/** @file
  Support routines for RDRAND instruction access.

Copyright (c) 2013 - 2018, Intel Corporation. All rights reserved.<BR>
(C) Copyright 2015 Hewlett Packard Enterprise Development LP<BR>
This program and the accompanying materials
are licensed and made available under the terms and conditions of the BSD License
which accompanies this distribution.  The full text of the license may be found at
http://opensource.org/licenses/bsd-license.php

THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/
#include <Library/RngLib.h>

#include "RdRand.h"
#include "AesCore.h"

/**
  Calls RDRAND to fill a buffer of arbitrary size with random bytes.

  @param[in]   Length        Size of the buffer, in bytes,  to fill with.
  @param[out]  RandBuffer    Pointer to the buffer to store the random result.

  @retval EFI_SUCCESS        Random bytes generation succeeded.
  @retval EFI_NOT_READY      Failed to request random bytes.

**/
EFI_STATUS
EFIAPI
RdRandGetBytes (
  IN UINTN         Length,
  OUT UINT8        *RandBuffer
  )
{
  BOOLEAN     IsRandom;
  UINT64      TempRand[2];

  while (Length > 0) {
    IsRandom = GetRandomNumber128 (TempRand);
    if (!IsRandom) {
      return EFI_NOT_READY;
    }
    if (Length >= sizeof (TempRand)) {
      WriteUnaligned64 ((UINT64*)RandBuffer, TempRand[0]);
      RandBuffer += sizeof (UINT64);
      WriteUnaligned64 ((UINT64*)RandBuffer, TempRand[1]);
      RandBuffer += sizeof (UINT64);
      Length -= sizeof (TempRand);
    } else {
      CopyMem (RandBuffer, TempRand, Length);
      Length = 0;
    }
  }

  return EFI_SUCCESS;
}

/**
  Creates a 128bit random value that is fully forward and backward prediction resistant,
  suitable for seeding a NIST SP800-90 Compliant, FIPS 1402-2 certifiable SW DRBG.
  This function takes multiple random numbers through RDRAND without intervening
  delays to ensure reseeding and performs AES-CBC-MAC over the data to compute the
  seed value.

  @param[out]  SeedBuffer    Pointer to a 128bit buffer to store the random seed.

  @retval EFI_SUCCESS        Random seed generation succeeded.
  @retval EFI_NOT_READY      Failed to request random bytes.

**/
EFI_STATUS
EFIAPI
RdRandGetSeed128 (
  OUT UINT8        *SeedBuffer
  )
{
  EFI_STATUS  Status;
  UINT8       RandByte[16];
  UINT8       Key[16];
  UINT8       Ffv[16];
  UINT8       Xored[16];
  UINT32      Index;
  UINT32      Index2;

  //
  // Chose an arbitary key and zero the feed_forward_value (FFV)
  //
  for (Index = 0; Index < 16; Index++) {
    Key[Index] = (UINT8) Index;
    Ffv[Index] = 0;
  }

  //
  // Perform CBC_MAC over 32 * 128 bit values, with 10us gaps between 128 bit value
  // The 10us gaps will ensure multiple reseeds within the HW RNG with a large design margin.
  //
  for (Index = 0; Index < 32; Index++) {
    MicroSecondDelay (10);
    Status = RdRandGetBytes (16, RandByte);
    if (EFI_ERROR (Status)) {
      return Status;
    }

    //
    // Perform XOR operations on two 128-bit value.
    //
    for (Index2 = 0; Index2 < 16; Index2++) {
      Xored[Index2] = RandByte[Index2] ^ Ffv[Index2];
    }

    AesEncrypt (Key, Xored, Ffv);
  }

  for (Index = 0; Index < 16; Index++) {
    SeedBuffer[Index] = Ffv[Index];
  }

  return EFI_SUCCESS;
}

/**
  Generate high-quality entropy source through RDRAND.

  @param[in]   Length        Size of the buffer, in bytes, to fill with.
  @param[out]  Entropy       Pointer to the buffer to store the entropy data.

  @retval EFI_SUCCESS        Entropy generation succeeded.
  @retval EFI_NOT_READY      Failed to request random data.

**/
EFI_STATUS
EFIAPI
RdRandGenerateEntropy (
  IN UINTN         Length,
  OUT UINT8        *Entropy
  )
{
  EFI_STATUS  Status;
  UINTN       BlockCount;
  UINT8       Seed[16];
  UINT8       *Ptr;

  Status     = EFI_NOT_READY;
  BlockCount = Length / 16;
  Ptr        = (UINT8 *)Entropy;

  //
  // Generate high-quality seed for DRBG Entropy
  //
  while (BlockCount > 0) {
    Status = RdRandGetSeed128 (Seed);
    if (EFI_ERROR (Status)) {
      return Status;
    }
    CopyMem (Ptr, Seed, 16);

    BlockCount--;
    Ptr = Ptr + 16;
  }

  //
  // Populate the remained data as request.
  //
  Status = RdRandGetSeed128 (Seed);
  if (EFI_ERROR (Status)) {
    return Status;
  }
  CopyMem (Ptr, Seed, (Length % 16));

  return Status;
}