linux-kernel - Re: [PATCH v2] x86/xen/efi: Initialize UEFI secure boot state during dom0 boot

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Date:   Wed, 11 Apr 2018 10:56:20 +0200
From:   Daniel Kiper <daniel.kiper@...cle.com>
To:     james.bottomley@...senpartnership.com, ard.biesheuvel@...aro.org
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, xen-devel@...ts.xenproject.org,
        boris.ostrovsky@...cle.com, eric.snowberg@...cle.com,
        hpa@...or.com, jgross@...e.com, konrad.wilk@...cle.com,
        mingo@...hat.com, tglx@...utronix.de
Subject: Re: [PATCH v2] x86/xen/efi: Initialize UEFI secure boot state during
 dom0 boot

On Wed, Apr 04, 2018 at 12:38:24PM +0200, Daniel Kiper wrote:
> On Tue, Apr 03, 2018 at 10:00:52AM -0700, James Bottomley wrote:
> > On Tue, 2018-04-03 at 18:07 +0200, Daniel Kiper wrote:
> > > On Tue, Apr 03, 2018 at 08:44:41AM -0700, James Bottomley wrote:
>
> [...]
>
> > > > This looks like a bad idea: you're duplicating the secure boot
> > > > check in
> > > >
> > > > drivers/firmware/efi/libstub/secureboot.c
> > > >
> > > > Which is an implementation of policy.  If we have to have policy in
> > > > the kernel, it should really only be in one place to prevent drift;
> > > > why can't you simply use the libstub efi_get_secureboot() so we're
> > > > not duplicating the implementation of policy?
> > >
> > > Well, here is the first version of this patch:
> > > https://lkml.org/lkml/2018/1/9/496 Ard did not like it. I was not
> > > happy too. In general both approaches are not perfect. More you can
> > > find in the discussion around this patchset. If you have better idea
> > > how to do that I am happy to implement it.
> >
> > One way might be simply to have the pre exit-boot-services code lay
> > down a variable containing the state which you pick up, rather than you
>
> Do you mean variable in kernel proper or something like that? If yes this
> is not possible. EFI Linux stub is not executed in Xen dom0. All UEFI
> infrastructure is owned and operated by Xen. Dom0 kernel can access some
> stuff in UEFI, including variables, via hypercall. However, when dom0
> runs only UEFI runtime services are available.
>
> > calling efi code separately and trying to use the insecure RT
>
> I am not sure why they are insecure.
>
> > variables.  That way there's a uniform view of the internal kernel
> > secure boot state that everyone can use.
>
> That would be perfect but I have a feeling that in form proposed above
> it is not possible.

Ping?

Daniel