osfmk/prng/entropy.h

   1 /*
   2  * Copyright (c) 2019 Apple Inc. All rights reserved.
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   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
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  13  * terms of an Apple operating system software license agreement.
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  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
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  27  */
  28
  29 #ifndef _PRNG_ENTROPY_H_
  30 #define _PRNG_ENTROPY_H_
  31
  32 #include <kern/kern_types.h>
  33 #include <sys/cdefs.h>
  34
  35 __BEGIN_DECLS
  36
  37 // This module is used to accumulate entropy from hardware interrupts
  38 // for consumption by a higher-level PRNG.
  39 //
  40 // The raw entropy samples are collected from CPU counters during
  41 // hardware interrupts. We do not perform synchronization before
  42 // reading the counter (unlike ml_get_timebase and similar functions).
  43 //
  44 // This entropy accumulator performs continuous health tests in
  45 // accordance with NIST SP 800-90B. The parameters have been chosen
  46 // with the expectation that test failures should never occur except
  47 // in case of catastrophic hardware failure.
  48
  49 typedef uint32_t entropy_sample_t;
  50
  51 // Called during startup to initialize internal data structures.
  52 void entropy_init(void);
  53
  54 // Called during hardware interrupts to collect entropy in per-CPU
  55 // structures.
  56 void entropy_collect(void);
  57
  58 // Called by the higher-level PRNG. The module performs continuous
  59 // health tests and decides whether to release entropy based on the
  60 // values of various counters. Returns negative in case of error
  61 // (e.g. health test failure).
  62 int32_t entropy_provide(size_t *entropy_size, void *entropy, void *arg);
  63
  64 extern entropy_sample_t *entropy_analysis_buffer;
  65 extern uint32_t entropy_analysis_buffer_size;
  66
  67 typedef struct entropy_health_stats {
  68         // A total count of times the test has been reset with a new
  69         // initial observation. This can be thought of as the number of
  70         // tests, but note that a single "test" can theoretically accrue
  71         // multiple failures.
  72         uint32_t reset_count;
  73
  74         // A total count of failures of this test instance since
  75         // boot. Since we do not expect any test failures (ever) in
  76         // practice, this counter should always be zero.
  77         uint32_t failure_count;
  78
  79         // The maximum count of times an initial observation has recurred
  80         // across all instances of this test.
  81         uint32_t max_observation_count;
  82 } entropy_health_stats_t;
  83
  84 extern int entropy_health_startup_done;
  85 extern entropy_health_stats_t entropy_health_rct_stats;
  86 extern entropy_health_stats_t entropy_health_apt_stats;
  87
  88 __END_DECLS
  89
  90 #endif /* _PRNG_ENTROPY_H_ */