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. > 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? Luis > The end result is mostly the same as what you're doing here, > and you'll also have a similar array of structs, but instead > of hardcoding 8-byte signatures of firmware files, you'll be > using GUIDs. I envision lots of interesting use cases for > a generic Firmware Volume file retrieval mechanism. What you > need to keep in mind though is that this approach only works > if the kernel is booted via the EFI stub. > > Thanks, > > Lukas > -- Do not panic -- 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
