TcgMorLockDxe.c

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#include <PiDxe.h>
#include <Guid/MemoryOverwriteControl.h>
#include <IndustryStandard/MemoryOverwriteRequestControlLock.h>
#include <Library/DebugLib.h>
#include <Library/BaseLib.h>
#include <Library/BaseMemoryLib.h>
#include "Variable.h"
 
#include <Protocol/VariablePolicy.h>
#include <Library/VariablePolicyHelperLib.h>
 
EFI_STATUS
SetVariableCheckHandlerMor (
  IN CHAR16    *VariableName,
  IN EFI_GUID  *VendorGuid,
  IN UINT32    Attributes,
  IN UINTN     DataSize,
  IN VOID      *Data
  )
{
  //
  // Just let it pass. No need provide protection for DXE version.
  //
  return EFI_SUCCESS;
}
 
EFI_STATUS
MorLockInit (
  VOID
  )
{
  //
  // Always clear variable to report unsupported to OS.
  // The reason is that the DXE version is not proper to provide *protection*.
  // BIOS should use SMM version variable driver to provide such capability.
  //
  VariableServiceSetVariable (
    MEMORY_OVERWRITE_REQUEST_CONTROL_LOCK_NAME,
    &gEfiMemoryOverwriteRequestControlLockGuid,
    0,                                          // Attributes
    0,                                          // DataSize
    NULL                                        // Data
    );
 
  //
  // The MOR variable can effectively improve platform security only when the
  // MorLock variable protects the MOR variable. In turn MorLock cannot be made
  // secure without SMM support in the platform firmware (see above).
  //
  // Thus, delete the MOR variable, should it exist for any reason (some OSes
  // are known to create MOR unintentionally, in an attempt to set it), then
  // also lock the MOR variable, in order to prevent other modules from
  // creating it.
  //
  VariableServiceSetVariable (
    MEMORY_OVERWRITE_REQUEST_VARIABLE_NAME,
    &gEfiMemoryOverwriteControlDataGuid,
    0,                                      // Attributes
    0,                                      // DataSize
    NULL                                    // Data
    );
 
  return EFI_SUCCESS;
}
 
VOID
MorLockInitAtEndOfDxe (
  VOID
  )
{
  EFI_STATUS                      Status;
  EDKII_VARIABLE_POLICY_PROTOCOL  *VariablePolicy;
 
  // First, we obviously need to locate the VariablePolicy protocol.
  Status = gBS->LocateProtocol (&gEdkiiVariablePolicyProtocolGuid, NULL, (VOID **)&VariablePolicy);
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a - Could not locate VariablePolicy protocol! %r\n", __func__, Status));
    return;
  }
 
  // If we're successful, go ahead and set the policies to protect the target variables.
  Status = RegisterBasicVariablePolicy (
             VariablePolicy,
             &gEfiMemoryOverwriteRequestControlLockGuid,
             MEMORY_OVERWRITE_REQUEST_CONTROL_LOCK_NAME,
             VARIABLE_POLICY_NO_MIN_SIZE,
             VARIABLE_POLICY_NO_MAX_SIZE,
             VARIABLE_POLICY_NO_MUST_ATTR,
             VARIABLE_POLICY_NO_CANT_ATTR,
             VARIABLE_POLICY_TYPE_LOCK_NOW
             );
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a - Could not lock variable %s! %r\n", __func__, MEMORY_OVERWRITE_REQUEST_CONTROL_LOCK_NAME, Status));
  }
 
  Status = RegisterBasicVariablePolicy (
             VariablePolicy,
             &gEfiMemoryOverwriteControlDataGuid,
             MEMORY_OVERWRITE_REQUEST_VARIABLE_NAME,
             VARIABLE_POLICY_NO_MIN_SIZE,
             VARIABLE_POLICY_NO_MAX_SIZE,
             VARIABLE_POLICY_NO_MUST_ATTR,
             VARIABLE_POLICY_NO_CANT_ATTR,
             VARIABLE_POLICY_TYPE_LOCK_NOW
             );
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a - Could not lock variable %s! %r\n", __func__, MEMORY_OVERWRITE_REQUEST_VARIABLE_NAME, Status));
  }
 
  return;
}