    		tmp = lfsr;
    		lfsr >>= 1;
    		if (tmp & 1)
    			lfsr ^= 0xE1;
    		tmp = dest_buf[i % CHACHA_KEY_SIZE];
    		dest_buf[i % CHACHA_KEY_SIZE] ^= src_buf[i % len] ^ lfsr;
    		lfsr += (tmp << 3) | (tmp >> 5);
    	}
    	spin_unlock_irqrestore(&primary_crng.lock, flags);
    	return 1;
    }
    
    static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
    {
    	unsigned long	flags;
    	int		i, num;
    	union {
    		__u8	block[CHACHA_BLOCK_SIZE];
    		__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,
    					CHACHA_KEY_SIZE);
    	}
    	spin_lock_irqsave(&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(&crng->lock, flags);
    	if (crng == &primary_crng && crng_init < 2) {
    		invalidate_batched_entropy();
    		numa_crng_init();
    		crng_init = 2;
    		process_random_ready_list();
    		wake_up_interruptible(&crng_init_wait);
    		kill_fasync(&fasync, SIGIO, POLL_IN);
    		pr_notice("crng init done\n");
    		if (unseeded_warning.missed) {
    			pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n",
    				  unseeded_warning.missed);
    			unseeded_warning.missed = 0;
    		}
    		if (urandom_warning.missed) {
    			pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
    				  urandom_warning.missed);
    			urandom_warning.missed = 0;
    		}
    	}
    }
    
    static void _extract_crng(struct crng_state *crng,
    			  __u8 out[CHACHA_BLOCK_SIZE])
    {
    	unsigned long v, flags;
    
    	if (crng_ready() &&
    	    (time_after(crng_global_init_time, crng->init_time) ||
    	     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(__u8 out[CHACHA_BLOCK_SIZE])
    {
    	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,
    				    __u8 tmp[CHACHA_BLOCK_SIZE], int used)
    {
    	unsigned long	flags;
    	__u32		*s, *d;
    	int		i;
    
    	used = round_up(used, sizeof(__u32));
    	if (used + CHACHA_KEY_SIZE > CHACHA_BLOCK_SIZE) {
    		extract_crng(tmp);
    		used = 0;
    	}
    	spin_lock_irqsave(&crng->lock, flags);
    	s = (__u32 *) &tmp[used];
    	d = &crng->state[4];
    	for (i=0; i < 8; i++)
    		*d++ ^= *s++;
    	spin_unlock_irqrestore(&crng->lock, flags);
    }
    
    static void crng_backtrack_protect(__u8 tmp[CHACHA_BLOCK_SIZE], 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 = CHACHA_BLOCK_SIZE;
    	__u8 tmp[CHACHA_BLOCK_SIZE] __aligned(4);
    	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, CHACHA_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;
    };
    
    #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() && size)
    		crng_slow_load(buf, size);
    
    	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;
    
    	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.
    	 */
    	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 estimate to 12 bits.
    	 */
    	credit_entropy_bits(r, min_t(int, fls(delta>>1), 11));
    }
    
    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 (unlikely(crng_init == 0)) {
    		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 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 (WARN_ON(entropy_count < 0)) {
    		pr_warn("negative entropy count: pool %s count %d\n",
    			r->name, entropy_count);
    		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 && ENTROPY_BITS(r) < 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_);
    			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_);
    	nbytes = account(r, nbytes, min, reserved);
    
    	return _extract_entropy(r, buf, nbytes, fips_enabled);
    }
    
    #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
    	if (__ratelimit(&unseeded_warning))
    		printk_deferred(KERN_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)
    {
    	__u8 tmp[CHACHA_BLOCK_SIZE] __aligned(4);
    
    	trace_get_random_bytes(nbytes, _RET_IP_);
    
    	while (nbytes >= CHACHA_BLOCK_SIZE) {
    		extract_crng(buf);
    		buf += CHACHA_BLOCK_SIZE;
    		nbytes -= CHACHA_BLOCK_SIZE;
    	}
    
    	if (nbytes > 0) {
    		extract_crng(tmp);
    		memcpy(buf, tmp, nbytes);
    		crng_backtrack_protect(tmp, nbytes);
    	} else
    		crng_backtrack_protect(tmp, CHACHA_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);
    
    
    /*
     * Each time the timer fires, we expect that we got an unpredictable
     * jump in the cycle counter. Even if the timer is running on another
     * CPU, the timer activity will be touching the stack of the CPU that is
     * generating entropy..
     *
     * Note that we don't re-arm the timer in the timer itself - we are
     * happy to be scheduled away, since that just makes the load more
     * complex, but we do not want the timer to keep ticking unless the
     * entropy loop is running.
     *
     * So the re-arming always happens in the entropy loop itself.
     */
    static void entropy_timer(struct timer_list *t)
    {
    	credit_entropy_bits(&input_pool, 1);
    }
    
    /*
     * If we have an actual cycle counter, see if we can
     * generate enough entropy with timing noise
     */
    static void try_to_generate_entropy(void)
    {
    	struct {
    		unsigned long now;
    		struct timer_list timer;
    	} stack;
    
    	stack.now = random_get_entropy();
    
    	/* Slow counter - or none. Don't even bother */
    	if (stack.now == random_get_entropy())
    		return;
    
    	timer_setup_on_stack(&stack.timer, entropy_timer, 0);
    	while (!crng_ready()) {
    		if (!timer_pending(&stack.timer))
    			mod_timer(&stack.timer, jiffies+1);
    		mix_pool_bytes(&input_pool, &stack.now, sizeof(stack.now));
    		schedule();
    		stack.now = random_get_entropy();
    	}
    
    	del_timer_sync(&stack.timer);
    	destroy_timer_on_stack(&stack.timer);
    	mix_pool_bytes(&input_pool, &stack.now, sizeof(stack.now));
    }
    
    /*
     * 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;
    
    	do {
    		int ret;
    		ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
    		if (ret)
    			return ret > 0 ? 0 : ret;
    
    		try_to_generate_entropy();
    	} while (!crng_ready());
    
    	return 0;
    }
    EXPORT_SYMBOL(wait_for_random_bytes);
    
    /*
     * Returns whether or not the urandom pool has been 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.
     *
     * Returns: true if the urandom pool has been seeded.
     *          false if the urandom pool has not been seeded.
     */
    bool rng_is_initialized(void)
    {
    	return crng_ready();
    }
    EXPORT_SYMBOL(rng_is_initialized);
    
    /*
     * 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.
     *
     * Return number of bytes filled in.
     */
    int __must_check get_random_bytes_arch(void *buf, int nbytes)
    {
    	int left = nbytes;
    	char *p = buf;
    
    	trace_get_random_bytes_arch(left, _RET_IP_);
    	while (left) {
    		unsigned long v;
    		int chunk = min_t(int, left, sizeof(unsigned long));
    
    		if (!arch_get_random_long(&v))
    			break;
    
    		memcpy(p, &v, chunk);
    		p += chunk;
    		left -= chunk;
    	}
    
    	return nbytes - left;
    }
    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 init_std_data(struct entropy_store *r)
    {
    	int i;
    	ktime_t now = ktime_get_real();
    	unsigned long rv;
    
    	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.
     */
    int __init rand_initialize(void)
    {
    	init_std_data(&input_pool);
    	crng_initialize_primary(&primary_crng);
    	crng_global_init_time = jiffies;
    	if (ratelimit_disable) {
    		urandom_warning.interval = 0;
    		unseeded_warning.interval = 0;
    	}
    	return 0;
    }
    
    #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
    urandom_read_nowarn(struct file *file, char __user *buf, size_t nbytes,
    		    loff_t *ppos)
    {
    	int ret;
    
    	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 ssize_t
    urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
    {
    	unsigned long flags;
    	static int maxwarn = 10;
    
    	if (!crng_ready() && maxwarn > 0) {
    		maxwarn--;
    		if (__ratelimit(&urandom_warning))
    			pr_notice("%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);
    	}
    
    	return urandom_read_nowarn(file, buf, nbytes, ppos);
    }
    
    static ssize_t
    random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
    {
    	int ret;
    
    	ret = wait_for_random_bytes();
    	if (ret != 0)
    		return ret;
    	return urandom_read_nowarn(file, buf, nbytes, ppos);
    }
    
    static __poll_t
    random_poll(struct file *file, poll_table * wait)
    {
    	__poll_t mask;
    
    	poll_wait(file, &crng_init_wait, wait);
    	poll_wait(file, &random_write_wait, wait);
    	mask = 0;
    	if (crng_ready())
    		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 t, buf[16];
    	const char __user *p = buffer;
    
    	while (count > 0) {
    		int b, i = 0;
    
    		bytes = min(count, sizeof(buf));
    		if (copy_from_user(&buf, p, bytes))
    			return -EFAULT;
    
    		for (b = bytes ; b > 0 ; b -= sizeof(__u32), i++) {
    			if (!arch_get_random_int(&t))
    				break;
    			buf[i] ^= t;
    		}
    
    		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;
    		return 0;
    	case RNDRESEEDCRNG:
    		if (!capable(CAP_SYS_ADMIN))
    			return -EPERM;
    		if (crng_init < 2)
    			return -ENODATA;
    		crng_reseed(&primary_crng, NULL);
    		crng_global_init_time = jiffies - 1;
    		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,
    	.compat_ioctl = compat_ptr_ioctl,
    	.fasync = random_fasync,
    	.llseek = noop_llseek,
    };
    
    const struct file_operations urandom_fops = {
    	.read  = urandom_read,
    	.write = random_write,
    	.unlocked_ioctl = random_ioctl,
    	.compat_ioctl = compat_ptr_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|GRND_INSECURE))
    		return -EINVAL;
    
    	/*
    	 * Requesting insecure and blocking randomness at the same time makes
    	 * no sense.
    	 */
    	if ((flags & (GRND_INSECURE|GRND_RANDOM)) == (GRND_INSECURE|GRND_RANDOM))
    		return -EINVAL;
    
    	if (count > INT_MAX)
    		count = INT_MAX;
    
    	if (!(flags & GRND_INSECURE) && !crng_ready()) {
    		if (flags & GRND_NONBLOCK)
    			return -EAGAIN;
    		ret = wait_for_random_bytes();
    		if (unlikely(ret))
    			return ret;
    	}
    	return urandom_read_nowarn(NULL, buf, count, NULL);
    }
    
    /********************************************************************
     *
     * Sysctl interface
     *
     ********************************************************************/
    
    #ifdef CONFIG_SYSCTL
    
    #include <linux/sysctl.h>
    
    static int min_write_thresh;
    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	= "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[CHACHA_BLOCK_SIZE / sizeof(u64)];
    		u32 entropy_u32[CHACHA_BLOCK_SIZE / sizeof(u32)];
    	};
    	unsigned int position;
    	spinlock_t batch_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) = {
    	.batch_lock	= __SPIN_LOCK_UNLOCKED(batched_entropy_u64.lock),
    };
    
    u64 get_random_u64(void)
    {
    	u64 ret;
    	unsigned long flags;
    	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);
    
    	batch = raw_cpu_ptr(&batched_entropy_u64);
    	spin_lock_irqsave(&batch->batch_lock, flags);
    	if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
    		extract_crng((u8 *)batch->entropy_u64);
    		batch->position = 0;
    	}
    	ret = batch->entropy_u64[batch->position++];
    	spin_unlock_irqrestore(&batch->batch_lock, flags);
    	return ret;
    }
    EXPORT_SYMBOL(get_random_u64);
    
    static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = {
    	.batch_lock	= __SPIN_LOCK_UNLOCKED(batched_entropy_u32.lock),
    };
    u32 get_random_u32(void)
    {
    	u32 ret;
    	unsigned long flags;
    	struct batched_entropy *batch;
    	static void *previous;
    
    	if (arch_get_random_int(&ret))
    		return ret;
    
    	warn_unseeded_randomness(&previous);
    
    	batch = raw_cpu_ptr(&batched_entropy_u32);
    	spin_lock_irqsave(&batch->batch_lock, flags);
    	if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) {
    		extract_crng((u8 *)batch->entropy_u32);
    		batch->position = 0;
    	}
    	ret = batch->entropy_u32[batch->position++];
    	spin_unlock_irqrestore(&batch->batch_lock, flags);
    	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;
    
    	for_each_possible_cpu (cpu) {
    		struct batched_entropy *batched_entropy;
    
    		batched_entropy = per_cpu_ptr(&batched_entropy_u32, cpu);
    		spin_lock_irqsave(&batched_entropy->batch_lock, flags);
    		batched_entropy->position = 0;
    		spin_unlock(&batched_entropy->batch_lock);
    
    		batched_entropy = per_cpu_ptr(&batched_entropy_u64, cpu);
    		spin_lock(&batched_entropy->batch_lock);
    		batched_entropy->position = 0;
    		spin_unlock_irqrestore(&batched_entropy->batch_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 (unlikely(crng_init == 0)) {
    		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);
    
    /* Handle random seed passed by bootloader.
     * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
     * it would be regarded as device data.
     * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
     */
    void add_bootloader_randomness(const void *buf, unsigned int size)
    {
    	if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
    		add_hwgenerator_randomness(buf, size, size * 8);
    	else
    		add_device_randomness(buf, size);
    }
    EXPORT_SYMBOL_GPL(add_bootloader_randomness);