Re: [PATCH RFC v2 0/2] Handle UEFI NX-restricted page tables

[Peter Jones <pjones@redhat.com>]

On Thu, Mar 03, 2022 at 08:47:59PM +0000, Matthew Garrett wrote:
> On Thu, Mar 03, 2022 at 04:42:07PM +0300, baskov@ispras.ru wrote:
> > On 2022-02-28 21:30, Matthew Garrett wrote:
> > > On Mon, Feb 28, 2022 at 05:45:53PM +0100, Ard Biesheuvel wrote:
> > > 
> > > > Given that this is a workaround for a very specific issue arising on
> > > > PI based implementations of UEFI, I consider this a quirk, and so I
> > > > think this approach is reasonable. I'd still like to gate it on some
> > > > kind of identification, though - perhaps something related to DMI like
> > > > the x86 core kernel does as well.
> > > 
> > > When the V1 patches were reviewed, you suggested allocating
> > > EFI_LOADER_CODE rather than EFI_LOADER_DATA. The example given for a
> > > failure case is when NxMemoryProtectionPolicy is set to 0x7fd4, in which
> > > case EFI_LOADER_CODE, EFI_BOOT_SERVICES_CODE and
> > > EFI_RUNTIEM_SERVICES_CODE should not have the nx policy applied. So it
> > > seems like your initial suggestion (s/LOADER_DATA/LOADER_CODE/) should
> > > have worked, even if there was disagreement about whether the spec
> > > required it to. Is this firmware applying a stricter policy?
> > 
> > Yes, this firmware is being modified to enforce stricter policy.
> 
> Ok. I think this should really go through the UEFI spec process - I 
> agree that from a strict interpretation of the spec, what this firmware 
> is doing is legitimate, but I don't like having a situation where we 
> have to depend on the DXE spec.

It's in the process of getting into the UEFI spec now as
https://bugzilla.tianocore.org/show_bug.cgi?id=3519 .

> How does Windows handle this? Just update the page tables itself for any 
> regions it needs during boot?

Microsoft's bootloader sets up its own pagetables, though I believe
they're switching it to use the (soon to be) standardized API.

-- 
        Peter