Enable NX support for ARM VMs

[dann frazier]

EDK2 2023.05-1 introduced the EFI Memory Attribute Protocol, which shim 15.7-0ubuntu1 detects and consumes to implement NX support. Unfortunately, due to bugs in shim's usage of this feature, this caused shim to sometimes crash when handing off execution to the next stage bootloader. We worked around this for mantic by disabling the EFI Memory Attribute Protocol. This bug is to track the tasks required to re-enable it.

shim needs to adopt this patch from upstream (not yet in a release):

  From c7b305152802c8db688605654f75e1195def9fd6 Mon Sep 17 00:00:00 2001
  From: Nicholas Bishop <REDACTED>
  Date: Mon, 19 Dec 2022 18:56:13 -0500
  Subject: [PATCH] pe: Align section size up to page size for mem attrs

  Setting memory attributes is generally done at page granularity, and
  this is enforced by checks in `get_mem_attrs` and
  `update_mem_attrs`. But unlike the section address, the section size
  isn't necessarily aligned to 4KiB. Round up the section size to fix
  this.

  Signed-off-by: Nicholas Bishop <REDACTED>

shim should also handle the 64KiB attribute requirements described in Comment #1 which is not yet addressed upstream (see the shim upstream task on this bug).

qemu-efi-{aarch64,arm} should also document this change in NEWS.Debian, as it will break VMs that have not yet updated to the latest version of shim. And we should also cover this in the Ubuntu release notes.

[Heinrich Schuchardt (xypron)]

Hello Dann,

The UEFI specification requires that if a 64 KiB page contains either of

– EfiRuntimeServicesCode
– EfiRuntimeServicesData
– EfiReserved
– EfiACPIMemoryNVS

then all 4KiB pages in the 64KiB page must use identical attributes.

So additionally to the cited patch you must ensure that buffer allocated with AllocatePages() in handle_image() for which you set memory attributes does not contain any of the above memory types. The easiest way to fulfill the requirement is appropriate alignment and rounding of the used memory. I can't find this in upstream shim.

Best regards

Heinrich