osfmk/prng/entropy.h

   1 /*
   2  * Copyright (c) 2019 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   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,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  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
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28
  29 #ifndef _PRNG_ENTROPY_H_
  30 #define _PRNG_ENTROPY_H_
  31
  32 __BEGIN_DECLS
  33
  34 #ifdef XNU_KERNEL_PRIVATE
  35
  36 // The below three definitions are utilized when the kernel is in
  37 // "normal" operation, that is when we are *not* interested in collecting
  38 // entropy.
  39
  40 // Indicates the number of bytes in the entropy buffer
  41 #define ENTROPY_BUFFER_BYTE_SIZE 32
  42
  43 // Indicates the number of uint32_t's in the entropy buffer
  44 #define ENTROPY_BUFFER_SIZE (ENTROPY_BUFFER_BYTE_SIZE / sizeof(uint32_t))
  45
  46 // Mask applied to EntropyData.sample_count to get an
  47 // index suitable for storing the next sample in
  48 // EntropyData.buffer. Note that ENTROPY_BUFFER_SIZE must be a power
  49 // of two for the following mask calculation to be valid.
  50 #define ENTROPY_BUFFER_INDEX_MASK (ENTROPY_BUFFER_SIZE - 1)
  51
  52 typedef struct entropy_data {
  53         /*
  54          * TODO: Should sample_count be volatile?  Are we exposed to any races that
  55          * we care about if it is not?
  56          */
  57
  58         // At 32 bits, this counter can overflow. Since we're primarily
  59         // interested in the delta from one read to the next, we don't
  60         // worry about this too much.
  61         uint32_t sample_count;
  62
  63         // We point to either a static array when operating normally or
  64         // a dynamically allocated array when we wish to collect entropy
  65         // data. This decision is based on the presence of the boot
  66         // argument "ebsz".
  67         uint32_t *buffer;
  68
  69         // The entropy buffer size in bytes. This must be a power of 2.
  70         uint32_t buffer_size;
  71
  72         // The mask used to index into the entropy buffer for storing
  73         // the next entropy sample.
  74         uint32_t buffer_index_mask;
  75
  76         // The mask used to include the previous entropy buffer contents
  77         // when updating the entropy buffer. When in entropy collection
  78         // mode this is set to zero so that we can gather the raw entropy.
  79         // In normal operation this is set to (uint32_t) -1.
  80         uint32_t ror_mask;
  81 } entropy_data_t;
  82
  83 extern entropy_data_t EntropyData;
  84
  85 /* Trace codes for DBG_SEC_KERNEL: */
  86 #define ENTROPY_READ(n) SECURITYDBG_CODE(DBG_SEC_KERNEL, n) /* n: 0 .. 3 */
  87
  88 #endif /* XNU_KERNEL_PRIVATE */
  89
  90 void entropy_buffer_init(void);
  91
  92 __END_DECLS
  93
  94 #endif /* _PRNG_ENTROPY_H_ */