MdePkg/Rng: Add GetRngGuid() to RngLib

The EFI_RNG_PROTOCOL can use the RngLib. The RngLib has multiple
implementations, some of them are unsafe (e.g. BaseRngLibTimerLib).
To allow the RngDxe to detect when such implementation is used,
add a GetRngGuid() function to the RngLib.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Kun Qin <kun.qin@microsoft.com>

MdeModulePkg/Library/BaseRngLibTimerLib/RngLibTimer.c

@@ -2,14 +2,18 @@
   BaseRng Library that uses the TimerLib to provide reasonably random numbers.
   Do not use this on a production system.
 
+  Copyright (c) 2023, Arm Limited. All rights reserved.
   Copyright (c) Microsoft Corporation.
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
 
 #include <Base.h>
+#include <Uefi.h>
 #include <Library/BaseLib.h>
+#include <Library/BaseMemoryLib.h>
 #include <Library/DebugLib.h>
 #include <Library/TimerLib.h>
+#include <Guid/RngAlgorithm.h>
 
 #define DEFAULT_DELAY_TIME_IN_MICROSECONDS  10
 
@@ -190,3 +194,27 @@ GetRandomNumber128 (
   // Read second 64 bits
   return GetRandomNumber64 (++Rand);
 }
+
+/**
+  Get a GUID identifying the RNG algorithm implementation.
+
+  @param [out] RngGuid  If success, contains the GUID identifying
+                        the RNG algorithm implementation.
+
+  @retval EFI_SUCCESS             Success.
+  @retval EFI_UNSUPPORTED         Not supported.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+GetRngGuid (
+  GUID  *RngGuid
+  )
+{
+  if (RngGuid == NULL) {
+    return EFI_INVALID_PARAMETER;
+  }
+
+  CopyMem (RngGuid, &gEdkiiRngAlgorithmUnSafe, sizeof (*RngGuid));
+  return EFI_SUCCESS;
+}