[PATCH v1 6/8] SecurityPkg/RngDxe: Use GetRngGuid() when probing RngLib

["PierreGondois" <pierre.gondois@arm.com>]

From: Pierre Gondois <pierre.gondois@arm.com>

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4151

The EFI_RNG_PROTOCOL can rely on 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,
a GetRngGuid() function was added in a previous patch.

The EFI_RNG_PROTOCOL can advertise multiple algorithms through
Guids. The PcdCpuRngSupportedAlgorithm is currently used to
advertise the RngLib in the Arm implementation.

The issues of doing that are:
- the RngLib implementation might not use CPU instructions,
  cf. the BaseRngLibTimerLib
- most platforms don't set PcdCpuRngSupportedAlgorithm

A GetRngGuid() was added to the RngLib in a previous patch,
allowing to identify the algorithm implemented by the RngLib.
Make use of this function.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
---
 .../RngDxe/AArch64/AArch64Algo.c              | 24 +++++++++----------
 .../RandomNumberGenerator/RngDxe/ArmRngDxe.c  |  6 ++++-
 .../RandomNumberGenerator/RngDxe/RngDxe.inf   |  5 ++--
 3 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c b/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
index e8be217f8a8c..a1ff7bd58fda 100644
--- a/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
+++ b/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
@@ -10,6 +10,7 @@
 #include <Library/DebugLib.h>
 #include <Library/MemoryAllocationLib.h>
 #include <Library/ArmTrngLib.h>
+#include <Library/RngLib.h>
 
 #include "RngDxeInternals.h"
 
@@ -28,9 +29,10 @@ GetAvailableAlgorithms (
   VOID
   )
 {
-  UINT64  DummyRand;
-  UINT16  MajorRevision;
-  UINT16  MinorRevision;
+  EFI_STATUS  Status;
+  UINT16      MajorRevision;
+  UINT16      MinorRevision;
+  GUID        RngGuid;
 
   // Rng algorithms 2 times, one for the allocation, one to populate.
   mAvailableAlgoArray = AllocateZeroPool (RNG_AVAILABLE_ALGO_MAX);
@@ -38,24 +40,22 @@ GetAvailableAlgorithms (
     return EFI_OUT_OF_RESOURCES;
   }
 
-  // Check RngGetBytes() before advertising PcdCpuRngSupportedAlgorithm.
-  if (!EFI_ERROR (RngGetBytes (sizeof (DummyRand), (UINT8 *)&DummyRand))) {
+  // Identify RngLib algorithm.
+  Status = GetRngGuid (&RngGuid);
+  if (!EFI_ERROR (Status)) {
     CopyMem (
       &mAvailableAlgoArray[mAvailableAlgoArrayCount],
-      PcdGetPtr (PcdCpuRngSupportedAlgorithm),
-      sizeof (EFI_RNG_ALGORITHM)
+      RngGuid,
+      sizeof (RngGuid)
       );
     mAvailableAlgoArrayCount++;
 
-    DEBUG_CODE_BEGIN ();
-    if (IsZeroGuid (PcdGetPtr (PcdCpuRngSupportedAlgorithm))) {
+    if (IsZeroGuid (&RngGuid)) {
       DEBUG ((
         DEBUG_WARN,
-        "PcdCpuRngSupportedAlgorithm should be a non-zero GUID\n"
+        "RngLib should have a non-zero GUID\n"
         ));
     }
-
-    DEBUG_CODE_END ();
   }
 
   // Raw algorithm (Trng)
diff --git a/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c b/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c
index ce49ff7ae661..78a18c5e1177 100644
--- a/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c
+++ b/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c
@@ -78,6 +78,7 @@ RngGetRNG (
 {
   EFI_STATUS  Status;
   UINTN       Index;
+  GUID        RngGuid;
 
   if ((This == NULL) || (RNGValueLength == 0) || (RNGValue == NULL)) {
     return EFI_INVALID_PARAMETER;
@@ -102,7 +103,10 @@ RngGetRNG (
   }
 
 FoundAlgo:
-  if (CompareGuid (RNGAlgorithm, PcdGetPtr (PcdCpuRngSupportedAlgorithm))) {
+  Status = GetRngGuid (&RngGuid);
+  if (!EFI_ERROR (Status) &&
+      CompareGuid (RNGAlgorithm, &RngGuid))
+  {
     Status = RngGetBytes (RNGValueLength, RNGValue);
     return Status;
   }
diff --git a/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf b/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
index d6c2d30195bf..aa5743387ed9 100644
--- a/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
+++ b/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
@@ -75,13 +75,12 @@ [Guids]
   gEfiRngAlgorithmX9313DesGuid        ## SOMETIMES_PRODUCES    ## GUID        # Unique ID of the algorithm for RNG
   gEfiRngAlgorithmX931AesGuid         ## SOMETIMES_PRODUCES    ## GUID        # Unique ID of the algorithm for RNG
   gEfiRngAlgorithmRaw                 ## SOMETIMES_PRODUCES    ## GUID        # Unique ID of the algorithm for RNG
+  gEfiRngAlgorithmArmRndr             ## SOMETIMES_PRODUCES    ## GUID        # Unique ID of the algorithm for RNG
+  gEfiRngAlgorithmUnSafe              ## SOMETIMES_PRODUCES    ## GUID        # Unique ID of the algorithm for RNG
 
 [Protocols]
   gEfiRngProtocolGuid                ## PRODUCES
 
-[Pcd.AARCH64]
-  gEfiMdePkgTokenSpaceGuid.PcdCpuRngSupportedAlgorithm      ## CONSUMES
-
 [Depex]
   TRUE
 
-- 
2.25.1