SecurityPkg/RngDxe: Add AArch64 RawAlgorithm support through ArmTrngLib

Bugzilla: 3668 (https://bugzilla.tianocore.org/show_bug.cgi?id=3668)

RawAlgorithm is used to provide access to entropy that is suitable
for cryptographic applications. Therefore, add RawAlgorithm support
that provides access to entropy using the ArmTrngLib.

Also remove unused UefiBootServicesTableLib library inclusion
and Status variable.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Acked-by: Jiewen Yao <jiewen.yao@intel.com>

SecurityPkg/RandomNumberGenerator/RngDxe/ArmTrng.c

@@ -0,0 +1,71 @@
+/** @file
+  RNG Driver to produce the UEFI Random Number Generator protocol.
+
+  The driver implements the EFI_RNG_ALGORITHM_RAW using the FW-TRNG
+  interface to provide entropy.
+
+  Copyright (c) 2021 - 2022, Arm Limited. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Library/BaseLib.h>
+#include <Library/BaseMemoryLib.h>
+#include <Library/DebugLib.h>
+#include <Library/ArmTrngLib.h>
+#include <Protocol/Rng.h>
+
+#include "RngDxeInternals.h"
+
+/**
+  Generate high-quality entropy source using a TRNG or 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  RETURN_SUCCESS            The function completed successfully.
+  @retval  RETURN_INVALID_PARAMETER  Invalid parameter.
+  @retval  RETURN_UNSUPPORTED        Function not implemented.
+  @retval  RETURN_BAD_BUFFER_SIZE    Buffer size is too small.
+  @retval  RETURN_NOT_READY          No Entropy available.
+**/
+EFI_STATUS
+EFIAPI
+GenerateEntropy (
+  IN  UINTN  Length,
+  OUT UINT8  *Entropy
+  )
+{
+  EFI_STATUS  Status;
+  UINTN       CollectedEntropyBits;
+  UINTN       RequiredEntropyBits;
+  UINTN       EntropyBits;
+  UINTN       Index;
+  UINTN       MaxBits;
+
+  ZeroMem (Entropy, Length);
+
+  RequiredEntropyBits  = (Length << 3);
+  Index                = 0;
+  CollectedEntropyBits = 0;
+  MaxBits              = GetArmTrngMaxSupportedEntropyBits ();
+  while (CollectedEntropyBits < RequiredEntropyBits) {
+    EntropyBits = MIN ((RequiredEntropyBits - CollectedEntropyBits), MaxBits);
+    Status      = GetArmTrngEntropy (
+                    EntropyBits,
+                    (Length - Index),
+                    &Entropy[Index]
+                    );
+    if (EFI_ERROR (Status)) {
+      // Discard the collected bits.
+      ZeroMem (Entropy, Length);
+      return Status;
+    }
+
+    CollectedEntropyBits += EntropyBits;
+    Index                += (EntropyBits >> 3);
+  } // while
+
+  return Status;
+}