Computer security: Boot guard validation.

EFI_STATUSBootGuardPei(EFI_PEI_SERVICES **PeiServices, VOID *Ppi)
{
    ...
Status = GetBootMode ();
    if ( EFI_ERROR( Status ) ) {
        return   Status;
    }
...
if ( (BootMode == BOOT_IN_RECOVERY_MODE) || (BootMode == BOOT_ON_FLASH_UPDATE) || BootMode == BOOT_ON_S3_RESUME) {
        return   Status;
    }
BootGuardVerifyTransitionPEItoDXEFlag = 0;
    ...
CalculateSha256(BootGuardHashKeySegment0);
    CalculateSha256(CurrentBootGuardHashKey0);
if ( !MemCmp(BootGuardHashKeySegment0, CurrentBootGuardHashKey0, 32) ) {
        BootGuardVerifyTransitionPEItoDXEFlag = 1;
    } else {
        BootGuardVerifyTransitionPEItoDXEFlag = 0;
        return   EFI_SUCCESS;
    }
    if ( !((BootGuardHashKeySegment1 == 0) {
        CalculateSha256 (BootGuardHashKeySegment1);
        CalculateSha256 (CurrentBootGuardHashKey1);
if ( !MemCmp(BootGuardHashKeySegment1, CurrentBootGuardHashKey1, 32) ) {
            BootGuardVerifyTransitionPEItoDXEFlag = 1;
        } else {
            BootGuardVerifyTransitionPEItoDXEFlag = 0;
            return EFI_SUCCESS;
        }
    }
return   Status;
}

EFI_STATUS BootGuardDxe(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
{
    ...
if ( BootGuardSupported() == FALSE ) {
        return   EFI_SUCCESS;
    }
...
BootMode  = GetBootMode();
    if ( (BootMode == BOOT_IN_RECOVERY_MODE) ||
(BootMode == BOOT_ON_FLASH_UPDATE) ) {
        return   EFI_SUCCESS;
    }
...
if ( BootGuardVerifyTransitionPEItoDXEFlag == 0 ) { BootGuardRegisterCallBack();
    }
return   EFI_SUCCESS;
}