Protection for stack and heap

The PiSmmCore maintains a memory map internally. (https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/PiSmmCore/Page.c) If an SMM module allocates the data with EfiRuntimeServicesCode, this data is marked as the code page. If the SMM module allocates the data with EfiRuntimeServicesData, this data is marked as the data page. This information is also exposed via the EDKII_PI_SMM_MEMORY_ATTRIBUTES_TABLE.

The same RO and XD policy is also applied to the normal SMM data region, such as stack and heap.