/* SPDX-License-Identifier: GPL-2.0-only */ #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; }