Platform/ARM/Juno: Use DxeRngLib.inf as default RngLib implementation

Juno's RngLib implementation is:
- BaseRngLib.inf if a secure RngLib is enforced
- BaseRngLibTimerLib.inf if a non-secure RngLib is tolerated

BaseRngLib.inf relies on the Arm's RNDR instruction. The instruction
returns a DRBG-generated random number. The DRBG used is considered
as secure.
The RNDR instruction is available if FEAT_RNG is set. The Juno doesn't
support it.

When security is enforced (i.e. ENABLE_UNSAFE_RNGLIB is not set),
the Juno cannot generate secure random numbers through the RngLib.
Secure random numbers could be generated by using the Juno's TRNG.
This can be done by:
- using the RngDxeLib implementation of the RngLib
- RngDxeLib relies on the RngDxe
- the RngDxe has access to the TRNG

Signed-off-by: Pierre Gondois <[email protected]>

Platform/ARM/JunoPkg/ArmJuno.dsc

@@ -45,6 +45,8 @@
   # Trng Supports.
   ArmMonitorLib|ArmPkg/Library/ArmMonitorLib/ArmMonitorLib.inf
   ArmTrngLib|ArmPkg/Library/ArmTrngLib/ArmTrngLib.inf
+  # Rng
+  RngLib|MdePkg/Library/DxeRngLib/DxeRngLib.inf
 
   NorFlashDeviceLib|Platform/ARM/Library/P30NorFlashDeviceLib/P30NorFlashDeviceLib.inf
   NorFlashPlatformLib|Platform/ARM/JunoPkg/Library/NorFlashJunoLib/NorFlashJunoLib.inf
@@ -407,6 +409,18 @@
   # SCMI Driver
   ArmPkg/Drivers/ArmScmiDxe/ArmScmiDxe.inf
 
+  #
+  # Rng
+  #
+  SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf {
+    <LibraryClasses>
+    !if $(ENABLE_UNSAFE_RNGLIB) == TRUE
+      RngLib|MdeModulePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.inf
+    !else
+      RngLib|MdePkg/Library/BaseRngLib/BaseRngLib.inf
+    !endif
+  }
+
 [Components.AARCH64]
   #
   # EBC