NetBSD/sys/kern/subr_cprng.c

/*	$NetBSD: subr_cprng.c,v 1.17 2013/06/13 00:55:01 tls Exp $ */

/*-
 * Copyright (c) 2011 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Thor Lancelot Simon.
 *
 * 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.
 * 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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``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 FOUNDATION OR CONTRIBUTORS
 * 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/types.h>
#include <sys/time.h>
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/kmem.h>
#include <sys/mutex.h>
#include <sys/rngtest.h>
#include <sys/rnd.h>
#include <dev/rnd_private.h>

#if defined(__HAVE_CPU_COUNTER)
#include <machine/cpu_counter.h>
#endif

#include <sys/cprng.h>

__KERNEL_RCSID(0, "$NetBSD: subr_cprng.c,v 1.17 2013/06/13 00:55:01 tls Exp $");

void
cprng_init(void)
{
	nist_ctr_initialize();
}

static inline uint32_t
cprng_counter(void)
{
	struct timeval tv;

#if defined(__HAVE_CPU_COUNTER)
	if (cpu_hascounter())
		return cpu_counter32();
#endif
	if (__predict_false(cold)) {
		/* microtime unsafe if clock not running yet */
		return 0;
	}
	microtime(&tv);
	return (tv.tv_sec * 1000000 + tv.tv_usec);
}

static void
cprng_strong_doreseed(cprng_strong_t *const c)
{
	uint32_t cc = cprng_counter();

	KASSERT(mutex_owned(&c->mtx));
	KASSERT(mutex_owned(&c->reseed.mtx));
	KASSERT(c->reseed.len == NIST_BLOCK_KEYLEN_BYTES);

	if (nist_ctr_drbg_reseed(&c->drbg, c->reseed.data, c->reseed.len,
				 &cc, sizeof(cc))) {
		panic("cprng %s: nist_ctr_drbg_reseed failed.", c->name);
	}
	memset(c->reseed.data, 0, c->reseed.len);

#ifdef RND_VERBOSE
	printf("cprng %s: reseeded with rnd_filled = %d\n", c->name,
							    rnd_filled);
#endif
	c->entropy_serial = rnd_filled;
	c->reseed.state = RSTATE_IDLE;
	if (c->flags & CPRNG_USE_CV) {
		cv_broadcast(&c->cv);
	}
	selnotify(&c->selq, 0, 0);
}

static void
cprng_strong_sched_reseed(cprng_strong_t *const c)
{
	KASSERT(mutex_owned(&c->mtx));
	if (mutex_tryenter(&c->reseed.mtx)) {
		switch (c->reseed.state) {
		    case RSTATE_IDLE:
			c->reseed.state = RSTATE_PENDING;
			c->reseed.len = NIST_BLOCK_KEYLEN_BYTES;
			rndsink_attach(&c->reseed);
			break;
		    case RSTATE_HASBITS:
			/* Just rekey the underlying generator now. */
			cprng_strong_doreseed(c);
			break;
		    case RSTATE_PENDING:
			if (c->entropy_serial != rnd_filled) {
				rndsink_detach(&c->reseed);
				rndsink_attach(&c->reseed);
			}
			break;
		    default:
			panic("cprng %s: bad reseed state %d",
			      c->name, c->reseed.state);
			break;
		}
		mutex_spin_exit(&c->reseed.mtx);
	}
#ifdef RND_VERBOSE
	else {
		printf("cprng %s: skipping sched_reseed, sink busy\n",
		       c->name);
	}
#endif
}

static void
cprng_strong_reseed(void *const arg)
{
	cprng_strong_t *c = arg;

	KASSERT(mutex_owned(&c->reseed.mtx));
	KASSERT(RSTATE_HASBITS == c->reseed.state);

	if (!mutex_tryenter(&c->mtx)) {
#ifdef RND_VERBOSE
	    printf("cprng: sink %s cprng busy, no reseed\n", c->reseed.name);
#endif
	    if (c->flags & CPRNG_USE_CV) {	/* XXX if flags change? */
        	cv_broadcast(&c->cv);
	    }
	    return;
	}

	cprng_strong_doreseed(c);
	mutex_exit(&c->mtx);
}

static size_t
cprng_entropy_try(uint8_t *key, size_t keylen)
{
	int r;
	r = rnd_extract_data(key, keylen, RND_EXTRACT_GOOD);
	if (r != keylen) {	/* Always fill in, for safety */
		rnd_extract_data(key + r, keylen - r, RND_EXTRACT_ANY);
	}
	return r;
}

cprng_strong_t *
cprng_strong_create(const char *const name, int ipl, int flags)
{
	cprng_strong_t *c;
	uint8_t key[NIST_BLOCK_KEYLEN_BYTES];
	int r, getmore = 0, hard = 0;
	uint32_t cc;

	c = kmem_alloc(sizeof(*c), KM_NOSLEEP);
	if (c == NULL) {
		return NULL;
	}
	c->flags = flags;
	strlcpy(c->name, name, sizeof(c->name));
	c->reseed.state = RSTATE_IDLE;
	c->reseed.cb = cprng_strong_reseed;
	c->reseed.arg = c;
	c->entropy_serial = rnd_initial_entropy ? rnd_filled : -1;
	mutex_init(&c->reseed.mtx, MUTEX_DEFAULT, IPL_VM);
	strlcpy(c->reseed.name, name, sizeof(c->reseed.name));

	mutex_init(&c->mtx, MUTEX_DEFAULT, ipl);

	if (c->flags & CPRNG_USE_CV) {
		cv_init(&c->cv, (const char *)c->name);
	}

	selinit(&c->selq);

	r = cprng_entropy_try(key, sizeof(key));
	if (r != sizeof(key)) {
		if (c->flags & CPRNG_INIT_ANY) {
#ifdef DEBUG
			/*
			 * If we have ever crossed the pool's
			 * minimum-entropy threshold, then we are
			 * providing cryptographically strong
			 * random output -- if not information-
			 * theoretically strong.  Warn elsewise.
			 */
			if (!rnd_initial_entropy) {
				printf("cprng %s: WARNING insufficient "
			 		"entropy at creation.\n", name);
			}
#endif
		} else {
			hard++;
		}
		getmore++;
	}
		
	if (nist_ctr_drbg_instantiate(&c->drbg, key, sizeof(key),
				      &cc, sizeof(cc), name, strlen(name))) {
		panic("cprng %s: instantiation failed.", name);
	}

	if (getmore) {
		/* Cause readers to wait for rekeying. */
		if (hard) {
			c->drbg.reseed_counter =
			    NIST_CTR_DRBG_RESEED_INTERVAL + 1;
		} else {
			c->drbg.reseed_counter =
			    (NIST_CTR_DRBG_RESEED_INTERVAL / 2) + 1;
		}
	}
	return c;
}

size_t
cprng_strong(cprng_strong_t *const c, void *const p, size_t len, int flags)
{
	uint32_t cc = cprng_counter();
#ifdef DEBUG
	int testfail = 0;
#endif
	if (len > CPRNG_MAX_LEN) {	/* XXX should we loop? */
		len = CPRNG_MAX_LEN;	/* let the caller loop if desired */
	}
	mutex_enter(&c->mtx);

	/* If we were initialized with the pool empty, rekey ASAP */
	if (__predict_false(c->entropy_serial == -1) && rnd_initial_entropy) {
		c->entropy_serial = 0;
		goto rekeyany;		/* We have _some_ entropy, use it. */
	}
		
	if (nist_ctr_drbg_generate(&c->drbg, p, len, &cc, sizeof(cc))) {
		/* A generator failure really means we hit the hard limit. */
rekeyany:
		if (c->flags & CPRNG_REKEY_ANY) {
			uint8_t key[NIST_BLOCK_KEYLEN_BYTES];

			if (cprng_entropy_try(key, sizeof(key)) !=
			    sizeof(key)) {
 				printf("cprng %s: WARNING "
				       "pseudorandom rekeying.\n", c->name);
			}
			cc = cprng_counter();
			if (nist_ctr_drbg_reseed(&c->drbg, key, sizeof(key),
			    &cc, sizeof(cc))) {
				panic("cprng %s: nist_ctr_drbg_reseed "
				      "failed.", c->name);
			}
			memset(key, 0, sizeof(key));
		} else {
			int wr;

			do {
				cprng_strong_sched_reseed(c);
				if ((flags & FNONBLOCK) ||
				    !(c->flags & CPRNG_USE_CV)) {
					len = 0;
					break;
				}
			/*
			 * XXX There's a race with the cv_broadcast
			 * XXX in cprng_strong_sched_reseed, because
			 * XXX of the use of tryenter in that function.
			 * XXX This "timedwait" hack works around it,
			 * XXX at the expense of occasionaly polling
			 * XXX for success on a /dev/random rekey.
			 */
				wr = cv_timedwait_sig(&c->cv, &c->mtx,
						      mstohz(100));
				if (wr == ERESTART) {
					mutex_exit(&c->mtx);
					return 0;
				}
			} while (nist_ctr_drbg_generate(&c->drbg, p,
							len, &cc,
							sizeof(cc)));
		}
	}

#ifdef DEBUG
	/*
	 * If the generator has just been keyed, perform
	 * the statistical RNG test.
	 */
	if (__predict_false(c->drbg.reseed_counter == 1) &&
	    (flags & FASYNC) == 0) {
		rngtest_t *rt = kmem_intr_alloc(sizeof(*rt), KM_NOSLEEP);

		if (rt) {

			strncpy(rt->rt_name, c->name, sizeof(rt->rt_name));

			if (nist_ctr_drbg_generate(&c->drbg, rt->rt_b,
		  	    sizeof(rt->rt_b), NULL, 0)) {
				panic("cprng %s: nist_ctr_drbg_generate "
				      "failed!", c->name);
		
			}
			testfail = rngtest(rt);

			if (testfail) {
				printf("cprng %s: failed statistical RNG "
				       "test.\n", c->name);
				c->drbg.reseed_counter =
				    NIST_CTR_DRBG_RESEED_INTERVAL + 1;
				len = 0;
			}
			memset(rt, 0, sizeof(*rt));
			kmem_intr_free(rt, sizeof(*rt));
		}
	}
#endif
	if (__predict_false(c->drbg.reseed_counter >
			     (NIST_CTR_DRBG_RESEED_INTERVAL / 2))) {
		cprng_strong_sched_reseed(c);
	} else if (rnd_full) {
		if (c->entropy_serial != rnd_filled) {
#ifdef RND_VERBOSE
			printf("cprng %s: reseeding from full pool "
			       "(serial %d vs pool %d)\n", c->name,
			       c->entropy_serial, rnd_filled);
#endif
			cprng_strong_sched_reseed(c);
		}
	}

	mutex_exit(&c->mtx);
	return len;
}

void
cprng_strong_destroy(cprng_strong_t *c)
{
	mutex_enter(&c->mtx);
	mutex_spin_enter(&c->reseed.mtx);

	if (c->flags & CPRNG_USE_CV) {
		KASSERT(!cv_has_waiters(&c->cv));
		cv_destroy(&c->cv);
	}
	seldestroy(&c->selq);

	if (RSTATE_PENDING == c->reseed.state) {
		rndsink_detach(&c->reseed);
	}
	mutex_spin_exit(&c->reseed.mtx);
	mutex_destroy(&c->reseed.mtx);

	nist_ctr_drbg_destroy(&c->drbg);

	mutex_exit(&c->mtx);
	mutex_destroy(&c->mtx);

	memset(c, 0, sizeof(*c));
	kmem_free(c, sizeof(*c));
}

int
cprng_strong_getflags(cprng_strong_t *const c)
{
	KASSERT(mutex_owned(&c->mtx));
	return c->flags;
}

void
cprng_strong_setflags(cprng_strong_t *const c, int flags)
{
	KASSERT(mutex_owned(&c->mtx));
	if (flags & CPRNG_USE_CV) {
		if (!(c->flags & CPRNG_USE_CV)) {
			cv_init(&c->cv, (const char *)c->name);
		}
	} else {
		if (c->flags & CPRNG_USE_CV) {
			KASSERT(!cv_has_waiters(&c->cv));
			cv_destroy(&c->cv);
		}
	}
	if (flags & CPRNG_REKEY_ANY) {
		if (!(c->flags & CPRNG_REKEY_ANY)) {
			if (c->flags & CPRNG_USE_CV) {
				cv_broadcast(&c->cv);
			}
			selnotify(&c->selq, 0, 0);
		}
	}
	c->flags = flags;
}