871 lines
26 KiB
C
871 lines
26 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 - 2020
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*
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* Design
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* ======
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*
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* See https://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 2.2.0 provided at https://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 osr; /* Oversample rate */
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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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/* Repetition Count Test */
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int rct_count; /* Number of stuck values */
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/* Adaptive Proportion Test for a significance level of 2^-30 */
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#define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */
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#define JENT_APT_WINDOW_SIZE 512 /* Data window size */
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/* LSB of time stamp to process */
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#define JENT_APT_LSB 16
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#define JENT_APT_WORD_MASK (JENT_APT_LSB - 1)
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unsigned int apt_observations; /* Number of collected observations */
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unsigned int apt_count; /* APT counter */
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unsigned int apt_base; /* APT base reference */
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unsigned int apt_base_set:1; /* APT base reference set? */
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unsigned int health_failure:1; /* Permanent health failure */
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};
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/* Flags that can be used to initialize the RNG */
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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_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_ESTUCK 8 /* Too many stuck results during init. */
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#define JENT_EHEALTH 9 /* Health test failed during initialization */
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#define JENT_ERCT 10 /* RCT failed during initialization */
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/*
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* The output n bits can receive more than n bits of min entropy, of course,
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* but the fixed output of the conditioning function can only asymptotically
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* approach the output size bits of min entropy, not attain that bound. Random
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* maps will tend to have output collisions, which reduces the creditable
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* output entropy (that is what SP 800-90B Section 3.1.5.1.2 attempts to bound).
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*
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* The value "64" is justified in Appendix A.4 of the current 90C draft,
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* and aligns with NIST's in "epsilon" definition in this document, which is
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* that a string can be considered "full entropy" if you can bound the min
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* entropy in each bit of output to at least 1-epsilon, where epsilon is
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* required to be <= 2^(-32).
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*/
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#define JENT_ENTROPY_SAFETY_FACTOR 64
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#include <linux/fips.h>
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#include "jitterentropy.h"
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/***************************************************************************
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* Adaptive Proportion Test
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*
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* This test complies with SP800-90B section 4.4.2.
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***************************************************************************/
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/*
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* Reset the APT counter
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*
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* @ec [in] Reference to entropy collector
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*/
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static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked)
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{
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/* Reset APT counter */
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ec->apt_count = 0;
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ec->apt_base = delta_masked;
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ec->apt_observations = 0;
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}
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/*
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* Insert a new entropy event into APT
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*
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* @ec [in] Reference to entropy collector
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* @delta_masked [in] Masked time delta to process
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*/
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static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked)
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{
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/* Initialize the base reference */
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if (!ec->apt_base_set) {
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ec->apt_base = delta_masked;
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ec->apt_base_set = 1;
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return;
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}
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if (delta_masked == ec->apt_base) {
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ec->apt_count++;
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if (ec->apt_count >= JENT_APT_CUTOFF)
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ec->health_failure = 1;
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}
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ec->apt_observations++;
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if (ec->apt_observations >= JENT_APT_WINDOW_SIZE)
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jent_apt_reset(ec, delta_masked);
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}
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/***************************************************************************
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* Stuck Test and its use as Repetition Count Test
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*
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* The Jitter RNG uses an enhanced version of the Repetition Count Test
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* (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical
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* back-to-back values, the input to the RCT is the counting of the stuck
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* values during the generation of one Jitter RNG output block.
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*
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* The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8.
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*
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* During the counting operation, the Jitter RNG always calculates the RCT
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* cut-off value of C. If that value exceeds the allowed cut-off value,
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* the Jitter RNG output block will be calculated completely but discarded at
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* the end. The caller of the Jitter RNG is informed with an error code.
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***************************************************************************/
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/*
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* Repetition Count Test as defined in SP800-90B section 4.4.1
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*
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* @ec [in] Reference to entropy collector
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* @stuck [in] Indicator whether the value is stuck
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*/
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static void jent_rct_insert(struct rand_data *ec, int stuck)
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{
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/*
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* If we have a count less than zero, a previous RCT round identified
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* a failure. We will not overwrite it.
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*/
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if (ec->rct_count < 0)
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return;
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if (stuck) {
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ec->rct_count++;
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/*
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* The cutoff value is based on the following consideration:
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* alpha = 2^-30 as recommended in FIPS 140-2 IG 9.8.
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* In addition, we require an entropy value H of 1/OSR as this
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* is the minimum entropy required to provide full entropy.
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* Note, we collect 64 * OSR deltas for inserting them into
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* the entropy pool which should then have (close to) 64 bits
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* of entropy.
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*
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* Note, ec->rct_count (which equals to value B in the pseudo
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* code of SP800-90B section 4.4.1) starts with zero. Hence
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* we need to subtract one from the cutoff value as calculated
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* following SP800-90B.
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*/
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if ((unsigned int)ec->rct_count >= (31 * ec->osr)) {
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ec->rct_count = -1;
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ec->health_failure = 1;
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}
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} else {
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ec->rct_count = 0;
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}
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}
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/*
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* Is there an RCT health test failure?
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*
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* @ec [in] Reference to entropy collector
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*
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* @return
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* 0 No health test failure
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* 1 Permanent health test failure
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*/
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static int jent_rct_failure(struct rand_data *ec)
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{
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if (ec->rct_count < 0)
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return 1;
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return 0;
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}
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static inline __u64 jent_delta(__u64 prev, __u64 next)
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{
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#define JENT_UINT64_MAX (__u64)(~((__u64) 0))
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return (prev < next) ? (next - prev) :
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(JENT_UINT64_MAX - prev + 1 + next);
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}
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/*
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* Stuck test by checking the:
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* 1st derivative of the jitter measurement (time delta)
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* 2nd derivative of the jitter measurement (delta of time deltas)
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* 3rd derivative 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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* @ec [in] Reference to entropy collector
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* @current_delta [in] 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 int jent_stuck(struct rand_data *ec, __u64 current_delta)
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{
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__u64 delta2 = jent_delta(ec->last_delta, current_delta);
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__u64 delta3 = jent_delta(ec->last_delta2, delta2);
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ec->last_delta = current_delta;
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ec->last_delta2 = delta2;
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/*
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* Insert the result of the comparison of two back-to-back time
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* deltas.
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*/
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jent_apt_insert(ec, current_delta);
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if (!current_delta || !delta2 || !delta3) {
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/* RCT with a stuck bit */
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jent_rct_insert(ec, 1);
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return 1;
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}
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/* RCT with a non-stuck bit */
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jent_rct_insert(ec, 0);
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return 0;
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}
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/*
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* Report any health test failures
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*
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* @ec [in] Reference to entropy collector
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*
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* @return
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* 0 No health test failure
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* 1 Permanent health test failure
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*/
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static int jent_health_failure(struct rand_data *ec)
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{
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return ec->health_failure;
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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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* 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 - 1) / 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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* 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 injects the individual bits of the time value into the
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* entropy pool using an LFSR.
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*
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* The code is deliberately inefficient with respect to the bit shifting
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* and shall stay that way. This function is the root cause why the code
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* shall be compiled without optimization. This function not only acts as
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* folding operation, but this function's execution is used to measure
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* the CPU execution time jitter. Any change to the loop in this function
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* implies that careful retesting must be done.
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*
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* @ec [in] entropy collector struct
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* @time [in] time stamp to be injected
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* @loop_cnt [in] if a value not equal to 0 is set, use the given value as
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* number of loops to perform the folding
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* @stuck [in] Is the time stamp identified as stuck?
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*
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* Output:
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* updated ec->data
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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 void jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt,
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int stuck)
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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 = ec->data;
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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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/*
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* Fibonacci LSFR with polynomial of
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* x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is
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* primitive according to
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* http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf
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* (the shift values are the polynomial values minus one
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* due to counting bits from 0 to 63). As the current
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* position is always the LSB, the polynomial only needs
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* to shift data in from the left without wrap.
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*/
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tmp ^= ((new >> 63) & 1);
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tmp ^= ((new >> 60) & 1);
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tmp ^= ((new >> 55) & 1);
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tmp ^= ((new >> 30) & 1);
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tmp ^= ((new >> 27) & 1);
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tmp ^= ((new >> 22) & 1);
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new <<= 1;
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new ^= tmp;
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}
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}
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/*
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* If the time stamp is stuck, do not finally insert the value into
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* the entropy pool. Although this operation should not do any harm
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* even when the time stamp has no entropy, SP800-90B requires that
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* any conditioning operation (SP800-90B considers the LFSR to be a
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* conditioning operation) to have an identical amount of input
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* data according to section 3.1.5.
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*/
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if (!stuck)
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ec->data = new;
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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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* @ec [in] 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 [in] if a value not equal to 0 is set, use the given value
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* number of loops to perform the LFSR
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*/
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static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
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{
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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;
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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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unsigned char *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
|
|
* 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;
|
|
}
|
|
}
|
|
|
|
/***************************************************************************
|
|
* 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 injected into the
|
|
* entropy pool.
|
|
*
|
|
* 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.
|
|
*
|
|
* @ec [in] Reference to entropy collector
|
|
*
|
|
* @return result of stuck test
|
|
*/
|
|
static int jent_measure_jitter(struct rand_data *ec)
|
|
{
|
|
__u64 time = 0;
|
|
__u64 current_delta = 0;
|
|
int stuck;
|
|
|
|
/* 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 = jent_delta(ec->prev_time, time);
|
|
ec->prev_time = time;
|
|
|
|
/* Check whether we have a stuck measurement. */
|
|
stuck = jent_stuck(ec, current_delta);
|
|
|
|
/* Now call the next noise sources which also injects the data */
|
|
jent_lfsr_time(ec, current_delta, 0, stuck);
|
|
|
|
return stuck;
|
|
}
|
|
|
|
/*
|
|
* Generator of one 64 bit random number
|
|
* Function fills rand_data->data
|
|
*
|
|
* @ec [in] Reference to entropy collector
|
|
*/
|
|
static void jent_gen_entropy(struct rand_data *ec)
|
|
{
|
|
unsigned int k = 0, safety_factor = 0;
|
|
|
|
if (fips_enabled)
|
|
safety_factor = JENT_ENTROPY_SAFETY_FACTOR;
|
|
|
|
/* priming of the ->prev_time value */
|
|
jent_measure_jitter(ec);
|
|
|
|
while (!jent_health_failure(ec)) {
|
|
/* If a stuck measurement is received, repeat measurement */
|
|
if (jent_measure_jitter(ec))
|
|
continue;
|
|
|
|
/*
|
|
* We multiply the loop value with ->osr to obtain the
|
|
* oversampling rate requested by the caller
|
|
*/
|
|
if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr))
|
|
break;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* 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.
|
|
*
|
|
* @ec [in] Reference to entropy collector
|
|
* @data [in] pointer to buffer for storing random data -- buffer must already
|
|
* exist
|
|
* @len [in] 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
|
|
* -2 RCT failed
|
|
* -3 APT test failed
|
|
*/
|
|
int jent_read_entropy(struct rand_data *ec, unsigned char *data,
|
|
unsigned int len)
|
|
{
|
|
unsigned char *p = data;
|
|
|
|
if (!ec)
|
|
return -1;
|
|
|
|
while (len > 0) {
|
|
unsigned int tocopy;
|
|
|
|
jent_gen_entropy(ec);
|
|
|
|
if (jent_health_failure(ec)) {
|
|
int ret;
|
|
|
|
if (jent_rct_failure(ec))
|
|
ret = -2;
|
|
else
|
|
ret = -3;
|
|
|
|
/*
|
|
* Re-initialize the noise source
|
|
*
|
|
* If the health test fails, the Jitter RNG remains
|
|
* in failure state and will return a health failure
|
|
* during next invocation.
|
|
*/
|
|
if (jent_entropy_init())
|
|
return ret;
|
|
|
|
/* Set APT to initial state */
|
|
jent_apt_reset(ec, 0);
|
|
ec->apt_base_set = 0;
|
|
|
|
/* Set RCT to initial state */
|
|
ec->rct_count = 0;
|
|
|
|
/* Re-enable Jitter RNG */
|
|
ec->health_failure = 0;
|
|
|
|
/*
|
|
* Return the health test failure status to the
|
|
* caller as the generated value is not appropriate.
|
|
*/
|
|
return ret;
|
|
}
|
|
|
|
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 (osr == 0)
|
|
osr = 1; /* minimum sampling rate is 1 */
|
|
entropy_collector->osr = osr;
|
|
|
|
/* 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);
|
|
}
|
|
|
|
int jent_entropy_init(void)
|
|
{
|
|
int i;
|
|
__u64 delta_sum = 0;
|
|
__u64 old_delta = 0;
|
|
unsigned int nonstuck = 0;
|
|
int time_backwards = 0;
|
|
int count_mod = 0;
|
|
int count_stuck = 0;
|
|
struct rand_data ec = { 0 };
|
|
|
|
/* Required for RCT */
|
|
ec.osr = 1;
|
|
|
|
/* 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.
|
|
*
|
|
* SP800-90B requires at least 1024 initial test cycles.
|
|
*/
|
|
#define TESTLOOPCOUNT 1024
|
|
#define CLEARCACHE 100
|
|
for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
|
|
__u64 time = 0;
|
|
__u64 time2 = 0;
|
|
__u64 delta = 0;
|
|
unsigned int lowdelta = 0;
|
|
int stuck;
|
|
|
|
/* Invoke core entropy collection logic */
|
|
jent_get_nstime(&time);
|
|
ec.prev_time = time;
|
|
jent_lfsr_time(&ec, time, 0, 0);
|
|
jent_get_nstime(&time2);
|
|
|
|
/* test whether timer works */
|
|
if (!time || !time2)
|
|
return JENT_ENOTIME;
|
|
delta = jent_delta(time, time2);
|
|
/*
|
|
* 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;
|
|
|
|
stuck = jent_stuck(&ec, delta);
|
|
|
|
/*
|
|
* 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 (i < CLEARCACHE)
|
|
continue;
|
|
|
|
if (stuck)
|
|
count_stuck++;
|
|
else {
|
|
nonstuck++;
|
|
|
|
/*
|
|
* Ensure that the APT succeeded.
|
|
*
|
|
* With the check below that count_stuck must be less
|
|
* than 10% of the overall generated raw entropy values
|
|
* it is guaranteed that the APT is invoked at
|
|
* floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times.
|
|
*/
|
|
if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) {
|
|
jent_apt_reset(&ec,
|
|
delta & JENT_APT_WORD_MASK);
|
|
if (jent_health_failure(&ec))
|
|
return JENT_EHEALTH;
|
|
}
|
|
}
|
|
|
|
/* Validate RCT */
|
|
if (jent_rct_failure(&ec))
|
|
return JENT_ERCT;
|
|
|
|
/* test whether we have an increasing timer */
|
|
if (!(time2 > time))
|
|
time_backwards++;
|
|
|
|
/* use 32 bit value to ensure compilation on 32 bit arches */
|
|
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 (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 (time_backwards > 3)
|
|
return JENT_ENOMONOTONIC;
|
|
|
|
/*
|
|
* 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_EVARVAR;
|
|
|
|
/*
|
|
* 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;
|
|
|
|
/*
|
|
* If we have more than 90% stuck results, then this Jitter RNG is
|
|
* likely to not work well.
|
|
*/
|
|
if ((TESTLOOPCOUNT/10 * 9) < count_stuck)
|
|
return JENT_ESTUCK;
|
|
|
|
return 0;
|
|
}
|