788 lines
24 KiB
C
788 lines
24 KiB
C
/*
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* Non-physical true random number generator based on timing jitter --
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* Jitter RNG standalone code.
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*
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* Copyright Stephan Mueller <smueller@chronox.de>, 2015
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*
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* Design
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* ======
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*
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* See http://www.chronox.de/jent.html
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*
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* License
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* =======
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, and the entire permission notice in its entirety,
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* including the disclaimer of warranties.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote
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* products derived from this software without specific prior
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* written permission.
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*
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* ALTERNATIVELY, this product may be distributed under the terms of
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* the GNU General Public License, in which case the provisions of the GPL2 are
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* required INSTEAD OF the above restrictions. (This clause is
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* necessary due to a potential bad interaction between the GPL and
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* the restrictions contained in a BSD-style copyright.)
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
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* WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
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* OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
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* USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*/
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/*
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* This Jitterentropy RNG is based on the jitterentropy library
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* version 1.1.0 provided at http://www.chronox.de/jent.html
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*/
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#ifdef __OPTIMIZE__
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#error "The CPU Jitter random number generator must not be compiled with optimizations. See documentation. Use the compiler switch -O0 for compiling jitterentropy.c."
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#endif
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typedef unsigned long long __u64;
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typedef long long __s64;
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typedef unsigned int __u32;
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#define NULL ((void *) 0)
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/* The entropy pool */
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struct rand_data {
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/* all data values that are vital to maintain the security
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* of the RNG are marked as SENSITIVE. A user must not
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* access that information while the RNG executes its loops to
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* calculate the next random value. */
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__u64 data; /* SENSITIVE Actual random number */
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__u64 old_data; /* SENSITIVE Previous random number */
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__u64 prev_time; /* SENSITIVE Previous time stamp */
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#define DATA_SIZE_BITS ((sizeof(__u64)) * 8)
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__u64 last_delta; /* SENSITIVE stuck test */
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__s64 last_delta2; /* SENSITIVE stuck test */
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unsigned int stuck:1; /* Time measurement stuck */
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unsigned int osr; /* Oversample rate */
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unsigned int stir:1; /* Post-processing stirring */
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unsigned int disable_unbias:1; /* Deactivate Von-Neuman unbias */
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#define JENT_MEMORY_BLOCKS 64
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#define JENT_MEMORY_BLOCKSIZE 32
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#define JENT_MEMORY_ACCESSLOOPS 128
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#define JENT_MEMORY_SIZE (JENT_MEMORY_BLOCKS*JENT_MEMORY_BLOCKSIZE)
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unsigned char *mem; /* Memory access location with size of
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* memblocks * memblocksize */
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unsigned int memlocation; /* Pointer to byte in *mem */
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unsigned int memblocks; /* Number of memory blocks in *mem */
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unsigned int memblocksize; /* Size of one memory block in bytes */
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unsigned int memaccessloops; /* Number of memory accesses per random
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* bit generation */
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};
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/* Flags that can be used to initialize the RNG */
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#define JENT_DISABLE_STIR (1<<0) /* Disable stirring the entropy pool */
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#define JENT_DISABLE_UNBIAS (1<<1) /* Disable the Von-Neuman Unbiaser */
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#define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more
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* entropy, saves MEMORY_SIZE RAM for
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* entropy collector */
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/* -- error codes for init function -- */
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#define JENT_ENOTIME 1 /* Timer service not available */
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#define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */
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#define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */
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#define JENT_EMINVARIATION 4 /* Timer variations too small for RNG */
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#define JENT_EVARVAR 5 /* Timer does not produce variations of
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* variations (2nd derivation of time is
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* zero). */
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#define JENT_EMINVARVAR 6 /* Timer variations of variations is tooi
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* small. */
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/***************************************************************************
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* Helper functions
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***************************************************************************/
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void jent_get_nstime(__u64 *out);
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__u64 jent_rol64(__u64 word, unsigned int shift);
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void *jent_zalloc(unsigned int len);
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void jent_zfree(void *ptr);
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int jent_fips_enabled(void);
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void jent_panic(char *s);
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void jent_memcpy(void *dest, const void *src, unsigned int n);
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/**
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* Update of the loop count used for the next round of
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* an entropy collection.
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*
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* Input:
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* @ec entropy collector struct -- may be NULL
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* @bits is the number of low bits of the timer to consider
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* @min is the number of bits we shift the timer value to the right at
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* the end to make sure we have a guaranteed minimum value
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*
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* @return Newly calculated loop counter
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*/
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static __u64 jent_loop_shuffle(struct rand_data *ec,
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unsigned int bits, unsigned int min)
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{
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__u64 time = 0;
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__u64 shuffle = 0;
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unsigned int i = 0;
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unsigned int mask = (1<<bits) - 1;
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jent_get_nstime(&time);
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/*
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* mix the current state of the random number into the shuffle
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* calculation to balance that shuffle a bit more
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*/
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if (ec)
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time ^= ec->data;
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/*
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* we fold the time value as much as possible to ensure that as many
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* bits of the time stamp are included as possible
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*/
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for (i = 0; (DATA_SIZE_BITS / bits) > i; i++) {
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shuffle ^= time & mask;
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time = time >> bits;
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}
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/*
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* We add a lower boundary value to ensure we have a minimum
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* RNG loop count.
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*/
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return (shuffle + (1<<min));
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}
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/***************************************************************************
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* Noise sources
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***************************************************************************/
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/**
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* CPU Jitter noise source -- this is the noise source based on the CPU
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* execution time jitter
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*
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* This function folds the time into one bit units by iterating
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* through the DATA_SIZE_BITS bit time value as follows: assume our time value
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* is 0xabcd
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* 1st loop, 1st shift generates 0xd000
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* 1st loop, 2nd shift generates 0x000d
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* 2nd loop, 1st shift generates 0xcd00
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* 2nd loop, 2nd shift generates 0x000c
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* 3rd loop, 1st shift generates 0xbcd0
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* 3rd loop, 2nd shift generates 0x000b
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* 4th loop, 1st shift generates 0xabcd
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* 4th loop, 2nd shift generates 0x000a
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* Now, the values at the end of the 2nd shifts are XORed together.
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*
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* The code is deliberately inefficient and shall stay that way. This function
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* is the root cause why the code shall be compiled without optimization. This
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* function not only acts as folding operation, but this function's execution
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* is used to measure the CPU execution time jitter. Any change to the loop in
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* this function implies that careful retesting must be done.
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*
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* Input:
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* @ec entropy collector struct -- may be NULL
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* @time time stamp to be folded
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* @loop_cnt if a value not equal to 0 is set, use the given value as number of
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* loops to perform the folding
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*
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* Output:
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* @folded result of folding operation
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*
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* @return Number of loops the folding operation is performed
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*/
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static __u64 jent_fold_time(struct rand_data *ec, __u64 time,
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__u64 *folded, __u64 loop_cnt)
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{
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unsigned int i;
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__u64 j = 0;
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__u64 new = 0;
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#define MAX_FOLD_LOOP_BIT 4
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#define MIN_FOLD_LOOP_BIT 0
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__u64 fold_loop_cnt =
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jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT);
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/*
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* testing purposes -- allow test app to set the counter, not
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* needed during runtime
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*/
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if (loop_cnt)
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fold_loop_cnt = loop_cnt;
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for (j = 0; j < fold_loop_cnt; j++) {
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new = 0;
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for (i = 1; (DATA_SIZE_BITS) >= i; i++) {
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__u64 tmp = time << (DATA_SIZE_BITS - i);
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tmp = tmp >> (DATA_SIZE_BITS - 1);
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new ^= tmp;
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}
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}
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*folded = new;
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return fold_loop_cnt;
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}
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/**
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* Memory Access noise source -- this is a noise source based on variations in
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* memory access times
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*
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* This function performs memory accesses which will add to the timing
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* variations due to an unknown amount of CPU wait states that need to be
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* added when accessing memory. The memory size should be larger than the L1
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* caches as outlined in the documentation and the associated testing.
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*
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* The L1 cache has a very high bandwidth, albeit its access rate is usually
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* slower than accessing CPU registers. Therefore, L1 accesses only add minimal
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* variations as the CPU has hardly to wait. Starting with L2, significant
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* variations are added because L2 typically does not belong to the CPU any more
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* and therefore a wider range of CPU wait states is necessary for accesses.
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* L3 and real memory accesses have even a wider range of wait states. However,
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* to reliably access either L3 or memory, the ec->mem memory must be quite
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* large which is usually not desirable.
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*
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* Input:
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* @ec Reference to the entropy collector with the memory access data -- if
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* the reference to the memory block to be accessed is NULL, this noise
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* source is disabled
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* @loop_cnt if a value not equal to 0 is set, use the given value as number of
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* loops to perform the folding
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*
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* @return Number of memory access operations
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*/
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static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
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{
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unsigned char *tmpval = NULL;
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unsigned int wrap = 0;
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__u64 i = 0;
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#define MAX_ACC_LOOP_BIT 7
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#define MIN_ACC_LOOP_BIT 0
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__u64 acc_loop_cnt =
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jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT);
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if (NULL == ec || NULL == ec->mem)
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return 0;
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wrap = ec->memblocksize * ec->memblocks;
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/*
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* testing purposes -- allow test app to set the counter, not
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* needed during runtime
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*/
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if (loop_cnt)
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acc_loop_cnt = loop_cnt;
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for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) {
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tmpval = ec->mem + ec->memlocation;
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/*
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* memory access: just add 1 to one byte,
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* wrap at 255 -- memory access implies read
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* from and write to memory location
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*/
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*tmpval = (*tmpval + 1) & 0xff;
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/*
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* Addition of memblocksize - 1 to pointer
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* with wrap around logic to ensure that every
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* memory location is hit evenly
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*/
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ec->memlocation = ec->memlocation + ec->memblocksize - 1;
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ec->memlocation = ec->memlocation % wrap;
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}
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return i;
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}
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/***************************************************************************
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* Start of entropy processing logic
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***************************************************************************/
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/**
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* Stuck test by checking the:
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* 1st derivation of the jitter measurement (time delta)
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* 2nd derivation of the jitter measurement (delta of time deltas)
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* 3rd derivation of the jitter measurement (delta of delta of time deltas)
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*
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* All values must always be non-zero.
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*
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* Input:
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* @ec Reference to entropy collector
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* @current_delta Jitter time delta
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*
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* @return
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* 0 jitter measurement not stuck (good bit)
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* 1 jitter measurement stuck (reject bit)
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*/
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static void jent_stuck(struct rand_data *ec, __u64 current_delta)
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{
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__s64 delta2 = ec->last_delta - current_delta;
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__s64 delta3 = delta2 - ec->last_delta2;
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ec->last_delta = current_delta;
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ec->last_delta2 = delta2;
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if (!current_delta || !delta2 || !delta3)
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ec->stuck = 1;
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}
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/**
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* This is the heart of the entropy generation: calculate time deltas and
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* use the CPU jitter in the time deltas. The jitter is folded into one
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* bit. You can call this function the "random bit generator" as it
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* produces one random bit per invocation.
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*
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* WARNING: ensure that ->prev_time is primed before using the output
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* of this function! This can be done by calling this function
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* and not using its result.
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*
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* Input:
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* @entropy_collector Reference to entropy collector
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*
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* @return One random bit
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*/
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static __u64 jent_measure_jitter(struct rand_data *ec)
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{
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__u64 time = 0;
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__u64 data = 0;
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__u64 current_delta = 0;
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/* Invoke one noise source before time measurement to add variations */
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jent_memaccess(ec, 0);
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/*
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* Get time stamp and calculate time delta to previous
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* invocation to measure the timing variations
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*/
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jent_get_nstime(&time);
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current_delta = time - ec->prev_time;
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ec->prev_time = time;
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/* Now call the next noise sources which also folds the data */
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jent_fold_time(ec, current_delta, &data, 0);
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/*
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* Check whether we have a stuck measurement. The enforcement
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* is performed after the stuck value has been mixed into the
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* entropy pool.
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*/
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jent_stuck(ec, current_delta);
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return data;
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}
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/**
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* Von Neuman unbias as explained in RFC 4086 section 4.2. As shown in the
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* documentation of that RNG, the bits from jent_measure_jitter are considered
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* independent which implies that the Von Neuman unbias operation is applicable.
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* A proof of the Von-Neumann unbias operation to remove skews is given in the
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* document "A proposal for: Functionality classes for random number
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* generators", version 2.0 by Werner Schindler, section 5.4.1.
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*
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* Input:
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* @entropy_collector Reference to entropy collector
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*
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* @return One random bit
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*/
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static __u64 jent_unbiased_bit(struct rand_data *entropy_collector)
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{
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do {
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__u64 a = jent_measure_jitter(entropy_collector);
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__u64 b = jent_measure_jitter(entropy_collector);
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if (a == b)
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continue;
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if (1 == a)
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return 1;
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else
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return 0;
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} while (1);
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}
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/**
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* Shuffle the pool a bit by mixing some value with a bijective function (XOR)
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* into the pool.
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*
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* The function generates a mixer value that depends on the bits set and the
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* location of the set bits in the random number generated by the entropy
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* source. Therefore, based on the generated random number, this mixer value
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* can have 2**64 different values. That mixer value is initialized with the
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* first two SHA-1 constants. After obtaining the mixer value, it is XORed into
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* the random number.
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*
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* The mixer value is not assumed to contain any entropy. But due to the XOR
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* operation, it can also not destroy any entropy present in the entropy pool.
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*
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* Input:
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* @entropy_collector Reference to entropy collector
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*/
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static void jent_stir_pool(struct rand_data *entropy_collector)
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{
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/*
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* to shut up GCC on 32 bit, we have to initialize the 64 variable
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* with two 32 bit variables
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*/
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union c {
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__u64 u64;
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__u32 u32[2];
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};
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/*
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* This constant is derived from the first two 32 bit initialization
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* vectors of SHA-1 as defined in FIPS 180-4 section 5.3.1
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*/
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union c constant;
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/*
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* The start value of the mixer variable is derived from the third
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* and fourth 32 bit initialization vector of SHA-1 as defined in
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* FIPS 180-4 section 5.3.1
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*/
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union c mixer;
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unsigned int i = 0;
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/*
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* Store the SHA-1 constants in reverse order to make up the 64 bit
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* value -- this applies to a little endian system, on a big endian
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* system, it reverses as expected. But this really does not matter
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* as we do not rely on the specific numbers. We just pick the SHA-1
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* constants as they have a good mix of bit set and unset.
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*/
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constant.u32[1] = 0x67452301;
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constant.u32[0] = 0xefcdab89;
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mixer.u32[1] = 0x98badcfe;
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mixer.u32[0] = 0x10325476;
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for (i = 0; i < DATA_SIZE_BITS; i++) {
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/*
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* get the i-th bit of the input random number and only XOR
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* the constant into the mixer value when that bit is set
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*/
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if ((entropy_collector->data >> i) & 1)
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mixer.u64 ^= constant.u64;
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mixer.u64 = jent_rol64(mixer.u64, 1);
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}
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entropy_collector->data ^= mixer.u64;
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}
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/**
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* Generator of one 64 bit random number
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* Function fills rand_data->data
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*
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* Input:
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* @ec Reference to entropy collector
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*/
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static void jent_gen_entropy(struct rand_data *ec)
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{
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unsigned int k = 0;
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|
|
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/* priming of the ->prev_time value */
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jent_measure_jitter(ec);
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|
|
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while (1) {
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__u64 data = 0;
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if (ec->disable_unbias == 1)
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data = jent_measure_jitter(ec);
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else
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data = jent_unbiased_bit(ec);
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|
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/* enforcement of the jent_stuck test */
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|
if (ec->stuck) {
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/*
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* We only mix in the bit considered not appropriate
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|
* without the LSFR. The reason is that if we apply
|
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* the LSFR and we do not rotate, the 2nd bit with LSFR
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* will cancel out the first LSFR application on the
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* bad bit.
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*
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* And we do not rotate as we apply the next bit to the
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|
* 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;
|
|
}
|