• Sai Praneeth's avatar
    efi/x86: Handle page faults occurring while running EFI runtime services · 3425d934
    Sai Praneeth authored
    Memory accesses performed by UEFI runtime services should be limited to:
    - reading/executing from EFI_RUNTIME_SERVICES_CODE memory regions
    - reading/writing from/to EFI_RUNTIME_SERVICES_DATA memory regions
    - reading/writing by-ref arguments
    - reading/writing from/to the stack.
    Accesses outside these regions may cause the kernel to hang because the
    memory region requested by the firmware isn't mapped in efi_pgd, which
    causes a page fault in ring 0 and the kernel fails to handle it, leading
    to die(). To save kernel from hanging, add an EFI specific page fault
    handler which recovers from such faults by
    1. If the efi runtime service is efi_reset_system(), reboot the machine
       through BIOS.
    2. If the efi runtime service is _not_ efi_reset_system(), then freeze
       efi_rts_wq and schedule a new process.
    The EFI page fault handler offers us two advantages:
    1. Avoid potential hangs caused by buggy firmware.
    2. Shout loud that the firmware is buggy and hence is not a kernel bug.
    Tested-by: default avatarBhupesh Sharma <bhsharma@redhat.com>
    Suggested-by: default avatarMatt Fleming <matt@codeblueprint.co.uk>
    Based-on-code-from: Ricardo Neri <ricardo.neri@intel.com>
    Signed-off-by: default avatarSai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
    Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
    [ardb: clarify commit log]
    Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>