freebsd-dev/sys/dev/random/random_harvestq.c

/*-
 * Copyright (c) 2017 Oliver Pinter
 * Copyright (c) 2017 W. Dean Freeman
 * Copyright (c) 2000-2015 Mark R V Murray
 * Copyright (c) 2013 Arthur Mesh
 * Copyright (c) 2004 Robert N. M. Watson
 * 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, this list of conditions and the following disclaimer
 *    in this position and unchanged.
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 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 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/ck.h>
#include <sys/conf.h>
#include <sys/epoch.h>
#include <sys/eventhandler.h>
#include <sys/hash.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/linker.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/mutex.h>
#include <sys/random.h>
#include <sys/sbuf.h>
#include <sys/sysctl.h>
#include <sys/unistd.h>

#include <machine/atomic.h>
#include <machine/cpu.h>

#include <crypto/rijndael/rijndael-api-fst.h>
#include <crypto/sha2/sha256.h>

#include <dev/random/hash.h>
#include <dev/random/randomdev.h>
#include <dev/random/random_harvestq.h>

#if defined(RANDOM_ENABLE_ETHER)
#define _RANDOM_HARVEST_ETHER_OFF 0
#else
#define _RANDOM_HARVEST_ETHER_OFF (1u << RANDOM_NET_ETHER)
#endif
#if defined(RANDOM_ENABLE_UMA)
#define _RANDOM_HARVEST_UMA_OFF 0
#else
#define _RANDOM_HARVEST_UMA_OFF (1u << RANDOM_UMA)
#endif

static void random_kthread(void);
static void random_sources_feed(void);

static u_int read_rate;

/*
 * Random must initialize much earlier than epoch, but we can initialize the
 * epoch code before SMP starts.  Prior to SMP, we can safely bypass
 * concurrency primitives.
 */
static __read_mostly bool epoch_inited;
static __read_mostly epoch_t rs_epoch;

/*
 * How many events to queue up. We create this many items in
 * an 'empty' queue, then transfer them to the 'harvest' queue with
 * supplied junk. When used, they are transferred back to the
 * 'empty' queue.
 */
#define	RANDOM_RING_MAX		1024
#define	RANDOM_ACCUM_MAX	8

/* 1 to let the kernel thread run, 0 to terminate, -1 to mark completion */
volatile int random_kthread_control;


/* Allow the sysadmin to select the broad category of
 * entropy types to harvest.
 */
__read_frequently u_int hc_source_mask;

struct random_sources {
	CK_LIST_ENTRY(random_sources)	 rrs_entries;
	struct random_source		*rrs_source;
};

static CK_LIST_HEAD(sources_head, random_sources) source_list =
    CK_LIST_HEAD_INITIALIZER(source_list);

SYSCTL_NODE(_kern_random, OID_AUTO, harvest, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "Entropy Device Parameters");

/*
 * Put all the harvest queue context stuff in one place.
 * this make is a bit easier to lock and protect.
 */
static struct harvest_context {
	/* The harvest mutex protects all of harvest_context and
	 * the related data.
	 */
	struct mtx hc_mtx;
	/* Round-robin destination cache. */
	u_int hc_destination[ENTROPYSOURCE];
	/* The context of the kernel thread processing harvested entropy */
	struct proc *hc_kthread_proc;
	/*
	 * Lockless ring buffer holding entropy events
	 * If ring.in == ring.out,
	 *     the buffer is empty.
	 * If ring.in != ring.out,
	 *     the buffer contains harvested entropy.
	 * If (ring.in + 1) == ring.out (mod RANDOM_RING_MAX),
	 *     the buffer is full.
	 *
	 * NOTE: ring.in points to the last added element,
	 * and ring.out points to the last consumed element.
	 *
	 * The ring.in variable needs locking as there are multiple
	 * sources to the ring. Only the sources may change ring.in,
	 * but the consumer may examine it.
	 *
	 * The ring.out variable does not need locking as there is
	 * only one consumer. Only the consumer may change ring.out,
	 * but the sources may examine it.
	 */
	struct entropy_ring {
		struct harvest_event ring[RANDOM_RING_MAX];
		volatile u_int in;
		volatile u_int out;
	} hc_entropy_ring;
	struct fast_entropy_accumulator {
		volatile u_int pos;
		uint32_t buf[RANDOM_ACCUM_MAX];
	} hc_entropy_fast_accumulator;
} harvest_context;

static struct kproc_desc random_proc_kp = {
	"rand_harvestq",
	random_kthread,
	&harvest_context.hc_kthread_proc,
};

/* Pass the given event straight through to Fortuna/Whatever. */
static __inline void
random_harvestq_fast_process_event(struct harvest_event *event)
{
	p_random_alg_context->ra_event_processor(event);
	explicit_bzero(event, sizeof(*event));
}

static void
random_kthread(void)
{
        u_int maxloop, ring_out, i;

	/*
	 * Locking is not needed as this is the only place we modify ring.out, and
	 * we only examine ring.in without changing it. Both of these are volatile,
	 * and this is a unique thread.
	 */
	for (random_kthread_control = 1; random_kthread_control;) {
		/* Deal with events, if any. Restrict the number we do in one go. */
		maxloop = RANDOM_RING_MAX;
		while (harvest_context.hc_entropy_ring.out != harvest_context.hc_entropy_ring.in) {
			ring_out = (harvest_context.hc_entropy_ring.out + 1)%RANDOM_RING_MAX;
			random_harvestq_fast_process_event(harvest_context.hc_entropy_ring.ring + ring_out);
			harvest_context.hc_entropy_ring.out = ring_out;
			if (!--maxloop)
				break;
		}
		random_sources_feed();
		/* XXX: FIX!! Increase the high-performance data rate? Need some measurements first. */
		for (i = 0; i < RANDOM_ACCUM_MAX; i++) {
			if (harvest_context.hc_entropy_fast_accumulator.buf[i]) {
				random_harvest_direct(harvest_context.hc_entropy_fast_accumulator.buf + i, sizeof(harvest_context.hc_entropy_fast_accumulator.buf[0]), RANDOM_UMA);
				harvest_context.hc_entropy_fast_accumulator.buf[i] = 0;
			}
		}
		/* XXX: FIX!! This is a *great* place to pass hardware/live entropy to random(9) */
		tsleep_sbt(&harvest_context.hc_kthread_proc, 0, "-", SBT_1S/10, 0, C_PREL(1));
	}
	random_kthread_control = -1;
	wakeup(&harvest_context.hc_kthread_proc);
	kproc_exit(0);
	/* NOTREACHED */
}
/* This happens well after SI_SUB_RANDOM */
SYSINIT(random_device_h_proc, SI_SUB_KICK_SCHEDULER, SI_ORDER_ANY, kproc_start,
    &random_proc_kp);

static void
rs_epoch_init(void *dummy __unused)
{
	rs_epoch = epoch_alloc("Random Sources", EPOCH_PREEMPT);
	epoch_inited = true;
}
SYSINIT(rs_epoch_init, SI_SUB_EPOCH, SI_ORDER_ANY, rs_epoch_init, NULL);

/*
 * Run through all fast sources reading entropy for the given
 * number of rounds, which should be a multiple of the number
 * of entropy accumulation pools in use; it is 32 for Fortuna.
 */
static void
random_sources_feed(void)
{
	uint32_t entropy[HARVESTSIZE];
	struct epoch_tracker et;
	struct random_sources *rrs;
	u_int i, n, local_read_rate;
	bool rse_warm;

	rse_warm = epoch_inited;

	/*
	 * Step over all of live entropy sources, and feed their output
	 * to the system-wide RNG.
	 */
	local_read_rate = atomic_readandclear_32(&read_rate);
	/* Perform at least one read per round */
	local_read_rate = MAX(local_read_rate, 1);
	/* But not exceeding RANDOM_KEYSIZE_WORDS */
	local_read_rate = MIN(local_read_rate, RANDOM_KEYSIZE_WORDS);
	if (rse_warm)
		epoch_enter_preempt(rs_epoch, &et);
	CK_LIST_FOREACH(rrs, &source_list, rrs_entries) {
		for (i = 0; i < p_random_alg_context->ra_poolcount*local_read_rate; i++) {
			n = rrs->rrs_source->rs_read(entropy, sizeof(entropy));
			KASSERT((n <= sizeof(entropy)), ("%s: rs_read returned too much data (%u > %zu)", __func__, n, sizeof(entropy)));
			/*
			 * Sometimes the HW entropy source doesn't have anything
			 * ready for us.  This isn't necessarily untrustworthy.
			 * We don't perform any other verification of an entropy
			 * source (i.e., length is allowed to be anywhere from 1
			 * to sizeof(entropy), quality is unchecked, etc), so
			 * don't balk verbosely at slow random sources either.
			 * There are reports that RDSEED on x86 metal falls
			 * behind the rate at which we query it, for example.
			 * But it's still a better entropy source than RDRAND.
			 */
			if (n == 0)
				continue;
			random_harvest_direct(entropy, n, rrs->rrs_source->rs_source);
		}
	}
	if (rse_warm)
		epoch_exit_preempt(rs_epoch, &et);
	explicit_bzero(entropy, sizeof(entropy));
}

void
read_rate_increment(u_int chunk)
{

	atomic_add_32(&read_rate, chunk);
}

/* ARGSUSED */
static int
random_check_uint_harvestmask(SYSCTL_HANDLER_ARGS)
{
	static const u_int user_immutable_mask =
	    (((1 << ENTROPYSOURCE) - 1) & (-1UL << RANDOM_PURE_START)) |
	    _RANDOM_HARVEST_ETHER_OFF | _RANDOM_HARVEST_UMA_OFF;

	int error;
	u_int value, orig_value;

	orig_value = value = hc_source_mask;
	error = sysctl_handle_int(oidp, &value, 0, req);
	if (error != 0 || req->newptr == NULL)
		return (error);

	if (flsl(value) > ENTROPYSOURCE)
		return (EINVAL);

	/*
	 * Disallow userspace modification of pure entropy sources.
	 */
	hc_source_mask = (value & ~user_immutable_mask) |
	    (orig_value & user_immutable_mask);
	return (0);
}
SYSCTL_PROC(_kern_random_harvest, OID_AUTO, mask,
    CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, NULL, 0,
    random_check_uint_harvestmask, "IU",
    "Entropy harvesting mask");

/* ARGSUSED */
static int
random_print_harvestmask(SYSCTL_HANDLER_ARGS)
{
	struct sbuf sbuf;
	int error, i;

	error = sysctl_wire_old_buffer(req, 0);
	if (error == 0) {
		sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
		for (i = ENTROPYSOURCE - 1; i >= 0; i--)
			sbuf_cat(&sbuf, (hc_source_mask & (1 << i)) ? "1" : "0");
		error = sbuf_finish(&sbuf);
		sbuf_delete(&sbuf);
	}
	return (error);
}
SYSCTL_PROC(_kern_random_harvest, OID_AUTO, mask_bin,
    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
    random_print_harvestmask, "A",
    "Entropy harvesting mask (printable)");

static const char *random_source_descr[ENTROPYSOURCE] = {
	[RANDOM_CACHED] = "CACHED",
	[RANDOM_ATTACH] = "ATTACH",
	[RANDOM_KEYBOARD] = "KEYBOARD",
	[RANDOM_MOUSE] = "MOUSE",
	[RANDOM_NET_TUN] = "NET_TUN",
	[RANDOM_NET_ETHER] = "NET_ETHER",
	[RANDOM_NET_NG] = "NET_NG",
	[RANDOM_INTERRUPT] = "INTERRUPT",
	[RANDOM_SWI] = "SWI",
	[RANDOM_FS_ATIME] = "FS_ATIME",
	[RANDOM_UMA] = "UMA", /* ENVIRONMENTAL_END */
	[RANDOM_PURE_OCTEON] = "PURE_OCTEON", /* PURE_START */
	[RANDOM_PURE_SAFE] = "PURE_SAFE",
	[RANDOM_PURE_GLXSB] = "PURE_GLXSB",
	[RANDOM_PURE_HIFN] = "PURE_HIFN",
	[RANDOM_PURE_RDRAND] = "PURE_RDRAND",
	[RANDOM_PURE_NEHEMIAH] = "PURE_NEHEMIAH",
	[RANDOM_PURE_RNDTEST] = "PURE_RNDTEST",
	[RANDOM_PURE_VIRTIO] = "PURE_VIRTIO",
	[RANDOM_PURE_BROADCOM] = "PURE_BROADCOM",
	[RANDOM_PURE_CCP] = "PURE_CCP",
	[RANDOM_PURE_DARN] = "PURE_DARN",
	[RANDOM_PURE_TPM] = "PURE_TPM",
	[RANDOM_PURE_VMGENID] = "VMGENID",
	/* "ENTROPYSOURCE" */
};

/* ARGSUSED */
static int
random_print_harvestmask_symbolic(SYSCTL_HANDLER_ARGS)
{
	struct sbuf sbuf;
	int error, i;
	bool first;

	first = true;
	error = sysctl_wire_old_buffer(req, 0);
	if (error == 0) {
		sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
		for (i = ENTROPYSOURCE - 1; i >= 0; i--) {
			if (i >= RANDOM_PURE_START &&
			    (hc_source_mask & (1 << i)) == 0)
				continue;
			if (!first)
				sbuf_cat(&sbuf, ",");
			sbuf_cat(&sbuf, !(hc_source_mask & (1 << i)) ? "[" : "");
			sbuf_cat(&sbuf, random_source_descr[i]);
			sbuf_cat(&sbuf, !(hc_source_mask & (1 << i)) ? "]" : "");
			first = false;
		}
		error = sbuf_finish(&sbuf);
		sbuf_delete(&sbuf);
	}
	return (error);
}
SYSCTL_PROC(_kern_random_harvest, OID_AUTO, mask_symbolic,
    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
    random_print_harvestmask_symbolic, "A",
    "Entropy harvesting mask (symbolic)");

/* ARGSUSED */
static void
random_harvestq_init(void *unused __unused)
{
	static const u_int almost_everything_mask =
	    (((1 << (RANDOM_ENVIRONMENTAL_END + 1)) - 1) &
	    ~_RANDOM_HARVEST_ETHER_OFF & ~_RANDOM_HARVEST_UMA_OFF);

	hc_source_mask = almost_everything_mask;
	RANDOM_HARVEST_INIT_LOCK();
	harvest_context.hc_entropy_ring.in = harvest_context.hc_entropy_ring.out = 0;
}
SYSINIT(random_device_h_init, SI_SUB_RANDOM, SI_ORDER_THIRD, random_harvestq_init, NULL);

/*
 * Subroutine to slice up a contiguous chunk of 'entropy' and feed it into the
 * underlying algorithm.  Returns number of bytes actually fed into underlying
 * algorithm.
 */
static size_t
random_early_prime(char *entropy, size_t len)
{
	struct harvest_event event;
	size_t i;

	len = rounddown(len, sizeof(event.he_entropy));
	if (len == 0)
		return (0);

	for (i = 0; i < len; i += sizeof(event.he_entropy)) {
		event.he_somecounter = (uint32_t)get_cyclecount();
		event.he_size = sizeof(event.he_entropy);
		event.he_source = RANDOM_CACHED;
		event.he_destination =
		    harvest_context.hc_destination[RANDOM_CACHED]++;
		memcpy(event.he_entropy, entropy + i, sizeof(event.he_entropy));
		random_harvestq_fast_process_event(&event);
	}
	explicit_bzero(entropy, len);
	return (len);
}

/*
 * Subroutine to search for known loader-loaded files in memory and feed them
 * into the underlying algorithm early in boot.  Returns the number of bytes
 * loaded (zero if none were loaded).
 */
static size_t
random_prime_loader_file(const char *type)
{
	uint8_t *keyfile, *data;
	size_t size;

	keyfile = preload_search_by_type(type);
	if (keyfile == NULL)
		return (0);

	data = preload_fetch_addr(keyfile);
	size = preload_fetch_size(keyfile);
	if (data == NULL)
		return (0);

	return (random_early_prime(data, size));
}

/*
 * This is used to prime the RNG by grabbing any early random stuff
 * known to the kernel, and inserting it directly into the hashing
 * module, currently Fortuna.
 */
/* ARGSUSED */
static void
random_harvestq_prime(void *unused __unused)
{
	size_t size;

	/*
	 * Get entropy that may have been preloaded by loader(8)
	 * and use it to pre-charge the entropy harvest queue.
	 */
	size = random_prime_loader_file(RANDOM_CACHED_BOOT_ENTROPY_MODULE);
	if (bootverbose) {
		if (size > 0)
			printf("random: read %zu bytes from preloaded cache\n",
			    size);
		else
			printf("random: no preloaded entropy cache\n");
	}
}
SYSINIT(random_device_prime, SI_SUB_RANDOM, SI_ORDER_MIDDLE, random_harvestq_prime, NULL);

/* ARGSUSED */
static void
random_harvestq_deinit(void *unused __unused)
{

	/* Command the hash/reseed thread to end and wait for it to finish */
	random_kthread_control = 0;
	while (random_kthread_control >= 0)
		tsleep(&harvest_context.hc_kthread_proc, 0, "harvqterm", hz/5);
}
SYSUNINIT(random_device_h_init, SI_SUB_RANDOM, SI_ORDER_THIRD, random_harvestq_deinit, NULL);

/*-
 * Entropy harvesting queue routine.
 *
 * This is supposed to be fast; do not do anything slow in here!
 * It is also illegal (and morally reprehensible) to insert any
 * high-rate data here. "High-rate" is defined as a data source
 * that will usually cause lots of failures of the "Lockless read"
 * check a few lines below. This includes the "always-on" sources
 * like the Intel "rdrand" or the VIA Nehamiah "xstore" sources.
 */
/* XXXRW: get_cyclecount() is cheap on most modern hardware, where cycle
 * counters are built in, but on older hardware it will do a real time clock
 * read which can be quite expensive.
 */
void
random_harvest_queue_(const void *entropy, u_int size, enum random_entropy_source origin)
{
	struct harvest_event *event;
	u_int ring_in;

	KASSERT(origin >= RANDOM_START && origin < ENTROPYSOURCE, ("%s: origin %d invalid\n", __func__, origin));
	RANDOM_HARVEST_LOCK();
	ring_in = (harvest_context.hc_entropy_ring.in + 1)%RANDOM_RING_MAX;
	if (ring_in != harvest_context.hc_entropy_ring.out) {
		/* The ring is not full */
		event = harvest_context.hc_entropy_ring.ring + ring_in;
		event->he_somecounter = (uint32_t)get_cyclecount();
		event->he_source = origin;
		event->he_destination = harvest_context.hc_destination[origin]++;
		if (size <= sizeof(event->he_entropy)) {
			event->he_size = size;
			memcpy(event->he_entropy, entropy, size);
		}
		else {
			/* Big event, so squash it */
			event->he_size = sizeof(event->he_entropy[0]);
			event->he_entropy[0] = jenkins_hash(entropy, size, (uint32_t)(uintptr_t)event);
		}
		harvest_context.hc_entropy_ring.in = ring_in;
	}
	RANDOM_HARVEST_UNLOCK();
}

/*-
 * Entropy harvesting fast routine.
 *
 * This is supposed to be very fast; do not do anything slow in here!
 * This is the right place for high-rate harvested data.
 */
void
random_harvest_fast_(const void *entropy, u_int size)
{
	u_int pos;

	pos = harvest_context.hc_entropy_fast_accumulator.pos;
	harvest_context.hc_entropy_fast_accumulator.buf[pos] ^= jenkins_hash(entropy, size, (uint32_t)get_cyclecount());
	harvest_context.hc_entropy_fast_accumulator.pos = (pos + 1)%RANDOM_ACCUM_MAX;
}

/*-
 * Entropy harvesting direct routine.
 *
 * This is not supposed to be fast, but will only be used during
 * (e.g.) booting when initial entropy is being gathered.
 */
void
random_harvest_direct_(const void *entropy, u_int size, enum random_entropy_source origin)
{
	struct harvest_event event;

	KASSERT(origin >= RANDOM_START && origin < ENTROPYSOURCE, ("%s: origin %d invalid\n", __func__, origin));
	size = MIN(size, sizeof(event.he_entropy));
	event.he_somecounter = (uint32_t)get_cyclecount();
	event.he_size = size;
	event.he_source = origin;
	event.he_destination = harvest_context.hc_destination[origin]++;
	memcpy(event.he_entropy, entropy, size);
	random_harvestq_fast_process_event(&event);
}

void
random_harvest_register_source(enum random_entropy_source source)
{

	hc_source_mask |= (1 << source);
}

void
random_harvest_deregister_source(enum random_entropy_source source)
{

	hc_source_mask &= ~(1 << source);
}

void
random_source_register(struct random_source *rsource)
{
	struct random_sources *rrs;

	KASSERT(rsource != NULL, ("invalid input to %s", __func__));

	rrs = malloc(sizeof(*rrs), M_ENTROPY, M_WAITOK);
	rrs->rrs_source = rsource;

	random_harvest_register_source(rsource->rs_source);

	printf("random: registering fast source %s\n", rsource->rs_ident);

	RANDOM_HARVEST_LOCK();
	CK_LIST_INSERT_HEAD(&source_list, rrs, rrs_entries);
	RANDOM_HARVEST_UNLOCK();
}

void
random_source_deregister(struct random_source *rsource)
{
	struct random_sources *rrs = NULL;

	KASSERT(rsource != NULL, ("invalid input to %s", __func__));

	random_harvest_deregister_source(rsource->rs_source);

	RANDOM_HARVEST_LOCK();
	CK_LIST_FOREACH(rrs, &source_list, rrs_entries)
		if (rrs->rrs_source == rsource) {
			CK_LIST_REMOVE(rrs, rrs_entries);
			break;
		}
	RANDOM_HARVEST_UNLOCK();

	if (rrs != NULL && epoch_inited)
		epoch_wait_preempt(rs_epoch);
	free(rrs, M_ENTROPY);
}

static int
random_source_handler(SYSCTL_HANDLER_ARGS)
{
	struct epoch_tracker et;
	struct random_sources *rrs;
	struct sbuf sbuf;
	int error, count;

	error = sysctl_wire_old_buffer(req, 0);
	if (error != 0)
		return (error);

	sbuf_new_for_sysctl(&sbuf, NULL, 64, req);
	count = 0;
	epoch_enter_preempt(rs_epoch, &et);
	CK_LIST_FOREACH(rrs, &source_list, rrs_entries) {
		sbuf_cat(&sbuf, (count++ ? ",'" : "'"));
		sbuf_cat(&sbuf, rrs->rrs_source->rs_ident);
		sbuf_cat(&sbuf, "'");
	}
	epoch_exit_preempt(rs_epoch, &et);
	error = sbuf_finish(&sbuf);
	sbuf_delete(&sbuf);
	return (error);
}
SYSCTL_PROC(_kern_random, OID_AUTO, random_sources, CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE,
	    NULL, 0, random_source_handler, "A",
	    "List of active fast entropy sources.");

MODULE_VERSION(random_harvestq, 1);