SecurityPkg/RngDxe: Use GetRngGuid() when probing RngLib

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 and place the unsage algorithm
at the last position in the mAvailableAlgoArray.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Jiewen Yao <Jiewen.yao@intel.com>
Tested-by: Kun Qin <kun.qin@microsoft.com>

3 files changed, 44 insertions, 21 deletions

diff --git a/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c b/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
index e8be217f8a..a270441ebb 100644
--- a/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
+++ b/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
@@ -10,6 +10,8 @@
 #include <Library/DebugLib.h>

 #include <Library/MemoryAllocationLib.h>

 #include <Library/ArmTrngLib.h>

+#include <Library/RngLib.h>

+#include <Guid/RngAlgorithm.h>

 

 #include "RngDxeInternals.h"

 

@@ -28,9 +30,13 @@ GetAvailableAlgorithms (
   VOID

   )

 {

-  UINT64  DummyRand;

-  UINT16  MajorRevision;

-  UINT16  MinorRevision;

+  EFI_STATUS  Status;

+  UINT16      MajorRevision;

+  UINT16      MinorRevision;

+  GUID        RngGuid;

+  BOOLEAN     UnSafeAlgo;

+

+  UnSafeAlgo = FALSE;

 

   // Rng algorithms 2 times, one for the allocation, one to populate.

   mAvailableAlgoArray = AllocateZeroPool (RNG_AVAILABLE_ALGO_MAX);

@@ -38,24 +44,29 @@ GetAvailableAlgorithms (
     return EFI_OUT_OF_RESOURCES;

   }

 

-  // Check RngGetBytes() before advertising PcdCpuRngSupportedAlgorithm.

-  if (!EFI_ERROR (RngGetBytes (sizeof (DummyRand), (UINT8 *)&DummyRand))) {

-    CopyMem (

-      &mAvailableAlgoArray[mAvailableAlgoArrayCount],

-      PcdGetPtr (PcdCpuRngSupportedAlgorithm),

-      sizeof (EFI_RNG_ALGORITHM)

-      );

-    mAvailableAlgoArrayCount++;

-

-    DEBUG_CODE_BEGIN ();

-    if (IsZeroGuid (PcdGetPtr (PcdCpuRngSupportedAlgorithm))) {

+  // Identify RngLib algorithm.

+  Status = GetRngGuid (&RngGuid);

+  if (!EFI_ERROR (Status)) {

+    if (IsZeroGuid (&RngGuid) ||

+        CompareGuid (&RngGuid, &gEdkiiRngAlgorithmUnSafe))

+    {

+      // Treat zero GUID as an unsafe algorithm

       DEBUG ((

         DEBUG_WARN,

-        "PcdCpuRngSupportedAlgorithm should be a non-zero GUID\n"

+        "RngLib uses an Unsafe algorithm and "

+        "must not be used for production builds.\n"

         ));

+      // Set the UnSafeAlgo flag to indicate an unsafe algorithm was found

+      // so that it can be added at the end of the algorithm list.

+      UnSafeAlgo = TRUE;

+    } else {

+      CopyMem (

+        &mAvailableAlgoArray[mAvailableAlgoArrayCount],

+        &RngGuid,

+        sizeof (RngGuid)

+        );

+      mAvailableAlgoArrayCount++;

     }

-

-    DEBUG_CODE_END ();

   }

 

   // Raw algorithm (Trng)

@@ -68,5 +79,15 @@ GetAvailableAlgorithms (
     mAvailableAlgoArrayCount++;

   }

 

+  // Add unsafe algorithm at the end of the list.

+  if (UnSafeAlgo) {

+    CopyMem (

+      &mAvailableAlgoArray[mAvailableAlgoArrayCount],

+      &gEdkiiRngAlgorithmUnSafe,

+      sizeof (EFI_RNG_ALGORITHM)

+      );

+    mAvailableAlgoArrayCount++;

+  }

+

   return EFI_SUCCESS;

 }

diff --git a/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c b/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c
index ce49ff7ae6..78a18c5e11 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 d6c2d30195..8704a64441 100644
--- a/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
+++ b/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
@@ -75,13 +75,11 @@
   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

+  gEdkiiRngAlgorithmUnSafe            ## SOMETIMES_PRODUCES    ## GUID        # Unique ID of the algorithm for RNG

 

 [Protocols]

   gEfiRngProtocolGuid                ## PRODUCES

 

-[Pcd.AARCH64]

-  gEfiMdePkgTokenSpaceGuid.PcdCpuRngSupportedAlgorithm      ## CONSUMES

-

 [Depex]

   TRUE