Impact of platform firmware on Linux kernel. Megha Dey, Sai Praneeth Prakhya Intel Open Source Technology Center

Transcription

1 Impact of platform firmware on Linux kernel Megha Dey, Sai Praneeth Prakhya Intel Open Source Technology Center

2 AGENDA Introduction to UEFI UEFI implementation bug crashing Linux Linux EFI subsystem bug affecting system stability Introduction to Linux UEFI Validation (LUV) project Make your UEFI system Linux ready with LUV

3 Introduction to UEFI UEFI (Unified Extensible Firmware Interface) is a specification that defines a software interface between an OS and platform firmware. OS EFI Firmware Hardware UEFI firmware vs legacy BIOS. UEFI forum members Many biggies like AMD, Apple, Dell, IBM, Microsoft etc.. and of course Intel. UEFI firmware, not only in PC and servers but also in embedded space. Embedded Linux Conference

4 UEFI Services Implemented as API s has code and data regions in memory. UEFI offers two types of services: 1. Boot time services: API s available to OS loader before ExitBootServices() 2. Runtime services: API s available to OS loader before and after ExitBootServices() Embedded Linux Conference

5 Boot Process Before ExitBootServices UEFI OS Loader Memory as seen by firmware Firmware controls system memory Memory accesses in physical mode Firmware owns system memory Embedded Linux Conference

6 Boot Process After ExitBootServices UEFI OS Loader Kernel Memory as seen by kernel ExitBootServices() Free Kernel controls system memory Physical addressing mode Before calling SetVirtualAddressMap() Reserved Free Embedded Linux Conference

7 Boot Process Virtual Address space Kernel Virtual Address space End Modules Modules High Kernel Mapping EFI Runtime Services ESPfix Area vmemmap vmalloc() area Low Kernel mapping Kernel space User space 0xffffffffff xffffffffa xffffffff xffffffef xffffff xffff xffff xffff xffff x Unused EFI Runtime Code EFI Runtime Data Unused EFI Runtime Data EFI Runtime Code Embedded Linux Conference

8 Illegal accesses by firmware Kernel Virtual Address space End Modules Modules High Kernel Mapping EFI Runtime Services ESPfix Area vmemmap vmalloc() area Low Kernel mapping Kernel space User space 0xffffffffff xffffffffa xffffffff xffffffef xffffff xffff xffff xffff xffff x Unused EFI Runtime Code EFI Runtime Data Unused EFI Runtime Data EFI Runtime Code Boot Data Embedded Linux Conference

9 Illegal access by EFI Runtime Service Embedded Linux Conference

10 Samsung laptops bricked by UEFI PC enthusiast reports Booting Linux bricks Samsung laptops Kernel hacker starts investigation Kernel uses EFI backed pstore BIOS code (SPI or Flash) Driver triggers H/W error EFI variables overwrites BIOS Mathew Garett founds astonishing facts Buggy firmware How Much is too much Kernel developer Embedded Linux Conference

11 Kernel bugs causing panic Kernel panics on BGRT enabled platform It s impossible to test for all cases No worries! We have a solution Enable all possible tables/features in OVMF and use Qemu + OVMF to find bugs Kernel developer LUV team Reference: BGRT - Boot Graphics Resource Table OVMF - Opensource Virtual Machine Firmware Embedded Linux Conference

12 Buggy firmware causes issues ESRT parsed successfully Failed to parse ESRT Same kernel booted on two different machines It s difficult tough to to catch find these errors No worries! We have a solution Enable all possible tables/features in OVMF and use Qemu + OVMF to find bugs QA Engineer LUV team ESRT - EFI System Resource Table Embedded Linux Conference

13 UEFI implementation is critical Things can go wrong during interactions between firmware and Linux kernel Faulty implementation of generic UEFI hurts Linux Linux UEFI Validation (LUV) project was started. Embedded Linux Conference

14 Why LUV? Fragmented Validation Strategy Linux workarounds, firmware not fixed No test-suite tests FW-OS interactions Embedded Linux Conference

15 Current Validation Strategy Pre-boot Boot Run-time Test gap FWTS UEFI SCT/PI Test gap Embedded Linux Conference

16 LUV: A unified framework Continuous Integration framework of upstream open source projects: Linux kernel Yocto Project Open source test-suites (eg. FWTS) LUV is a complete Linux distro!! Embedded Linux Conference

17 LUV: Covering the entire spectrum Pre-boot LUV Embedded Linux Conference

18 LUV: Detect bugs early At boot time: At run-time: Illegally accessed EFI boot data region fixed by EFI specific page fault handler in kernel Embedded Linux Conference

19 LUV: Easy to use Plug and play Diskless boot Boot on Virtual Machine luv.img Embedded Linux Conference

20 LUV: Easy to contribute LUV is open source! Test manager runner parser reporter Foo Test suite Foo Test suite Foo Test suite Foo Test suite Embedded Linux Conference

21 LUV: Available features Results are saved for viewing 1. If (USB Stick) - Saved in LUV_RESULTS folder 2. If (Net Boot) - Saved to HTTP server 3. If (VM) - Saved in the results partition of luv.img Debug via network using Netconsole. Telemetrics mechanism to send error report to the LUV server incase of crash. Lists all available DSMs on a platform. Future feature: Add support for more bootloaders. Embedded Linux Conference

22 LUV: Path to better firmware Collaborate Comprehensive Quality Community Consolidates various open source test-suites Test the entire software stack Detect firmware/kernel bugs early Easy to use Easy to contribute Embedded Linux Conference

23 What do you need? Tell us your needs to better validate your firmware! Join US Credits Neri Ricardo Matt Fleming Gayatri Kammela Naresh Bhat And many more contributors Embedded Linux Conference

24 Thank you. Any Questions?