[PATCH 0/7] efi: Various tidy-ups and drop the default

[Mark Kettenis]

> From: Simon Glass <sjg at chromium.org>
> Date: Mon, 28 Jun 2021 08:18:26 -0600
> 
> Hi Tom, Mark,
> 
> On Mon, 28 Jun 2021 at 07:37, Tom Rini <trini at konsulko.com> wrote:
> >
> > On Mon, Jun 28, 2021 at 10:38:50AM +0200, Mark Kettenis wrote:
> > > > From: Simon Glass <sjg at chromium.org>
> > > > Date: Sun, 27 Jun 2021 19:48:34 -0600
> > > >
> > > > It has come to light that EFI_LOADER adds an extraordinary amount of
> > > > code to U-Boot. For example, with nokia_rx51 the size delta is about
> > > > 90KB. About 170 boards explicitly disable the option, but is is clear
> > > > that many more could, thus saving image size and boot time.
> > >
> > > EFI_LOADER used to be a lot smaller.  It is great to see that over the
> > > years UEFI support has become more complete, but a lot of that new
> > > code implements features that are not at all essential for just
> > > booting an OS from storage.  If that growth leads to the suggestion to
> > > disable EFI_LOADER completely by default, we're putting the cart
> > > before the horse.
> >
> > Well, I see I forgot to prefix my patch with RFC, but I hadn't found
> > EFI_LOADER being used in the wild on armv7, but wasn't sure about the
> > BSD families.  I did see that Debian doesn't use it, and that Armbian
> > doesn't even use it on aarch64.
> >
> > > > The current situation is affecting U-Boot's image as a svelt bootloader.
> > >
> > > Really?  I know UEFI has a bad reputation in the Open Source world,
> > > and some of its Microsoft-isms are really annoying (yay UCS-2).  But
> > > it works, it provides a standardized approach across several platforms
> > > (ARMv7, AMRv8, RISC-V) and the industry seems to like it.  Personally
> > > I'd wish the industry had standardized on Open Firmware instead, but
> > > that ship sailed a long time ago...
> > >
> > > I find it hard to imagine that 90k is a serious amount of storage for
> > > something that is going to include a multi-MB Linux kernel.  This
> > > isn't code that lives in SPL or TPL where severe size restrictions
> > > apply.
> >
> > In one of those cases where I need to pop back in to the other (Nokia
> > N900 specific) thread and see if the big size reduction really was just
> > disabling EFI_LOADER, it's perhaps just one of those "fun" things about
> > Kconfig and anything other than "make oldconfig" for spotting new config
> > options that default to enabled.
> 
> Yes it will be interesting to see what you find there. My results on
> nokia_rx51 were something like this:
> 
> default
>         arm: (for 1/1 boards) all +129370.0 bss +1136.0 data +7399.0
> rodata +10989.0 text +109846.0
> 
> without ebbr
>        arm: (for 1/1 boards) all +38460.0 bss +1040.0 data +2375.0
> rodata +5333.0 text +29712.0
> 
> with various other things:
> CONFIG_OF_LIBFDT_ASSUME_MASK=7
> # CONFIG_OF_TRANSLATE is not set
> # CONFIG_SIMPLE_BUS is not set
> # CONFIG_TI_SYSC is not set
> # CONFIG_CMD_FDT is not set
> 
>        arm: (for 1/1 boards) all +19170.0 bss -16.0 data +360.0 rodata
> +3274.0 text +15552.0
> 
> (Mark, in the same email:)
> > > FIT simply isn't fit for purpose (pun intended).  It only really works
> > > for booting Linux, and forces people to combine u-boot, kernel,
> > > initial ramdisk and other firmware components into a single image.
> > > That is really undesirable as:
> > > - This makes it sigificantly harder to update individual components of
> > >   such an image.  Making it hard to update a kernel is obviously a
> > >   serious security risk.
> > > - This makes it impossible to build an OS install image that works om
> > >   multiple boards/SoCs.
> 
> 
> I would really like to understand this better. The whole thing is a
> complete mystery to me.
> 
> Firstly I have sometimes fiddled with booting other OSes using FIT. It
> seemed OK. I can't see why it only works with Linux.

Well, you could of course rework the boot flow of other OSes such that
booting them includes some sort of FIT if you really wanted to.  I But
an OS like OpenBSD comes with its own bootloader that is essential in
the boot flow.  On OpenBSD armv7/arm64/riscv64 it adds some essential
properties to the device tree.  Besides, the kernel itself relies on a
valid EFI memory map.

> Secondly, I don't expect that U-Boot itself would be in the FIT.

So the FIT would only contain the OS kernel and other OS components?
What about the FIT that is used on some arm64 platforms to combine
U-Boot and TF-A?  I guess you can have multiple FITs...

> Thirdly, do you really want the kernel and initrd to be separate? At
> least in the systems I have used, they are built together, even having
> the same name, e.g.:
> 
> initrd.img-5.10.40-1rodete1-amd64
> System.map-5.10.40-1rodete1-amd64
> vmlinuz-5.10.28-1rodete2-amd64

I don't really use Linux on these platforms.  But I'd expect the
normal package management tools of my Linux distribution to build
those as necessary and place them in the root file system where the
bootloader picks them up.  And as a distro developer, I'd like to have
the same approach work on all Linux systems, regardless the specific
firmware they're running (EDK2, U-Boot or something completely
different).  Ideally that wouldn't even depend on the architecture.

Now Armbian takes a different approach, and does treat most systems
they provide as special snowflakes, providing flash images for each
board.  But that doesn't scale and makes for a fairly crappy user
experience.  They don't always support booting a mainline kernel.  And
updating the kernel often requires installing special packages.

> Finally, for the firmware components, do you mean system firmware? If
> so, I would expect it to be more convenient to distribute updates to
> that separately, although I suppose they could be combined with the
> kernel if the combinatorial explosion can be contained. What is the
> problem, exactly? (If you mean peripheral firmware, I would expect
> fwupd to handle that.)

I guess I mean system firmware.  Essentially everything that runs on
the system before my OS bootloader runs.  So for me, U-Boot is part of
the system firmware even if it sometimes happens to live on removable
media.

> What exactly is impossible? Can you please be more specific?

So let me explain what we want for OpenBSD.  We really want a uniform
user experience across platforms, and don't want to maintain different
codepaths for special snowflake platforms that might exist for a
specific architecture.

Installing OpenBSD on a machine should be as simple as dd'ing the
installer to some boot media, plugging it in and powering the machine
on.  Now this is somewhat tricky to achieve on some hardware targetted
by U-Boot as they don't come with usable system firmware on the board
itself.  But on those boards you can mostly get away with having
U-Boot on uSD or eMMC and the OS installer on USB.

Updating the OpenBSD kernel should be as simple as copying the kernel
to /bsd.  Since the root filesystem uses the UFS/FFS filesystem, this
means that whatever we use as a bootloader must be able to read from
that filesystem.  To make sure the kernel is properly seeded with
entropy, the OpenBSD bootloader has some additional tricks up its
sleeve.  It will replace a special segment in the kernel with random
data before handing control to the kernel.  On platforms that support
it, it will try to use a firmware-provided RNG to do this (and EFI
supports this) but also mix in some random data from a file on the
UFS/FFS filesystem.  It will actually mark that file as "used" after
reading it to throw a warning when the file is reused when the machine
is rebooted (it should have been filled with fresh new entropy).  So
you really need to use the OpenBSD bootloader instead loading an
OpenBSD kernel directly from system firmware.

Updating the OpenBSD bootloader should be as simple as running
installboot(8) from within the OS.

This all works on pretty much any architecture that OpenBSD supports.
And right now, thanks to EFI_LOADER support in U-Boot, we have a
nearly uniform boot flow on amd64, arm64, armv7 and riscv64.
 
> FIT is just a container. It seems to have been rejected by the EFI
> crew at some point. Perhaps I just need to try to use it with one of
> the distros out there, to actually understand what is going on here.
> But any help is appreciated.

It just doesn't make sense for us to use a container just because the
system firmware (U-Boot) insists on it.  The kernel lives in the root
UFS/FFS filesystem and the bootloader lives on an MS-DOS filesystem on
the root disk.

> > > > EFI_LOADER is required by EBBR, a new boot standard which aims to
> > > > bring in UEFI protocols to U-Boot. But EBRR is not required for
> > > > booting. U-Boot already provides support for FIT, the 'bootm' command
> > > > and a suitable hand-off to Linux. EBRR has made the decision to create
> > > > a parallel infrastructure, e.g. does not use FIT, nor U-Boot's signing
> > > > infrastructure.
> > >
> > > EFI_LOADER is required to boot FreeBSD and OpenBSD on several
> > > platforms as well as generic Linux distros.  For example
> > > OpenBSD/armv7, OpenBSD/arm64 and OpenBSD/riscv64 all rely on
> > > EFI_LOADER to boot and have done so for the last 4 years.  The fact
> > > that ARM has embraced UEFI as an embedded boot standard and branded it
> > > EBBR really isn't all that relevant.
> >
> > To be clear here, I like EFI_LOADER.  I too do wish some other
> > technologies had become dominant for technical rather than inertia
> > reasons, but here we are.  Having played around with it on aarch64,
> > there are some pretty nice comes-along-with parts to it.
> >
> > What I hadn't seen, and am only a little skeptical of still, is how far
> > backwards in generations it's going to be used on.  The general wish is
> > that users nor off the shelf OS groups need to rebuild U-Boot for a
> > given board, and instead it just works.  The number of new designs for
> > 32bit parts is no where near the number of new designs for 64bit parts.
> > So what we're seeing in U-Boot now is people updating support on their
> > older designs, and not necessarily caring about using EFI_LOADER.
> 
> In a reply to one of the patches in this series, Heinrich mentions a
> few problems that need resolving (devices for partitions and file
> handles). Both of those features should first be added to U-Boot, so
> EFI can then use that support. In general, EFI has tried to work
> beside driver model, creating its own parallel tables, etc. I have
> tried to influence this at various points along the way, including at
> the start and I'm happy to dig out those threads if it helps. But I
> wasn't kidding. it really needs to be addressed. I would love to see
> Linaro (for example) organise something here and take this on. I am
> very happy to help.
> 
> Regards,
> Simon
>