UEFI v2.6 introduces EFI_MEMORY_ATTRIBUTES_TABLE which describes memory
protections that may be applied to EFI Runtime code and data regions by
kernel. This enables kernel to map these regions more strictly thereby
increasing security. Presently, the only valid bits for attribute field
of a memory descriptor are EFI_MEMORY_RO and EFI_MEMORY_XP, hence use
these bits to update mappings in efi_pgd.

UEFI specification recommends to use this feature instead of
EFI_PROPERTIES_TABLE and hence while updating efi mappings we first
check for EFI_MEMORY_ATTRIBUTES_TABLE and if it's present we update
mappings according to this table and hence disregarding
EFI_PROPERTIES_TABLE even if it's published by firmware. We consider
EFI_PROPERTIES_TABLE only when EFI_MEMORY_ATTRIBUTES_TABLE is absent.
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Lee, Chun-Yi <jlee@suse.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ricardo Neri <ricardo.neri@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>