Message-ID: <6799073.kogoi3ZHUp@myon.chronox.de>
Date:	Tue, 04 Feb 2014 13:39:16 +0100
From:	Stephan Mueller <smueller@...onox.de>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Jörn Engel <joern@...fs.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	macro@...ux-mips.org, ralf@...ux-mips.org, dave.taht@...il.com,
	blogic@...nwrt.org, andrewmcgr@...il.com, geert@...ux-m68k.org,
	tg@...bsd.de, sandyinchina@...il.com
Subject: [PATCH 1/5] CPU Jitter RNG


The jitterentropy-base.c file implements the CPU Jitter RNG as
documented at http://www.chronox.de/jent/doc/CPU-Jitter-NPTRNG.html.
The associated header file makes the RNG available to the remainder
of the kernel.

The CPU Jitter RNG delivers entropy on demand. Therefore, it only
causes system overhead when entropy is requested. The RNG delivers
entropy even at early boot time, sufficient to satisfy the earliest
users of random numbers.

The RNG is based on a high-resolution timer like the x86 RDTSC
instruction. The generated random bit stream does not show any
statistical significant patterns. The output of the random number
generator passes all standard statistical tools analyzing the quality
of a random data stream.

The documentation discusses the noise sources, including quantitative
analyses in chapter 6 of the aforementioned document.

Testing of the code on a large number of CPUs and operating systems
is performed as outlined in chapter 5 and the appendix of the mentioned
document.

Signed-off-by: Stephan Mueller <smueller@...onox.de>
---
 drivers/char/jitterentropy-base.c | 665 ++++++++++++++++++++++++++++++++++++++
 include/linux/jitterentropy.h     | 164 ++++++++++
 2 files changed, 829 insertions(+)
 create mode 100644 drivers/char/jitterentropy-base.c
 create mode 100644 include/linux/jitterentropy.h

diff --git a/drivers/char/jitterentropy-base.c b/drivers/char/jitterentropy-base.c
new file mode 100644
index 0000000..950877c
--- /dev/null
+++ b/drivers/char/jitterentropy-base.c
@@ -0,0 +1,665 @@
+/*
+ * Non-physical true random number generator based on timing jitter.
+ *
+ * Copyright Stephan Mueller <smueller@...onox.de>, 2014
+ *
+ * Design
+ * ======
+ *
+ * See documentation in http://www.chronox.de.
+ *
+ * License
+ * =======
+ *
+ * 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, and the entire permission notice in its entirety,
+ *    including the disclaimer of warranties.
+ * 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.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior
+ *    written permission.
+ *
+ * ALTERNATIVELY, this product may be distributed under the terms of
+ * the GNU General Public License, in which case the provisions of the GPL are
+ * required INSTEAD OF the above restrictions.  (This clause is
+ * necessary due to a potential bad interaction between the GPL and
+ * the restrictions contained in a BSD-style copyright.)
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
+ * WHICH ARE HEREBY 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 NOT ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ */
+
+#include <linux/jitterentropy.h>
+
+#ifdef __OPTIMIZE__
+ #error "The CPU Jitter random number generator must not be compiled with optimizations. See documentation. Use the compiler switch -O0 for compiling jitterentropy-base.c."
+#endif
+
+/*
+ * Update of the loop count used for the next round of
+ * an entropy collection.
+ *
+ * Input:
+ * @bits is the number of low bits of the timer to consider
+ * @min is the number of bits we shift the timer value to the right at
+ * 	the end to make sure we have a guaranteed minimum value
+ *
+ * Return:
+ * Newly calculated loop counter
+ */
+static unsigned int jent_loop_shuffle(unsigned int bits, unsigned int min)
+{
+	__u64 time = 0;
+	jent_get_nstime(&time);
+
+	/* we take the low bit of the timer which implies any
+	 * value between 0 and 2^(bits + 1) - 1 */
+	time = time << (64 - bits);
+	time = time >> (64 - bits);
+
+	/* We add a lower boundary value to ensure we have a minimum
+	 * RNG loop count. */
+	return (time + (1<<min));
+}
+
+static unsigned int jent_loop_fold_shuffle(void)
+{
+/* Number of low bits of timer that are used to determine the next
+ * folding loop counter */
+#define MAX_FOLD_LOOP_BIT 4
+#define MIN_FOLD_LOOP_BIT 0
+	return jent_loop_shuffle(MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT);
+}
+ 
+/***************************************************************************
+ * Noise sources
+ ***************************************************************************/
+
+/*
+ * CPU Jitter noise source -- this is the noise source based on the CPU
+ * 			      execution time jitter
+ *
+ * This function folds the time into TIME_ENTROPY_BITS bits by iterating
+ * through the DATA_SIZE_BITS bit time value as follows: assume our time value
+ * is 0xaaabbbcccddd, TIME_ENTROPY_BITS is 3
+ * 1st loop, 1st shift generates 0xddd000000000
+ * 1st loop, 2nd shift generates 0x000000000ddd
+ * 2nd loop, 1st shift generates 0xcccddd000000
+ * 2nd loop, 2nd shift generates 0x000000000ccc
+ * 3rd loop, 1st shift generates 0xbbbcccddd000
+ * 3rd loop, 2nd shift generates 0x000000000bbb
+ * 4th loop, 1st shift generates 0xaaabbbcccddd
+ * 4th loop, 2nd shift generates 0x000000000aaa
+ * Now, the values at the end of the 2nd shifts are XORed together.
+ * Note, the loop only performs (DATA_SIZE_BITS / TIME_SIZE) iterations. If the
+ * division is not complete, it takes the lower bound (e.g. 64 / 3 would result
+ * 21). Thus, the upmost bits that are less than TIME_SIZE in size (which are
+ * assumed to have no entropy to begin with) are discarded.
+ *
+ * The code is deliberately inefficient and shall stay that way. This function
+ * is the root cause why the code shall be compiled without optimization. This
+ * function not only acts as folding operation, but this function's execution
+ * is used to measure the CPU execution time jitter. Any change to the loop in
+ * this function implies that careful retesting must be done.
+ *
+ * Input:
+ * @time time stamp to be folded
+ * @loop_cnt if a value not equal to 0 is set, use the given value as number of
+ *	     loops to perform the folding
+ *
+ * Output:
+ * @folded result of folding operation
+ *
+ * Return:
+ * Number of loops the folding operation is performed
+ */
+static unsigned int jent_fold_time(__u64 time, __u64 *folded,
+				   unsigned int loop_cnt)
+{
+	int i, j;
+	__u64 new = 0;
+	unsigned int fold_loop_cnt = jent_loop_fold_shuffle();
+
+	/* testing purposes -- allow test app to set the counter, not
+	 * needed during runtime */
+	if(loop_cnt)
+		fold_loop_cnt = loop_cnt;
+	for(j = 0; j < fold_loop_cnt; j++)
+	{
+		new = 0;
+		for(i = 1; (DATA_SIZE_BITS / TIME_ENTROPY_BITS) >= i; i++)
+		{
+			__u64 tmp = time << (DATA_SIZE_BITS - (TIME_ENTROPY_BITS * i));
+			tmp = tmp >> (DATA_SIZE_BITS - TIME_ENTROPY_BITS);
+			new ^= tmp;
+		}
+	}
+	*folded = new;
+	return fold_loop_cnt;
+}
+
+/* 
+ * Memory Access noise source -- this is a noise source based on variations in
+ * 				 memory access times
+ *
+ * This function performs memory accesses which will add to the timing
+ * variations due to an unknown amount of CPU wait states that need to be
+ * added when accessing memory. The memory size should be larger than the L1
+ * caches as outlined in the documentation and the associated testing.
+ *
+ * The L1 cache has a very high bandwidth, albeit its access rate is  usually
+ * slower than accessing CPU registers. Therefore, L1 accesses only add minimal
+ * variations as the CPU has hardly to wait. Starting with L2, significant
+ * variations are added because L2 typically does not belong to the CPU any more
+ * and therefore a wider range of CPU wait states is necessary for accesses.
+ * L3 and real memory accesses have even a wider range of wait states. However,
+ * to reliably access either L3 or memory, the ec->mem memory must be quite large
+ * which is usually not desirable.
+ *
+ * Input:
+ * @ec Reference to the entropy collector with the memory access data -- if
+ *     the reference to the memory block to be accessed is NULL, this noise
+ *     source is disabled
+ *
+ * Output:
+ * nothing -- the state of the memory access data in @ec is updated
+ *
+ * Return:
+ * Number of memory access operations
+ */
+static unsigned int jent_memaccess(struct rand_data *ec)
+{
+	unsigned char *tmpval = NULL;
+	unsigned long wrap = 0;
+	unsigned int i = 0;
+
+	if(NULL == ec || NULL == ec->mem)
+		return 0;
+
+	wrap = ec->memblocksize * ec->memblocks - 1;
+
+	for(i = 0; i < ec->memaccessloops; i++)
+	{
+		tmpval = ec->mem + ec->memlocation;
+		/* memory access: just add 1 to one byte,
+		 * wrap at 255 -- memory access implies read
+		 * from and write to memory location */
+		*tmpval = (*tmpval + 1) & 0xff;
+		/* Addition of memblocksize - 1 to pointer
+		 * with wrap around logic to ensure that every
+		 * memory location is hit evenly
+		 */
+		ec->memlocation = ec->memlocation + ec->memblocksize - 1;
+		if(ec->memlocation > wrap)
+			ec->memlocation -= wrap;
+	}
+
+	return i;
+}
+
+/***************************************************************************
+ * Start of entropy processing logic
+ ***************************************************************************/
+
+/*
+ * This is the heart of the entropy generation: calculate time deltas and
+ * use the CPU jitter in the time deltas. The jitter is folded into one
+ * bit. You can call this function the "random bit generator" as it
+ * produces one random bit per invocation.
+ *
+ * WARNING: ensure that ->prev_time is primed before using the output
+ * 	    of this function! This can be done by calling this function
+ * 	    and not using its result.
+ *
+ * Input:
+ * @entropy_collector Reference to entropy collector
+ *
+ * Return:
+ * One random bit
+ *
+ */
+static __u64 jent_measure_jitter(struct rand_data *entropy_collector)
+{
+	__u64 time = 0;
+	__u64 delta = 0;
+	__u64 data = 0;
+
+	/* Invoke one noise source before time measurement to add variations */
+	jent_memaccess(entropy_collector);
+
+	/* Get time stamp and calculate time delta to previous invocation 
+	 * to measure the timing variations with the previous invocation */
+	jent_get_nstime(&time);
+	delta = time - entropy_collector->prev_time;
+	entropy_collector->prev_time = time;
+
+	/* Now call the next noise sources which also folds the data */
+	jent_fold_time(delta, &data, 0);
+
+	return data;
+}
+
+/*
+ * Von Neuman unbias as explained in RFC 4086 section 4.2. As shown in the
+ * documentation of that RNG, the bits from jent_measure_jitter are considered
+ * independent which implies that the Von Neuman unbias operation is applicable.
+ * A proof of the Von-Neumann unbias operation to remove skews is given in the
+ * document "A proposal for: Functionality classes for random number
+ * generators", version 2.0 by Werner Schindler, section 5.4.1.
+ *
+ * Input:
+ * @entropy_collector Reference to entropy collector
+ *
+ * Return:
+ * One random bit
+ */
+static __u64 jent_unbiased_bit(struct rand_data *entropy_collector)
+{
+	if(1 == entropy_collector->disable_unbias)
+		return (jent_measure_jitter(entropy_collector));
+	do
+	{
+		__u64 a = jent_measure_jitter(entropy_collector);
+		__u64 b = jent_measure_jitter(entropy_collector);
+		if(a == b)
+			continue;
+		if(1 == a)
+			return 1;
+		else
+			return 0;
+	} while(1);
+}
+
+/*
+ * Shuffle the pool a bit by mixing some value with a bijective function (XOR)
+ * into the pool.
+ *
+ * The function generates a mixer value that depends on the bits set and the
+ * location of the set bits in the random number generated by the entropy
+ * source. Therefore, based on the generated random number, this mixer value
+ * can have 2**64 different values. That mixer value is initialized with the
+ * first two SHA-1 constants. After obtaining the mixer value, it is XORed into
+ * the random number.
+ *
+ * The mixer value is not assumed to contain any entropy. But due to the XOR
+ * operation, it can also not destroy any entropy present in the entropy pool.
+ *
+ * Input:
+ * @entropy_collector Reference to entropy collector
+ *
+ * Output:
+ * nothing
+ */
+static void jent_stir_pool(struct rand_data *entropy_collector)
+{
+	/* to shut up GCC on 32 bit, we have to initialize the 64 variable
+	 * with two 32 bit variables */
+	union c {
+		__u64 u64;
+		__u32 u32[2];
+	};
+	/* This constant is derived from the first two 32 bit initialization
+	 * vectors of SHA-1 as defined in FIPS 180-4 section 5.3.1 */
+	union c constant;
+	/* The start value of the mixer variable is derived from the third
+	 * and fourth 32 bit initialization vector of SHA-1 as defined in
+	 * FIPS 180-4 section 5.3.1 */
+	union c mixer;
+	int i = 0;
+
+	/* Store the SHA-1 constants in reverse order to make up the 64 bit
+	 * value -- this applies to a little endian system, on a big endian
+	 * system, it reverses as expected. But this really does not matter
+	 * as we do not rely on the specific numbers. We just pick the SHA-1
+	 * constants as they have a good mix of bit set and unset. */
+	constant.u32[1] = 0x67452301;
+	constant.u32[0] = 0xefcdab89;
+	mixer.u32[1] = 0x98badcfe;
+	mixer.u32[0] = 0x10325476;
+
+	for(i = 0; i < DATA_SIZE_BITS; i++)
+	{
+		/* get the i-th bit of the input random number and only XOR
+		 * the constant into the mixer value when that bit is set */
+		if((entropy_collector->data >> i) & 0x0000000000000001)
+			mixer.u64 ^= constant.u64;
+		mixer.u64 = rol64(mixer.u64, 1);
+	}
+	entropy_collector->data ^= mixer.u64;
+}
+
+/*
+ * Generator of one 64 bit random number
+ * Function fills rand_data->data
+ *
+ * Input:
+ * @entropy_collector Reference to entropy collector
+ *
+ * Return:
+ * Number of loops the entropy collection is performed.
+ */
+static void jent_gen_entropy(struct rand_data *entropy_collector)
+{
+	unsigned int k;
+
+	/* number of loops for the entropy collection depends on the size of
+	 * the random number and the size of the folded value. We want to
+	 * ensure that we pass over each bit of the random value once with the
+	 * folded value.  E.g. if we have a random value of 64 bits and 2 bits
+	 * of folded size, we need 32 entropy collection loops. If the random
+	 * value size is not divisible by the folded value size, we have as
+	 * many loops to cover each random number value bit at least once. E.g.
+	 * 64 bits random value size and the folded value is 3 bits, we need 22
+	 * loops to cover the 64 bits at least once. */
+	/* We multiply the loop value with ->osr to obtain the oversampling
+	 * rate requested by the caller */
+	for (k = 0;
+	     k < ((((DATA_SIZE_BITS - 1) / TIME_ENTROPY_BITS) + 1) *
+		  entropy_collector->osr);
+	     k++)
+	{
+		__u64 data = 0;
+		/* priming of the ->prev_time value in first loop iteration */
+		if(!k)
+			jent_measure_jitter(entropy_collector);
+
+		data = jent_unbiased_bit(entropy_collector);
+		entropy_collector->data ^= data;
+		entropy_collector->data = rol64(entropy_collector->data,
+						TIME_ENTROPY_BITS);
+	}
+	if(entropy_collector->stir)
+		jent_stir_pool(entropy_collector);
+}
+
+/* the continuous test required by FIPS 140-2 -- the function automatically
+ * primes the test if needed.
+ *
+ * Return:
+ * 0 if FIPS test passed
+ * < 0 if FIPS test failed
+ */
+static int jent_fips_test(struct rand_data *entropy_collector)
+{
+	if(!jent_fips_enabled())
+		return 0;
+
+	/* shall we somehow allow the caller to reset that? Probably
+	 * not, because the caller can de-allocate the entropy collector
+	 * instance and set up a new one. */
+	if(entropy_collector->fips_fail)
+		return -1;
+
+	/* prime the FIPS test */
+	if(!entropy_collector->old_data)
+	{
+		entropy_collector->old_data = entropy_collector->data;
+		jent_gen_entropy(entropy_collector);
+	}
+
+	if(entropy_collector->data == entropy_collector->old_data)
+	{
+		entropy_collector->fips_fail = 1;
+		return -1;
+	}
+
+	entropy_collector->old_data = entropy_collector->data;
+
+	return 0;
+}
+
+/*
+ * Entry function: Obtain entropy for the caller.
+ *
+ * This function invokes the entropy gathering logic as often to generate
+ * as many bytes as requested by the caller. The entropy gathering logic
+ * creates 64 bit per invocation.
+ *
+ * This function truncates the last 64 bit entropy value output to the exact
+ * size specified by the caller.
+ *
+ * @data: pointer to buffer for storing random data -- buffer must already
+ *        exist
+ * @len: size of the buffer, specifying also the requested number of random
+ *       in bytes
+ *
+ * return: number of bytes returned when request is fulfilled or an error
+ *
+ * The following error codes can occur:
+ * 	-1	FIPS 140-2 continuous self test failed
+ * 	-2	entropy_collector is NULL
+ */
+int jent_read_entropy(struct rand_data *entropy_collector,
+		      char *data, size_t len)
+{
+	char *p = data;
+	int ret = 0;
+	size_t orig_len = len;
+
+	if(NULL == entropy_collector)
+		return -2;
+
+	while (0 < len)
+	{
+		size_t tocopy;
+		jent_gen_entropy(entropy_collector);
+		ret = jent_fips_test(entropy_collector);
+		if(0 > ret)
+			return ret;
+
+		if((DATA_SIZE_BITS / 8) < len)
+			tocopy = (DATA_SIZE_BITS / 8);
+		else
+			tocopy = len;
+		memcpy(p, &entropy_collector->data, tocopy);
+
+		len -= tocopy;
+		p += tocopy;
+	}
+
+	/* To be on the safe side, we generate one more round of entropy
+	 * which we do not give out to the caller. That round shall ensure
+	 * that in case the calling application crashes, memory dumps, pages
+	 * out, or due to the CPU Jitter RNG lingering in memory for long
+	 * time without being moved and an attacker cracks the application,
+	 * all he reads in the entropy pool is a value that is NEVER EVER
+	 * being used for anything. Thus, he does NOT see the previous value
+	 * that was returned to the caller for cryptographic purposes.
+	 */
+	/* If we use secured memory, do not use that precaution as the secure
+	 * memory protects the entropy pool. Moreover, note that using this
+	 * call reduces the speed of the RNG by up to half */
+#ifndef CONFIG_CRYPTO_CPU_JITTERENTROPY_SECURE_MEMORY
+	jent_gen_entropy(entropy_collector);
+#endif
+
+	return orig_len;
+}
+
+/***************************************************************************
+ * Initialization logic
+ ***************************************************************************/
+
+struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
+					       unsigned int flags)
+{
+	struct rand_data *entropy_collector;
+
+	entropy_collector = jent_zalloc(sizeof(struct rand_data));
+	if(NULL == entropy_collector)
+		return NULL;
+
+	if(!(flags & JENT_DISABLE_MEMORY_ACCESS))
+	{
+		/* Allocate memory for adding variations based on memory
+		 * access
+		 */
+		entropy_collector->mem = 
+			(unsigned char *)jent_zalloc(JENT_MEMORY_SIZE);
+		if(NULL == entropy_collector->mem)
+		{
+			jent_zfree(entropy_collector, sizeof(struct rand_data));
+			return NULL;
+		}
+		entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE;
+		entropy_collector->memblocks = JENT_MEMORY_BLOCKS;
+		entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS;
+	}
+
+	/* verify and set the oversampling rate */
+	if(0 == osr)
+		osr = 1; /* minimum sampling rate is 1 */
+	entropy_collector->osr = osr;
+
+	entropy_collector->stir = 1;
+	if(flags & JENT_DISABLE_STIR)
+		entropy_collector->stir = 0;
+	if(flags & JENT_DISABLE_UNBIAS)
+		entropy_collector->disable_unbias = 1;
+
+	/* fill the data pad with non-zero values */
+	jent_gen_entropy(entropy_collector);
+
+	/* initialize the FIPS 140-2 continuous test if needed */
+	jent_fips_test(entropy_collector);
+
+	return entropy_collector;
+}
+
+void jent_entropy_collector_free(struct rand_data *entropy_collector)
+{
+	
+	jent_zfree(entropy_collector->mem, JENT_MEMORY_SIZE);
+	jent_zfree(entropy_collector, sizeof(struct rand_data));
+	entropy_collector = NULL;
+}
+
+int jent_entropy_init(void)
+{
+	int i;
+	__u64 delta_sum = 0;
+	__u64 old_delta = 0;
+	int time_backwards = 0;
+	int count_var = 0;
+	int count_mod = 0;
+
+	/* We could perform statistical tests here, but the problem is
+	 * that we only have a few loop counts to do testing. These
+	 * loop counts may show some slight skew and we produce
+	 * false positives.
+	 *
+	 * Moreover, only old systems show potentially problematic
+	 * jitter entropy that could potentially be caught here. But
+	 * the RNG is intended for hardware that is available or widely
+	 * used, but not old systems that are long out of favor. Thus,
+	 * no statistical tests.
+	 */
+
+	/* We could add a check for system capabilities such as clock_getres or
+	 * check for CONFIG_X86_TSC, but it does not make much sense as the
+	 * following sanity checks verify that we have a high-resolution
+	 * timer. */
+	/* TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
+	 * definitely too little. */
+#define TESTLOOPCOUNT 300
+#define CLEARCACHE 100
+	for(i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++)
+	{
+		__u64 time = 0;
+		__u64 time2 = 0;
+		__u64 folded = 0;
+		__u64 delta = 0;
+
+		jent_get_nstime(&time);
+		jent_fold_time(time, &folded, 1<<MIN_FOLD_LOOP_BIT);
+		jent_get_nstime(&time2);
+
+		/* test whether timer works */
+		if(!time || !time2)
+			return ENOTIME;
+		delta = time2 - time;
+		/* test whether timer is fine grained enough to provide
+		 * delta even when called shortly after each other -- this
+		 * implies that we also have a high resolution timer */
+		if(!delta)
+			return ECOARSETIME;
+		/* TIME_ENTROPY_BITS states the absolute minimum entropy we
+		 * assume the time variances have. As we also check for
+		 * delta of deltas, we ensure that there is a varying delta
+		 * value, preventing identical time spans */
+		if(TIME_ENTROPY_BITS > delta)
+			return EMINVARIATION;
+
+		/* up to here we did not modify any variable that will be
+		 * evaluated later, but we already performed some work. Thus we
+		 * already have had an impact on the caches, branch prediction,
+		 * etc. with the goal to clear it to get the worst case
+		 * measurements. */
+		if(CLEARCACHE > i)
+			continue;
+
+		/* test whether we have an increasing timer */
+		if(!(time2 > time))
+			time_backwards++;
+
+		if(!(delta % 100))
+			count_mod++;
+
+		/* ensure that we have a varying delta timer which is necessary
+		 * for the calculation of entropy -- perform this check
+		 * only after the first loop is executed as we need to prime
+		 * the old_data value */
+		if(i)
+		{
+			if(delta != old_delta)
+				count_var++;
+			if(delta > old_delta)
+				delta_sum += (delta - old_delta);
+			else
+				delta_sum += (old_delta - delta);
+		}
+		old_delta = delta;
+
+	}
+
+	/* we allow up to three times the time running backwards.
+	 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus,
+	 * if such an operation just happens to interfere with our test, it
+	 * should not fail. The value of 3 should cover the NTP case being
+	 * performed during our test run. */
+	if(3 < time_backwards)
+		return ENOMONOTONIC;
+	/* Error if the time variances are always identical */
+	if(!delta_sum)
+		return EVARVAR;
+
+	/* Variations of deltas of time must on average be larger
+	 * than TIME_ENTROPY_BITS to ensure the entropy estimation
+	 * implied with TIME_ENTROPY_BITS is preserved */
+	if(!(delta_sum / TESTLOOPCOUNT) > TIME_ENTROPY_BITS)
+		return EMINVARVAR;
+
+	/* Ensure that we have variations in the time stamp below 10 for at least
+	 * 10% of all checks -- on some platforms, the counter increments in
+	 * multiples of 100, but not always */
+	if((TESTLOOPCOUNT/10 * 9) < count_mod)
+		return ECOARSETIME;
+
+	return 0;
+}
+
diff --git a/include/linux/jitterentropy.h b/include/linux/jitterentropy.h
new file mode 100644
index 0000000..5953e2f
--- /dev/null
+++ b/include/linux/jitterentropy.h
@@ -0,0 +1,164 @@
+/*
+ * Non-physical true random number generator based on timing jitter.
+ *
+ * Copyright Stephan Mueller <smueller@...onox.de>, 2014
+ *
+ * License
+ * =======
+ *
+ * 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, and the entire permission notice in its entirety,
+ *    including the disclaimer of warranties.
+ * 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.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior
+ *    written permission.
+ *
+ * ALTERNATIVELY, this product may be distributed under the terms of
+ * the GNU General Public License, in which case the provisions of the GPL are
+ * required INSTEAD OF the above restrictions.  (This clause is
+ * necessary due to a potential bad interaction between the GPL and
+ * the restrictions contained in a BSD-style copyright.)
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
+ * WHICH ARE HEREBY 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 NOT ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ */
+
+#ifndef _JITTERENTROPY_H
+#define _JITTERENTROPY_H
+
+#include <linux/slab.h> /* needed for kzalloc */
+#include <linux/module.h> /* needed for random_get_entropy */
+#include <linux/fips.h> /* needed for fips_enabled */
+#include <linux/time.h> /* needed for __getnstimeofday */
+
+static inline void jent_get_nstime(__u64 *out)
+{
+	struct timespec ts;
+	__u64 tmp = 0;
+
+	tmp = random_get_entropy();
+
+	/* If random_get_entropy does not return a value invoke __getnstimeofday
+	 * hoping that there are timers we can work with.
+	 *
+	 * The list of available timers can be obtained from
+	 * /sys/devices/system/clocksource/clocksource0/available_clocksource
+	 * and are registered with clocksource_register()
+	 */
+	if((0 == tmp) &&
+	   (0 == timekeeping_valid_for_hres()) && 
+	   (0 == __getnstimeofday(&ts)))
+	{
+		tmp = ts.tv_sec;
+		tmp = tmp << 32;
+		tmp = tmp | ts.tv_nsec;
+	}
+
+	*out = tmp;
+}
+
+static inline void *jent_zalloc(size_t len)
+{
+	/* We consider kernel memory as secure -- if somebody breaks it,
+	 * the user has much more pressing problems than the state of our
+	 * RNG */
+#define CONFIG_CRYPTO_CPU_JITTERENTROPY_SECURE_MEMORY
+	return kzalloc(len, GFP_KERNEL);
+}
+static inline void jent_zfree(void *ptr, unsigned int len)
+{
+	kzfree(ptr);
+}
+
+static inline int jent_fips_enabled(void)
+{
+	return fips_enabled;
+}
+
+/* The entropy pool */
+struct rand_data
+{
+	/* all data values that are vital to maintain the security
+	 * of the RNG are marked as SENSITIVE. A user must not
+	 * access that information while the RNG executes its loops to
+	 * calculate the next random value. */
+	__u64 data;		/* SENSITIVE Actual random number */
+	__u64 prev_time;	/* SENSITIVE Previous time stamp */
+#define DATA_SIZE_BITS ((sizeof(__u64)) * 8)
+	__u64 old_data;		/* SENSITIVE FIPS continuous test */
+	unsigned int osr;	/* Oversample rate */
+	unsigned int fips_fail:1;	/* FIPS status */
+	unsigned int stir:1;		/* Post-processing stirring */
+	unsigned int disable_unbias:1;	/* Deactivate Von-Neuman unbias */
+#define JENT_MEMORY_BLOCKS 64
+#define JENT_MEMORY_BLOCKSIZE 32
+#define JENT_MEMORY_ACCESSLOOPS 128
+#define JENT_MEMORY_SIZE (JENT_MEMORY_BLOCKS*JENT_MEMORY_BLOCKSIZE)
+	unsigned char *mem;	/* Memory access location with size of
+				 * memblocks * memblocksize */
+	unsigned int memlocation; /* Pointer to byte in *mem */
+	unsigned int memblocks;	/* Number of memory blocks in *mem */
+	unsigned int memblocksize; /* Size of one memory block in bytes */
+	unsigned int memaccessloops; /* Number of memory accesses per random
+				      * bit generation */
+};
+
+/* Flags that can be used to initialize the RNG */
+#define JENT_DISABLE_STIR (1<<0) /* Disable stirring the entropy pool */
+#define JENT_DISABLE_UNBIAS (1<<1) /* Disable Von Neuman unbias */
+#define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more
+					     entropy, saves MEMORY_SIZE RAM for
+					     entropy collector */
+
+/* Number of low bits of the time value that we want to consider */
+#define TIME_ENTROPY_BITS 1
+
+#define DRIVER_NAME     "jitterentropy"
+
+/* -- BEGIN Main interface functions -- */
+
+/* Number of low bits of the time value that we want to consider */
+/* get raw entropy */
+int jent_read_entropy(struct rand_data *entropy_collector,
+		      char *data, size_t len);
+/* initialize an instance of the entropy collector */
+struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
+	       				       unsigned int flags);
+/* clearing of entropy collector */
+void jent_entropy_collector_free(struct rand_data *entropy_collector);
+
+/* initialization of entropy collector */
+int jent_entropy_init(void);
+
+/* -- END of Main interface functions -- */
+
+/* -- BEGIN error codes for init function -- */
+#define ENOTIME  	1 /* Timer service not available */
+#define ECOARSETIME	2 /* Timer too coarse for RNG */
+#define ENOMONOTONIC	3 /* Timer is not monotonic increasing */
+#define EMINVARIATION	4 /* Timer variations too small for RNG */
+#define EVARVAR		5 /* Timer does not produce variations of variations
+			     (2nd derivation of time is zero) */
+#define EMINVARVAR	6 /* Timer variations of variations is too small */
+#define EPROGERR	7 /* Programming error */
+
+/* -- END of statistical test function -- */
+
+#endif /* _JITTERENTROPY_H */
+
-- 
1.8.5.3


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