cpython/Objects/mimalloc/random.c

/* ----------------------------------------------------------------------------
Copyright (c) 2019-2021, Microsoft Research, Daan Leijen
This is free software; you can redistribute it and/or modify it under the
terms of the MIT license. A copy of the license can be found in the file
"LICENSE" at the root of this distribution.
-----------------------------------------------------------------------------*/
#include "mimalloc.h"
#include "mimalloc/internal.h"
#include "mimalloc/prim.h"    // _mi_prim_random_buf
#include <string.h>       // memset

/* ----------------------------------------------------------------------------
We use our own PRNG to keep predictable performance of random number generation
and to avoid implementations that use a lock. We only use the OS provided
random source to initialize the initial seeds. Since we do not need ultimate
performance but we do rely on the security (for secret cookies in secure mode)
we use a cryptographically secure generator (chacha20).
-----------------------------------------------------------------------------*/

#define MI_CHACHA_ROUNDS …


/* ----------------------------------------------------------------------------
Chacha20 implementation as the original algorithm with a 64-bit nonce
and counter: https://en.wikipedia.org/wiki/Salsa20
The input matrix has sixteen 32-bit values:
Position  0 to  3: constant key
Position  4 to 11: the key
Position 12 to 13: the counter.
Position 14 to 15: the nonce.

The implementation uses regular C code which compiles very well on modern compilers.
(gcc x64 has no register spills, and clang 6+ uses SSE instructions)
-----------------------------------------------------------------------------*/

static inline uint32_t rotl(uint32_t x, uint32_t shift) { … }

static inline void qround(uint32_t x[16], size_t a, size_t b, size_t c, size_t d) { … }

static void chacha_block(mi_random_ctx_t* ctx)
{ … }

static uint32_t chacha_next32(mi_random_ctx_t* ctx) { … }

static inline uint32_t read32(const uint8_t* p, size_t idx32) { … }

static void chacha_init(mi_random_ctx_t* ctx, const uint8_t key[32], uint64_t nonce)
{ … }

static void chacha_split(mi_random_ctx_t* ctx, uint64_t nonce, mi_random_ctx_t* ctx_new) { … }


/* ----------------------------------------------------------------------------
Random interface
-----------------------------------------------------------------------------*/

#if MI_DEBUG>1
static bool mi_random_is_initialized(mi_random_ctx_t* ctx) {
  return (ctx != NULL && ctx->input[0] != 0);
}
#endif

void _mi_random_split(mi_random_ctx_t* ctx, mi_random_ctx_t* ctx_new) { … }

uintptr_t _mi_random_next(mi_random_ctx_t* ctx) { … }


/* ----------------------------------------------------------------------------
To initialize a fresh random context.
If we cannot get good randomness, we fall back to weak randomness based on a timer and ASLR.
-----------------------------------------------------------------------------*/

uintptr_t _mi_os_random_weak(uintptr_t extra_seed) { … }

static void mi_random_init_ex(mi_random_ctx_t* ctx, bool use_weak) { … }

void _mi_random_init(mi_random_ctx_t* ctx) { … }

void _mi_random_init_weak(mi_random_ctx_t * ctx) { … }

void _mi_random_reinit_if_weak(mi_random_ctx_t * ctx) { … }

/* --------------------------------------------------------
test vectors from <https://tools.ietf.org/html/rfc8439>
----------------------------------------------------------- */
/*
static bool array_equals(uint32_t* x, uint32_t* y, size_t n) {
  for (size_t i = 0; i < n; i++) {
    if (x[i] != y[i]) return false;
  }
  return true;
}
static void chacha_test(void)
{
  uint32_t x[4] = { 0x11111111, 0x01020304, 0x9b8d6f43, 0x01234567 };
  uint32_t x_out[4] = { 0xea2a92f4, 0xcb1cf8ce, 0x4581472e, 0x5881c4bb };
  qround(x, 0, 1, 2, 3);
  mi_assert_internal(array_equals(x, x_out, 4));

  uint32_t y[16] = {
       0x879531e0,  0xc5ecf37d,  0x516461b1,  0xc9a62f8a,
       0x44c20ef3,  0x3390af7f,  0xd9fc690b,  0x2a5f714c,
       0x53372767,  0xb00a5631,  0x974c541a,  0x359e9963,
       0x5c971061,  0x3d631689,  0x2098d9d6,  0x91dbd320 };
  uint32_t y_out[16] = {
       0x879531e0,  0xc5ecf37d,  0xbdb886dc,  0xc9a62f8a,
       0x44c20ef3,  0x3390af7f,  0xd9fc690b,  0xcfacafd2,
       0xe46bea80,  0xb00a5631,  0x974c541a,  0x359e9963,
       0x5c971061,  0xccc07c79,  0x2098d9d6,  0x91dbd320 };
  qround(y, 2, 7, 8, 13);
  mi_assert_internal(array_equals(y, y_out, 16));

  mi_random_ctx_t r = {
    { 0x61707865, 0x3320646e, 0x79622d32, 0x6b206574,
      0x03020100, 0x07060504, 0x0b0a0908, 0x0f0e0d0c,
      0x13121110, 0x17161514, 0x1b1a1918, 0x1f1e1d1c,
      0x00000001, 0x09000000, 0x4a000000, 0x00000000 },
    {0},
    0
  };
  uint32_t r_out[16] = {
       0xe4e7f110, 0x15593bd1, 0x1fdd0f50, 0xc47120a3,
       0xc7f4d1c7, 0x0368c033, 0x9aaa2204, 0x4e6cd4c3,
       0x466482d2, 0x09aa9f07, 0x05d7c214, 0xa2028bd9,
       0xd19c12b5, 0xb94e16de, 0xe883d0cb, 0x4e3c50a2 };
  chacha_block(&r);
  mi_assert_internal(array_equals(r.output, r_out, 16));
}
*/