sys/kern/kern_nrandom.c

/*
 * Copyright (c) 2004, 2005, 2006 Robin J Carey. 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,
 *    without modification, immediately at the beginning of the file.
 * 2. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 *
 * $DragonFly: src/sys/kern/kern_nrandom.c,v 1.7 2008/08/01 04:42:30 dillon Exp $
 */
/*			   --- NOTES ---
 *
 * Note: The word "entropy" is often incorrectly used to describe
 * random data. The word "entropy" originates from the science of
 * Physics. The correct descriptive definition would be something
 * along the lines of "seed", "unpredictable numbers" or
 * "unpredictable data".
 *
 * Note: Some /dev/[u]random implementations save "seed" between
 * boots which represents a security hazard since an adversary
 * could acquire this data (since it is stored in a file). If
 * the unpredictable data used in the above routines is only
 * generated during Kernel operation, then an adversary can only
 * acquire that data through a Kernel security compromise and/or
 * a cryptographic algorithm failure/cryptanalysis.
 *
 * Note: On FreeBSD-4.11, interrupts have to be manually enabled
 * using the rndcontrol(8) command.
 *
 *		--- DESIGN (FreeBSD-4.11 based) ---
 *
 *   The rnddev module automatically initializes itself the first time
 * it is used (client calls any public rnddev_*() interface routine).
 * Both CSPRNGs are initially seeded from the precise nano[up]time() routines.
 * Tests show this method produces good enough results, suitable for intended
 * use. It is necessary for both CSPRNGs to be completely seeded, initially.
 *
 *   After initialization and during Kernel operation the only suitable
 * unpredictable data available is:
 *
 *	(1) Keyboard scan-codes.
 *	(2) Nanouptime acquired by a Keyboard/Read-Event.
 *	(3) Suitable interrupt source; hard-disk/ATA-device.
 *
 *      (X) Mouse-event (xyz-data unsuitable); NOT IMPLEMENTED.
 *
 *   This data is added to both CSPRNGs in real-time as it happens/
 * becomes-available. Additionally, unpredictable (?) data may be
 * acquired from a true-random number generator if such a device is
 * available to the system (not advisable !).
 *   Nanouptime() acquired by a Read-Event is a very important aspect of
 * this design, since it ensures that unpredictable data is added to
 * the CSPRNGs even if there are no other sources.
 *   The nanouptime() Kernel routine is used since time relative to
 * boot is less adversary-known than time itself.
 *
 *   This design has been thoroughly tested with debug logging
 * and the output from both /dev/random and /dev/urandom has
 * been tested with the DIEHARD test-suite; both pass.
 *
 * MODIFICATIONS MADE TO ORIGINAL "kern_random.c":
 *
 * 6th July 2005:
 *
 * o Changed ReadSeed() function to schedule future read-seed-events
 *   by at least one second. Previous implementation used a randomised
 *   scheduling { 0, 1, 2, 3 seconds }.
 * o Changed SEED_NANOUP() function to use a "previous" accumulator
 *   algorithm similar to ReadSeed(). This ensures that there is no
 *   way that an adversary can tell what number is being added to the
 *   CSPRNGs, since the number added to the CSPRNGs at Event-Time is
 *   the sum of nanouptime()@Event and an unknown/secret number.
 * o Changed rnddev_add_interrupt() function to schedule future
 *   interrupt-events by at least one second. Previous implementation
 *   had no scheduling algorithm which allowed an "interrupt storm"
 *   to occur resulting in skewed data entering into the CSPRNGs.
 *
 *
 * 9th July 2005:
 *
 * o Some small cleanups and change all internal functions to be
 *   static/private.
 * o Removed ReadSeed() since its functionality is already performed
 *   by another function { rnddev_add_interrupt_OR_read() } and remove
 *   the silly rndByte accumulator/feedback-thing (since multipying by
 *   rndByte could yield a value of 0).
 * o Made IBAA/L14 public interface become static/private;
 *   Local to this file (not changed to that in the original C modules).
 *
 * 16th July 2005:
 *
 * o SEED_NANOUP() -> NANOUP_EVENT() function rename.
 * o Make NANOUP_EVENT() handle the time-buffering directly so that all
 *   time-stamp-events use this single time-buffer (including keyboard).
 *   This removes dependancy on "time_second" Kernel variable.
 * o Removed second-time-buffer code in rnddev_add_interrupt_OR_read (void).
 * o Rewrote the time-buffering algorithm in NANOUP_EVENT() to use a
 *   randomised time-delay range.
 *
 * 12th Dec 2005:
 *
 * o Updated to (hopefully final) L15 algorithm.
 *
 * 12th June 2006:
 *
 * o Added missing (u_char *) cast in RnddevRead() function.
 * o Changed copyright to 3-clause BSD license and cleaned up the layout
 *   of this file.
 */

#include <sys/types.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/poll.h>
#include <sys/event.h>
#include <sys/random.h>
#include <sys/systimer.h>
#include <sys/time.h>
#include <sys/proc.h>
#include <sys/lock.h>
#include <sys/sysctl.h>
#include <sys/spinlock.h>
#include <machine/clock.h>

#include <sys/thread2.h>
#include <sys/spinlock2.h>
#include <sys/mplock2.h>

/*
 * Portability note: The u_char/unsigned char type is used where
 * uint8_t from <stdint.h> or u_int8_t from <sys/types.h> should really
 * be being used. On FreeBSD, it is safe to make the assumption that these
 * different types are equivalent (on all architectures).
 * The FreeBSD <sys/crypto/rc4> module also makes this assumption.
 */

/*------------------------------ IBAA ----------------------------------*/

/*-------------------------- IBAA CSPRNG -------------------------------*/

/*
 * NOTE: The original source code from which this source code (IBAA)
 *       was taken has no copyright/license. The algorithm has no patent
 *       and is freely/publicly available from:
 *
 *           http://www.burtleburtle.net/bob/rand/isaac.html
 */

/*
 * ^ means XOR, & means bitwise AND, a<<b means shift a by b.
 * barrel(a) shifts a 19 bits to the left, and bits wrap around
 * ind(x) is (x AND 255), or (x mod 256)
 */
typedef	u_int32_t	u4;   /* unsigned four bytes, 32 bits */

#define	ALPHA		(8)
#define	SIZE		(1 << ALPHA)
#define MASK		(SIZE - 1)
#define	ind(x)		((x) & (SIZE - 1))
#define	barrel(a)	(((a) << 20) ^ ((a) >> 12))  /* beta=32,shift=20 */

static void IBAA
(
	u4 *m,		/* Memory: array of SIZE ALPHA-bit terms */
	u4 *r,		/* Results: the sequence, same size as m */
	u4 *aa,		/* Accumulator: a single value */
	u4 *bb,		/* the previous result */
	u4 *counter	/* counter */
)
{
	u4 a, b, x, y, i;

	a = *aa;
	b = *bb + *counter;
	++*counter;
	for (i = 0; i < SIZE; ++i) {
		x = m[i];
		a = barrel(a) + m[ind(i + (SIZE / 2))];	/* set a */
		m[i] = y = m[ind(x)] + a + b;		/* set m */
		r[i] = b = m[ind(y >> ALPHA)] + x;	/* set r */
	}
	*bb = b; *aa = a;
}

/*-------------------------- IBAA CSPRNG -------------------------------*/


static u4	IBAA_memory[SIZE];
static u4	IBAA_results[SIZE];
static u4	IBAA_aa;
static u4	IBAA_bb;
static u4	IBAA_counter;

static volatile int IBAA_byte_index;


static void	IBAA_Init(void);
static void	IBAA_Call(void);
static void	IBAA_Seed(const u_int32_t val);
static u_char	IBAA_Byte(void);

/*
 * Initialize IBAA.
 */
static void
IBAA_Init(void)
{
	size_t	i;

	for (i = 0; i < SIZE; ++i) {
		IBAA_memory[i] = i;
	}
	IBAA_aa = IBAA_bb = 0;
	IBAA_counter = 0;
	IBAA_byte_index = sizeof(IBAA_results);	/* force IBAA_Call() */
}

/*
 * PRIVATE: Call IBAA to produce 256 32-bit u4 results.
 */
static void
IBAA_Call (void)
{
	IBAA(IBAA_memory, IBAA_results, &IBAA_aa, &IBAA_bb, &IBAA_counter);
	IBAA_byte_index = 0;
}

/*
 * Add a 32-bit u4 seed value into IBAAs memory.  Mix the low 4 bits
 * with 4 bits of PNG data to reduce the possibility of a seeding-based
 * attack.
 */
static void
IBAA_Seed (const u_int32_t val)
{
	static int memIndex;
	u4 *iptr;

	iptr = &IBAA_memory[memIndex & MASK];
	*iptr = ((*iptr << 3) | (*iptr >> 29)) + (val ^ (IBAA_Byte() & 15));
	++memIndex;
}

/*
 * Extract a byte from IBAAs 256 32-bit u4 results array.
 *
 * NOTE: This code is designed to prevent MP races from taking
 * IBAA_byte_index out of bounds.
 */
static u_char
IBAA_Byte(void)
{
	u_char result;
	int index;

	index = IBAA_byte_index;
	if (index == sizeof(IBAA_results)) {
		IBAA_Call();
		index = 0;
	}
	result = ((u_char *)IBAA_results)[index];
	IBAA_byte_index = index + 1;
	return result;
}

/*------------------------------ IBAA ----------------------------------*/


/*------------------------------- L15 ----------------------------------*/

/*
 * IMPORTANT NOTE: LByteType must be exactly 8-bits in size or this software
 * will not function correctly.
 */
typedef unsigned char	LByteType;

#define	L15_STATE_SIZE	256

static LByteType	L15_x, L15_y;
static LByteType	L15_start_x;
static LByteType	L15_state[L15_STATE_SIZE];

/*
 * PRIVATE FUNCS:
 */

static void		L15_Swap(const LByteType pos1, const LByteType pos2);
static void		L15_InitState(void);
static void		L15_KSA(const LByteType * const key,
				const size_t keyLen);
static void		L15_Discard(const LByteType numCalls);

/*
 * PUBLIC INTERFACE:
 */
static void		L15(const LByteType * const key, const size_t keyLen);
static LByteType	L15_Byte(void);
static void		L15_Vector(const LByteType * const key,
				const size_t keyLen);

static __inline void
L15_Swap(const LByteType pos1, const LByteType pos2)
{
	const LByteType	save1 = L15_state[pos1];

	L15_state[pos1] = L15_state[pos2];
	L15_state[pos2] = save1;
}

static void
L15_InitState (void)
{
	size_t i;
	for (i = 0; i < L15_STATE_SIZE; ++i)
		L15_state[i] = i;
}

#define  L_SCHEDULE(xx)						\
								\
for (i = 0; i < L15_STATE_SIZE; ++i) {				\
    L15_Swap(i, (stateIndex += (L15_state[i] + (xx))));		\
}

static void
L15_KSA (const LByteType * const key, const size_t keyLen)
{
	size_t	i, keyIndex;
	LByteType stateIndex = 0;

	L_SCHEDULE(keyLen);
	for (keyIndex = 0; keyIndex < keyLen; ++keyIndex) {
		L_SCHEDULE(key[keyIndex]);
	}
}

static void
L15_Discard(const LByteType numCalls)
{
	LByteType i;
	for (i = 0; i < numCalls; ++i) {
		(void)L15_Byte();
	}
}


/*
 * PUBLIC INTERFACE:
 */
static void
L15(const LByteType * const key, const size_t keyLen)
{
	L15_x = L15_start_x = 0;
	L15_y = L15_STATE_SIZE - 1;
	L15_InitState();
	L15_KSA(key, keyLen);
	L15_Discard(L15_Byte());
}

static LByteType
L15_Byte(void)
{
	LByteType z;

	L15_Swap(L15_state[L15_x], L15_y);
	z = (L15_state [L15_x++] + L15_state[L15_y--]);
	if (L15_x == L15_start_x) {
		--L15_y;
	}
	return (L15_state[z]);
}

static void
L15_Vector (const LByteType * const key, const size_t keyLen)
{
	L15_KSA(key, keyLen);
}

/*------------------------------- L15 ----------------------------------*/

/************************************************************************
 *				KERNEL INTERFACE			*
 ************************************************************************
 *
 * By Robin J Carey and Matthew Dillon.
 */

static int rand_thread_signal = 1;
static void NANOUP_EVENT(void);
static thread_t rand_td;
static struct spinlock rand_spin;

static int nrandevents;
SYSCTL_INT(_kern, OID_AUTO, nrandevents, CTLFLAG_RD, &nrandevents, 0, "");
static int seedenable;
SYSCTL_INT(_kern, OID_AUTO, seedenable, CTLFLAG_RW, &seedenable, 0, "");

/*
 * Called from early boot
 */
void
rand_initialize(void)
{
	struct timespec	now;
	int i;

	spin_init(&rand_spin);

	/* Initialize IBAA. */
	IBAA_Init();

	/* Initialize L15. */
	nanouptime(&now);
	L15((const LByteType *)&now.tv_nsec, sizeof(now.tv_nsec));
	for (i = 0; i < (SIZE / 2); ++i) {
		nanotime(&now);
		IBAA_Seed(now.tv_nsec);
		L15_Vector((const LByteType *)&now.tv_nsec,
			   sizeof(now.tv_nsec));
		nanouptime(&now);
		IBAA_Seed(now.tv_nsec);
		L15_Vector((const LByteType *)&now.tv_nsec,
			   sizeof(now.tv_nsec));
	}

	/*
	 * Warm up the generator to get rid of weak initial states.
	 */
	for (i = 0; i < 10; ++i)
		IBAA_Call();
}

/*
 * Keyboard events
 */
void
add_keyboard_randomness(u_char scancode)
{
	spin_lock(&rand_spin);
	L15_Vector((const LByteType *) &scancode, sizeof (scancode));
	spin_unlock(&rand_spin);
	add_interrupt_randomness(0);
}

/*
 * Interrupt events.  This is SMP safe and allowed to race.
 */
void
add_interrupt_randomness(int intr)
{
	if (rand_thread_signal == 0) {
		rand_thread_signal = 1;
		lwkt_schedule(rand_td);
	}
}

/*
 * True random number source
 */
void
add_true_randomness(int val)
{
	spin_lock(&rand_spin);
	IBAA_Seed(val);
	L15_Vector((const LByteType *) &val, sizeof (val));
	++nrandevents;
	spin_unlock(&rand_spin);
}

int
add_buffer_randomness(const char *buf, int bytes)
{
	int error;
	int i;

	if (seedenable && securelevel <= 0) {
		while (bytes >= sizeof(int)) {
			add_true_randomness(*(const int *)buf);
			buf += sizeof(int);
			bytes -= sizeof(int);
		}
		error = 0;

		/*
		 * Warm up the generator to get rid of weak initial states.
		 */
		for (i = 0; i < 10; ++i)
			IBAA_Call();
	} else {
		error = EPERM;
	}
	return (error);
}

/*
 * Poll (always succeeds)
 */
int
random_poll(cdev_t dev, int events)
{
	int revents = 0;

	if (events & (POLLIN | POLLRDNORM))
		revents |= events & (POLLIN | POLLRDNORM);
	if (events & (POLLOUT | POLLWRNORM))
		revents |= events & (POLLOUT | POLLWRNORM);

	return (revents);
}

/*
 * Kqueue filter (always succeeds)
 */
int
random_filter_read(struct knote *kn, long hint)
{
	return (1);
}

/*
 * Heavy weight random number generator.  May return less then the
 * requested number of bytes.
 */
u_int
read_random(void *buf, u_int nbytes)
{
	u_int i;

	spin_lock(&rand_spin);
	for (i = 0; i < nbytes; ++i)
		((u_char *)buf)[i] = IBAA_Byte();
	spin_unlock(&rand_spin);
	add_interrupt_randomness(0);
	return(i);
}

/*
 * Lightweight random number generator.  Must return requested number of
 * bytes.
 */
u_int
read_random_unlimited(void *buf, u_int nbytes)
{
	u_int i;

	spin_lock(&rand_spin);
	for (i = 0; i < nbytes; ++i)
		((u_char *)buf)[i] = L15_Byte();
	spin_unlock(&rand_spin);
	add_interrupt_randomness(0);
	return (i);
}

/*
 * Random number generator helper thread.  This limits code overhead from
 * high frequency events by delaying the clearing of rand_thread_signal.
 *
 * MPSAFE thread
 */
static
void
rand_thread_loop(void *dummy)
{
	int count;

	for (;;) {
		NANOUP_EVENT ();
		spin_lock(&rand_spin);
		count = (int)(L15_Byte() * hz / (256 * 10) + hz / 10 + 1);
		spin_unlock(&rand_spin);
		tsleep(rand_td, 0, "rwait", count);
		crit_enter();
		lwkt_deschedule_self(rand_td);
		cpu_sfence();
		rand_thread_signal = 0;
		crit_exit();
		lwkt_switch();
	}
}

static
void
rand_thread_init(void)
{
	lwkt_create(rand_thread_loop, NULL, &rand_td, NULL, 0, 0, "random");
}

SYSINIT(rand, SI_SUB_HELPER_THREADS, SI_ORDER_ANY, rand_thread_init, 0);

/*
 * Time-buffered event time-stamping. This is necessary to cutoff higher
 * event frequencies, e.g. an interrupt occuring at 25Hz. In such cases
 * the CPU is being chewed and the timestamps are skewed (minimal variation).
 * Use a nano-second time-delay to limit how many times an Event can occur
 * in one second; <= 5Hz. Note that this doesn't prevent time-stamp skewing.
 * This implementation randmoises the time-delay between events, which adds
 * a layer of security/unpredictability with regard to read-events (a user
 * controlled input).
 *
 * Note: now.tv_nsec should range [ 0 - 1000,000,000 ].
 * Note: "ACCUM" is a security measure (result = capped-unknown + unknown),
 *       and also produces an uncapped (>=32-bit) value.
 */
static void
NANOUP_EVENT(void)
{
	static struct timespec	ACCUM = { 0, 0 };
	static struct timespec	NEXT  = { 0, 0 };
	struct timespec		now;

	nanouptime(&now);
	spin_lock(&rand_spin);
	if ((now.tv_nsec > NEXT.tv_nsec) || (now.tv_sec != NEXT.tv_sec)) {
		/*
		 * Randomised time-delay: 200e6 - 350e6 ns; 5 - 2.86 Hz.
		 */
		unsigned long one_mil;
		unsigned long timeDelay;

		one_mil = 1000000UL;	/* 0.001 s */
		timeDelay = (one_mil * 200) +
			    (((unsigned long)ACCUM.tv_nsec % 151) * one_mil);
		NEXT.tv_nsec = now.tv_nsec + timeDelay;
		NEXT.tv_sec = now.tv_sec;
		ACCUM.tv_nsec += now.tv_nsec;

		/*
		 * The TSC, if present, generally has an even higher
		 * resolution.  Integrate a portion of it into our seed.
		 */
		if (tsc_present)
			ACCUM.tv_nsec ^= rdtsc() & 255;

		IBAA_Seed(ACCUM.tv_nsec);
		L15_Vector((const LByteType *)&ACCUM.tv_nsec,
			   sizeof(ACCUM.tv_nsec));
		++nrandevents;
	}
	spin_unlock(&rand_spin);
}