blob: 4f5e5791a4cbf43deccbf4b24dc90b5b74a4659b [file] [log] [blame]
/* 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;
/* CRNGT_BLOCK_SIZE is the number of bytes in a “block” for the purposes of the
* continuous random number generator test in FIPS 140-2, section 4.9.2. */
#define CRNGT_BLOCK_SIZE 16
/* 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;
/* last_block contains the previous block from |CRYPTO_sysrand|. */
uint8_t last_block[CRNGT_BLOCK_SIZE];
/* last_block_valid is non-zero iff |last_block| contains data from
* |CRYPTO_sysrand|. */
int last_block_valid;
};
/* 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_get()[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(struct rand_thread_state *state,
uint8_t seed[CTR_DRBG_ENTROPY_LEN]) {
if (!state->last_block_valid) {
CRYPTO_sysrand(state->last_block, sizeof(state->last_block));
state->last_block_valid = 1;
}
/* 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));
/* See FIPS 140-2, section 4.9.2. This is the “continuous random number
* generator test” which causes the program to randomly abort. Hopefully the
* rate of failure is small enough not to be a problem in practice. */
if (CRYPTO_memcmp(state->last_block, entropy, CRNGT_BLOCK_SIZE) == 0) {
abort();
}
for (size_t i = CRNGT_BLOCK_SIZE; i < sizeof(entropy);
i += CRNGT_BLOCK_SIZE) {
if (CRYPTO_memcmp(entropy + i - CRNGT_BLOCK_SIZE, entropy + i,
CRNGT_BLOCK_SIZE) == 0) {
abort();
}
}
OPENSSL_memcpy(state->last_block,
entropy + sizeof(entropy) - CRNGT_BLOCK_SIZE,
CRNGT_BLOCK_SIZE);
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(struct rand_thread_state *state,
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;
}
state->last_block_valid = 0;
uint8_t seed[CTR_DRBG_ENTROPY_LEN];
rand_get_seed(state, 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(state, 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. This can be expensive (one read per |RAND_bytes| call)
* and so can be disabled by applications that we have ensured don't fork
* and aren't at risk of VM cloning. */
if (!rand_fork_unsafe_buffering_enabled()) {
CRYPTO_sysrand(additional_data, sizeof(additional_data));
} else {
OPENSSL_memset(additional_data, 0, 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);
}