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Date:   Thu, 5 Apr 2018 02:28:06 +0200
From:   Ard Biesheuvel <>
To:     Hans de Goede <>
Cc:     Peter Jones <>,
        "Luis R. Rodriguez" <>,
        Lukas Wunner <>,
        Greg Kroah-Hartman <>,
        Thomas Gleixner <>,
        Kalle Valo <>,
        Arend Van Spriel <>,
        Ingo Molnar <>,
        "H . Peter Anvin" <>,
        Linux Kernel Mailing List <>,
        Dave Olsthoorn <>,
        "the arch/x86 maintainers" <>,, Will Deacon <>,
        Andy Lutomirski <>,
        Matt Fleming <>,
        David Howells <>,
        Mimi Zohar <>,
        Josh Triplett <>,
        Matthew Garrett <>,
        One Thousand Gnomes <>,
        Linus Torvalds <>,,,
        Kees Cook <>,,
        Bjorn Andersson <>,
        Torsten Duwe <>
Subject: Re: [PATCH 2/2] efi: Add embedded peripheral firmware support

On 4 April 2018 at 22:25, Hans de Goede <> wrote:
> HI,
> On 04-04-18 19:18, Peter Jones wrote:
>> On Tue, Apr 03, 2018 at 06:58:48PM +0000, Luis R. Rodriguez wrote:
>>> On Tue, Apr 03, 2018 at 08:07:11PM +0200, Lukas Wunner wrote:
>>>> On Tue, Apr 03, 2018 at 10:33:25AM +0200, Hans de Goede wrote:
>>>>> I asked Peter Jones for suggestions how to extract this during boot and
>>>>> he suggested seeing if there was a copy of the firmware in the
>>>>> EFI_BOOT_SERVICES_CODE memory segment, which it turns out there is.
>>>>> My patch to add support for this contains a table of device-model (dmi
>>>>> strings), firmware header (first 64 bits), length and crc32 and then if
>>>>> we boot on a device-model which is in the table the code scans the
>>>>> EFI_BOOT_SERVICES_CODE for the prefix, if found checks the crc and
>>>>> caches the firmware for later use by request-firmware.
>>>>> So I just do a brute-force search for the firmware, this really is
>>>>> hack,
>>>>> nothing standard about it I'm afraid. But it works on 4 different x86
>>>>> tablets I have and makes the touchscreen work OOTB on them, so I
>>>>> believe
>>>>> it is a worthwhile hack to have.
>>>> The EFI Firmware Volume contains a kind of filesystem with files
>>>> identified by GUIDs.  Those files include EFI drivers, ACPI tables,
>>>> DMI data and so on.  It is actually quite common for vendors to
>>>> also include device firmware on the Firmware Volume.  Apple is doing
>>>> this to ship firmware updates e.g. for the GMUX controller found on
>>>> dual GPU MacBook Pros.  If they want to update the controller's
>>>> firmware, they include it in a BIOS update, and an EFI driver checks
>>>> on boot if the firmware update for the controller is necessary and
>>>> if so, flashes it.
>>>> The firmware files you're looking for are almost certainly included
>>>> on the Firmware Volume as individual files.
>>> What Hans implemented seems to have been for a specific x86 hack, best if
>>> we
>>> confirm if indeed they are present on the Firmware Volume.
>> To be honest, I'm a bit skeptical about the firmware volume approach.
>> Tools like UEFITool[0] and uefi-firmware-parser[1] have existed for
>> years, still don't seem to reliably parse firmware images I see in the
>> wild, and have a fairly regular need for fixes.  These are tools
>> maintained by smart people who are making a real effort, and it still
>> looks pretty hard to do a good job that applies across a lot of
>> platforms.
>> So I'd rather use Hans's existing patches, at least for now, and if
>> someone is interested in hacking on making an efi firmware volume parser
>> for the kernel, switch them to that when such a thing is ready.
>> [0]
>> [1]
>>>> Rather than scraping
>>>> the EFI memory for firmware, I think it would be cleaner and more
>>>> elegant if you just retrieve the files you're interested in from
>>>> the Firmware Volume.
>>>> We're doing something similar with Apple EFI properties, see
>>>> 58c5475aba67 and c9cc3aaa0281.
>>>> Basically what you need to do to implement this approach is:
>>>> * Determine the GUIDs used by vendors for the files you're interested
>>>>    in.  Either dump the Firmware Volume or take an EFI update as
>>>>    shipped by the vendor, then feed it to UEFIExtract:
>>>>    * Add the EFI Firmware Volume Protocol to include/linux/efi.h:
>>>> * Amend arch/x86/boot/compressed/eboot.c to read the files with the
>>>>    GUIDs you're interested in into memory and pass the files to the
>>>>    kernel as setup_data payloads.
>>>> * Once the kernel has booted, make the files you've retrieved
>>>>    available to device drivers as firmware blobs.
>>> Happen to know if devices using Firmware Volumes also sign their firmware
>>> and if hw checks the firmware at load time?
>> It varies on a per-device basis, of course.  Most new Intel machines as
>> of Haswell *should* be verifying their system firmware via Boot Guard,
>> which both checks an RSA signature and measures the firmware into the
>> TPM, but as with everything of this nature, there are certainly vendors
>> that screw it up. (I think AMD has something similar, but I'm really not
>> sure.)
> Lukas, thank you for your suggestions on this, but I doubt that these
> devices use the Firmware Volume stuff.

Aren't Firmware Volumes a PI thing rather than a UEFI thing?

> These are really cheap x86 Windows 10 tablets, everything about them is
> simply hacked together by the manufacturer till it boots Windows10 and
> then it is shipped to the customer without receiving any update
> afterwards ever.
> What you are describing sounds like significantly more work then
> the vendor just embedding the firmware as a char firmware[] in their
> EFI mouse driver.
> That combined with Peter's worries about difficulties parsing the
> Firmware Volume stuff, makes me believe that it is best to just
> stick with my current approach as Peter suggests.
> Regards,
> Hans

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