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

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Date:   Fri, 25 Mar 2022 09:06:31 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Baskov Evgeniy <baskov@...ras.ru>
Cc:     Matthew Garrett <mjg59@...f.ucam.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Jones <pjones@...hat.com>
Subject: Re: [PATCH RFC v2 0/2] Handle UEFI NX-restricted page tables

On Thu, 24 Mar 2022 at 17:39, <baskov@...ras.ru> wrote:
>
> On 2022-03-18 19:37, Peter Jones wrote:
> > On Thu, Mar 03, 2022 at 08:47:59PM +0000, Matthew Garrett wrote:
> >> On Thu, Mar 03, 2022 at 04:42:07PM +0300, baskov@...ras.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.
>
> The third version of the patch is the most close in structure
> to the proposed protocol. And until the protocol is standardized and
> implemented on problematic firmware, I think, it remains the better
> solution in terms of simplicity and further porting to the new
> protocol.
>
> It is desirable to get the issue resolved, and make the kernel stricter
> comply to the spec, without waiting for the new API implementation.
> And later, switch the kernel to be using the protocol with
> subsequent patches as soon as it gets usable.
>
> So, is there a chance for these patches to be accepted in current
> form, or with some modifications?
>

I am fine with taking the v3, as it is the most likely to only affect
the systems that actually need this change in behavior.

So unless there are any objections, I will queue these up after the
merge window.