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, int limit) */
35ENTRY(rdrand_rng)
36	movl	%esi,	%ecx
37	shrl	$3,	%ecx	/* Divide by 8 to get 64-bit word count */
38
39	xorq	%rbx, 	%rbx
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	addl	$1, 	%ebx
65	addq	$8,	%rdi
66
67	/*
68	 * If we haven't already read enough random words,
69	 * loop again.
70	 */
71	cmpl	%ecx, 	%ebx
72	jl	loop
73out:
74	/* return the number of stored random bytes (random words * 8) */
75	shll	$3,	%ebx
76	movl	%ebx, 	%eax
77	ret
78END(rdrand_rng)
79