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/* SPDX-License-Identifier: GPL-2.0-only */
/* This file is part of the coreboot project. */
#include <random.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;
}
#if ENV_X86_64
/*
* 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;
}
#endif
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
if (rdrand_64(rand))
return 0;
#endif
if (rdrand_32(&rand_high) && rdrand_32(&rand_low)) {
*rand = ((uint64_t)rand_high << 32) |
(uint64_t)rand_low;
return 0;
}
}
return -1;
}
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