crypto/io/swrand.c

	swrand.c revision ae115bc77f6fcde83175c75b4206dc2e50747966
/*
 * 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 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

/*
 * 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>

#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 int leftover_bytes;      /* leftover length */

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 = NULL;
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 %I%"
};

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
};

static crypto_provider_info_t swrand_prov_info = {
    CRYPTO_SPI_VERSION_1,
    "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;

    /*
     * Register with KCF. If the registration fails, return error.
     */
    if ((ret = crypto_register_provider(&swrand_prov_info,
        &swrand_prov_handle)) != CRYPTO_SUCCESS) {
        cmn_err(CE_WARN, "swrand : Kernel Random Number Provider "
            "disabled for /dev/random use");
        return (EACCES);
    }

    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) {
        mutex_destroy(&srndpool_lock);
        mutex_destroy(&buffer_lock);
        cv_destroy(&srndpool_read_cv);
        (void) crypto_unregister_provider(swrand_prov_handle);
        return (ENOMEM);
    }

    if ((ret = mod_install(&modlinkage)) != 0) {
        mutex_destroy(&srndpool_lock);
        mutex_destroy(&buffer_lock);
        cv_destroy(&srndpool_read_cv);
        physmem_ent_fini(&entsrc);
        (void) crypto_unregister_provider(swrand_prov_handle);
        return (ret);
    }

    /* Schedule periodic mixing of the pool. */
    mutex_enter(&srndpool_lock);
    swrand_schedule_timeout();
    mutex_exit(&srndpool_lock);

    return (0);
}

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;

    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, entropy_bits/8);
        entropy_bits -= bytes * 8;
        BUMP_SWRAND_STATS(ss_entOut, bytes * 8);
        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);
        }

        /*
         * Hash the digest again before output to obscure
         * what was fed back to the pool.
         */
        HashInit(&hashctx);
        HashUpdate(&hashctx, digest, HASHSIZE);
        if (len >= HASHSIZE)
            HashFinal(ptr, &hashctx);
        else {
            HashFinal(digest, &hashctx);
            bcopy(digest, ptr, bytes);
            leftover_bytes = HASHSIZE - bytes;
            bcopy(digest + bytes, leftover, leftover_bytes);
        }

        len -= bytes;
        ptr += bytes;
        BUMP_SWRAND_STATS(ss_bytesOut, bytes);
    }
    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 > RNDPOOLSIZE * 8)
        entropy_bits = RNDPOOLSIZE * 8;

    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 = MEMBLOCKSIZE << 3;
    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 >= RNDPOOLSIZE * 8) {
            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->next) {
            if (block < pmem->size / MEMBLOCKSIZE)
                break;
            block -= pmem->size / MEMBLOCKSIZE;
        }

        ASSERT(pmem != NULL);

        offset = pmem->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->next) {
        entsrc.nblocks += pmem->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);
}