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/* 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>
#if defined(BORINGSSL_FIPS)
#include <unistd.h>
#endif
#include <openssl/chacha.h>
#include <openssl/cpu.h>
#include <openssl/mem.h>
#include "internal.h"
#include "../../internal.h"
#include "../delocate.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
#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, const 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;
}
const size_t remainder = len - len_multiple8;
if (remainder != 0) {
assert(remainder < 8);
uint8_t rand_buf[8];
if (!CRYPTO_rdrand(rand_buf)) {
return 0;
}
OPENSSL_memcpy(buf + len_multiple8, rand_buf, remainder);
}
#if defined(BORINGSSL_FIPS_BREAK_CRNG)
// This breaks the "continuous random number generator test" defined in FIPS
// 140-2, section 4.9.2, and implemented in rand_get_seed().
OPENSSL_memset(buf, 0, len);
#endif
return 1;
}
#else
static int hwrand(uint8_t *buf, size_t len) {
return 0;
}
#endif
// rand_state contains an RNG state.
struct rand_state {
CTR_DRBG_STATE drbg;
// next forms a NULL-terminated linked-list of all free |rand_state| objects.
struct rand_state *next;
// calls is the number of generate calls made on |drbg| since it was last
// (re)seeded. This is bound by |kReseedInterval|.
unsigned calls;
#if defined(BORINGSSL_FIPS)
// next_all forms another NULL-terminated linked-list, this time of all
// |rand_state| objects that have been allocated including those that might
// currently be in use.
struct rand_state *next_all;
// 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;
#endif
};
#if defined(BORINGSSL_FIPS)
static void rand_get_seed(struct rand_state *state,
uint8_t seed[CTR_DRBG_ENTROPY_LEN]) {
if (!state->last_block_valid) {
if (!hwrand(state->last_block, sizeof(state->last_block))) {
CRYPTO_sysrand(state->last_block, sizeof(state->last_block));
}
state->last_block_valid = 1;
}
// We overread from /dev/urandom or RDRAND by a factor of 10 and XOR to
// whiten.
#define FIPS_OVERREAD 10
uint8_t entropy[CTR_DRBG_ENTROPY_LEN * FIPS_OVERREAD];
if (!hwrand(entropy, sizeof(entropy))) {
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) {
fprintf(stderr, "CRNGT failed.\n");
BORINGSSL_FIPS_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) {
fprintf(stderr, "CRNGT failed.\n");
BORINGSSL_FIPS_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_state *state,
uint8_t seed[CTR_DRBG_ENTROPY_LEN]) {
// If not in FIPS mode, we don't overread from the system entropy source and
// we don't depend only on the hardware RDRAND.
CRYPTO_sysrand(seed, CTR_DRBG_ENTROPY_LEN);
}
#endif
// rand_state_free_list is a list of currently free, |rand_state| structures.
// When a thread needs a |rand_state| it picks the head element of this list and
// allocs a new one if the list is empty. Once it's finished, it pushes the
// state back onto the front of the list.
//
// Previously we used a thread-local state but for processes with large numbers
// of threads this can result in excessive memory usage. Since we don't free
// |rand_state| objects, the number of objects in memory will eventually equal
// the maximum concurrency of |RAND_bytes|.
DEFINE_BSS_GET(struct rand_state *, rand_state_free_list);
// rand_state_lock protects |rand_state_free_list| (and |rand_state_all_list|,
// in FIPS mode).
DEFINE_STATIC_MUTEX(rand_state_lock);
#if defined(BORINGSSL_FIPS)
// rand_state_all_list is the head of a linked-list of all |rand_state| objects
// in the process. This is needed because FIPS requires that they be zeroed on
// process exit.
DEFINE_BSS_GET(struct rand_state *, rand_state_all_list);
// rand_drbg_lock is taken in write mode by |rand_state_clear_all|, and
// in read mode by any operation on the |drbg| member of |rand_state|.
// This ensures that, in the event that a thread races destructor functions, we
// never return bogus random data. At worst, the thread will deadlock.
DEFINE_STATIC_MUTEX(rand_drbg_lock);
static void rand_state_clear_all(void) __attribute__((destructor));
static void rand_state_clear_all(void) {
CRYPTO_STATIC_MUTEX_lock_write(rand_drbg_lock_bss_get());
CRYPTO_STATIC_MUTEX_lock_write(rand_state_lock_bss_get());
for (struct rand_state *cur = *rand_state_all_list_bss_get();
cur != NULL; cur = cur->next_all) {
CTR_DRBG_clear(&cur->drbg);
}
// Both locks are deliberately left locked so that any threads that are still
// running will hang if they try to call |RAND_bytes|.
}
#endif
// rand_state_init seeds a |rand_state|.
static void rand_state_init(struct rand_state *state) {
OPENSSL_memset(state, 0, sizeof(struct rand_state));
uint8_t seed[CTR_DRBG_ENTROPY_LEN];
rand_get_seed(state, seed);
if (!CTR_DRBG_init(&state->drbg, seed, NULL, 0)) {
abort();
}
}
// rand_state_get pops a |rand_state| from the head of
// |rand_state_free_list| and returns it. If the list is empty, it
// creates a fresh |rand_state| and returns that instead.
static struct rand_state *rand_state_get(void) {
struct rand_state *state = NULL;
CRYPTO_STATIC_MUTEX_lock_write(rand_state_lock_bss_get());
state = *rand_state_free_list_bss_get();
if (state != NULL) {
*rand_state_free_list_bss_get() = state->next;
}
CRYPTO_STATIC_MUTEX_unlock_write(rand_state_lock_bss_get());
if (state != NULL) {
return state;
}
state = OPENSSL_malloc(sizeof(struct rand_state));
if (state == NULL) {
return NULL;
}
rand_state_init(state);
#if defined(BORINGSSL_FIPS)
CRYPTO_STATIC_MUTEX_lock_write(rand_state_lock_bss_get());
state->next_all = *rand_state_all_list_bss_get();
*rand_state_all_list_bss_get() = state;
CRYPTO_STATIC_MUTEX_unlock_write(rand_state_lock_bss_get());
#endif
return state;
}
// rand_state_put pushes |state| onto |rand_state_free_list|.
static void rand_state_put(struct rand_state *state) {
CRYPTO_STATIC_MUTEX_lock_write(rand_state_lock_bss_get());
state->next = *rand_state_free_list_bss_get();
*rand_state_free_list_bss_get() = state;
CRYPTO_STATIC_MUTEX_unlock_write(rand_state_lock_bss_get());
}
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;
}
// 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];
}
struct rand_state stack_state;
struct rand_state *state = rand_state_get();
if (state == NULL) {
// If the system is out of memory, use an ephemeral state on the
// stack.
state = &stack_state;
rand_state_init(state);
}
if (state->calls >= kReseedInterval) {
uint8_t seed[CTR_DRBG_ENTROPY_LEN];
rand_get_seed(state, seed);
#if defined(BORINGSSL_FIPS)
// Take a read lock around accesses to |state->drbg|. This is needed to
// avoid returning bad entropy if we race with
// |rand_state_clear_all|.
//
// This lock must be taken after any calls to |CRYPTO_sysrand| to avoid a
// bug on ppc64le. glibc may implement pthread locks by wrapping user code
// in a hardware transaction, but, on some older versions of glibc and the
// kernel, syscalls made with |syscall| did not abort the transaction.
CRYPTO_STATIC_MUTEX_lock_read(rand_drbg_lock_bss_get());
#endif
if (!CTR_DRBG_reseed(&state->drbg, seed, NULL, 0)) {
abort();
}
state->calls = 0;
} else {
#if defined(BORINGSSL_FIPS)
CRYPTO_STATIC_MUTEX_lock_read(rand_drbg_lock_bss_get());
#endif
}
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);
}
#if defined(BORINGSSL_FIPS)
CRYPTO_STATIC_MUTEX_unlock_read(rand_drbg_lock_bss_get());
#endif
if (state != &stack_state) {
rand_state_put(state);
}
}
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);
}