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/AArch64/RngDxe.c

@@ -1,11 +1,13 @@
 /** @file
   RNG Driver to produce the UEFI Random Number Generator protocol.
 
-  The driver will use the RNDR instruction to produce random numbers.
+  The driver can use RNDR instruction (through the RngLib and if FEAT_RNG is
+  present) to produce random numbers. It also uses the Arm FW-TRNG interface
+  to implement EFI_RNG_ALGORITHM_RAW.
 
   RNG Algorithms defined in UEFI 2.4:
    - EFI_RNG_ALGORITHM_SP800_90_CTR_256_GUID
-   - EFI_RNG_ALGORITHM_RAW                    - Unsupported
+   - EFI_RNG_ALGORITHM_RAW
    - EFI_RNG_ALGORITHM_SP800_90_HMAC_256_GUID
    - EFI_RNG_ALGORITHM_SP800_90_HASH_256_GUID
    - EFI_RNG_ALGORITHM_X9_31_3DES_GUID        - Unsupported
@@ -26,12 +28,14 @@
 #include <Library/MemoryAllocationLib.h>
 #include <Library/UefiBootServicesTableLib.h>
 #include <Library/RngLib.h>
+#include <Library/DebugLib.h>
+#include <Library/ArmTrngLib.h>
 #include <Protocol/Rng.h>
 
 #include "RngDxeInternals.h"
 
 // Maximum number of Rng algorithms.
-#define RNG_AVAILABLE_ALGO_MAX  1
+#define RNG_AVAILABLE_ALGO_MAX  2
 
 /** Allocate and initialize mAvailableAlgoArray with the available
     Rng algorithms. Also update mAvailableAlgoArrayCount.
@@ -46,8 +50,9 @@ GetAvailableAlgorithms (
   )
 {
   UINT64  DummyRand;
+  UINT16  MajorRevision;
+  UINT16  MinorRevision;
 
-  // Allocate RNG_AVAILABLE_ALGO_MAX entries to avoid evaluating
   // Rng algorithms 2 times, one for the allocation, one to populate.
   mAvailableAlgoArray = AllocateZeroPool (RNG_AVAILABLE_ALGO_MAX);
   if (mAvailableAlgoArray == NULL) {
@@ -64,6 +69,16 @@ GetAvailableAlgorithms (
     mAvailableAlgoArrayCount++;
   }
 
+  // Raw algorithm (Trng)
+  if (!EFI_ERROR (GetArmTrngVersion (&MajorRevision, &MinorRevision))) {
+    CopyMem (
+      &mAvailableAlgoArray[mAvailableAlgoArrayCount],
+      &gEfiRngAlgorithmRaw,
+      sizeof (EFI_RNG_ALGORITHM)
+      );
+    mAvailableAlgoArrayCount++;
+  }
+
   return EFI_SUCCESS;
 }
 
@@ -141,6 +156,11 @@ FoundAlgo:
     return Status;
   }
 
+  // Raw algorithm (Trng)
+  if (CompareGuid (RNGAlgorithm, &gEfiRngAlgorithmRaw)) {
+    return GenerateEntropy (RNGValueLength, RNGValue);
+  }
+
   //
   // Other algorithms are unsupported by this driver.
   //