SecurityPkg/RandomNumberGenerator/RngDxe/IA32/AsmRdRand.asm

   1 ;------------------------------------------------------------------------------
   2 ;
   3 ; Copyright (c) 2013, Intel Corporation. All rights reserved.<BR>
   4 ; This program and the accompanying materials
   5 ; are licensed and made available under the terms and conditions of the BSD License
   6 ; which accompanies this distribution.  The full text of the license may be found at
   7 ; http://opensource.org/licenses/bsd-license.php.
   8 ;
   9 ; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 ; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11 ;
  12 ; Module Name:
  13 ;
  14 ;   AsmRdRand.Asm
  15 ;
  16 ; Abstract:
  17 ;
  18 ;   Implementation for 16-, and 32- invocations of RDRAND instruction under 32bit platform.
  19 ;
  20 ; Notes:
  21 ;
  22 ;   Visual Studio coding practices do not use inline asm since multiple compilers and
  23 ;   architectures are supported assembler not recognizing rdrand instruction so using DB's.
  24 ;
  25 ;------------------------------------------------------------------------------
  26
  27     .586P
  28     .model flat, C
  29     .code
  30
  31 ;------------------------------------------------------------------------------
  32 ;  Generate a 16 bit random number
  33 ;  Return TRUE if Rand generated successfully, or FALSE if not
  34 ;
  35 ;  BOOLEAN EFIAPI RdRand16Step (UINT16 *Rand);   ECX
  36 ;------------------------------------------------------------------------------
  37 RdRand16Step  PROC
  38     ; rdrand   ax                  ; generate a 16 bit RN into ax, CF=1 if RN generated ok, otherwise CF=0
  39     db     0fh, 0c7h, 0f0h         ; rdrand r16:  "0f c7 /6  ModRM:r/m(w)"
  40     jb     rn16_ok                 ; jmp if CF=1
  41     xor    eax, eax                ; reg=0 if CF=0
  42     ret                            ; return with failure status
  43 rn16_ok:
  44     mov    [ecx], ax
  45     mov    eax, 1
  46     ret
  47 RdRand16Step ENDP
  48
  49 ;------------------------------------------------------------------------------
  50 ;  Generate a 32 bit random number
  51 ;    Return TRUE if Rand generated successfully, or FALSE if not
  52 ;
  53 ;  BOOLEAN EFIAPI RdRand32Step (UINT32 *Rand);   ECX
  54 ;------------------------------------------------------------------------------
  55 RdRand32Step  PROC
  56     ; rdrand   eax                 ; generate a 32 bit RN into eax, CF=1 if RN generated ok, otherwise CF=0
  57     db     0fh, 0c7h, 0f0h         ; rdrand r32:  "0f c7 /6  ModRM:r/m(w)"
  58     jb     rn32_ok                 ; jmp if CF=1
  59     xor    eax, eax                ; reg=0 if CF=0
  60     ret                            ; return with failure status
  61 rn32_ok:
  62     mov    [ecx], eax
  63     mov    eax,  1
  64     ret
  65 RdRand32Step  ENDP
  66
  67     END