| /* |
| * Non-physical true random number generator based on timing jitter -- |
| * Jitter RNG standalone code. |
| * |
| * Copyright Stephan Mueller <smueller@chronox.de>, 2015 |
| * |
| * Design |
| * ====== |
| * |
| * See http://www.chronox.de/jent.html |
| * |
| * 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 GPL2 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. |
| */ |
| |
| /* |
| * This Jitterentropy RNG is based on the jitterentropy library |
| * version 1.1.0 provided at http://www.chronox.de/jent.html |
| */ |
| |
| #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.c." |
| #endif |
| |
| typedef unsigned long long __u64; |
| typedef long long __s64; |
| typedef unsigned int __u32; |
| #define NULL ((void *) 0) |
| |
| /* 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 old_data; /* SENSITIVE Previous random number */ |
| __u64 prev_time; /* SENSITIVE Previous time stamp */ |
| #define DATA_SIZE_BITS ((sizeof(__u64)) * 8) |
| __u64 last_delta; /* SENSITIVE stuck test */ |
| __s64 last_delta2; /* SENSITIVE stuck test */ |
| unsigned int stuck:1; /* Time measurement stuck */ |
| unsigned int osr; /* Oversample rate */ |
| 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 the Von-Neuman Unbiaser */ |
| #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more |
| * entropy, saves MEMORY_SIZE RAM for |
| * entropy collector */ |
| |
| /* -- error codes for init function -- */ |
| #define JENT_ENOTIME 1 /* Timer service not available */ |
| #define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */ |
| #define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */ |
| #define JENT_EMINVARIATION 4 /* Timer variations too small for RNG */ |
| #define JENT_EVARVAR 5 /* Timer does not produce variations of |
| * variations (2nd derivation of time is |
| * zero). */ |
| #define JENT_EMINVARVAR 6 /* Timer variations of variations is tooi |
| * small. */ |
| |
| /*************************************************************************** |
| * Helper functions |
| ***************************************************************************/ |
| |
| void jent_get_nstime(__u64 *out); |
| __u64 jent_rol64(__u64 word, unsigned int shift); |
| void *jent_zalloc(unsigned int len); |
| void jent_zfree(void *ptr); |
| int jent_fips_enabled(void); |
| void jent_panic(char *s); |
| void jent_memcpy(void *dest, const void *src, unsigned int n); |
| |
| /** |
| * Update of the loop count used for the next round of |
| * an entropy collection. |
| * |
| * Input: |
| * @ec entropy collector struct -- may be NULL |
| * @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 __u64 jent_loop_shuffle(struct rand_data *ec, |
| unsigned int bits, unsigned int min) |
| { |
| __u64 time = 0; |
| __u64 shuffle = 0; |
| unsigned int i = 0; |
| unsigned int mask = (1<<bits) - 1; |
| |
| jent_get_nstime(&time); |
| /* |
| * mix the current state of the random number into the shuffle |
| * calculation to balance that shuffle a bit more |
| */ |
| if (ec) |
| time ^= ec->data; |
| /* |
| * we fold the time value as much as possible to ensure that as many |
| * bits of the time stamp are included as possible |
| */ |
| for (i = 0; (DATA_SIZE_BITS / bits) > i; i++) { |
| shuffle ^= time & mask; |
| time = time >> bits; |
| } |
| |
| /* |
| * We add a lower boundary value to ensure we have a minimum |
| * RNG loop count. |
| */ |
| return (shuffle + (1<<min)); |
| } |
| |
| /*************************************************************************** |
| * Noise sources |
| ***************************************************************************/ |
| |
| /** |
| * CPU Jitter noise source -- this is the noise source based on the CPU |
| * execution time jitter |
| * |
| * This function folds the time into one bit units by iterating |
| * through the DATA_SIZE_BITS bit time value as follows: assume our time value |
| * is 0xabcd |
| * 1st loop, 1st shift generates 0xd000 |
| * 1st loop, 2nd shift generates 0x000d |
| * 2nd loop, 1st shift generates 0xcd00 |
| * 2nd loop, 2nd shift generates 0x000c |
| * 3rd loop, 1st shift generates 0xbcd0 |
| * 3rd loop, 2nd shift generates 0x000b |
| * 4th loop, 1st shift generates 0xabcd |
| * 4th loop, 2nd shift generates 0x000a |
| * Now, the values at the end of the 2nd shifts are XORed together. |
| * |
| * 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: |
| * @ec entropy collector struct -- may be NULL |
| * @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 __u64 jent_fold_time(struct rand_data *ec, __u64 time, |
| __u64 *folded, __u64 loop_cnt) |
| { |
| unsigned int i; |
| __u64 j = 0; |
| __u64 new = 0; |
| #define MAX_FOLD_LOOP_BIT 4 |
| #define MIN_FOLD_LOOP_BIT 0 |
| __u64 fold_loop_cnt = |
| jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT); |
| |
| /* |
| * 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) >= i; i++) { |
| __u64 tmp = time << (DATA_SIZE_BITS - i); |
| |
| tmp = tmp >> (DATA_SIZE_BITS - 1); |
| 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 |
| * @loop_cnt if a value not equal to 0 is set, use the given value as number of |
| * loops to perform the folding |
| * |
| * @return Number of memory access operations |
| */ |
| static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt) |
| { |
| unsigned char *tmpval = NULL; |
| unsigned int wrap = 0; |
| __u64 i = 0; |
| #define MAX_ACC_LOOP_BIT 7 |
| #define MIN_ACC_LOOP_BIT 0 |
| __u64 acc_loop_cnt = |
| jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); |
| |
| if (NULL == ec || NULL == ec->mem) |
| return 0; |
| wrap = ec->memblocksize * ec->memblocks; |
| |
| /* |
| * testing purposes -- allow test app to set the counter, not |
| * needed during runtime |
| */ |
| if (loop_cnt) |
| acc_loop_cnt = loop_cnt; |
| |
| for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); 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; |
| ec->memlocation = ec->memlocation % wrap; |
| } |
| return i; |
| } |
| |
| /*************************************************************************** |
| * Start of entropy processing logic |
| ***************************************************************************/ |
| |
| /** |
| * Stuck test by checking the: |
| * 1st derivation of the jitter measurement (time delta) |
| * 2nd derivation of the jitter measurement (delta of time deltas) |
| * 3rd derivation of the jitter measurement (delta of delta of time deltas) |
| * |
| * All values must always be non-zero. |
| * |
| * Input: |
| * @ec Reference to entropy collector |
| * @current_delta Jitter time delta |
| * |
| * @return |
| * 0 jitter measurement not stuck (good bit) |
| * 1 jitter measurement stuck (reject bit) |
| */ |
| static void jent_stuck(struct rand_data *ec, __u64 current_delta) |
| { |
| __s64 delta2 = ec->last_delta - current_delta; |
| __s64 delta3 = delta2 - ec->last_delta2; |
| |
| ec->last_delta = current_delta; |
| ec->last_delta2 = delta2; |
| |
| if (!current_delta || !delta2 || !delta3) |
| ec->stuck = 1; |
| } |
| |
| /** |
| * 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 *ec) |
| { |
| __u64 time = 0; |
| __u64 data = 0; |
| __u64 current_delta = 0; |
| |
| /* Invoke one noise source before time measurement to add variations */ |
| jent_memaccess(ec, 0); |
| |
| /* |
| * Get time stamp and calculate time delta to previous |
| * invocation to measure the timing variations |
| */ |
| jent_get_nstime(&time); |
| current_delta = time - ec->prev_time; |
| ec->prev_time = time; |
| |
| /* Now call the next noise sources which also folds the data */ |
| jent_fold_time(ec, current_delta, &data, 0); |
| |
| /* |
| * Check whether we have a stuck measurement. The enforcement |
| * is performed after the stuck value has been mixed into the |
| * entropy pool. |
| */ |
| jent_stuck(ec, current_delta); |
| |
| 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) |
| { |
| 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 |
| */ |
| 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; |
| unsigned 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) & 1) |
| mixer.u64 ^= constant.u64; |
| mixer.u64 = jent_rol64(mixer.u64, 1); |
| } |
| entropy_collector->data ^= mixer.u64; |
| } |
| |
| /** |
| * Generator of one 64 bit random number |
| * Function fills rand_data->data |
| * |
| * Input: |
| * @ec Reference to entropy collector |
| */ |
| static void jent_gen_entropy(struct rand_data *ec) |
| { |
| unsigned int k = 0; |
| |
| /* priming of the ->prev_time value */ |
| jent_measure_jitter(ec); |
| |
| while (1) { |
| __u64 data = 0; |
| |
| if (ec->disable_unbias == 1) |
| data = jent_measure_jitter(ec); |
| else |
| data = jent_unbiased_bit(ec); |
| |
| /* enforcement of the jent_stuck test */ |
| if (ec->stuck) { |
| /* |
| * We only mix in the bit considered not appropriate |
| * without the LSFR. The reason is that if we apply |
| * the LSFR and we do not rotate, the 2nd bit with LSFR |
| * will cancel out the first LSFR application on the |
| * bad bit. |
| * |
| * And we do not rotate as we apply the next bit to the |
| * current bit location again. |
| */ |
| ec->data ^= data; |
| ec->stuck = 0; |
| continue; |
| } |
| |
| /* |
| * Fibonacci LSFR with polynom of |
| * x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is |
| * primitive according to |
| * http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf |
| * (the shift values are the polynom values minus one |
| * due to counting bits from 0 to 63). As the current |
| * position is always the LSB, the polynom only needs |
| * to shift data in from the left without wrap. |
| */ |
| ec->data ^= data; |
| ec->data ^= ((ec->data >> 63) & 1); |
| ec->data ^= ((ec->data >> 60) & 1); |
| ec->data ^= ((ec->data >> 55) & 1); |
| ec->data ^= ((ec->data >> 30) & 1); |
| ec->data ^= ((ec->data >> 27) & 1); |
| ec->data ^= ((ec->data >> 22) & 1); |
| ec->data = jent_rol64(ec->data, 1); |
| |
| /* |
| * We multiply the loop value with ->osr to obtain the |
| * oversampling rate requested by the caller |
| */ |
| if (++k >= (DATA_SIZE_BITS * ec->osr)) |
| break; |
| } |
| if (ec->stir) |
| jent_stir_pool(ec); |
| } |
| |
| /** |
| * 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 void jent_fips_test(struct rand_data *ec) |
| { |
| if (!jent_fips_enabled()) |
| return; |
| |
| /* prime the FIPS test */ |
| if (!ec->old_data) { |
| ec->old_data = ec->data; |
| jent_gen_entropy(ec); |
| } |
| |
| if (ec->data == ec->old_data) |
| jent_panic("jitterentropy: Duplicate output detected\n"); |
| |
| ec->old_data = ec->data; |
| } |
| |
| /** |
| * 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. |
| * |
| * Input: |
| * @ec Reference to entropy collector |
| * @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 0 when request is fulfilled or an error |
| * |
| * The following error codes can occur: |
| * -1 entropy_collector is NULL |
| */ |
| int jent_read_entropy(struct rand_data *ec, unsigned char *data, |
| unsigned int len) |
| { |
| unsigned char *p = data; |
| |
| if (!ec) |
| return -1; |
| |
| while (0 < len) { |
| unsigned int tocopy; |
| |
| jent_gen_entropy(ec); |
| jent_fips_test(ec); |
| if ((DATA_SIZE_BITS / 8) < len) |
| tocopy = (DATA_SIZE_BITS / 8); |
| else |
| tocopy = len; |
| jent_memcpy(p, &ec->data, tocopy); |
| |
| len -= tocopy; |
| p += tocopy; |
| } |
| |
| return 0; |
| } |
| |
| /*************************************************************************** |
| * 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 (!entropy_collector) |
| return NULL; |
| |
| if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { |
| /* Allocate memory for adding variations based on memory |
| * access |
| */ |
| entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE); |
| if (!entropy_collector->mem) { |
| jent_zfree(entropy_collector); |
| 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); |
| |
| return entropy_collector; |
| } |
| |
| void jent_entropy_collector_free(struct rand_data *entropy_collector) |
| { |
| jent_zfree(entropy_collector->mem); |
| entropy_collector->mem = NULL; |
| jent_zfree(entropy_collector); |
| 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; |
| unsigned int lowdelta = 0; |
| |
| jent_get_nstime(&time); |
| jent_fold_time(NULL, time, &folded, 1<<MIN_FOLD_LOOP_BIT); |
| jent_get_nstime(&time2); |
| |
| /* test whether timer works */ |
| if (!time || !time2) |
| return JENT_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 JENT_ECOARSETIME; |
| |
| /* |
| * 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++; |
| |
| /* |
| * Avoid modulo of 64 bit integer to allow code to compile |
| * on 32 bit architectures. |
| */ |
| lowdelta = time2 - time; |
| if (!(lowdelta % 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 JENT_ENOMONOTONIC; |
| /* Error if the time variances are always identical */ |
| if (!delta_sum) |
| return JENT_EVARVAR; |
| |
| /* |
| * Variations of deltas of time must on average be larger |
| * than 1 to ensure the entropy estimation |
| * implied with 1 is preserved |
| */ |
| if (delta_sum <= 1) |
| return JENT_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 JENT_ECOARSETIME; |
| |
| return 0; |
| } |