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      1 /*
      2  * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
      3  *
      4  * Licensed under the Apache License 2.0 (the "License").  You may not use
      5  * this file except in compliance with the License.  You can obtain a copy
      6  * in the file LICENSE in the source distribution or at
      7  * https://www.openssl.org/source/license.html
      8  */
      9 
     10 #include "internal/cryptlib.h"
     11 #include <openssl/opensslconf.h>
     12 #include "crypto/rand_pool.h"
     13 #include "prov/seeding.h"
     14 
     15 #ifdef OPENSSL_RAND_SEED_RDTSC
     16 /*
     17  * IMPORTANT NOTE:  It is not currently possible to use this code
     18  * because we are not sure about the amount of randomness it provides.
     19  * Some SP800-90B tests have been run, but there is internal skepticism.
     20  * So for now this code is not used.
     21  */
     22 #error "RDTSC enabled?  Should not be possible!"
     23 
     24 /*
     25  * Acquire entropy from high-speed clock
     26  *
     27  * Since we get some randomness from the low-order bits of the
     28  * high-speed clock, it can help.
     29  *
     30  * Returns the total entropy count, if it exceeds the requested
     31  * entropy count. Otherwise, returns an entropy count of 0.
     32  */
     33 size_t ossl_prov_acquire_entropy_from_tsc(RAND_POOL *pool)
     34 {
     35     unsigned char c;
     36     int i;
     37 
     38     if ((OPENSSL_ia32cap_P[0] & (1 << 4)) != 0) {
     39         for (i = 0; i < TSC_READ_COUNT; i++) {
     40             c = (unsigned char)(OPENSSL_rdtsc() & 0xFF);
     41             ossl_rand_pool_add(pool, &c, 1, 4);
     42         }
     43     }
     44     return ossl_rand_pool_entropy_available(pool);
     45 }
     46 #else
     47 NON_EMPTY_TRANSLATION_UNIT
     48 #endif
     49