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
401:
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	2f
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	1b
712:
72	/* return the number of stored random bytes. */
73	movq	%r11, 	%rax
74	ret
75END(padlock_rng)
76