On Wed, 5 Jun 2019 at 21:28, Tom Rini <trini(a)konsulko.com> wrote:
>
> On Wed, Jun 05, 2019 at 08:30:12PM +0200, Ard Biesheuvel wrote:
> > On Wed, 5 Jun 2019 at 19:30, Tom Rini <trini(a)konsulko.com> wrote:
> > >
> > > On Wed, Jun 05, 2019 at 06:14:08PM +0100, Mark Brown wrote:
> > > > On Wed, Jun 05, 2019 at 02:16:11PM +0200, Ard Biesheuvel wrote:
> > > >
> > > > > The idea of EBBR is to move away from a vertically integrated model,
> > > > > and permit systems or appliances to use packaged OSes in the field,
> > > > > similar to how this is being done on servers today. The idea that it
> > > > > is required for, say, company X shipping product Yrev0, to upstream a
> > > > > new rev of the DT in order to tweak their board and ship product Yrev1
> > > > > is simply ridiculous. It doesn't scale, and we shouldn't care - the DT
> > > > > bindings is what we care about, and if it adheres to those, the
> > > > > platform can provide any DT it wants, and there is no reason the
> > > > > kernel devs should ever need to look at it.
> > > >
> > > > I don't think anyone is particularly suggesting that (at least not in
> > > > the portions of the thread I read properly, I have to confess I was
> > > > skimming a bunch of it)?
> > >
> > > Just so we're all on the same page, we do understand that someone
> > > somewhere is providing Yrev0.dtb and Yrev1.dtb, yes? Or are we
> > > expecting someone to be run-time fixing up Yboard.dtb for rev0 vs rev1
> > > vs .. ?
> >
> > Let me put it like this: company X is not interested in having to
> > engage with the distros to get Yrev1.dtb into the OS, nor do they want
> > to be forced to start from an official DTB and apply deltas to make it
> > correct. You ship a board with some description of the board that the
> > OS can understand - this is how the OS identifies which hardware it
> > runs on: the DT description.
>
> Where does this description that's coming with the board come from?
> That _matters_ if you want to have any idea what will be able to use it.
>
>From the platform, not from the OS. How the firmware achieves that is
left unspecified by EBBR, it only mandates that it is passed to the OS
via a config table.
> > > > > For development, things are obviously different, I understand that.
> > > > > Shipping DTs for devboards makes sense, especially while the DT
> > > > > bindings are not set in stone yet. But imposing this model for
> > > > > production is unsustainable.
> > > >
> > > > I don't think I've particularly seen anyone trying to do that for
> > > > anything other than devboards, like Tom says people with actual products
> > > > usually don't even consider it. It's more that there is this devboard
> > > > case where the DTs are currently in kernel and a lot of the people
> > > > hacking on things are using devboards if only for want of anything else
> > > > so they naturally end up caring about that case.
> > >
> > > Keep in mind that the in-kernel dev board ones _are_ important as that's
> > > what you start your custom platform from, 9 times out of 10. It's quite
> > > often the case of "OK, $vendor gave us schematics for EVB, lets cut what
> > > we don't need and tweak" with a matching set of cuts and tweaks to the
> > > dts for the EVB. In the case of carrier+SOM it's just adding to, if
> > > using the stock carrier, or again adapting things for the custom
> > > carrier.
> >
> > Of course. But how is this relevant? I am not saying DTs have to be
> > truly original works, just that the OS should not be the one providing
> > it.
>
> Because we've been talking about where the device tree comes from, and I
> keep trying to point out that we are no where near a proven record of
> "DTB is always valid and functional with the Linux Kernel from here
> on out". There's not the tooling nor review to enforce that and there's
> a few examples every year (of just in-tree device trees, not custom end
> products) where it gets broken.
>
So now, you are saying companies should only ship products with
devices trees that have been reviewed by the kernel community?
This makes no sense to me whatsoever: the DT *bindings* are the
contract that we have with the platforms. If someone ships a DT that
adheres to the bindings, we are on the hook to fix it. If someone
ships a broken DT, it is their problem and they are fix it in their OS
fork, or they issue a firmware update that fixes it.
> > > But maybe it's just me that's confused about what "shipping" means in
> > > this context. Almost no one bothers "shipping" the DTS files for a
> > > custom product to mainline Linux as no one is supposed to be running
> > > anything other than the provided software on the custom device and so it
> > > goes where ever it goes for that products needs and support plans.
> > > Rarely does a board, devboard or finished end-user product, ship with a
> > > DTB file stored stand-alone in a flash chip, that is intended as the
> > > final forever DTB. It's just another part of
> > > firmware-by-which-I-mean-the-whole-software-stack.
> >
> > Who said anything about the DT being stored in a flash chip? I already
> > explained more than once that it is up to the firmware to decide *how*
> > it stores the DT, and the filesystem is fine if it does not care about
> > security or if it implements some form of authentication.
>
> It's been stated I believe in other parts of this thread or perhaps I'm
> just thinking of the many other times people have talked about hardware
> shipping a device tree. If the hardware is shipping the DTB to use,
> it's often stored someplace other than normal storage so that it's not
> overwritten by accident. Similar to ACPI tables :)
>
> > The point is that we are trying to move from this custom device model
> > to a model where you can run a generic distro, without having to put
> > the burden on the OS vendor to bundle a DT for every platform that it
> > will ever run on, which is especially tricky if those platforms do not
> > exist yet.
>
> So we are, or are not trying to come up with recommendations for
> shipping a DTB file for hardware?
>
I'm not sure i understand the question, but EBBR is not just a
recommendation. If you want to claim EBBR compliance, your platform
should be able to boot an OS that comes without bundled DTB images.
> > > Which is why my whole point here has been that the DTB needs to be
> > > treated and signature checked just like any other part of what's being
> > > loaded (kernel, initrd, grub and grub.conf OR systemd-boot and
> > > systemd-boot.conf, etc, etc).
> > >
> >
> > Again, I am not arguing that the DT should be linked into the firmware
> > executable, I am only saying that UEFI secure boot is not appropriate
> > for authenticating it (and that the OS should not be providing it)
>
> Are you just saying "the DT exists in the config table GUID, it is good"
> and ignoring the question of how the DT is put into the config table and
> any sort of "it is good" test?
>
So now we are policing the DT as well, and checking whether it is
'good' or not? The platform knows best how to describe the hardware,
so it is the hardware that provides the DT period. If a crappy product
provides a crappy DT, then you will get a crappy experience, just as
you might expect.
> Finally, is UEFI secure boot appropriate for authentication of the
> initrd? The bootloader config files?
>
No. initrd is a file system interpreted by the Linux kernel, and we
already have ways to authenticate that (unless you build it into the
kernel image, in which case you get it for free)
bootloader config files are an implementation detail of the
bootloader, and the same reasoning applies: UEFI secure boot
authenticates the OS to the platform, not the other way around. If the
firmware wants to sign its config files, it can, and it might even
reuse some of the crypto code that UEFI secure boot uses. But it is
not part of UEFI secure boot.
On Wed, 5 Jun 2019 at 19:30, Tom Rini <trini(a)konsulko.com> wrote:
>
> On Wed, Jun 05, 2019 at 06:14:08PM +0100, Mark Brown wrote:
> > On Wed, Jun 05, 2019 at 02:16:11PM +0200, Ard Biesheuvel wrote:
> >
> > > The idea of EBBR is to move away from a vertically integrated model,
> > > and permit systems or appliances to use packaged OSes in the field,
> > > similar to how this is being done on servers today. The idea that it
> > > is required for, say, company X shipping product Yrev0, to upstream a
> > > new rev of the DT in order to tweak their board and ship product Yrev1
> > > is simply ridiculous. It doesn't scale, and we shouldn't care - the DT
> > > bindings is what we care about, and if it adheres to those, the
> > > platform can provide any DT it wants, and there is no reason the
> > > kernel devs should ever need to look at it.
> >
> > I don't think anyone is particularly suggesting that (at least not in
> > the portions of the thread I read properly, I have to confess I was
> > skimming a bunch of it)?
>
> Just so we're all on the same page, we do understand that someone
> somewhere is providing Yrev0.dtb and Yrev1.dtb, yes? Or are we
> expecting someone to be run-time fixing up Yboard.dtb for rev0 vs rev1
> vs .. ?
>
Let me put it like this: company X is not interested in having to
engage with the distros to get Yrev1.dtb into the OS, nor do they want
to be forced to start from an official DTB and apply deltas to make it
correct. You ship a board with some description of the board that the
OS can understand - this is how the OS identifies which hardware it
runs on: the DT description.
> > > For development, things are obviously different, I understand that.
> > > Shipping DTs for devboards makes sense, especially while the DT
> > > bindings are not set in stone yet. But imposing this model for
> > > production is unsustainable.
> >
> > I don't think I've particularly seen anyone trying to do that for
> > anything other than devboards, like Tom says people with actual products
> > usually don't even consider it. It's more that there is this devboard
> > case where the DTs are currently in kernel and a lot of the people
> > hacking on things are using devboards if only for want of anything else
> > so they naturally end up caring about that case.
>
> Keep in mind that the in-kernel dev board ones _are_ important as that's
> what you start your custom platform from, 9 times out of 10. It's quite
> often the case of "OK, $vendor gave us schematics for EVB, lets cut what
> we don't need and tweak" with a matching set of cuts and tweaks to the
> dts for the EVB. In the case of carrier+SOM it's just adding to, if
> using the stock carrier, or again adapting things for the custom
> carrier.
>
Of course. But how is this relevant? I am not saying DTs have to be
truly original works, just that the OS should not be the one providing
it.
> But maybe it's just me that's confused about what "shipping" means in
> this context. Almost no one bothers "shipping" the DTS files for a
> custom product to mainline Linux as no one is supposed to be running
> anything other than the provided software on the custom device and so it
> goes where ever it goes for that products needs and support plans.
> Rarely does a board, devboard or finished end-user product, ship with a
> DTB file stored stand-alone in a flash chip, that is intended as the
> final forever DTB. It's just another part of
> firmware-by-which-I-mean-the-whole-software-stack.
>
Who said anything about the DT being stored in a flash chip? I already
explained more than once that it is up to the firmware to decide *how*
it stores the DT, and the filesystem is fine if it does not care about
security or if it implements some form of authentication.
The point is that we are trying to move from this custom device model
to a model where you can run a generic distro, without having to put
the burden on the OS vendor to bundle a DT for every platform that it
will ever run on, which is especially tricky if those platforms do not
exist yet.
> Which is why my whole point here has been that the DTB needs to be
> treated and signature checked just like any other part of what's being
> loaded (kernel, initrd, grub and grub.conf OR systemd-boot and
> systemd-boot.conf, etc, etc).
>
Again, I am not arguing that the DT should be linked into the firmware
executable, I am only saying that UEFI secure boot is not appropriate
for authenticating it (and that the OS should not be providing it)
On Wed, 5 Jun 2019 at 14:59, Tom Rini <trini(a)konsulko.com> wrote:
>
> On Wed, Jun 05, 2019 at 09:17:04AM +0100, Graeme Gregory wrote:
> > On Wed, 5 Jun 2019 at 07:36, Ard Biesheuvel <ard.biesheuvel(a)linaro.org>
> > wrote:
> >
> > > On Wed, 5 Jun 2019 at 00:41, Tom Rini <trini(a)konsulko.com> wrote:
> > > >
> > > ...
> > >
> > > > It depends on what you mean by "OS provided". The DTS files come from
> > > > the Linux Kernel sources, full stop.
> > >
> > > That is the mistake we should try to fix.
> > >
> > > We have DT bindings, which define the contract between the OS on one
> > > side, and the platform on the other side. This means it is the
> > > platform's job to present a DT description that adheres to those
> > > [stable] bindings.
> > >
> > > Today's development model of developing DT bindings in lockstep with
> > > the drivers, and then bundling DT files with the OS is completely
> > > unsustainable, since it doesn't scale, and it demonstrably results in
> > > DT bindings that get modified without any regard for devices that are
> > > already in the field (MacchiatoBin is a good example).
> > >
> > > So it doesn't really matter where the kernel *sources* come from, as
> > > long as the platform provides its own DT, which does not change just
> > > because the kernel changes.
> > >
> > > It is already defined how the platform provides this DT on a UEFI
> > > system, i.e., via a configuration table with a known GUID. How the
> > > firmware popiulates this memory is an implementation detail: if it
> > > wants to load it from a signed file in the file system, that is fine,
> > > as long as it is not the OS providing this file to the firmware.
> > >
> > >
> > I agree, people seem to be conflating where DT is stored in source control
> > over where it should be supplied to OS.
> >
> > Just because the DT is in linux kernel git does not mean you can't build it
> > into the u-boot for your board.
> >
> > In fact I bet u-boot maintainer would love patches for updates ;-)
>
> Right. But there's also confusion about where the DTB is to be found.
> Whereas ACPI is "burned in" the DTB (generally) is not and will not be.
> It will be loaded from storage, so in the context of this overall
> thread, figuring out how to verify the signature on the DTB is a main
> use case.
>
There is no confusion at all. On a UEFI/EBBR system, the DT shall be
provided to the OS via a config table using the established GUID. How
the firmware achieves that is left unspecified. The fact that it may
be loaded from storage does not make it part of the packaged OS, it is
still a component of the platform.
But based on this discussion, I will argue going forward that
- the firmware must not rely on the OS to put DT images under known
names into known locations in the file system,
- the firmware provides this DT regardless of which keys are loaded
into the uefi secure boot keyring, IOW, if i choose to put only the
RedHat certificate in db because that is all i care about, I don't
want to end up with a bricked system because the DT was loaded via the
secure boot stack and was signed with the Microsoft keyring.
Btw, the fact that Authenticode/PE-COFF does not permit multiple
signatures does not make things any easier.
On Wed, 5 Jun 2019 at 13:14, Mark Brown <broonie(a)kernel.org> wrote:
>
> On Wed, Jun 05, 2019 at 11:18:44AM +0100, Steve McIntyre wrote:
>
> > Nod. We're *way* past the time where this should have stopped. How on
> > earth do we get to common DT useful for all bootloaders, OSes (etc.)
> > if people still consider the bundled, changing sources in the Linux
> > tree to be canonical?
>
> It's a chicken and egg situation - for the platforms where nobody is
> actually shipping systems with a separate device tree it's easy for
> people to miss accidental incompatibilities without noticing, or decide
> that deliberate incompatibilites won't be noticed. If there's users
> making noise that's a lot harder to do. Pushing on EBBR is going to
> help there, and it'd really help if there were more hardware built with
> separate boot storage :/
>
> Some of the platforms *are* doing a good job of not needlessly churning
> their device trees (they're just not very noticable since things just
> work and they make no noise), and even without people worrying about
> separately distributed DTs widely adopted in tree bindings are doing a
> lot for stability due to the number of places that would need updates
> for incompatibilites (and also avoiding the DMI quirk tables ACPI relies
> on which is nice).
I am not disagreeing with any of this. But it is helpful to keep in
mind that, in the context what we are trying to achieve, the
requirement/expectation that a DT lives on git.kernel.org and gets
packaged and shipped by the distro makes no sense at all.
The idea of EBBR is to move away from a vertically integrated model,
and permit systems or appliances to use packaged OSes in the field,
similar to how this is being done on servers today. The idea that it
is required for, say, company X shipping product Yrev0, to upstream a
new rev of the DT in order to tweak their board and ship product Yrev1
is simply ridiculous. It doesn't scale, and we shouldn't care - the DT
bindings is what we care about, and if it adheres to those, the
platform can provide any DT it wants, and there is no reason the
kernel devs should ever need to look at it.
For development, things are obviously different, I understand that.
Shipping DTs for devboards makes sense, especially while the DT
bindings are not set in stone yet. But imposing this model for
production is unsustainable.
On Wed, 5 Jun 2019 at 00:41, Tom Rini <trini(a)konsulko.com> wrote:
>
...
> It depends on what you mean by "OS provided". The DTS files come from
> the Linux Kernel sources, full stop.
That is the mistake we should try to fix.
We have DT bindings, which define the contract between the OS on one
side, and the platform on the other side. This means it is the
platform's job to present a DT description that adheres to those
[stable] bindings.
Today's development model of developing DT bindings in lockstep with
the drivers, and then bundling DT files with the OS is completely
unsustainable, since it doesn't scale, and it demonstrably results in
DT bindings that get modified without any regard for devices that are
already in the field (MacchiatoBin is a good example).
So it doesn't really matter where the kernel *sources* come from, as
long as the platform provides its own DT, which does not change just
because the kernel changes.
It is already defined how the platform provides this DT on a UEFI
system, i.e., via a configuration table with a known GUID. How the
firmware popiulates this memory is an implementation detail: if it
wants to load it from a signed file in the file system, that is fine,
as long as it is not the OS providing this file to the firmware.
> That doesn't mean they're embedded
> within the kernel image. They're usually going to be pulled from the
> filesystem.
>
> --
> Tom
On Wed, 5 Jun 2019 at 00:34, Tom Rini <trini(a)konsulko.com> wrote:
>
> On Tue, Jun 04, 2019 at 06:14:16PM -0400, Francois Ozog wrote:
> > Le mar. 4 juin 2019 à 17:31, Tom Rini <trini(a)konsulko.com> a écrit :
> >
...
> > I think it may be good to validate but not provide. There is no Linux
> > provided ACPI table right ? So I get the point to validate a DT.
>
> There's "Linux provided" ACPI tables when someone has to decompile,
> fixup and re-compile their DSDT files.
>
> Or perhaps a better way to think of it is that yes, there's "Linux
> provided ACPI tables" when vendors are developing their hardware and
> correcting their ACPI tables. Same thing with DT, by and large (as
> overlays and secure boot are a can of worms to worry about later).
Secure boot enabled Linux does not permit this model. Side loading of
DSDTs/SSDTs is disabled by the hardening patchset that all the distros
carry for secure boot enabled kernels.
Le mar. 4 juin 2019 à 17:31, Tom Rini <trini(a)konsulko.com> a écrit :
> On Tue, Jun 04, 2019 at 10:25:23AM -0400, Francois Ozog wrote:
> > On Tue, 4 Jun 2019 at 10:17, Heinrich Schuchardt <xypron.glpk(a)gmx.de>
> wrote:
> >
> > >
> > >
> > > On 6/4/19 3:55 PM, Francois Ozog wrote:
> > > > On Tue, 4 Jun 2019 at 09:49, Ard Biesheuvel <
> ard.biesheuvel(a)linaro.org>
> > > > wrote:
> > > >
> > > >>
> > > >>
> > > >> On Tue, 4 Jun 2019 at 15:44, Francois Ozog <
> francois.ozog(a)linaro.org>
> > > >> wrote:
> > > >>
> > > >>> Hi Ard,
> > > >>>
> > > >>> On Fri, 31 May 2019 at 13:35, Ard Biesheuvel <
> > > ard.biesheuvel(a)linaro.org>
> > > >>> wrote:
> > > >>>
> > > >>>> On Fri, 31 May 2019 at 19:25, Ilias Apalodimas
> > > >>>> <ilias.apalodimas(a)linaro.org> wrote:
> > > >>>>>
> > > >>>>> Hi Grant,
> > > >>>>>> I see two ways to handle this that fits with the Secure Boot
> > > >>>>>> authentication path:
> > > >>>>>>
> > > >>>>>> Option 1: Leave it to the OS loader
> > > >>>>>> We could simply say that if the OS wants to replace the DTB,
> then it
> > > >>>>>> should take care of authentication itself within the OS loader
> > > >>>> (possibly
> > > >>>>>> the in-kernel UEFI stub) and install a replacement DTB in the
> > > >>>>>> configuration table before calling exit boot services. In this
> > > >>>> scenario,
> > > >>>>>> U-Boot doesn't authenticate the DTB at all.
> > > >>>>>>
> > > >>>>>> In fact, Option 1 is pretty close to what is required for the
> > > initrd.
> > > >>>>>>
> > > >>>>>> I wonder if it is possible to wrap the DTB with a PE/COFF so
> that
> > > >>>> the os
> > > >>>>>> loader can use load_image to authenticate and retrieve the data
> > > >>>> without
> > > >>>>>> actually executing the image. That would allow for the DTB &
> initrd
> > > >>>> to
> > > >>>>>> be authenticated in the same way as the kernel.
> > > >>>>> I asked around on this prior to the email, but i think it boils
> down
> > > to
> > > >>>>> "UEFI is intended to authenticate bootable images for the
> platform",
> > > >>>> so i doubt
> > > >>>>> this will be allowed.
> > > >>>>>
> > > >>>>
> > > >>>> The point I raised when we discussed this is that UEFI is an
> interface
> > > >>>> between the firmware and the OS, and it is up to the firmware to
> > > >>>> *provide* the DT not the other way around.
> > > >>>>
> > > >>>> Whether the firmware reuses some of the existing machinery if it
> > > >>>> chooses to load the DT it provides from an arbitrary file on the
> file
> > > >>>> system is an implementation detail, and shouldn't be part of how
> we
> > > >>>> design the interface. The more we standardize this and the more we
> > > >>>> make it similar to how the OS loader is authenticated, the more
> likely
> > > >>>> it becomes that it will be relied upon for DTs that are bundled
> with
> > > >>>> the OS, which is a practice we are trying very hard to move away
> from.
> > > >>>>
> > > >>>
> > > >>> I have the impression that OS provided DT is a bad solution to a
> real
> > > >>> problem:
> > > >>> There should be a Firmware hardware environment (what to
> initialize,
> > > >>> use...) and a OS hardware environment.
> > > >>> Both should be signed, and controlled by the firmware.
> > > >>> So I would try to find a way to supply firmware with two DTs, or
> more
> > > >>> likely one DT and one OS overlay (if overlays can remove some
> > > hardware).
> > > >>>
> > > >>>
> > > >>
> > > >> If the OS provides a DT to itself, what is the point of pretending
> that
> > > it
> > > >> has been authenticated to the firmware?
> > > >>
> > > > Agreed, that is stupid! I mispresented my idea: I talk about two DTs
> > > > controlled by hardware/Firmware provider. OS shall be a consumer
> only.
> > > >
> > > >
> > >
> > > In a perfect world firmware would provide the authoritative source of
> > > the device tree. The current situation has device trees developed in
> the
> > > context of Linux and U-Boot picking them up. U-Boot is lagging far
> > > behind Linux. Whenever I wanted to change a device tree in U-Boot I was
> > > told to first get that change into Linux. I see no commitment to change
> > > this process.
> > >
> > > Device-trees are provided by U-Boot to Linux as UEFI configuration
> > > tables. If a device-tree is malicious it may lead to the destruction of
> > > hardware. So whatever U-Boot provides as a device-tree to Linux should
> > > be validated.
> > >
> > In a perfect world, U-Boot shall lead and we should work towards that if
> > not in place. There is no sch a thing as a Linux validated ACPI table, so
> > why for DT?
>
> There _is_ such a thing as a validated ACPI table and functionally ACPI
> tables on x86 are validated with Windows. This is no different.
>
I think it may be good to validate but not provide. There is no Linux
provided ACPI table right ? So I get the point to validate a DT.
>
> --
> Tom
>
--
François-Frédéric Ozog | *Director Linaro Edge & Fog Computing Group*
T: +33.67221.6485
francois.ozog(a)linaro.org | Skype: ffozog
Le mar. 4 juin 2019 à 17:27, Tom Rini <trini(a)konsulko.com> a écrit :
> On Tue, Jun 04, 2019 at 10:21:54AM -0400, Francois Ozog wrote:
> > On Tue, 4 Jun 2019 at 10:00, Ard Biesheuvel <ard.biesheuvel(a)linaro.org>
> > wrote:
> >
> > >
> > >
> > > On Tue, 4 Jun 2019 at 15:55, Francois Ozog <francois.ozog(a)linaro.org>
> > > wrote:
> > >
> > >>
> > >>
> > >> On Tue, 4 Jun 2019 at 09:49, Ard Biesheuvel <
> ard.biesheuvel(a)linaro.org>
> > >> wrote:
> > >>
> > >>>
> > >>>
> > >>> On Tue, 4 Jun 2019 at 15:44, Francois Ozog <francois.ozog(a)linaro.org
> >
> > >>> wrote:
> > >>>
> > >>>> Hi Ard,
> > >>>>
> > >>>> On Fri, 31 May 2019 at 13:35, Ard Biesheuvel <
> ard.biesheuvel(a)linaro.org>
> > >>>> wrote:
> > >>>>
> > >>>>> On Fri, 31 May 2019 at 19:25, Ilias Apalodimas
> > >>>>> <ilias.apalodimas(a)linaro.org> wrote:
> > >>>>> >
> > >>>>> > Hi Grant,
> > >>>>> > > I see two ways to handle this that fits with the Secure Boot
> > >>>>> > > authentication path:
> > >>>>> > >
> > >>>>> > > Option 1: Leave it to the OS loader
> > >>>>> > > We could simply say that if the OS wants to replace the DTB,
> then
> > >>>>> it
> > >>>>> > > should take care of authentication itself within the OS loader
> > >>>>> (possibly
> > >>>>> > > the in-kernel UEFI stub) and install a replacement DTB in the
> > >>>>> > > configuration table before calling exit boot services. In this
> > >>>>> scenario,
> > >>>>> > > U-Boot doesn't authenticate the DTB at all.
> > >>>>> > >
> > >>>>> > > In fact, Option 1 is pretty close to what is required for the
> > >>>>> initrd.
> > >>>>> > >
> > >>>>> > > I wonder if it is possible to wrap the DTB with a PE/COFF so
> that
> > >>>>> the os
> > >>>>> > > loader can use load_image to authenticate and retrieve the data
> > >>>>> without
> > >>>>> > > actually executing the image. That would allow for the DTB &
> > >>>>> initrd to
> > >>>>> > > be authenticated in the same way as the kernel.
> > >>>>> > I asked around on this prior to the email, but i think it boils
> down
> > >>>>> to
> > >>>>> > "UEFI is intended to authenticate bootable images for the
> platform",
> > >>>>> so i doubt
> > >>>>> > this will be allowed.
> > >>>>> >
> > >>>>>
> > >>>>> The point I raised when we discussed this is that UEFI is an
> interface
> > >>>>> between the firmware and the OS, and it is up to the firmware to
> > >>>>> *provide* the DT not the other way around.
> > >>>>>
> > >>>>> Whether the firmware reuses some of the existing machinery if it
> > >>>>> chooses to load the DT it provides from an arbitrary file on the
> file
> > >>>>> system is an implementation detail, and shouldn't be part of how we
> > >>>>> design the interface. The more we standardize this and the more we
> > >>>>> make it similar to how the OS loader is authenticated, the more
> likely
> > >>>>> it becomes that it will be relied upon for DTs that are bundled
> with
> > >>>>> the OS, which is a practice we are trying very hard to move away
> from.
> > >>>>>
> > >>>>
> > >>>> I have the impression that OS provided DT is a bad solution to a
> real
> > >>>> problem:
> > >>>> There should be a Firmware hardware environment (what to initialize,
> > >>>> use...) and a OS hardware environment.
> > >>>> Both should be signed, and controlled by the firmware.
> > >>>> So I would try to find a way to supply firmware with two DTs, or
> more
> > >>>> likely one DT and one OS overlay (if overlays can remove some
> hardware).
> > >>>>
> > >>>>
> > >>>
> > >>> If the OS provides a DT to itself, what is the point of pretending
> that
> > >>> it has been authenticated to the firmware?
> > >>>
> > >> Agreed, that is stupid! I mispresented my idea: I talk about two DTs
> > >> controlled by hardware/Firmware provider. OS shall be a consumer only.
> > >>
> > >>
> > >>
> > > But my point remains the same. If we are accommodating a model where
> the
> > > DT is shipped with the OS, the OS can deal with authenticating the DTB
> > > files. If the firmware provides the DT, it is a firmware implementation
> > > detail how and where it keeps the DTB files internally, as long as it
> uses
> > > the official way (i.e., via a UEFI config table) to expose the DT to
> the OS.
> > >
> > > Rolling all of this into secure boot support (which deals with
> > > authenticating OS components/loaders to the firmware) is something we
> > > should avoid.
> > >
> > Agreed. There is no such a thing as an OS provided ACPI table.... yet we
> > allow that for DT... strange isn't it?
>
> I think we're getting a bit side tracked. And, depending on what you
> want to call people having to fixup and recompile DSDT to fix issues...
> :)
>
> The Linux Kernel happens to be the (generally) authoritative source of
> DT files, rather than the hardware manufacturer.
>
To me it looks like walking on the head. I don’t see any OS providing an
ACPI table. I think I understand why it happened. But to me it looks like a
wrong solution to a real use case: firmware hardware execution
environnement is different (probably smaller) than os execution environment.
I think this is more about EBBR and it’s compliance. What shall be the
right policy ? And then we refine EBBR.
>
> > So as a reference platform we can say that an OS provided DT is NOT part
> of
> > the picture. Yet if a vendor still wants to do it, it will be able to. We
> > just don't care.
> >
> > Now, in the context of standard OTA across SoCs, what shall be
> standardized
> > to support the two DTs (for firmware execution and for OS execution). Are
> > we considering UBoot firmware as a "blob" that embeds those two DTs?
> Might
> > be good enough.
>
> The common case is NOT going to be that the DT is provided embedded
> within the hardware, please keep that in mind.
>
EBBR says: “Similarly, devices retained by firmware (i.e., not discoverable
by the OS) shall not be accessed by the OS.” so an OS provided DT is a
recipe for failure.
>
> --
> Tom
>
--
François-Frédéric Ozog | *Director Linaro Edge & Fog Computing Group*
T: +33.67221.6485
francois.ozog(a)linaro.org | Skype: ffozog
Hello all,
Continuing the discussions we had on securing the boot flow and OS as much as
possible, we came up with the following idea.
We are currently sorting out what's needed to add UEFI Secure Boot in U-Boot.
This will cover the next payload (shim/grub2/shim depending on board needs).
In order to provide better overall security for the OS we'll need to at least
verify DTB (if provided externally), initramfs and kernel modules.
1. For the kernel modules we can use kernel module signing facilities [1]
2. In case someone wants to provide an external DTB, we can use FIT images
to secure that. The FIT images will contain the DTB(s) we need. Those will
only be used if the authentication process succeeds. This will allow us to
verify DTBs without introducing any new functionality to U-Boot.
3. We need to verify initramfs as well. This can be accomplished in various ways.
Packing kernel + initramfs or using dm-verity are the two obvious ones but we
are open to suggestions.
This also makes the development process for LEDGE pretty clear. We'll have to
add UEFI Secure Boot implementation on U-Boot *only* since the rest of the
functionality can be achieved with the existing code (minor adjustments might be
needed though).
What do you think?
[1] https://www.kernel.org/doc/html/v4.15/admin-guide/module-signing.html
Thanks
/Ilias
Hi Tom,
On Fri, May 31, 2019 at 11:05:20AM -0400, Tom Rini wrote:
> On Fri, May 31, 2019 at 02:40:32PM +0100, Steve McIntyre wrote:
> > On Tue, May 28, 2019 at 02:04:23PM +0300, Ilias Apalodimas wrote:
> > >> >
> > >> > The tl;dr purpose of my e-mail was 'Is implementing UEFI Secure Boot for the
> > >> > EFI playloads
> > >>
> > >> I think that you'd better explain why you stick to *UEFI* secure boot.
> > >
> > >The main reason is distro support. Since distros use a number of different ways
> > >of booting up on arm boards, using UEFI is the obvious way to unify that (and
> > >alrady supported on some) regardless of the bootloader. UEFI secure boot
> > >provides a common approach to security instead of 'per bootloader' solutions
> >
> > Yup, absolutely (says the Debian EFI team lead) ...
>
> The other things we need to keep in mind is that (based on my own
> experience implementing UEFI secure boot on an x8664 platform), we are
> not looking at a case of "make an existing solution function on other
> architectures" but rather "there's some good concepts here and an
> implementation waiting to be figured out".
We agree here. From Grant's proposal's #1 and #2, i'd prefer seeing something
similar to #2 implemented.
I'd prefer having the option to authenticate DTB/initramfs from the 'main
bootloader', than delegating that to some EFI payload, mostly for fragmentation
reasons
Thanks
/Ilias
