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

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Message-ID: <20180403160712.GL26100@olila.local.net-space.pl>
Date:   Tue, 3 Apr 2018 18:07:12 +0200
From:   Daniel Kiper <daniel.kiper@...cle.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, xen-devel@...ts.xenproject.org,
        ard.biesheuvel@...aro.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 Tue, Apr 03, 2018 at 08:44:41AM -0700, James Bottomley wrote:
> On Tue, 2018-04-03 at 16:39 +0200, Daniel Kiper wrote:
> > Initialize UEFI secure boot state during dom0 boot. Otherwise the
> > kernel
> > may not even know that it runs on secure boot enabled platform.
> >
> > Signed-off-by: Daniel Kiper <daniel.kiper@...cle.com>
> > ---
> >  arch/x86/xen/efi.c                        |   57
> > +++++++++++++++++++++++++++++
> >  drivers/firmware/efi/libstub/secureboot.c |    3 ++
> >  2 files changed, 60 insertions(+)
> >
> > diff --git a/arch/x86/xen/efi.c b/arch/x86/xen/efi.c
> > index a18703b..1804b27 100644
> > --- a/arch/x86/xen/efi.c
> > +++ b/arch/x86/xen/efi.c
> > @@ -115,6 +115,61 @@ static efi_system_table_t __init
> > *xen_efi_probe(void)
> >  	return &efi_systab_xen;
> >  }
> >  
> > +/*
> > + * Determine whether we're in secure boot mode.
> > + *
> > + * Please keep the logic in sync with
> > + * drivers/firmware/efi/libstub/secureboot.c:efi_get_secureboot().
> > + */
> > +static enum efi_secureboot_mode xen_efi_get_secureboot(void)
> > +{
> > +	static efi_guid_t efi_variable_guid =
> > EFI_GLOBAL_VARIABLE_GUID;
> > +	static efi_guid_t shim_guid = EFI_SHIM_LOCK_GUID;
> > +	efi_status_t status;
> > +	u8 moksbstate, secboot, setupmode;
> > +	unsigned long size;
> > +
> > +	size = sizeof(secboot);
> > +	status = efi.get_variable(L"SecureBoot", &efi_variable_guid,
> > +				  NULL, &size, &secboot);
> > +
> > +	if (status == EFI_NOT_FOUND)
> > +		return efi_secureboot_mode_disabled;
> > +
> > +	if (status != EFI_SUCCESS)
> > +		goto out_efi_err;
> > +
> > +	size = sizeof(setupmode);
> > +	status = efi.get_variable(L"SetupMode", &efi_variable_guid,
> > +				  NULL, &size, &setupmode);
> > +
> > +	if (status != EFI_SUCCESS)
> > +		goto out_efi_err;
> > +
> > +	if (secboot == 0 || setupmode == 1)
> > +		return efi_secureboot_mode_disabled;
> > +
> > +	/* See if a user has put the shim into insecure mode. */
> > +	size = sizeof(moksbstate);
> > +	status = efi.get_variable(L"MokSBStateRT", &shim_guid,
> > +				  NULL, &size, &moksbstate);
> > +
> > +	/* If it fails, we don't care why. Default to secure. */
> > +	if (status != EFI_SUCCESS)
> > +		goto secure_boot_enabled;
> > +
> > +	if (moksbstate == 1)
> > +		return efi_secureboot_mode_disabled;
> > +
> > + secure_boot_enabled:
> > +	pr_info("UEFI Secure Boot is enabled.\n");
> > +	return efi_secureboot_mode_enabled;
> > +
> > + out_efi_err:
> > +	pr_err("Could not determine UEFI Secure Boot status.\n");
> > +	return efi_secureboot_mode_unknown;
> > +}
> > +
>
> 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.

Daniel