SecurityPkg/RngDxe: Correctly update mAvailableAlgoArrayCount

mAvailableAlgoArrayCount holds the count of available RNG algorithms.
In a following patch, its value will be used to prevent the
EFI_RNG_PROTOCOL to be installed if no RNG algorithm is available.

Correctly set/reset the value for all implementations.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c

@@ -40,6 +40,7 @@ FreeAvailableAlgorithms (
   VOID
   )
 {
+  mAvailableAlgoArrayCount = 0;
   FreePool (mAvailableAlgoArray);
   return;
 }

SecurityPkg/RandomNumberGenerator/RngDxe/Rand/RngDxe.c

@@ -26,6 +26,11 @@
 
 #include "RngDxeInternals.h"
 
+//
+// Count of Rng algorithms.
+//
+#define RNG_ALGORITHM_COUNT  2
+
 /** Allocate and initialize mAvailableAlgoArray with the available
     Rng algorithms. Also update mAvailableAlgoArrayCount.
 
@@ -38,6 +43,7 @@ GetAvailableAlgorithms (
   VOID
   )
 {
+  mAvailableAlgoArrayCount = RNG_ALGORITHM_COUNT;
   return EFI_SUCCESS;
 }
 
@@ -49,6 +55,7 @@ FreeAvailableAlgorithms (
   VOID
   )
 {
+  mAvailableAlgoArrayCount = 0;
   return;
 }
 
@@ -164,7 +171,7 @@ RngGetInfo (
     return EFI_INVALID_PARAMETER;
   }
 
-  RequiredSize = 2 * sizeof (EFI_RNG_ALGORITHM);
+  RequiredSize = RNG_ALGORITHM_COUNT * sizeof (EFI_RNG_ALGORITHM);
 
   if (*RNGAlgorithmListSize < RequiredSize) {
     *RNGAlgorithmListSize = RequiredSize;