84 lines
2.1 KiB
C
84 lines
2.1 KiB
C
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/*
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* This file is part of the coreboot project.
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*
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* Copyright 2017 Intel Corporation.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; version 2 of the License.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*/
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#include <random.h>
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#include <rules.h>
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/*
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* Intel recommends that applications attempt 10 retries in a tight loop
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* in the unlikely event that the RDRAND instruction does not successfully
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* return a random number. The odds of ten failures in a row would in fact
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* be an indication of a larger CPU issue.
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*/
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#define RDRAND_RETRY_LOOPS 10
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/*
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* Generate a 32-bit random number through RDRAND instruction.
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* Carry flag is set on RDRAND success and 0 on failure.
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*/
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static inline uint8_t rdrand_32(uint32_t *rand)
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{
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uint8_t carry;
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__asm__ __volatile__(
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".byte 0x0f; .byte 0xc7; .byte 0xf0; setc %1"
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: "=a" (*rand), "=qm" (carry));
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return carry;
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}
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/*
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* Generate a 64-bit random number through RDRAND instruction.
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* Carry flag is set on RDRAND success and 0 on failure.
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*/
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static inline uint8_t rdrand_64(uint64_t *rand)
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{
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uint8_t carry;
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__asm__ __volatile__(
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".byte 0x48; .byte 0x0f; .byte 0xc7; .byte 0xf0; setc %1"
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: "=a" (*rand), "=qm" (carry));
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return carry;
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}
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int get_random_number_32(uint32_t *rand)
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{
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int i;
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/* Perform a loop call until RDRAND succeeds or returns failure. */
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for (i = 0; i < RDRAND_RETRY_LOOPS; i++) {
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if (rdrand_32(rand))
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return 0;
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}
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return -1;
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}
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int get_random_number_64(uint64_t *rand)
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{
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int i;
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uint32_t rand_high, rand_low;
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/* Perform a loop call until RDRAND succeeds or returns failure. */
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for (i = 0; i < RDRAND_RETRY_LOOPS; i++) {
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if (ENV_X86_64 && rdrand_64(rand))
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return 0;
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else if (rdrand_32(&rand_high) && rdrand_32(&rand_low)) {
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*rand = ((uint64_t)rand_high << 32) |
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(uint64_t)rand_low;
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return 0;
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}
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}
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return -1;
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}
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