/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Software based random number provider for the Kernel Cryptographic
 * Framework (KCF). This provider periodically collects unpredictable input
 * from external sources and processes it into a pool of entropy (randomness)
 * in order to satisfy requests for random bits from kCF. It implements
 * software-based mixing, extraction, and generation algorithms.
 *
 * A history note: The software-based algorithms in this file used to be
 * part of the /dev/random driver.
 */

#include <sys/types.h>
#include <sys/errno.h>
#include <sys/debug.h>
#include <vm/seg_kmem.h>
#include <vm/hat.h>
#include <sys/systm.h>
#include <sys/memlist.h>
#include <sys/cmn_err.h>
#include <sys/ksynch.h>
#include <sys/random.h>
#include <sys/ddi.h>
#include <sys/mman.h>
#include <sys/sysmacros.h>
#include <sys/mem_config.h>
#include <sys/time.h>
#include <sys/crypto/spi.h>
#include <sys/sha1.h>
#include <sys/sunddi.h>
#include <sys/modctl.h>
#include <sys/hold_page.h>
#include <rng/fips_random.h>

#define RNDPOOLSIZE             1024    /* Pool size in bytes */
#define HASHBUFSIZE             64      /* Buffer size used for pool mixing */
#define MAXMEMBLOCKS            16384   /* Number of memory blocks to scan */
#define MEMBLOCKSIZE            4096    /* Size of memory block to read */
#define MINEXTRACTBITS          160     /* Min entropy level for extraction */
#define TIMEOUT_INTERVAL        5       /* Periodic mixing interval in secs */

/* Hash-algo generic definitions. For now, they are SHA1's. */
#define HASHSIZE                20
#define HASH_CTX                SHA1_CTX
#define HashInit(ctx)           SHA1Init((ctx))
#define HashUpdate(ctx, p, s)   SHA1Update((ctx), (p), (s))
#define HashFinal(d, ctx)       SHA1Final((d), (ctx))

/* Physical memory entropy source */
typedef struct physmem_entsrc_s {
        uint8_t *parity;                /* parity bit vector */
        caddr_t pmbuf;                  /* buffer for memory block */
        uint32_t nblocks;               /* number of  memory blocks */
        int entperblock;                /* entropy bits per block read */
        hrtime_t last_diff;             /* previous time to process a block */
        hrtime_t last_delta;            /* previous time delta */
        hrtime_t last_delta2;           /* previous 2nd order time delta */
} physmem_entsrc_t;

static uint32_t srndpool[RNDPOOLSIZE/4];        /* Pool of random bits */
static uint32_t buffer[RNDPOOLSIZE/4];  /* entropy mixed in later */
static int buffer_bytes;                /* bytes written to buffer */
static uint32_t entropy_bits;           /* pool's current amount of entropy */
static kmutex_t srndpool_lock;          /* protects r/w accesses to the pool, */
                                        /* and the global variables */
static kmutex_t buffer_lock;            /* protects r/w accesses to buffer */
static kcondvar_t srndpool_read_cv;     /* serializes poll/read syscalls */
static int pindex;                      /* Global index for adding/extracting */
                                        /* from the pool */
static int bstart, bindex;              /* Global vars for adding/extracting */
                                        /* from the buffer */
static uint8_t leftover[HASHSIZE];      /* leftover output */
static uint32_t swrand_XKEY[6];         /* one extra word for getentropy */
static int leftover_bytes;              /* leftover length */
static uint32_t previous_bytes[HASHSIZE/BYTES_IN_WORD]; /* prev random bytes */

static physmem_entsrc_t entsrc;         /* Physical mem as an entropy source */
static timeout_id_t rnd_timeout_id;
static int snum_waiters;
static crypto_kcf_provider_handle_t swrand_prov_handle = 0;
swrand_stats_t swrand_stats;

static int physmem_ent_init(physmem_entsrc_t *);
static void physmem_ent_fini(physmem_entsrc_t *);
static void physmem_ent_gen(physmem_entsrc_t *);
static int physmem_parity_update(uint8_t *, uint32_t, int);
static void physmem_count_blocks();
static void rnd_dr_callback_post_add(void *, pgcnt_t);
static int rnd_dr_callback_pre_del(void *, pgcnt_t);
static void rnd_dr_callback_post_del(void *, pgcnt_t, int);
static void rnd_handler(void *arg);
static void swrand_init();
static void swrand_schedule_timeout(void);
static int swrand_get_entropy(uint8_t *ptr, size_t len, boolean_t);
static void swrand_add_entropy(uint8_t *ptr, size_t len, uint16_t entropy_est);
static void swrand_add_entropy_later(uint8_t *ptr, size_t len);

/* Dynamic Reconfiguration related declarations */
kphysm_setup_vector_t rnd_dr_callback_vec = {
        KPHYSM_SETUP_VECTOR_VERSION,
        rnd_dr_callback_post_add,
        rnd_dr_callback_pre_del,
        rnd_dr_callback_post_del
};

extern struct mod_ops mod_cryptoops;

/*
 * Module linkage information for the kernel.
 */
static struct modlcrypto modlcrypto = {
        &mod_cryptoops,
        "Kernel Random number Provider"
};

static struct modlinkage modlinkage = {
        MODREV_1,
        (void *)&modlcrypto,
        NULL
};

/*
 * CSPI information (entry points, provider info, etc.)
 */
static void swrand_provider_status(crypto_provider_handle_t, uint_t *);

static crypto_control_ops_t swrand_control_ops = {
        swrand_provider_status
};

static int swrand_seed_random(crypto_provider_handle_t, crypto_session_id_t,
    uchar_t *, size_t, uint_t, uint32_t, crypto_req_handle_t);
static int swrand_generate_random(crypto_provider_handle_t,
    crypto_session_id_t, uchar_t *, size_t, crypto_req_handle_t);

static crypto_random_number_ops_t swrand_random_number_ops = {
        swrand_seed_random,
        swrand_generate_random
};

static crypto_ops_t swrand_crypto_ops = {
        &swrand_control_ops,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        &swrand_random_number_ops,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
};

static crypto_provider_info_t swrand_prov_info = {
        CRYPTO_SPI_VERSION_4,
        "Kernel Random Number Provider",
        CRYPTO_SW_PROVIDER,
        {&modlinkage},
        NULL,
        &swrand_crypto_ops,
        0,
        NULL
};

int
_init(void)
{
        int ret;
        hrtime_t ts;
        time_t now;

        mutex_init(&srndpool_lock, NULL, MUTEX_DEFAULT, NULL);
        mutex_init(&buffer_lock, NULL, MUTEX_DEFAULT, NULL);
        cv_init(&srndpool_read_cv, NULL, CV_DEFAULT, NULL);
        entropy_bits = 0;
        pindex = 0;
        bindex = 0;
        bstart = 0;
        snum_waiters = 0;
        leftover_bytes = 0;
        buffer_bytes = 0;

        /*
         * Initialize the pool using
         * . 2 unpredictable times: high resolution time since the boot-time,
         *   and the current time-of-the day.
         * . The initial physical memory state.
         */
        ts = gethrtime();
        swrand_add_entropy((uint8_t *)&ts, sizeof (ts), 0);

        (void) drv_getparm(TIME, &now);
        swrand_add_entropy((uint8_t *)&now, sizeof (now), 0);

        ret = kphysm_setup_func_register(&rnd_dr_callback_vec, NULL);
        ASSERT(ret == 0);

        if (physmem_ent_init(&entsrc) != 0) {
                ret = ENOMEM;
                goto exit1;
        }

        if ((ret = mod_install(&modlinkage)) != 0)
                goto exit2;

        /* Schedule periodic mixing of the pool. */
        mutex_enter(&srndpool_lock);
        swrand_schedule_timeout();
        mutex_exit(&srndpool_lock);
        (void) swrand_get_entropy((uint8_t *)swrand_XKEY, HASHSIZE, B_TRUE);
        bcopy(swrand_XKEY, previous_bytes, HASHSIZE);

        /* Register with KCF. If the registration fails, return error. */
        if (crypto_register_provider(&swrand_prov_info, &swrand_prov_handle)) {
                (void) mod_remove(&modlinkage);
                ret = EACCES;
                goto exit2;
        }

        return (0);

exit2:
        physmem_ent_fini(&entsrc);
exit1:
        mutex_destroy(&srndpool_lock);
        mutex_destroy(&buffer_lock);
        cv_destroy(&srndpool_read_cv);
        return (ret);
}

int
_info(struct modinfo *modinfop)
{
        return (mod_info(&modlinkage, modinfop));
}

/*
 * Control entry points.
 */
/* ARGSUSED */
static void
swrand_provider_status(crypto_provider_handle_t provider, uint_t *status)
{
        *status = CRYPTO_PROVIDER_READY;
}

/*
 * Random number entry points.
 */
/* ARGSUSED */
static int
swrand_seed_random(crypto_provider_handle_t provider, crypto_session_id_t sid,
    uchar_t *buf, size_t len, uint_t entropy_est, uint32_t flags,
    crypto_req_handle_t req)
{
        /* The entropy estimate is always 0 in this path */
        if (flags & CRYPTO_SEED_NOW)
                swrand_add_entropy(buf, len, 0);
        else
                swrand_add_entropy_later(buf, len);
        return (CRYPTO_SUCCESS);
}

/* ARGSUSED */
static int
swrand_generate_random(crypto_provider_handle_t provider,
    crypto_session_id_t sid, uchar_t *buf, size_t len, crypto_req_handle_t req)
{
        if (crypto_kmflag(req) == KM_NOSLEEP)
                (void) swrand_get_entropy(buf, len, B_TRUE);
        else
                (void) swrand_get_entropy(buf, len, B_FALSE);

        return (CRYPTO_SUCCESS);
}

/*
 * Extraction of entropy from the pool.
 *
 * Returns "len" random bytes in *ptr.
 * Try to gather some more entropy by calling physmem_ent_gen() when less than
 * MINEXTRACTBITS are present in the pool.
 * Will block if not enough entropy was available and the call is blocking.
 */
static int
swrand_get_entropy(uint8_t *ptr, size_t len, boolean_t nonblock)
{
        int i, bytes;
        HASH_CTX hashctx;
        uint8_t digest[HASHSIZE], *pool;
        uint32_t tempout[HASHSIZE/BYTES_IN_WORD];
        int size;

        mutex_enter(&srndpool_lock);
        if (leftover_bytes > 0) {
                bytes = min(len, leftover_bytes);
                bcopy(leftover, ptr, bytes);
                len -= bytes;
                ptr += bytes;
                leftover_bytes -= bytes;
                if (leftover_bytes > 0)
                        ovbcopy(leftover+bytes, leftover, leftover_bytes);
        }

        while (len > 0) {
                /* Check if there is enough entropy */
                while (entropy_bits < MINEXTRACTBITS) {

                        physmem_ent_gen(&entsrc);

                        if (entropy_bits < MINEXTRACTBITS &&
                            nonblock == B_TRUE) {
                                mutex_exit(&srndpool_lock);
                                return (EAGAIN);
                        }

                        if (entropy_bits < MINEXTRACTBITS) {
                                ASSERT(nonblock == B_FALSE);
                                snum_waiters++;
                                if (cv_wait_sig(&srndpool_read_cv,
                                    &srndpool_lock) == 0) {
                                        snum_waiters--;
                                        mutex_exit(&srndpool_lock);
                                        return (EINTR);
                                }
                                snum_waiters--;
                        }
                }

                /* Figure out how many bytes to extract */
                bytes = min(HASHSIZE, len);
                bytes = min(bytes, CRYPTO_BITS2BYTES(entropy_bits));
                entropy_bits -= CRYPTO_BYTES2BITS(bytes);
                BUMP_SWRAND_STATS(ss_entOut, CRYPTO_BYTES2BITS(bytes));
                swrand_stats.ss_entEst = entropy_bits;

                /* Extract entropy by hashing pool content */
                HashInit(&hashctx);
                HashUpdate(&hashctx, (uint8_t *)srndpool, RNDPOOLSIZE);
                HashFinal(digest, &hashctx);

                /*
                 * Feed the digest back into the pool so next
                 * extraction produces different result
                 */
                pool = (uint8_t *)srndpool;
                for (i = 0; i < HASHSIZE; i++) {
                        pool[pindex++] ^= digest[i];
                        /* pindex modulo RNDPOOLSIZE */
                        pindex &= (RNDPOOLSIZE - 1);
                }

                /* LINTED E_BAD_PTR_CAST_ALIGN */
                fips_random_inner(swrand_XKEY, tempout, (uint32_t *)digest);

                if (len >= HASHSIZE) {
                        size = HASHSIZE;
                } else {
                        size = min(bytes, HASHSIZE);
                }

                /*
                 * FIPS 140-2: Continuous RNG test - each generation
                 * of an n-bit block shall be compared with the previously
                 * generated block. Test shall fail if any two compared
                 * n-bit blocks are equal.
                 */
                for (i = 0; i < HASHSIZE/BYTES_IN_WORD; i++) {
                        if (tempout[i] != previous_bytes[i])
                                break;
                }

                if (i == HASHSIZE/BYTES_IN_WORD) {
                        cmn_err(CE_WARN, "swrand: The value of 160-bit block "
                            "random bytes are same as the previous one.\n");
                        /* discard random bytes and return error */
                        return (EIO);
                }

                bcopy(tempout, previous_bytes, HASHSIZE);

                bcopy(tempout, ptr, size);
                if (len < HASHSIZE) {
                        leftover_bytes = HASHSIZE - bytes;
                        bcopy((uint8_t *)tempout + bytes, leftover,
                            leftover_bytes);
                }

                ptr += size;
                len -= size;
                BUMP_SWRAND_STATS(ss_bytesOut, size);
        }

        /* Zero out sensitive information */
        bzero(digest, HASHSIZE);
        bzero(tempout, HASHSIZE);
        mutex_exit(&srndpool_lock);
        return (0);
}

#define SWRAND_ADD_BYTES(ptr, len, i, pool)             \
        ASSERT((ptr) != NULL && (len) > 0);             \
        BUMP_SWRAND_STATS(ss_bytesIn, (len));           \
        while ((len)--) {                               \
                (pool)[(i)++] ^= *(ptr);                \
                (ptr)++;                                \
                (i) &= (RNDPOOLSIZE - 1);               \
        }

/* Write some more user-provided entropy to the pool */
static void
swrand_add_bytes(uint8_t *ptr, size_t len)
{
        uint8_t *pool = (uint8_t *)srndpool;

        ASSERT(MUTEX_HELD(&srndpool_lock));
        SWRAND_ADD_BYTES(ptr, len, pindex, pool);
}

/*
 * Add bytes to buffer. Adding the buffer to the random pool
 * is deferred until the random pool is mixed.
 */
static void
swrand_add_bytes_later(uint8_t *ptr, size_t len)
{
        uint8_t *pool = (uint8_t *)buffer;

        ASSERT(MUTEX_HELD(&buffer_lock));
        SWRAND_ADD_BYTES(ptr, len, bindex, pool);
        buffer_bytes += len;
}

#undef SWRAND_ADD_BYTES

/* Mix the pool */
static void
swrand_mix_pool(uint16_t entropy_est)
{
        int i, j, k, start;
        HASH_CTX hashctx;
        uint8_t digest[HASHSIZE];
        uint8_t *pool = (uint8_t *)srndpool;
        uint8_t *bp = (uint8_t *)buffer;

        ASSERT(MUTEX_HELD(&srndpool_lock));

        /* add deferred bytes */
        mutex_enter(&buffer_lock);
        if (buffer_bytes > 0) {
                if (buffer_bytes >= RNDPOOLSIZE) {
                        for (i = 0; i < RNDPOOLSIZE/4; i++) {
                                srndpool[i] ^= buffer[i];
                                buffer[i] = 0;
                        }
                        bstart = bindex = 0;
                } else {
                        for (i = 0; i < buffer_bytes; i++) {
                                pool[pindex++] ^= bp[bstart];
                                bp[bstart++] = 0;
                                pindex &= (RNDPOOLSIZE - 1);
                                bstart &= (RNDPOOLSIZE - 1);
                        }
                        ASSERT(bstart == bindex);
                }
                buffer_bytes = 0;
        }
        mutex_exit(&buffer_lock);

        start = 0;
        for (i = 0; i < RNDPOOLSIZE/HASHSIZE + 1; i++) {
                HashInit(&hashctx);

                /* Hash a buffer centered on a block in the pool */
                if (start + HASHBUFSIZE <= RNDPOOLSIZE)
                        HashUpdate(&hashctx, &pool[start], HASHBUFSIZE);
                else {
                        HashUpdate(&hashctx, &pool[start],
                            RNDPOOLSIZE - start);
                        HashUpdate(&hashctx, pool,
                            HASHBUFSIZE - RNDPOOLSIZE + start);
                }
                HashFinal(digest, &hashctx);

                /* XOR the hash result back into the block */
                k = (start + HASHSIZE) & (RNDPOOLSIZE - 1);
                for (j = 0; j < HASHSIZE; j++) {
                        pool[k++] ^= digest[j];
                        k &= (RNDPOOLSIZE - 1);
                }

                /* Slide the hash buffer and repeat with next block */
                start = (start + HASHSIZE) & (RNDPOOLSIZE - 1);
        }

        entropy_bits += entropy_est;
        if (entropy_bits > CRYPTO_BYTES2BITS(RNDPOOLSIZE))
                entropy_bits = CRYPTO_BYTES2BITS(RNDPOOLSIZE);

        swrand_stats.ss_entEst = entropy_bits;
        BUMP_SWRAND_STATS(ss_entIn, entropy_est);
}

static void
swrand_add_entropy_later(uint8_t *ptr, size_t len)
{
        mutex_enter(&buffer_lock);
        swrand_add_bytes_later(ptr, len);
        mutex_exit(&buffer_lock);
}

static void
swrand_add_entropy(uint8_t *ptr, size_t len, uint16_t entropy_est)
{
        mutex_enter(&srndpool_lock);
        swrand_add_bytes(ptr, len);
        swrand_mix_pool(entropy_est);
        mutex_exit(&srndpool_lock);
}

/*
 * The physmem_* routines below generate entropy by reading blocks of
 * physical memory.  Entropy is gathered in a couple of ways:
 *
 *  - By reading blocks of physical memory and detecting if changes
 *    occurred in the blocks read.
 *
 *  - By measuring the time it takes to load and hash a block of memory
 *    and computing the differences in the measured time.
 *
 * The first method was used in the CryptoRand implementation.  Physical
 * memory is divided into blocks of fixed size.  A block of memory is
 * chosen from the possible blocks and hashed to produce a digest.  This
 * digest is then mixed into the pool.  A single bit from the digest is
 * used as a parity bit or "checksum" and compared against the previous
 * "checksum" computed for the block.  If the single-bit checksum has not
 * changed, no entropy is credited to the pool.  If there is a change,
 * then the assumption is that at least one bit in the block has changed.
 * The possible locations within the memory block of where the bit change
 * occurred is used as a measure of entropy.  For example, if a block
 * size of 4096 bytes is used, about log_2(4096*8)=15 bits worth of
 * entropy is available.  Because the single-bit checksum will miss half
 * of the changes, the amount of entropy credited to the pool is doubled
 * when a change is detected.  With a 4096 byte block size, a block
 * change will add a total of 30 bits of entropy to the pool.
 *
 * The second method measures the amount of time it takes to read and
 * hash a physical memory block (as described above).  The time measured
 * can vary depending on system load, scheduling and other factors.
 * Differences between consecutive measurements are computed to come up
 * with an entropy estimate.  The first, second, and third order delta is
 * calculated to determine the minimum delta value.  The number of bits
 * present in this minimum delta value is the entropy estimate.  This
 * entropy estimation technique using time deltas is similar to that used
 * in /dev/random implementations from Linux/BSD.
 */

static int
physmem_ent_init(physmem_entsrc_t *entsrc)
{
        uint8_t *ptr;
        int i;

        bzero(entsrc, sizeof (*entsrc));

        /*
         * The maximum entropy amount in bits per block of memory read is
         * log_2(MEMBLOCKSIZE * 8);
         */
        i = CRYPTO_BYTES2BITS(MEMBLOCKSIZE);
        while (i >>= 1)
                entsrc->entperblock++;

        /* Initialize entsrc->nblocks */
        physmem_count_blocks();

        if (entsrc->nblocks == 0) {
                cmn_err(CE_WARN, "no memory blocks to scan!");
                return (-1);
        }

        /* Allocate space for the parity vector and memory page */
        entsrc->parity = kmem_alloc(howmany(entsrc->nblocks, 8),
            KM_SLEEP);
        entsrc->pmbuf = vmem_alloc(heap_arena, PAGESIZE, VM_SLEEP);


        /* Initialize parity vector with bits from the pool */
        i = howmany(entsrc->nblocks, 8);
        ptr = entsrc->parity;
        while (i > 0) {
                if (i > RNDPOOLSIZE) {
                        bcopy(srndpool, ptr, RNDPOOLSIZE);
                        mutex_enter(&srndpool_lock);
                        swrand_mix_pool(0);
                        mutex_exit(&srndpool_lock);
                        ptr += RNDPOOLSIZE;
                        i -= RNDPOOLSIZE;
                } else {
                        bcopy(srndpool, ptr, i);
                        break;
                }
        }

        /* Generate some entropy to further initialize the pool */
        mutex_enter(&srndpool_lock);
        physmem_ent_gen(entsrc);
        entropy_bits = 0;
        mutex_exit(&srndpool_lock);

        return (0);
}

static void
physmem_ent_fini(physmem_entsrc_t *entsrc)
{
        if (entsrc->pmbuf != NULL)
                vmem_free(heap_arena, entsrc->pmbuf, PAGESIZE);
        if (entsrc->parity != NULL)
                kmem_free(entsrc->parity, howmany(entsrc->nblocks, 8));
        bzero(entsrc, sizeof (*entsrc));
}

static void
physmem_ent_gen(physmem_entsrc_t *entsrc)
{
        struct memlist *pmem;
        offset_t offset, poffset;
        pfn_t pfn;
        int i, nbytes, len, ent = 0;
        uint32_t block, oblock;
        hrtime_t ts1, ts2, diff, delta, delta2, delta3;
        uint8_t digest[HASHSIZE];
        HASH_CTX ctx;
        page_t *pp;

        /*
         * Use each 32-bit quantity in the pool to pick a memory
         * block to read.
         */
        for (i = 0; i < RNDPOOLSIZE/4; i++) {

                /* If the pool is "full", stop after one block */
                if (entropy_bits + ent >= CRYPTO_BYTES2BITS(RNDPOOLSIZE)) {
                        if (i > 0)
                                break;
                }

                /*
                 * This lock protects reading of phys_install.
                 * Any changes to this list, by DR, are done while
                 * holding this lock. So, holding this lock is sufficient
                 * to handle DR also.
                 */
                memlist_read_lock();

                /* We're left with less than 4K of memory after DR */
                ASSERT(entsrc->nblocks > 0);

                /* Pick a memory block to read */
                block = oblock = srndpool[i] % entsrc->nblocks;

                for (pmem = phys_install; pmem != NULL; pmem = pmem->ml_next) {
                        if (block < pmem->ml_size / MEMBLOCKSIZE)
                                break;
                        block -= pmem->ml_size / MEMBLOCKSIZE;
                }

                ASSERT(pmem != NULL);

                offset = pmem->ml_address + block * MEMBLOCKSIZE;

                if (!address_in_memlist(phys_install, offset, MEMBLOCKSIZE)) {
                        memlist_read_unlock();
                        continue;
                }

                /*
                 * Do an initial check to see if the address is safe
                 */
                if (plat_hold_page(offset >> PAGESHIFT, PLAT_HOLD_NO_LOCK, NULL)
                    == PLAT_HOLD_FAIL) {
                        memlist_read_unlock();
                        continue;
                }

                /*
                 * Figure out which page to load to read the
                 * memory block.  Load the page and compute the
                 * hash of the memory block.
                 */
                len = MEMBLOCKSIZE;
                ts1 = gethrtime();
                HashInit(&ctx);
                while (len) {
                        pfn = offset >> PAGESHIFT;
                        poffset = offset & PAGEOFFSET;
                        nbytes = PAGESIZE - poffset < len ?
                            PAGESIZE - poffset : len;

                        /*
                         * Re-check the offset, and lock the frame.  If the
                         * page was given away after the above check, we'll
                         * just bail out.
                         */
                        if (plat_hold_page(pfn, PLAT_HOLD_LOCK, &pp) ==
                            PLAT_HOLD_FAIL)
                                break;

                        hat_devload(kas.a_hat, entsrc->pmbuf,
                            PAGESIZE, pfn, PROT_READ,
                            HAT_LOAD_NOCONSIST | HAT_LOAD_LOCK);

                        HashUpdate(&ctx, (uint8_t *)entsrc->pmbuf + poffset,
                            nbytes);

                        hat_unload(kas.a_hat, entsrc->pmbuf, PAGESIZE,
                            HAT_UNLOAD_UNLOCK);

                        plat_release_page(pp);

                        len -= nbytes;
                        offset += nbytes;
                }
                /* We got our pages. Let the DR roll */
                memlist_read_unlock();

                /* See if we had to bail out due to a page being given away */
                if (len)
                        continue;

                HashFinal(digest, &ctx);
                ts2 = gethrtime();

                /*
                 * Compute the time it took to load and hash the
                 * block and compare it against the previous
                 * measurement. The delta of the time values
                 * provides a small amount of entropy.  The
                 * minimum of the first, second, and third order
                 * delta is used to estimate how much entropy
                 * is present.
                 */
                diff = ts2 - ts1;
                delta = diff - entsrc->last_diff;
                if (delta < 0)
                        delta = -delta;
                delta2 = delta - entsrc->last_delta;
                if (delta2 < 0)
                        delta2 = -delta2;
                delta3 = delta2 - entsrc->last_delta2;
                if (delta3 < 0)
                        delta3 = -delta3;
                entsrc->last_diff = diff;
                entsrc->last_delta = delta;
                entsrc->last_delta2 = delta2;

                if (delta > delta2)
                        delta = delta2;
                if (delta > delta3)
                        delta = delta3;
                delta2 = 0;
                while (delta >>= 1)
                        delta2++;
                ent += delta2;

                /*
                 * If the memory block has changed, credit the pool with
                 * the entropy estimate.  The entropy estimate is doubled
                 * because the single-bit checksum misses half the change
                 * on average.
                 */
                if (physmem_parity_update(entsrc->parity, oblock,
                    digest[0] & 1))
                        ent += 2 * entsrc->entperblock;

                /* Add the entropy bytes to the pool */
                swrand_add_bytes(digest, HASHSIZE);
                swrand_add_bytes((uint8_t *)&ts1, sizeof (ts1));
                swrand_add_bytes((uint8_t *)&ts2, sizeof (ts2));
        }

        swrand_mix_pool(ent);
}

static int
physmem_parity_update(uint8_t *parity_vec, uint32_t block, int parity)
{
        /* Test and set the parity bit, return 1 if changed */
        if (parity == ((parity_vec[block >> 3] >> (block & 7)) & 1))
                return (0);
        parity_vec[block >> 3] ^= 1 << (block & 7);
        return (1);
}

/* Compute number of memory blocks available to scan */
static void
physmem_count_blocks()
{
        struct memlist *pmem;

        memlist_read_lock();
        entsrc.nblocks = 0;
        for (pmem = phys_install; pmem != NULL; pmem = pmem->ml_next) {
                entsrc.nblocks += pmem->ml_size / MEMBLOCKSIZE;
                if (entsrc.nblocks > MAXMEMBLOCKS) {
                        entsrc.nblocks = MAXMEMBLOCKS;
                        break;
                }
        }
        memlist_read_unlock();
}

/*
 * Dynamic Reconfiguration call-back functions
 */

/* ARGSUSED */
static void
rnd_dr_callback_post_add(void *arg, pgcnt_t delta)
{
        /* More memory is available now, so update entsrc->nblocks. */
        physmem_count_blocks();
}

/* Call-back routine invoked before the DR starts a memory removal. */
/* ARGSUSED */
static int
rnd_dr_callback_pre_del(void *arg, pgcnt_t delta)
{
        return (0);
}

/* Call-back routine invoked after the DR starts a memory removal. */
/* ARGSUSED */
static void
rnd_dr_callback_post_del(void *arg, pgcnt_t delta, int cancelled)
{
        /* Memory has shrunk, so update entsrc->nblocks. */
        physmem_count_blocks();
}

/* Timeout handling to gather entropy from physmem events */
static void
swrand_schedule_timeout(void)
{
        clock_t ut;     /* time in microseconds */

        ASSERT(MUTEX_HELD(&srndpool_lock));
        /*
         * The new timeout value is taken from the pool of random bits.
         * We're merely reading the first 32 bits from the pool here, not
         * consuming any entropy.
         * This routine is usually called right after stirring the pool, so
         * srndpool[0] will have a *fresh* random value each time.
         * The timeout multiplier value is a random value between 0.7 sec and
         * 1.748575 sec (0.7 sec + 0xFFFFF microseconds).
         * The new timeout is TIMEOUT_INTERVAL times that multiplier.
         */
        ut = 700000 + (clock_t)(srndpool[0] & 0xFFFFF);
        rnd_timeout_id = timeout(rnd_handler, NULL,
            TIMEOUT_INTERVAL * drv_usectohz(ut));
}

/*ARGSUSED*/
static void
rnd_handler(void *arg)
{
        mutex_enter(&srndpool_lock);

        physmem_ent_gen(&entsrc);
        if (snum_waiters > 0)
                cv_broadcast(&srndpool_read_cv);
        swrand_schedule_timeout();

        mutex_exit(&srndpool_lock);
}