xref: /xnu-8020.121.3/osfmk/prng/entropy.h (revision fdd8201d7b966f0c3ea610489d29bd841d358941)

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#ifndef _PRNG_ENTROPY_H_
#define _PRNG_ENTROPY_H_

#include <kern/kern_types.h>
#include <kern/bits.h>
#include <sys/cdefs.h>

__BEGIN_DECLS

// This module is used to accumulate entropy from hardware interrupts
// for consumption by a higher-level PRNG.
//
// The raw entropy samples are collected from CPU counters during
// hardware interrupts. We do not perform synchronization before
// reading the counter (unlike ml_get_timebase and similar functions).
//
// This entropy accumulator performs continuous health tests in
// accordance with NIST SP 800-90B. The parameters have been chosen
// with the expectation that test failures should never occur except
// in case of catastrophic hardware failure.

typedef uint32_t entropy_sample_t;

// Called during startup to initialize internal data structures.
void entropy_init(void);

// Called during hardware interrupts to collect entropy in per-CPU
// structures.
void entropy_collect(void);

// Called by the higher-level PRNG. The module performs continuous
// health tests and decides whether to release entropy based on the
// values of various counters. Returns negative in case of error
// (e.g. health test failure).
int32_t entropy_provide(size_t *entropy_size, void *entropy, void *arg);

// Called internally when entropy_provide() is called or when exporting
// analysis entropy with the "kern.entropy.analysis.filter" sysctl. This
// function applies a filter to input entropy and returns a bitmap indicating
// whether a particular sample is counted. The return value is the count of
// samples that passed the filter. "filter" may be NULL in which case only
// the number of unfiltered samples that passed the filter will be calculated.
//
// Each bit in the bitmap_t "filter" indicates whether a sample
// is kept (when the bit is set) or filtered (when the bit is not set).
// In other words, "bitmap_test(filter, n)" indicates whether
// "sample[n]" is kept.
uint32_t entropy_filter(uint32_t sample_count, entropy_sample_t *samples, uint32_t filter_count, bitmap_t *filter);

#if (DEVELOPMENT || DEBUG)
#define ENTROPY_ANALYSIS_SUPPORTED 1
#else
#define ENTROPY_ANALYSIS_SUPPORTED 0
#endif

#define ENTROPY_ANALYSIS_BOOTARG "entropy-analysis-sample-count"

#if ENTROPY_ANALYSIS_SUPPORTED
// Whether analysis is enabled via the "ENTROPY_ANALYSIS_BOOTARG" boot-arg
extern int entropy_analysis_enabled;

// The size (in bytes) of the filter
extern uint32_t entropy_analysis_filter_size;

// The size (in bytes) of the entropy analysis buffer
extern uint32_t entropy_analysis_buffer_size;
// The maximum number of entropy_sample_t elements in the analysis buffer
extern uint32_t entropy_analysis_max_sample_count;

// The number of entropy_sample_t elements in the analysis buffer
extern uint32_t entropy_analysis_sample_count;

extern entropy_sample_t *entropy_analysis_buffer;
#endif  // ENTROPY_ANALYSIS_SUPPORTED

typedef struct entropy_health_stats {
	// A total count of times the test has been reset with a new
	// initial observation. This can be thought of as the number of
	// tests, but note that a single "test" can theoretically accrue
	// multiple failures.
	uint32_t reset_count;

	// A total count of failures of this test instance since
	// boot. Since we do not expect any test failures (ever) in
	// practice, this counter should always be zero.
	uint32_t failure_count;

	// The maximum count of times an initial observation has recurred
	// across all instances of this test.
	uint32_t max_observation_count;
} entropy_health_stats_t;

extern int entropy_health_startup_done;
extern entropy_health_stats_t entropy_health_rct_stats;
extern entropy_health_stats_t entropy_health_apt_stats;

// The total number of samples processed
extern uint64_t entropy_filter_total_sample_count;
// The number of samples that passed the filter
extern uint64_t entropy_filter_accepted_sample_count;
// The number of samples that were rejected by the filters
extern uint64_t entropy_filter_rejected_sample_count;


__END_DECLS

#endif /* _PRNG_ENTROPY_H_ */