xref: /dragonfly/sys/dev/crypto/rdrand/rdrand_harvest_x86_64.S (revision df5c0f32875b9ea77d002c2f672af88fec0b7ff7) 
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
401:
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       2f
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        1b
732:
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