1/* 2 * Copyright (c) 2011 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 padlock_rng(uint8_t *out, long limit) */ 35ENTRY(padlock_rng) 36 movq %rsi, %rcx 37 38 movq $3, %rdx 39 xorq %r11, %r11 40loop: 41 /* 42 * edx: (input) quality factor of rng entropy 43 * rdi: (input) buffer for random data 44 autoincremented at end of instruction 45 * eax: (output) rng status word 46 */ 47 .byte 0x0f, 0xa7, 0xc0 /* xstore-rng */ 48 49 50 /* 51 * The lower 5 bits of %eax contain the number of random 52 * bytes stored. 53 * If no bytes were stored, there is no more entropy 54 * available, so we finish up. 55 */ 56 andq $0x1f, %rax 57 jz out 58 59 /* 60 * Increment the count of stored random bytes. The buffer pointer 61 * in rdi is auto-incremented by the xstore-rng instruction. 62 */ 63 addq %rax, %r11 64 65 /* 66 * If we haven't already read enough random bytes, 67 * loop again. 68 */ 69 cmpq %rcx, %r11 70 jl loop 71out: 72 /* return the number of stored random bytes. */ 73 movq %r11, %rax 74 ret 75END(padlock_rng) 76