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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Thu, 5 Apr 2018 02:28:06 +0200
Message-ID: <CAKv+Gu_-AQp-+s2ojoDYicHm30QyQNXjECBBM0D8Rs9L5+n3RA@mail.gmail.com>
Subject: Re: [PATCH 2/2] efi: Add embedded peripheral firmware support
To:     Hans de Goede <hdegoede@redhat.com>
Cc:     Peter Jones <pjones@redhat.com>,
        "Luis R. Rodriguez" <mcgrof@kernel.org>,
        Lukas Wunner <lukas@wunner.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Kalle Valo <kvalo@codeaurora.org>,
        Arend Van Spriel <arend.vanspriel@broadcom.com>,
        Ingo Molnar <mingo@redhat.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dave Olsthoorn <dave@bewaar.me>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        linux-efi@vger.kernel.org, Will Deacon <will.deacon@arm.com>,
        Andy Lutomirski <luto@kernel.org>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        David Howells <dhowells@redhat.com>,
        Mimi Zohar <zohar@linux.vnet.ibm.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Matthew Garrett <mjg59@srcf.ucam.org>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        dmitry.torokhov@gmail.com, mfuzzey@parkeon.com,
        Kees Cook <keescook@chromium.org>, nbroeking@me.com,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Torsten Duwe <duwe@suse.de>
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On 4 April 2018 at 22:25, Hans de Goede <hdegoede@redhat.com> 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] git@github.com:LongSoft/UEFITool.git
>> [1] git@github.com:theopolis/uefi-firmware-parser.git
>>
>>>> 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:
>>>>    https://github.com/LongSoft/UEFITool
>>>>    * Add the EFI Firmware Volume Protocol to include/linux/efi.h:
>>>>
>>>> https://www.intel.com/content/dam/doc/reference-guide/efi-firmware-file-volume-specification.pdf
>>>>
>>>> * 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
>