MonotonicCounter.c

Go to the documentation of this file.

 
#include <Uefi.h>
 
#include <Protocol/MonotonicCounter.h>
#include <Guid/MtcVendor.h>
 
#include <Library/BaseLib.h>
#include <Library/UefiDriverEntryPoint.h>
#include <Library/UefiRuntimeLib.h>
#include <Library/DebugLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/UefiRuntimeServicesTableLib.h>
 
//
// The handle to install Monotonic Counter Architctural Protocol
//
EFI_HANDLE  mMonotonicCounterHandle = NULL;
 
//
// The current monotonic counter value
//
UINT64  mEfiMtc;
 
//
// Event to update the monotonic Counter's high part when low part overflows.
//
EFI_EVENT  mEfiMtcEvent;
 
EFI_STATUS
EFIAPI
MonotonicCounterDriverGetNextMonotonicCount (
  OUT UINT64  *Count
  )
{
  EFI_TPL  OldTpl;
 
  //
  // Cannot be called after ExitBootServices()
  //
  if (EfiAtRuntime ()) {
    return EFI_UNSUPPORTED;
  }
 
  //
  // Check input parameters
  //
  if (Count == NULL) {
    return EFI_INVALID_PARAMETER;
  }
 
  //
  // Update the monotonic counter with a lock
  //
  OldTpl = gBS->RaiseTPL (TPL_HIGH_LEVEL);
  *Count = mEfiMtc;
  mEfiMtc++;
  gBS->RestoreTPL (OldTpl);
 
  //
  // If the low 32-bit counter overflows (MSB bit toggled),
  // then signal that the high part needs update now.
  //
  if ((((UINT32)mEfiMtc) ^ ((UINT32)*Count)) & BIT31) {
    gBS->SignalEvent (mEfiMtcEvent);
  }
 
  return EFI_SUCCESS;
}
 
EFI_STATUS
EFIAPI
MonotonicCounterDriverGetNextHighMonotonicCount (
  OUT UINT32  *HighCount
  )
{
  EFI_TPL  OldTpl;
 
  //
  // Check input parameters
  //
  if (HighCount == NULL) {
    return EFI_INVALID_PARAMETER;
  }
 
  if (!EfiAtRuntime ()) {
    //
    // Use a lock if called before ExitBootServices()
    //
    OldTpl     = gBS->RaiseTPL (TPL_HIGH_LEVEL);
    *HighCount = (UINT32)RShiftU64 (mEfiMtc, 32) + 1;
    mEfiMtc    = LShiftU64 (*HighCount, 32);
    gBS->RestoreTPL (OldTpl);
  } else {
    *HighCount = (UINT32)RShiftU64 (mEfiMtc, 32) + 1;
    mEfiMtc    = LShiftU64 (*HighCount, 32);
  }
 
  //
  // Update the NV variable to match the new high part
  //
  return EfiSetVariable (
           MTC_VARIABLE_NAME,
           &gMtcVendorGuid,
           EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_RUNTIME_ACCESS | EFI_VARIABLE_BOOTSERVICE_ACCESS,
           sizeof (UINT32),
           HighCount
           );
}
 
VOID
EFIAPI
EfiMtcEventHandler (
  IN EFI_EVENT  Event,
  IN VOID       *Context
  )
{
  UINT32  HighCount;
 
  MonotonicCounterDriverGetNextHighMonotonicCount (&HighCount);
}
 
EFI_STATUS
EFIAPI
MonotonicCounterDriverInitialize (
  IN EFI_HANDLE        ImageHandle,
  IN EFI_SYSTEM_TABLE  *SystemTable
  )
{
  EFI_STATUS  Status;
  UINT32      HighCount;
  UINTN       BufferSize;
 
  //
  // Make sure the Monotonic Counter Architectural Protocol has not been installed in the system yet.
  //
  ASSERT_PROTOCOL_ALREADY_INSTALLED (NULL, &gEfiMonotonicCounterArchProtocolGuid);
 
  //
  // Initialize event to handle low-part overflow
  //
  Status = gBS->CreateEvent (
                  EVT_NOTIFY_SIGNAL,
                  TPL_CALLBACK,
                  EfiMtcEventHandler,
                  NULL,
                  &mEfiMtcEvent
                  );
  ASSERT_EFI_ERROR (Status);
 
  //
  // Read the last high part
  //
  BufferSize = sizeof (UINT32);
  Status     = EfiGetVariable (
                 MTC_VARIABLE_NAME,
                 &gMtcVendorGuid,
                 NULL,
                 &BufferSize,
                 &HighCount
                 );
  if (EFI_ERROR (Status)) {
    HighCount = 0;
  }
 
  //
  // Set the current value
  //
  mEfiMtc = LShiftU64 (HighCount, 32);
 
  //
  // Increment the upper 32 bits for this boot
  // Continue even if it fails.  It will only fail if the variable services are
  // not functional.
  //
  MonotonicCounterDriverGetNextHighMonotonicCount (&HighCount);
 
  //
  // Fill in the EFI Boot Services and EFI Runtime Services Monotonic Counter Fields
  //
  gBS->GetNextMonotonicCount     = MonotonicCounterDriverGetNextMonotonicCount;
  gRT->GetNextHighMonotonicCount = MonotonicCounterDriverGetNextHighMonotonicCount;
 
  //
  // Install the Monotonic Counter Architctural Protocol onto a new handle
  //
  Status = gBS->InstallMultipleProtocolInterfaces (
                  &mMonotonicCounterHandle,
                  &gEfiMonotonicCounterArchProtocolGuid,
                  NULL,
                  NULL
                  );
  ASSERT_EFI_ERROR (Status);
 
  return EFI_SUCCESS;
}