Re: [edk2-devel] [PATCH] ArmVirtPkg: Allow EFI memory attributes protocol to be disabled

["Gerd Hoffmann" <kraxel@redhat.com>]

  Hi,

> But what we might do is invent a way to avoid setting the XP attribute
> on the entire region based on some heuristic. Given that the main
> purpose of the EFI memory attribute protocol is to provide the ability
> to remove XP (and set RO instead), perhaps we can avoid the set
> entirely? Just brainstorming here.

Can the fault handler deal with this?  Set a flag somewhere, print a
big'n'fat error message, wait 5 secs, reset machine?  After reset the
firmware will see the flag and come up in 'compat' instead of 'strict'
mode.

Not sure what a good place for such a flag would be.  Do we have other
options than a non-volatile efi variable?  When using a efi variable we
probably should add an 'expires' timestamp, so the machine doesn't stay
in 'compat' mode forever.

> (cc'ing Taylor and Oliver given that this is related to the memory
> policy work as well) Perhaps we can use the fact that the active image
> is non-NX compat to make some tweaks?

Memory policies would be another candidate which could possibly use a
less strict profile in 'compat' mode.  I'd love to see memory policies
land for the February stable tag.

> What I really want to avoid is derail our effort to tighten things
> down and comply with the NX compat related policies, by adding some
> build time control that the distros will enable now and never disable
> again, citing backward compat concerns.

Sure, I want that too.  Having an runtime switch is already an
improvement over having a compile time switch.  Having this working
fully automatic would be even better of course.

> And the deafening silence from the shim developers is not an
> encouragement either.

Indeed.

take care,
  Gerd



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