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