Mark DMA memory allocations XP by default

[os-d]

Preface

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Description

When allocating memory for a non-coherent DMA device, the current core code removes the XP attribute, allowing code to execute from that region. This is a security vulnerability and unneeded. This change updates to mark the region as XP when allocating memory for the non-coherent DMA device.

These allocations in this function are limited to EfiBootServicesData and EfiRuntimeServicesData, which we expect to be XP.

This also updates a comment in PRM code that has a similar looking pattern, but does not clear EFI_MEMORY_XP because it does not pass any CPU arch attributes to the SetMemorySpaceAttributes which that function interprets as a request to not clear any attributes.

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    validation improvement, ...
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How This Was Tested

Tested on QEMU and a physical platform.

Integration Instructions

N/A.