openssl/providers/implementations/rands/seeding/rand_cpu_x86.c

/*
 * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the Apache License 2.0 (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#include "internal/cryptlib.h"
#include <openssl/opensslconf.h>
#include "prov/rand_pool.h"
#include "prov/seeding.h"

#ifdef OPENSSL_RAND_SEED_RDCPU
size_t OPENSSL_ia32_rdseed_bytes(unsigned char *buf, size_t len);
size_t OPENSSL_ia32_rdrand_bytes(unsigned char *buf, size_t len);

/*
 * Acquire entropy using Intel-specific cpu instructions
 *
 * Uses the RDSEED instruction if available, otherwise uses
 * RDRAND if available.
 *
 * For the differences between RDSEED and RDRAND, and why RDSEED
 * is the preferred choice, see https://goo.gl/oK3KcN
 *
 * Returns the total entropy count, if it exceeds the requested
 * entropy count. Otherwise, returns an entropy count of 0.
 */
size_t prov_acquire_entropy_from_cpu(RAND_POOL *pool)
{
    size_t bytes_needed;
    unsigned char *buffer;

    bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
    if (bytes_needed > 0) {
        buffer = rand_pool_add_begin(pool, bytes_needed);

        if (buffer != NULL) {
            /* Whichever comes first, use RDSEED, RDRAND or nothing */
            if ((OPENSSL_ia32cap_P[2] & (1 << 18)) != 0) {
                if (OPENSSL_ia32_rdseed_bytes(buffer, bytes_needed)
                    == bytes_needed) {
                    rand_pool_add_end(pool, bytes_needed, 8 * bytes_needed);
                }
            } else if ((OPENSSL_ia32cap_P[1] & (1 << (62 - 32))) != 0) {
                if (OPENSSL_ia32_rdrand_bytes(buffer, bytes_needed)
                    == bytes_needed) {
                    rand_pool_add_end(pool, bytes_needed, 8 * bytes_needed);
                }
            } else {
                rand_pool_add_end(pool, 0, 0);
            }
        }
    }

    return rand_pool_entropy_available(pool);
}
#else
NON_EMPTY_TRANSLATION_UNIT
#endif