1/* 2 * Copyright (c) 2012 Alex Hornung <alex@alexhornung.com>. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in 13 * the documentation and/or other materials provided with the 14 * distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 19 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 20 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 21 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 22 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 23 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 24 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 25 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 26 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 */ 29 30#include <machine/asmacros.h> 31 32 .text 33 34/* int rdrand_rng(uint8_t *out, long limit) */ 35ENTRY(rdrand_rng) 36 movq %rsi, %rcx 37 shrq $3, %rcx /* Divide by 8 to get 64-bit word count */ 38 39 xorq %r11, %r11 40loop: 41 /* 42 * rdx: (output) entropy 43 */ 44 rdrand %rdx /* rdrand64 */ 45 46 /* 47 * The carry flag (CF) determines if the instruction was 48 * successful or not. 49 * 50 * CF = 0: Random value not available at time of execution. 51 */ 52 jae out 53 54 /* 55 * The operation was successful, so store the random data 56 * from the register into our buffer. 57 */ 58 movq %rdx, (%rdi) 59 60 /* 61 * Increment the count of stored random words as well as the 62 * buffer pointer in rdi. 63 */ 64 addq $1, %r11 65 addq $8, %rdi 66 67 /* 68 * If we haven't already read enough random words, 69 * loop again. 70 */ 71 cmpq %rcx, %r11 72 jl loop 73out: 74 /* return the number of stored random bytes (random words * 8) */ 75 shlq $3, %r11 76 movq %r11, %rax 77 ret 78END(rdrand_rng) 79