VariablePolicySmmDxe.c

 
#include <Library/BaseLib.h>
#include <Library/UefiLib.h>
#include <Library/DebugLib.h>
#include <Library/SafeIntLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/BaseMemoryLib.h>
#include <Library/MemoryAllocationLib.h>
 
#include <Protocol/VariablePolicy.h>
#include <Protocol/MmCommunication2.h>
 
#include <Guid/VarCheckPolicyMmi.h>
 
#include "Variable.h"
 
EDKII_VARIABLE_POLICY_PROTOCOL  mVariablePolicyProtocol;
EFI_MM_COMMUNICATION2_PROTOCOL  *mMmCommunication;
 
VOID      *mMmCommunicationBuffer;
UINTN     mMmCommunicationBufferSize;
EFI_LOCK  mMmCommunicationLock;
 
STATIC
EFI_STATUS
InternalMmCommunicate (
  IN OUT VOID   *CommBuffer,
  IN OUT UINTN  *CommSize
  )
{
  EFI_STATUS  Status;
 
  if ((CommBuffer == NULL) || (CommSize == NULL)) {
    return EFI_INVALID_PARAMETER;
  }
 
  Status = mMmCommunication->Communicate (mMmCommunication, CommBuffer, CommBuffer, CommSize);
  return Status;
}
 
STATIC
EFI_STATUS
EFIAPI
ProtocolDisableVariablePolicy (
  VOID
  )
{
  EFI_STATUS                    Status;
  EFI_MM_COMMUNICATE_HEADER     *CommHeader;
  VAR_CHECK_POLICY_COMM_HEADER  *PolicyHeader;
  UINTN                         BufferSize;
 
  // Check the PCD for convenience.
  // This would also be rejected by the lib, but why go to MM if we don't have to?
  if (!PcdGetBool (PcdAllowVariablePolicyEnforcementDisable)) {
    return EFI_WRITE_PROTECTED;
  }
 
  AcquireLockOnlyAtBootTime (&mMmCommunicationLock);
 
  // Set up the MM communication.
  BufferSize   = mMmCommunicationBufferSize;
  CommHeader   = mMmCommunicationBuffer;
  PolicyHeader = (VAR_CHECK_POLICY_COMM_HEADER *)&CommHeader->Data;
  CopyGuid (&CommHeader->HeaderGuid, &gVarCheckPolicyLibMmiHandlerGuid);
  CommHeader->MessageLength = BufferSize - OFFSET_OF (EFI_MM_COMMUNICATE_HEADER, Data);
  PolicyHeader->Signature   = VAR_CHECK_POLICY_COMM_SIG;
  PolicyHeader->Revision    = VAR_CHECK_POLICY_COMM_REVISION;
  PolicyHeader->Command     = VAR_CHECK_POLICY_COMMAND_DISABLE;
 
  Status = InternalMmCommunicate (CommHeader, &BufferSize);
  DEBUG ((DEBUG_VERBOSE, "%a - MmCommunication returned %r.\n", __func__, Status));
 
  ReleaseLockOnlyAtBootTime (&mMmCommunicationLock);
 
  return (EFI_ERROR (Status)) ? Status : PolicyHeader->Result;
}
 
STATIC
EFI_STATUS
EFIAPI
ProtocolIsVariablePolicyEnabled (
  OUT BOOLEAN  *State
  )
{
  EFI_STATUS                               Status;
  EFI_MM_COMMUNICATE_HEADER                *CommHeader;
  VAR_CHECK_POLICY_COMM_HEADER             *PolicyHeader;
  VAR_CHECK_POLICY_COMM_IS_ENABLED_PARAMS  *CommandParams;
  UINTN                                    BufferSize;
 
  if (State == NULL) {
    return EFI_INVALID_PARAMETER;
  }
 
  AcquireLockOnlyAtBootTime (&mMmCommunicationLock);
 
  // Set up the MM communication.
  BufferSize    = mMmCommunicationBufferSize;
  CommHeader    = mMmCommunicationBuffer;
  PolicyHeader  = (VAR_CHECK_POLICY_COMM_HEADER *)&CommHeader->Data;
  CommandParams = (VAR_CHECK_POLICY_COMM_IS_ENABLED_PARAMS *)(PolicyHeader + 1);
  CopyGuid (&CommHeader->HeaderGuid, &gVarCheckPolicyLibMmiHandlerGuid);
  CommHeader->MessageLength = BufferSize - OFFSET_OF (EFI_MM_COMMUNICATE_HEADER, Data);
  PolicyHeader->Signature   = VAR_CHECK_POLICY_COMM_SIG;
  PolicyHeader->Revision    = VAR_CHECK_POLICY_COMM_REVISION;
  PolicyHeader->Command     = VAR_CHECK_POLICY_COMMAND_IS_ENABLED;
 
  Status = InternalMmCommunicate (CommHeader, &BufferSize);
  DEBUG ((DEBUG_VERBOSE, "%a - MmCommunication returned %r.\n", __func__, Status));
 
  if (!EFI_ERROR (Status)) {
    Status = PolicyHeader->Result;
    *State = CommandParams->State;
  }
 
  ReleaseLockOnlyAtBootTime (&mMmCommunicationLock);
 
  return Status;
}
 
STATIC
EFI_STATUS
EFIAPI
ProtocolRegisterVariablePolicy (
  IN CONST VARIABLE_POLICY_ENTRY  *NewPolicy
  )
{
  EFI_STATUS                    Status;
  EFI_MM_COMMUNICATE_HEADER     *CommHeader;
  VAR_CHECK_POLICY_COMM_HEADER  *PolicyHeader;
  VOID                          *PolicyBuffer;
  UINTN                         BufferSize;
  UINTN                         RequiredSize;
 
  if (NewPolicy == NULL) {
    return EFI_INVALID_PARAMETER;
  }
 
  // First, make sure that the required size does not exceed the capabilities
  // of the MmCommunication buffer.
  RequiredSize = OFFSET_OF (EFI_MM_COMMUNICATE_HEADER, Data) + sizeof (VAR_CHECK_POLICY_COMM_HEADER);
  Status       = SafeUintnAdd (RequiredSize, NewPolicy->Size, &RequiredSize);
  if (EFI_ERROR (Status) || (RequiredSize > mMmCommunicationBufferSize)) {
    DEBUG ((
      DEBUG_ERROR,
      "%a - Policy too large for buffer! %r, %d > %d \n",
      __func__,
      Status,
      RequiredSize,
      mMmCommunicationBufferSize
      ));
    return EFI_OUT_OF_RESOURCES;
  }
 
  AcquireLockOnlyAtBootTime (&mMmCommunicationLock);
 
  // Set up the MM communication.
  BufferSize   = mMmCommunicationBufferSize;
  CommHeader   = mMmCommunicationBuffer;
  PolicyHeader = (VAR_CHECK_POLICY_COMM_HEADER *)&CommHeader->Data;
  PolicyBuffer = (VOID *)(PolicyHeader + 1);
  CopyGuid (&CommHeader->HeaderGuid, &gVarCheckPolicyLibMmiHandlerGuid);
  CommHeader->MessageLength = BufferSize - OFFSET_OF (EFI_MM_COMMUNICATE_HEADER, Data);
  PolicyHeader->Signature   = VAR_CHECK_POLICY_COMM_SIG;
  PolicyHeader->Revision    = VAR_CHECK_POLICY_COMM_REVISION;
  PolicyHeader->Command     = VAR_CHECK_POLICY_COMMAND_REGISTER;
 
  // Copy the policy into place. This copy is safe because we've already tested above.
  CopyMem (PolicyBuffer, NewPolicy, NewPolicy->Size);
 
  Status = InternalMmCommunicate (CommHeader, &BufferSize);
  DEBUG ((DEBUG_VERBOSE, "%a - MmCommunication returned %r.\n", __func__, Status));
 
  ReleaseLockOnlyAtBootTime (&mMmCommunicationLock);
 
  return (EFI_ERROR (Status)) ? Status : PolicyHeader->Result;
}
 
STATIC
EFI_STATUS
DumpVariablePolicyHelper (
  IN  UINT32   PageRequested,
  OUT UINT32   *TotalSize,
  OUT UINT32   *PageSize,
  OUT BOOLEAN  *HasMore,
  OUT UINT8    **Buffer
  )
{
  EFI_STATUS                         Status;
  EFI_MM_COMMUNICATE_HEADER          *CommHeader;
  VAR_CHECK_POLICY_COMM_HEADER       *PolicyHeader;
  VAR_CHECK_POLICY_COMM_DUMP_PARAMS  *CommandParams;
  UINTN                              BufferSize;
 
  if ((TotalSize == NULL) || (PageSize == NULL) || (HasMore == NULL) || (Buffer == NULL)) {
    return EFI_INVALID_PARAMETER;
  }
 
  // Set up the MM communication.
  BufferSize    = mMmCommunicationBufferSize;
  CommHeader    = mMmCommunicationBuffer;
  PolicyHeader  = (VAR_CHECK_POLICY_COMM_HEADER *)&CommHeader->Data;
  CommandParams = (VAR_CHECK_POLICY_COMM_DUMP_PARAMS *)(PolicyHeader + 1);
  CopyGuid (&CommHeader->HeaderGuid, &gVarCheckPolicyLibMmiHandlerGuid);
  CommHeader->MessageLength = BufferSize - OFFSET_OF (EFI_MM_COMMUNICATE_HEADER, Data);
  PolicyHeader->Signature   = VAR_CHECK_POLICY_COMM_SIG;
  PolicyHeader->Revision    = VAR_CHECK_POLICY_COMM_REVISION;
  PolicyHeader->Command     = VAR_CHECK_POLICY_COMMAND_DUMP;
 
  CommandParams->PageRequested = PageRequested;
 
  Status = InternalMmCommunicate (CommHeader, &BufferSize);
  DEBUG ((DEBUG_VERBOSE, "%a - MmCommunication returned %r.\n", __func__, Status));
 
  if (!EFI_ERROR (Status)) {
    Status     = PolicyHeader->Result;
    *TotalSize = CommandParams->TotalSize;
    *PageSize  = CommandParams->PageSize;
    *HasMore   = CommandParams->HasMore;
    *Buffer    = (UINT8 *)(CommandParams + 1);
  }
 
  return Status;
}
 
STATIC
EFI_STATUS
EFIAPI
ProtocolDumpVariablePolicy (
  OUT UINT8      *Policy OPTIONAL,
  IN OUT UINT32  *Size
  )
{
  EFI_STATUS  Status;
  UINT8       *Source;
  UINT8       *Destination;
  UINT32      PolicySize;
  UINT32      PageSize;
  BOOLEAN     HasMore;
  UINT32      PageIndex;
 
  if ((Size == NULL) || ((*Size > 0) && (Policy == NULL))) {
    return EFI_INVALID_PARAMETER;
  }
 
  AcquireLockOnlyAtBootTime (&mMmCommunicationLock);
 
  // Repeat this whole process until we either have a failure case or get the entire buffer.
  do {
    // First, we must check the zero page to determine the buffer size and
    // reset the internal state.
    PolicySize = 0;
    PageSize   = 0;
    HasMore    = FALSE;
    Status     = DumpVariablePolicyHelper (0, &PolicySize, &PageSize, &HasMore, &Source);
    if (EFI_ERROR (Status)) {
      break;
    }
 
    // If we're good, we can at least check the required size now.
    if (*Size < PolicySize) {
      *Size  = PolicySize;
      Status = EFI_BUFFER_TOO_SMALL;
      break;
    }
 
    // On further thought, let's update the size either way.
    *Size = PolicySize;
    // And get ready to ROCK.
    Destination = Policy;
 
    // Keep looping and copying until we're either done or freak out.
    for (PageIndex = 1; !EFI_ERROR (Status) && HasMore && PageIndex < MAX_UINT32; PageIndex++) {
      Status = DumpVariablePolicyHelper (PageIndex, &PolicySize, &PageSize, &HasMore, &Source);
      if (!EFI_ERROR (Status)) {
        CopyMem (Destination, Source, PageSize);
        Destination += PageSize;
      }
    }
 
    // Next, we check to see whether
  } while (Status == EFI_TIMEOUT);
 
  ReleaseLockOnlyAtBootTime (&mMmCommunicationLock);
 
  // There's currently no use for this, but it shouldn't be hard to implement.
  return Status;
}
 
STATIC
EFI_STATUS
EFIAPI
ProtocolLockVariablePolicy (
  VOID
  )
{
  EFI_STATUS                    Status;
  EFI_MM_COMMUNICATE_HEADER     *CommHeader;
  VAR_CHECK_POLICY_COMM_HEADER  *PolicyHeader;
  UINTN                         BufferSize;
 
  AcquireLockOnlyAtBootTime (&mMmCommunicationLock);
 
  // Set up the MM communication.
  BufferSize   = mMmCommunicationBufferSize;
  CommHeader   = mMmCommunicationBuffer;
  PolicyHeader = (VAR_CHECK_POLICY_COMM_HEADER *)&CommHeader->Data;
  CopyGuid (&CommHeader->HeaderGuid, &gVarCheckPolicyLibMmiHandlerGuid);
  CommHeader->MessageLength = BufferSize - OFFSET_OF (EFI_MM_COMMUNICATE_HEADER, Data);
  PolicyHeader->Signature   = VAR_CHECK_POLICY_COMM_SIG;
  PolicyHeader->Revision    = VAR_CHECK_POLICY_COMM_REVISION;
  PolicyHeader->Command     = VAR_CHECK_POLICY_COMMAND_LOCK;
 
  Status = InternalMmCommunicate (CommHeader, &BufferSize);
  DEBUG ((DEBUG_VERBOSE, "%a - MmCommunication returned %r.\n", __func__, Status));
 
  ReleaseLockOnlyAtBootTime (&mMmCommunicationLock);
 
  return (EFI_ERROR (Status)) ? Status : PolicyHeader->Result;
}
 
STATIC
EFI_STATUS
InternalProtocolGetVariablePolicyInfo (
  IN      UINT32 Command,
  IN      CONST CHAR16 *VariableName,
  IN      CONST EFI_GUID *VendorGuid,
  IN OUT  UINTN *VariablePolicyVariableNameBufferSize, OPTIONAL
  OUT     VOID                        *VariablePolicy,
  OUT     CHAR16                      *VariablePolicyVariableName             OPTIONAL
  )
{
  EFI_STATUS                             Status;
  CHAR16                                 *OutputVariableName;
  EFI_MM_COMMUNICATE_HEADER              *CommHeader;
  VAR_CHECK_POLICY_COMM_HEADER           *PolicyHeader;
  VAR_CHECK_POLICY_COMM_GET_INFO_PARAMS  *CommandParams;
  UINTN                                  AllowedOutputVariableNameSize;
  UINTN                                  BufferSize;
  UINTN                                  VariableNameSize;
 
  if ((VariableName == NULL) || (VendorGuid == NULL) || (VariablePolicy == NULL)) {
    return EFI_INVALID_PARAMETER;
  }
 
  switch (Command) {
    case VAR_CHECK_POLICY_COMMAND_GET_INFO:
    case VAR_CHECK_POLICY_COMMAND_GET_LOCK_VAR_STATE_INFO:
      break;
    default:
      return EFI_INVALID_PARAMETER;
  }
 
  AcquireLockOnlyAtBootTime (&mMmCommunicationLock);
 
  VariableNameSize = StrnSizeS (
                       VariableName,
                       (VAR_CHECK_POLICY_MM_GET_INFO_BUFFER_SIZE - VAR_CHECK_POLICY_COMM_GET_INFO_PARAMS_END)
                       );
  if (VariableNameSize >= (VAR_CHECK_POLICY_MM_GET_INFO_BUFFER_SIZE - VAR_CHECK_POLICY_COMM_GET_INFO_PARAMS_END)) {
    Status = EFI_INVALID_PARAMETER;
    goto Done;
  }
 
  if ((VariablePolicyVariableName != NULL) && (VariablePolicyVariableNameBufferSize == NULL)) {
    return EFI_INVALID_PARAMETER;
    goto Done;
  }
 
  BufferSize = mMmCommunicationBufferSize;
  CommHeader = mMmCommunicationBuffer;
 
  Status =  SafeUintnSub (
              VAR_CHECK_POLICY_MM_GET_INFO_BUFFER_SIZE,
              VariableNameSize,
              &AllowedOutputVariableNameSize
              );
  if (EFI_ERROR (Status)) {
    Status = EFI_INVALID_PARAMETER;
    goto Done;
  }
 
  if (VariablePolicyVariableNameBufferSize != NULL) {
    AllowedOutputVariableNameSize = MIN (AllowedOutputVariableNameSize, *VariablePolicyVariableNameBufferSize);
  } else {
    AllowedOutputVariableNameSize = 0;
  }
 
  PolicyHeader  = (VAR_CHECK_POLICY_COMM_HEADER *)&CommHeader->Data;
  CommandParams = (VAR_CHECK_POLICY_COMM_GET_INFO_PARAMS *)(PolicyHeader + 1);
 
  CopyGuid (&CommHeader->HeaderGuid, &gVarCheckPolicyLibMmiHandlerGuid);
  CommHeader->MessageLength = BufferSize - OFFSET_OF (EFI_MM_COMMUNICATE_HEADER, Data);
  PolicyHeader->Signature   = VAR_CHECK_POLICY_COMM_SIG;
  PolicyHeader->Revision    = VAR_CHECK_POLICY_COMM_REVISION;
  PolicyHeader->Command     = Command;
 
  ZeroMem ((VOID *)&CommandParams->OutputPolicyEntry, sizeof (CommandParams->OutputPolicyEntry));
  CopyGuid (&CommandParams->InputVendorGuid, VendorGuid);
  Status = SafeUintnToUint32 (VariableNameSize, &CommandParams->InputVariableNameSize);
  if (EFI_ERROR (Status)) {
    Status = EFI_INVALID_PARAMETER;
    goto Done;
  }
 
  Status = SafeUintnToUint32 (AllowedOutputVariableNameSize, &CommandParams->OutputVariableNameSize);
  if (EFI_ERROR (Status)) {
    Status = EFI_INVALID_PARAMETER;
    goto Done;
  }
 
  if (AllowedOutputVariableNameSize > 0) {
    Status =  StrnCpyS (
                CommandParams->InputVariableName,
                AllowedOutputVariableNameSize / sizeof (CHAR16),
                VariableName,
                (UINTN)CommandParams->InputVariableNameSize / sizeof (CHAR16)
                );
    ASSERT_EFI_ERROR (Status);
  }
 
  Status = InternalMmCommunicate (CommHeader, &BufferSize);
  if (Status == EFI_SUCCESS) {
    CopyMem (
      VariablePolicy,
      (VOID *)&CommandParams->OutputPolicyEntry,
      (Command == VAR_CHECK_POLICY_COMMAND_GET_INFO) ?
      sizeof (CommandParams->OutputPolicyEntry.VariablePolicy) :
      sizeof (CommandParams->OutputPolicyEntry.LockOnVarStatePolicy)
      );
 
    if (VariablePolicyVariableNameBufferSize == NULL) {
      if (VariablePolicyVariableName != NULL) {
        Status = EFI_INVALID_PARAMETER;
      }
 
      goto Done;
    }
 
    if (PolicyHeader->Result == EFI_BUFFER_TOO_SMALL) {
      *VariablePolicyVariableNameBufferSize = (UINTN)CommandParams->OutputVariableNameSize;
      goto Done;
    }
 
    if (PolicyHeader->Result == EFI_SUCCESS) {
      if (CommandParams->OutputVariableNameSize > 0) {
        Status =  SafeUintnAdd (
                    ((UINTN)CommandParams + VAR_CHECK_POLICY_COMM_GET_INFO_PARAMS_END),
                    (UINTN)CommandParams->InputVariableNameSize,
                    (UINTN *)&OutputVariableName
                    );
        if (EFI_ERROR (Status)) {
          Status = EFI_BAD_BUFFER_SIZE;
          goto Done;
        }
 
        Status =  StrnCpyS (
                    VariablePolicyVariableName,
                    *VariablePolicyVariableNameBufferSize / sizeof (CHAR16),
                    OutputVariableName,
                    (UINTN)CommandParams->OutputVariableNameSize
                    );
        ASSERT_EFI_ERROR (Status);
        *VariablePolicyVariableNameBufferSize = (UINTN)CommandParams->OutputVariableNameSize;
      } else {
        // A variable policy variable name is not present. Return values according to interface.
        *VariablePolicyVariableNameBufferSize = 0;
      }
    }
  }
 
Done:
  ReleaseLockOnlyAtBootTime (&mMmCommunicationLock);
 
  return (EFI_ERROR (Status)) ? Status : PolicyHeader->Result;
}
 
STATIC
EFI_STATUS
EFIAPI
ProtocolGetVariablePolicyInfo (
  IN      CONST CHAR16 *VariableName,
  IN      CONST EFI_GUID *VendorGuid,
  IN OUT  UINTN *VariablePolicyVariableNameBufferSize, OPTIONAL
  OUT     VARIABLE_POLICY_ENTRY       *VariablePolicy,
  OUT     CHAR16                      *VariablePolicyVariableName             OPTIONAL
  )
{
  return InternalProtocolGetVariablePolicyInfo (
           VAR_CHECK_POLICY_COMMAND_GET_INFO,
           VariableName,
           VendorGuid,
           VariablePolicyVariableNameBufferSize,
           VariablePolicy,
           VariablePolicyVariableName
           );
}
 
STATIC
EFI_STATUS
EFIAPI
ProtocolGetLockOnVariableStateVariablePolicyInfo (
  IN      CONST CHAR16 *VariableName,
  IN      CONST EFI_GUID *VendorGuid,
  IN OUT  UINTN *VariableLockPolicyVariableNameBufferSize, OPTIONAL
  OUT     VARIABLE_LOCK_ON_VAR_STATE_POLICY   *VariablePolicy,
  OUT     CHAR16                              *VariableLockPolicyVariableName             OPTIONAL
  )
{
  return InternalProtocolGetVariablePolicyInfo (
           VAR_CHECK_POLICY_COMMAND_GET_LOCK_VAR_STATE_INFO,
           VariableName,
           VendorGuid,
           VariableLockPolicyVariableNameBufferSize,
           VariablePolicy,
           VariableLockPolicyVariableName
           );
}
 
STATIC
EFI_STATUS
InitMmCommonCommBuffer (
  IN OUT  UINTN  *BufferSize,
  OUT     VOID   **LocatedBuffer
  )
{
  EFI_STATUS  Status;
 
  Status = EFI_SUCCESS;
 
  // Make sure that we're working with good pointers.
  if ((BufferSize == NULL) || (LocatedBuffer == NULL)) {
    return EFI_INVALID_PARAMETER;
  }
 
  // Allocate the runtime memory for the comm buffer.
  *LocatedBuffer = AllocateRuntimePool (*BufferSize);
  if (*LocatedBuffer == NULL) {
    Status      = EFI_OUT_OF_RESOURCES;
    *BufferSize = 0;
  }
 
  EfiInitializeLock (&mMmCommunicationLock, TPL_NOTIFY);
 
  return Status;
}
 
STATIC
VOID
EFIAPI
VariablePolicyVirtualAddressCallback (
  IN  EFI_EVENT  Event,
  IN  VOID       *Context
  )
{
  EfiConvertPointer (0, (VOID **)&mMmCommunication);
  EfiConvertPointer (0, (VOID **)&mMmCommunicationBuffer);
}
 
EFI_STATUS
EFIAPI
VariablePolicySmmDxeMain (
  IN    EFI_HANDLE        ImageHandle,
  IN    EFI_SYSTEM_TABLE  *SystemTable
  )
{
  EFI_STATUS  Status;
  BOOLEAN     ProtocolInstalled;
  BOOLEAN     VirtualAddressChangeRegistered;
  EFI_EVENT   VirtualAddressChangeEvent;
 
  Status                         = EFI_SUCCESS;
  ProtocolInstalled              = FALSE;
  VirtualAddressChangeRegistered = FALSE;
 
  // Update the minimum buffer size.
  mMmCommunicationBufferSize = VAR_CHECK_POLICY_MM_COMM_BUFFER_SIZE;
  // Locate the shared comm buffer to use for sending MM commands.
  Status = InitMmCommonCommBuffer (&mMmCommunicationBufferSize, &mMmCommunicationBuffer);
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a - Failed to locate a viable MM comm buffer! %r\n", __func__, Status));
    ASSERT_EFI_ERROR (Status);
    return Status;
  }
 
  // Locate the MmCommunication protocol.
  Status = gBS->LocateProtocol (&gEfiMmCommunication2ProtocolGuid, NULL, (VOID **)&mMmCommunication);
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a - Failed to locate MmCommunication protocol! %r\n", __func__, Status));
    ASSERT_EFI_ERROR (Status);
    return Status;
  }
 
  // Configure the VariablePolicy protocol structure.
  mVariablePolicyProtocol.Revision                                 = EDKII_VARIABLE_POLICY_PROTOCOL_REVISION;
  mVariablePolicyProtocol.DisableVariablePolicy                    = ProtocolDisableVariablePolicy;
  mVariablePolicyProtocol.IsVariablePolicyEnabled                  = ProtocolIsVariablePolicyEnabled;
  mVariablePolicyProtocol.RegisterVariablePolicy                   = ProtocolRegisterVariablePolicy;
  mVariablePolicyProtocol.DumpVariablePolicy                       = ProtocolDumpVariablePolicy;
  mVariablePolicyProtocol.LockVariablePolicy                       = ProtocolLockVariablePolicy;
  mVariablePolicyProtocol.GetVariablePolicyInfo                    = ProtocolGetVariablePolicyInfo;
  mVariablePolicyProtocol.GetLockOnVariableStateVariablePolicyInfo = ProtocolGetLockOnVariableStateVariablePolicyInfo;
 
  // Register all the protocols and return the status.
  Status = gBS->InstallMultipleProtocolInterfaces (
                  &ImageHandle,
                  &gEdkiiVariablePolicyProtocolGuid,
                  &mVariablePolicyProtocol,
                  NULL
                  );
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a - Failed to install protocol! %r\n", __func__, Status));
    goto Exit;
  } else {
    ProtocolInstalled = TRUE;
  }
 
  // Normally, we might want to register a callback
  // to lock the interface, but this is integrated
  // into the existing callbacks in VaraiableSmm.c
  // and VariableDxe.c.
 
  //
  // Register a VirtualAddressChange callback for the MmComm protocol and Comm buffer.
  Status = gBS->CreateEventEx (
                  EVT_NOTIFY_SIGNAL,
                  TPL_NOTIFY,
                  VariablePolicyVirtualAddressCallback,
                  NULL,
                  &gEfiEventVirtualAddressChangeGuid,
                  &VirtualAddressChangeEvent
                  );
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a - Failed to create VirtualAddressChange event! %r\n", __func__, Status));
    goto Exit;
  } else {
    VirtualAddressChangeRegistered = TRUE;
  }
 
Exit:
  //
  // If we're about to return a failed status (and unload this driver), we must first undo anything that
  // has been successfully done.
  if (EFI_ERROR (Status)) {
    if (ProtocolInstalled) {
      gBS->UninstallProtocolInterface (&ImageHandle, &gEdkiiVariablePolicyProtocolGuid, &mVariablePolicyProtocol);
    }
 
    if (VirtualAddressChangeRegistered) {
      gBS->CloseEvent (VirtualAddressChangeEvent);
    }
  }
 
  return Status;
}