From: Sai Praneeth <sai.praneeth.prakhya@xxxxxxxxx> There may exist some buggy UEFI firmware implementations that might access efi regions other than EFI_RUNTIME_SERVICES_<CODE/DATA> even after the kernel has assumed control of the platform. This violates UEFI specification. If selected, this debug option will print a warning message if the UEFI firmware tries to access any memory region which it shouldn't. Along with the warning, the efi page fault handler will also try to recover from the page fault triggered by the firmware so that the machine doesn't hang. Suggested-by: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> Based-on-code-from: Ricardo Neri <ricardo.neri@xxxxxxxxx> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@xxxxxxxxx> Cc: Al Stone <astone@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Bhupesh Sharma <bhsharma@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> --- arch/x86/Kconfig | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index f1dbb4ee19d7..cc840710ae3e 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1957,6 +1957,24 @@ config EFI_MIXED If unsure, say N. +config EFI_PAGE_FAULT_HANDLER + bool "EFI page fault handler support" if EXPERT + depends on EFI + help + Enable this debug feature so that the kernel can recover from page + faults caused by buggy firmware. Also, + 1. If the page fault is caused by efi_reset_system(), then the + platform is rebooted through BIOS. + 2. If the page fault is caused by any other efi runtime service, + then the kernel freezes efi_rts_wq (work queue that runs efi + runtime services) and schedules a new process. Also, it disables + EFI Runtime Services, so that it will never again call buggy + firmware. + Please see the UEFI specification for details on the expectations + of memory usage. + + If unsure, say N. + config SECCOMP def_bool y prompt "Enable seccomp to safely compute untrusted bytecode" -- 2.7.4
