linux-kernel - Re: [PATCH v4 2/2] Support ESRT in Xen dom0

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YzdszknqsmWsPsMZ@itl-email>
Date:   Fri, 30 Sep 2022 18:25:14 -0400
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Peter Jones <pjones@...hat.com>, Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org
Subject: Re: [PATCH v4 2/2] Support ESRT in Xen dom0

On Fri, Sep 30, 2022 at 10:59:49PM +0200, Ard Biesheuvel wrote:
> On Fri, 30 Sept 2022 at 22:21, Demi Marie Obenour
> <demi@...isiblethingslab.com> wrote:
> >
> > On Fri, Sep 30, 2022 at 09:11:19PM +0200, Ard Biesheuvel wrote:
> > > On Fri, 30 Sept 2022 at 20:21, Demi Marie Obenour
> > > <demi@...isiblethingslab.com> wrote:
> > > >
> > > > On Fri, Sep 30, 2022 at 06:36:11PM +0200, Ard Biesheuvel wrote:
> > > > > On Fri, 30 Sept 2022 at 01:02, Demi Marie Obenour
> > > > > <demi@...isiblethingslab.com> wrote:
> > > > > >
> > > > > > fwupd requires access to the EFI System Resource Table (ESRT) to
> > > > > > discover which firmware can be updated by the OS.  Currently, Linux does
> > > > > > not expose the ESRT when running as a Xen dom0.  Therefore, it is not
> > > > > > possible to use fwupd in a Xen dom0, which is a serious problem for e.g.
> > > > > > Qubes OS.
> > > > > >
> > > > > > Before Xen 4.17, this was not fixable due to hypervisor limitations.
> > > > > > The UEFI specification requires the ESRT to be in EfiBootServicesData
> > > > > > memory, which Xen will use for whatever purposes it likes.  Therefore,
> > > > > > Linux cannot safely access the ESRT, as Xen may have overwritten it.
> > > > > >
> > > > > > Starting with Xen 4.17, Xen checks if the ESRT is in EfiBootServicesData
> > > > > > or EfiRuntimeServicesData memory.  If the ESRT is in EfiBootServicesData
> > > > > > memory, Xen replaces the ESRT with a copy in memory that it has
> > > > > > reserved.  Such memory is currently of type EFI_RUNTIME_SERVICES_DATA,
> > > > > > but in the future it will be of type EFI_ACPI_RECLAIM_MEMORY.  This
> > > > > > ensures that the ESRT can safely be accessed by the OS.
> > > > > >
> > > > > > When running as a Xen dom0, use the new
> > > > > > xen_config_table_memory_region_max() function to determine if Xen has
> > > > > > reserved the ESRT and, if so, find the end of the memory region
> > > > > > containing it.  This allows programs such as fwupd which require the
> > > > > > ESRT to run under Xen, and so makes fwupd support in Qubes OS possible.
> > > > > >
> > > > > > Signed-off-by: Demi Marie Obenour <demi@...isiblethingslab.com>
> > > > >
> > > > > Why do we need this patch? I'd expect esrt_table_exists() to return
> > > > > false when patch 1/2 is applied.
> > > >
> > > > efi_enabled(EFI_MEMMAP) is false under Xen, so there needs to be an
> > > > alternative way to get the end of the memory region containing the ESRT.
> > > > That is what this patch provides.
> > >
> > > OK. I don't think we need that to be honest. When running under Xen,
> > > we should be able to assume that the ESRT does not span multiple
> > > memory regions arbitrarily, so we can just omit this check if
> > > !efi_enabled(EFI_MEMMAP)
> > >
> > > IIRC (and Peter would know), we are trying to filter out descriptors
> > > that are completely bogus here: zero lenght, zero address, etc etc. I
> > > don't think we need that for Xen.
> >
> > Xen doesn’t uninstall bogus ESRTs, so there is no less reason to worry
> > under Xen than on bare hardware.
> 
> That may be true. But if Xen needs dom0 to be able to cross reference
> the EFI memory map, it should provide one (and set EFI_MEMMAP to
> enabled).

I agree, but it is also a significant amount of work compared to this
patch.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)