MdeModulePkg NonDiscoverablePciDeviceIo: MMIO Memory XP By Default

[apop5]

Description

When allocating memory for a non-discoverable PCI device's IO, 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-discoverable PCI device.

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

• [ ] Breaking change?
  • Breaking change - Does this PR cause a break in build or boot behavior?
  • Examples: Does it add a new library class or move a module to a different repo.
• [ ] Impacts security?
  • Security - Does this PR have a direct security impact?
  • Examples: Crypto algorithm change or buffer overflow fix.
• [ ] Includes tests?
  • Tests - Does this PR include any explicit test code?
  • Examples: Unit tests or integration tests.

How This Was Tested

Tested on QEMU and a physical platform.

Integration Instructions

N/A

[lgao4]

I agree this change is correct. Do you find any impact on the real platform?

[apop5]

I agree this change is correct. Do you find any impact on the real platform?

@os-d pointed out that this needs another changed, based on #5944 and the fix up in #5999.

On a real platform, there is no visible changes aside from the generated Paging Audit Report looking better because there are less regions with RWX.

[os-d]

To add to @apop5's statement, there is an impact on physical systems with this change, the MMIO allocated by this driver is not mapped executable any longer which fixes a security risk. Prior to this change, the MMIO regions allocated here would overwrite the attributes and make the region RWX.

[apop5]

This should be ready.