On 4 April 2018 at 22:25, Hans de Goede <hdegoede@xxxxxxxxxx> 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@xxxxxxxxxx:LongSoft/UEFITool.git >> [1] git@xxxxxxxxxx: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 > -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
