[PATCH] RFC: Support an EFI-loader bootflow
Simon Glass
sjg at chromium.org
Mon Sep 6 12:41:55 CEST 2021
Hi Heinrich,
On Fri, 3 Sept 2021 at 10:30, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
>
>
> On 9/3/21 10:53 AM, Simon Glass wrote:
> > Hi Takahiro,
> >
> > On Thu, 2 Sept 2021 at 20:27, AKASHI Takahiro
> > <takahiro.akashi at linaro.org> wrote:
> >>
> >> Simon,
> >>
> >> On Thu, Sep 02, 2021 at 10:40:57AM -0600, Simon Glass wrote:
> >>> Hi Takahiro,
> >>>
> >>> On Tue, 31 Aug 2021 at 00:14, AKASHI Takahiro
> >>> <takahiro.akashi at linaro.org> wrote:
> >>>>
> >>>> Simon,
> >>>>
> >>>> On Sat, Aug 28, 2021 at 02:35:21PM -0600, Simon Glass wrote:
> >>>>> This is just a demonstration of how to support EFI loader using bootflow.
> >>>>> Various things need cleaning up, not least that the naming needs to be
> >>>>> finalised. I will deal with that in the v2 series.
> >>>>>
> >>>>> In order to support multiple methods of booting from the same device, we
> >>>>> should probably separate out the different implementations (syslinux,
> >>>>> EFI loader
> >>>>
> >>>> I still believe that we'd better add "removable media" support
> >>>> to UEFI boot manager first (and then probably call this functionality
> >> ^^^^^^^^^^^^^^^^^^^^^^^^^^
> >>
> >>>> from bootflow?).
> >>>>
> >>>> I admit that, in this case, we will have an issue that we will not
> >>>> recognize any device which is plugged in dynamically after UEFI
> >>>> subsystem is initialized. But this issue will potentially exist
> >>>> even with your approach.
> >>>
> >>> That can be fixed by dropping the UEFI tables and using driver model
> >>> instead. I may have mentioned that :-)
> >>
> >> I'm afraid that you don't get my point above.
> >>
> >>>>
> >>>>> and soon bootmgr,
> >>>>
> >>>> What will you expect in UEFI boot manager case?
> >>>> Boot parameters (options) as well as the boot order are well defined
> >>>> by BootXXXX and BootOrder variables. How are they fit into your scheme?
> >>>
> >>> I haven't looked at boot manager yet, but I can't imagine it
> >>> presenting an insurmountable challenge.
> >>
> >> I don't say it's challenging.
> >> Since you have not yet explained your idea about how to specify
> >> the *boot order* in your scheme, I wonder how "BootXXXX"/"BootOrder"
> >> be treated and honored.
> >> There might be a parallel world again.
> >
> > Well as I mentioned, I haven't looked at it yet. The original question
> > was how to do EFI LOADER and I did a patch to show that.
> >
> > Are we likely to see mixed-boot environments, that use distro boot for
> > some OSes and EFI for others? I hope not as it would be confusing. EFI
> > is the parallel world, as I see it.
> >
> > It should be easy enough for the 'bootmgr' bootflow to read the EFI
> > variables and select the correct ordering. As I understand it, EFI
> > does not support lazy boot, so it is acceptable to probe all the
> > devices before selecting one?
> >
> >>
> >>>>
> >>>> But anyway, we can use the following commands to run a specific
> >>>> boot flow in UEFI world:
> >>>> => efidebug boot next 1(or whatever else); bootefi bootmgr
> >>>
> >>> OK.
> >>>
> >>> As you probably noticed I was trying to have bootflow connect directly
> >>> to the code that does the booting so that 'CONFIG_CMDLINE' can be
> >>> disabled (e.g. for security reasons) and the boot will still work.
> >>
> >> # Maybe, it sounds kinda chicken and egg.
> >>
> >> Even now, you can code this way :)
> >>
> >> efi_set_variable(u"BootNext", ..., u"Boot0001");
> >> do_efibootmgr();
> >>
> >> That's it. My concern is what I mentioned above.
> >
> > OK. But then you would need to export those functions. I think it
> > would be better to split up the logic a bit and move things out of the
> > cmd/ directory (at some point).
> >
> >>
> >> Just a note:
> >> In the current distro_bootcmd, UEFI boot manager is also called
> >> *every time* one of boot media in "boot_targets" is scanned/enumerated.
> >> But it will make little sense because the current boot manager only
> >> allows/requires users to specify both the boot device and the image file
> >> path explicitly in a boot option, i.e. "BootXXXX" variable, and tries
> >> all the boot options in "BootOrder" until it successfully launches
> >> one of those images.
> >
> > Yes, is the idea of lazy boot entirely impossible? Or is it still
> > possible to do that to some extent, e.g. by scanning until you find
> > the first thing in the boot order?
> >
> >>
> >>>>
> >>>>> Chromium OS, Android, VBE) into pluggable
> >>>>> drivers and number them as we do with partitions. For now the sequence
> >>>>> number is used to determine both the partition number and the
> >>>>> implementation to use.
> >>>>>
> >>>>> The same boot command is used as before ('bootflow scan -lb') so there is
> >>>>> no change to that. It can boot both Fedora 31 and 34, for example.
> >>>>>
> >>>>> Signed-off-by: Simon Glass <sjg at chromium.org>
> >>>>> ---
> >>>>> See u-boot-dm/bmea for the tree containing this patch and the series
> >>>>> that it relies on:
> >>>>>
> >>>>> https://patchwork.ozlabs.org/project/uboot/list/?series=258654&state=*
> >>>>>
> >>>
> >>> [..]
> >>>
> >>>>> +static int efiload_read_file(struct blk_desc *desc, int partnum,
> >>>>> + struct bootflow *bflow)
> >>>>> +{
> >>>>> + const struct udevice *media_dev;
> >>>>> + int size = bflow->size;
> >>>>> + char devnum_str[9];
> >>>>> + char dirname[200];
> >>>>> + loff_t bytes_read;
> >>>>> + char *last_slash;
> >>>>> + ulong addr;
> >>>>> + char *buf;
> >>>>> + int ret;
> >>>>> +
> >>>>> + /* Sadly FS closes the file after fs_size() so we must redo this */
> >>>>> + ret = fs_set_blk_dev_with_part(desc, partnum);
> >>>>> + if (ret)
> >>>>> + return log_msg_ret("set", ret);
> >>>>> +
> >>>>> + buf = malloc(size + 1);
> >>>>> + if (!buf)
> >>>>> + return log_msg_ret("buf", -ENOMEM);
> >>>>> + addr = map_to_sysmem(buf);
> >>>>> +
> >>>>> + ret = fs_read(bflow->fname, addr, 0, 0, &bytes_read);
> >>>>> + if (ret) {
> >>>>> + free(buf);
> >>>>> + return log_msg_ret("read", ret);
> >>>>> + }
> >>>>> + if (size != bytes_read)
> >>>>> + return log_msg_ret("bread", -EINVAL);
> >>>>> + buf[size] = '\0';
> >>>>> + bflow->state = BOOTFLOWST_LOADED;
> >>>>> + bflow->buf = buf;
> >>>>> +
> >>>>> + /*
> >>>>> + * This is a horrible hack to tell EFI about this boot device. Once we
> >>>>> + * unify EFI with the rest of U-Boot we can clean this up. The same hack
> >>>>> + * exists in multiple places, e.g. in the fs, tftp and load commands.
> >>>>
> >>>> Which part do you call a "horrible hack"? efi_set_bootdev()?
> >>>> In fact, there are a couple of reason why we need to call this function:
> >>>> 1. to remember a device to create a dummy device path for the loaded
> >>>> image later,
> >>>> 2. to remember a size of loaded image which is used for sanity check and
> >>>> image authentication later,
> >>>> 3. to avoid those parameters being remembered accidentally by "loading" dtb
> >>>> and/or other binaries than the image itself,
> >>>>
> >>>> I hope that (1) and (2) will be avoidable if we modify the current
> >>>> implementation (and bootefi syntax), and then we won't need (3).
> >>>
> >>> Yes thank you...I do understand why it is needed now, but it is
> >>> basically due to the the fat that EFI has its own driver structures.
> >>> Once we stop those, it will go away.
> >>
> >> Here, my point is, even under the current implementation, we will
> >> be able to eliminate efi_set_bootdev() with some tweaks.
> >>
> >> In other words, even you could integrate UEFI into the device model,
> >> the issue (2), for example, would still remain unsolved.
> >> In case of (2), we use the *size* information for sanity check against
> >> image's header information as well as calculating a hash value for
> >> UEFI secure boot when efi_load_image() is called. Even if the integration
> >> is done, we need to pass on the size information to "bootefi <addr>"
> >> command implicitly or explicitly.
> >
> > If you look at 'struct bootflow' you can see that it stores the size.
> > It can easily store other info as needed by EFI. So I don't think we
> > need that hack in the end, when things are using bootflow.
> >
> >>
> >>>>
> >>>>> + * Once we can clean up the EFI code to make proper use of driver model,
> >>>>> + * this can go away.
> >>>>
> >>>> My point is, however, that this kind of cleanup is irrelevant to
> >>>> whether we use driver model or not.
> >>>
> >>> Are you sure? Without driver model how are you going to reference a
> >>> udevice? If not that, how are you going to reference a device? The
> >>> tables in the UEFI implementation were specifically added to avoid
> >>> relying on driver model. It is a crying shame that I did not push back
> >>> harder on this at the time.
> >>
> >> I hope you will get my point in the previous comment now.
> >
> > Well yes I do, but I don't understand why there is such resistance to
> > sorting out the EFI implementation? It is quite a mess at the moment.
> > I think the first step is to drop the non-DM code, but the second is
> > to drop the parallel tables that EFI keeps about each device.
>
>
> Concerning these "parallel" tables. Please, have a look at the UEFI spec
> to understand what a handle, a protocol interface, and an event are.
>
> I also gave as short overview in
> https://archive.fosdem.org/2020/schedule/event/firmware_duwu/ starting
> at slide 10 or 08:00 of the video.
>
> Handles may refer to devices, to drivers or anything else.
> Handles are both to be created by U-Boot and by EFI binaries that we
> execute.
>
> On these handles protocol interfaces can be installed. These may be
> those defined in the UEFI spec or something completely independent. The
> protocol interfaces contain pointers to functions and additional data.
>
> Further objects are events. These may contain references to an event
> handler function that is called when the event is triggered.
Thank you for the info. I did read the entire spec some years ago
(about 6 I think) and have dug into bits of it since. I do find the
naming confusing so I cannot claim to understand it. The use of void *
everywhere is a pain.. I will doubtless take another look.
U-Boot does have devices, which have a (single) uclass and API. It
also has drivers. After all, the EFI tables are created from U-Boot
data structures, so presumably there is some correspondence.
>
> None of the above objects matches one to one to objects in the driver
> model. But we can use some integration:
>
> When a U-Boot device is probed we must create the UEFI handle and
> install the expected protocols on it.
>
> When a U-Boot device is removed we must destroy the handle. There are
> certain conditions under which a protocol must not be removed from a
> handle and the handle cannot be destroyed. In this case removing a
> device should not be possible.
I wish this had been done from the beginning, but we may as well start
now. It is quite a complicated task at this point.
Can we pick one data structure that we can make ephemeral, using only
the DM structs and features? Can we look at what features need to be
added (such as partition devices?) and add those to U-Boot?
What would be easiest as a starting point? How about struct
efi_system_partition?
Or perhaps could we drop efi_disk_register() and have it scan the disk
'on the fly' when needed?
There must be something that can be done here. I am sure there is a
mismatch of concepts/API, but some of these mismatches are features
that U-Boot could add and some can be 'thinned down' so that UEFI is
not such a lot of code.
Regards,
Simon
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