On Fri, 22 Apr, at 02:51:23PM, Mark Rutland wrote: > The UEFI spec allows runtime services to be called with interrupts > masked or unmasked, and if a runtime service function needs to mask > interrupts, it must restore the mask to its original state before > returning (i.e. from the PoV of the OS, this does not change across a > call). Firmware should never unmask exceptions, as these may then be > taken by the OS unexpectedly. > > Unfortunately, some firmware has been seen to unmask IRQs (and > potentially other maskable exceptions) across runtime services calls, > leaving irq flags corrupted after returning from a runtime services > function call. This may be detected by the IRQ tracing code, but often > goes unnoticed, leaving a potentially disastrous bug hidden. > > This patch detects when the irq flags are corrupted by an EFI runtime > services call, logging the call and specific corruption to the console. > While restoring the expected value of the flags is insufficient to avoid > problems, we do so to avoid redundant warnings from elsewhere (e.g. IRQ > tracing). > > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> > Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> > Cc: linux-efi@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > --- > drivers/firmware/efi/runtime-wrappers.c | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > I'm not sure about the LOCKDEP_NOW_UNRELIABLE here. If FW unmasks IRQs there's > the potential for deadlock, but arguably by the time we've detected the flag > corruption the danger has passed. I'm erring on the side of caution here > setting it, but perhaps that's not the best idea? I think it makes sense to leave it as-is, not least to guard against future changes we make to the kernel side that might have lockdep side effects when this bug is triggered. -- 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
