MdePkg/DxeRngLib: Request raw algorithm instead of default

The DxeRngLib tries to generate a random number using the 3 NIST
SP 800-90 compliant DRBG algorithms, i.e. 256-bits CTR, HASH and HMAC.
If none of the call is successful, the fallback option is the default
RNG algorithm of the EFI_RNG_PROTOCOL. This default algorithm might
be an unsafe implementation.

Try requesting the Raw algorithm before requesting the default one.

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

MdePkg/Library/DxeRngLib/DxeRngLib.c

@@ -65,9 +65,15 @@ GenerateRandomNumberViaNist800Algorithm (
     return Status;
   }
 
+  Status = RngProtocol->GetRNG (RngProtocol, &gEfiRngAlgorithmRaw, BufferSize, Buffer);
+  DEBUG ((DEBUG_INFO, "%a: GetRNG algorithm Raw - Status = %r\n", __func__, Status));
+  if (!EFI_ERROR (Status)) {
+    return Status;
+  }
+
   // If all the other methods have failed, use the default method from the RngProtocol
   Status = RngProtocol->GetRNG (RngProtocol, NULL, BufferSize, Buffer);
-  DEBUG ((DEBUG_INFO, "%a: GetRNG algorithm Hash-256 - Status = %r\n", __func__, Status));
+  DEBUG ((DEBUG_INFO, "%a: GetRNG algorithm default - Status = %r\n", __func__, Status));
   if (!EFI_ERROR (Status)) {
     return Status;
   }