boringssl/crypto/rand/rand.c

/* Copyright (c) 2014, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <openssl/rand.h>

#include <assert.h>
#include <limits.h>
#include <string.h>

#include <openssl/chacha.h>
#include <openssl/cpu.h>
#include <openssl/mem.h>

#include "internal.h"
#include "../internal.h"


/* It's assumed that the operating system always has an unfailing source of
 * entropy which is accessed via |CRYPTO_sysrand|. (If the operating system
 * entropy source fails, it's up to |CRYPTO_sysrand| to abort the process—we
 * don't try to handle it.)
 *
 * In addition, the hardware may provide a low-latency RNG. Intel's rdrand
 * instruction is the canonical example of this. When a hardware RNG is
 * available we don't need to worry about an RNG failure arising from fork()ing
 * the process or moving a VM, so we can keep thread-local RNG state and use it
 * as an additional-data input to CTR-DRBG.
 *
 * (We assume that the OS entropy is safe from fork()ing and VM duplication.
 * This might be a bit of a leap of faith, esp on Windows, but there's nothing
 * that we can do about it.) */

/* kReseedInterval is the number of generate calls made to CTR-DRBG before
 * reseeding. */
static const unsigned kReseedInterval = 4096;

/* rand_thread_state contains the per-thread state for the RNG. */
struct rand_thread_state {
  CTR_DRBG_STATE drbg;
  /* calls is the number of generate calls made on |drbg| since it was last
   * (re)seeded. This is bound by |kReseedInterval|. */
  unsigned calls;
};

/* rand_thread_state_free frees a |rand_thread_state|. This is called when a
 * thread exits. */
static void rand_thread_state_free(void *state_in) {
  if (state_in == NULL) {
    return;
  }

  struct rand_thread_state *state = state_in;
  CTR_DRBG_clear(&state->drbg);
  OPENSSL_free(state);
}

#if defined(OPENSSL_X86_64) && !defined(OPENSSL_NO_ASM) && \
    !defined(BORINGSSL_UNSAFE_DETERMINISTIC_MODE)

/* These functions are defined in asm/rdrand-x86_64.pl */
extern int CRYPTO_rdrand(uint8_t out[8]);
extern int CRYPTO_rdrand_multiple8_buf(uint8_t *buf, size_t len);

static int have_rdrand(void) {
  return (OPENSSL_ia32cap_P[1] & (1u << 30)) != 0;
}

static int hwrand(uint8_t *buf, size_t len) {
  if (!have_rdrand()) {
    return 0;
  }

  const size_t len_multiple8 = len & ~7;
  if (!CRYPTO_rdrand_multiple8_buf(buf, len_multiple8)) {
    return 0;
  }
  len -= len_multiple8;

  if (len != 0) {
    assert(len < 8);

    uint8_t rand_buf[8];
    if (!CRYPTO_rdrand(rand_buf)) {
      return 0;
    }
    OPENSSL_memcpy(buf + len_multiple8, rand_buf, len);
  }

  return 1;
}

#else

static int hwrand(uint8_t *buf, size_t len) {
  return 0;
}

#endif

#if defined(BORINGSSL_FIPS)

static void rand_get_seed(uint8_t seed[CTR_DRBG_ENTROPY_LEN]) {
  /* We overread from /dev/urandom by a factor of 10 and XOR to whiten. */
#define FIPS_OVERREAD 10
  uint8_t entropy[CTR_DRBG_ENTROPY_LEN * FIPS_OVERREAD];
  CRYPTO_sysrand(entropy, sizeof(entropy));

  OPENSSL_memcpy(seed, entropy, CTR_DRBG_ENTROPY_LEN);

  for (size_t i = 1; i < FIPS_OVERREAD; i++) {
    for (size_t j = 0; j < CTR_DRBG_ENTROPY_LEN; j++) {
      seed[j] ^= entropy[CTR_DRBG_ENTROPY_LEN * i + j];
    }
  }
}

#else

static void rand_get_seed(uint8_t seed[CTR_DRBG_ENTROPY_LEN]) {
  /* If not in FIPS mode, we don't overread from the system entropy source. */
  CRYPTO_sysrand(seed, CTR_DRBG_ENTROPY_LEN);
}

#endif

void RAND_bytes_with_additional_data(uint8_t *out, size_t out_len,
                                     const uint8_t user_additional_data[32]) {
  if (out_len == 0) {
    return;
  }

  struct rand_thread_state stack_state;
  struct rand_thread_state *state =
      CRYPTO_get_thread_local(OPENSSL_THREAD_LOCAL_RAND);

  if (state == NULL) {
    state = OPENSSL_malloc(sizeof(struct rand_thread_state));
    if (state == NULL ||
        !CRYPTO_set_thread_local(OPENSSL_THREAD_LOCAL_RAND, state,
                                 rand_thread_state_free)) {
      /* If the system is out of memory, use an ephemeral state on the
       * stack. */
      state = &stack_state;
    }

    uint8_t seed[CTR_DRBG_ENTROPY_LEN];
    rand_get_seed(seed);
    if (!CTR_DRBG_init(&state->drbg, seed, NULL, 0)) {
      abort();
    }
    state->calls = 0;
  }

  if (state->calls >= kReseedInterval) {
    uint8_t seed[CTR_DRBG_ENTROPY_LEN];
    rand_get_seed(seed);
    if (!CTR_DRBG_reseed(&state->drbg, seed, NULL, 0)) {
      abort();
    }
    state->calls = 0;
  }

  /* Additional data is mixed into every CTR-DRBG call to protect, as best we
   * can, against forks & VM clones. We do not over-read this information and
   * don't reseed with it so, from the point of view of FIPS, this doesn't
   * provide “prediction resistance”. But, in practice, it does. */
  uint8_t additional_data[32];
  if (!hwrand(additional_data, sizeof(additional_data))) {
    /* Without a hardware RNG to save us from address-space duplication, the OS
     * entropy is used. */
    CRYPTO_sysrand(additional_data, sizeof(additional_data));
  }

  for (size_t i = 0; i < sizeof(additional_data); i++) {
    additional_data[i] ^= user_additional_data[i];
  }

  int first_call = 1;
  while (out_len > 0) {
    size_t todo = out_len;
    if (todo > CTR_DRBG_MAX_GENERATE_LENGTH) {
      todo = CTR_DRBG_MAX_GENERATE_LENGTH;
    }

    if (!CTR_DRBG_generate(&state->drbg, out, todo, additional_data,
                           first_call ? sizeof(additional_data) : 0)) {
      abort();
    }

    out += todo;
    out_len -= todo;
    state->calls++;
    first_call = 0;
  }

  if (state == &stack_state) {
    CTR_DRBG_clear(&state->drbg);
  }

  return;
}

int RAND_bytes(uint8_t *out, size_t out_len) {
  static const uint8_t kZeroAdditionalData[32] = {0};
  RAND_bytes_with_additional_data(out, out_len, kZeroAdditionalData);
  return 1;
}

int RAND_pseudo_bytes(uint8_t *buf, size_t len) {
  return RAND_bytes(buf, len);
}

void RAND_seed(const void *buf, int num) {
  /* OpenSSH calls |RAND_seed| before jailing on the assumption that any needed
   * file descriptors etc will be opened. */
  uint8_t unused;
  RAND_bytes(&unused, sizeof(unused));
}

int RAND_load_file(const char *path, long num) {
  if (num < 0) {  /* read the "whole file" */
    return 1;
  } else if (num <= INT_MAX) {
    return (int) num;
  } else {
    return INT_MAX;
  }
}

const char *RAND_file_name(char *buf, size_t num) { return NULL; }

void RAND_add(const void *buf, int num, double entropy) {}

int RAND_egd(const char *path) {
  return 255;
}

int RAND_poll(void) {
  return 1;
}

int RAND_status(void) {
  return 1;
}

static const struct rand_meth_st kSSLeayMethod = {
  RAND_seed,
  RAND_bytes,
  RAND_cleanup,
  RAND_add,
  RAND_pseudo_bytes,
  RAND_status,
};

RAND_METHOD *RAND_SSLeay(void) {
  return (RAND_METHOD*) &kSSLeayMethod;
}

void RAND_set_rand_method(const RAND_METHOD *method) {}

void RAND_cleanup(void) {}