[PATCHv2 0/6] efi: detect erroneous firmware IRQ manipulation

Matt Fleming
2016-04-25T11:19:23Z

On Mon, 25 Apr, at 12:04:55PM, Mark Rutland wrote:
> On Mon, Apr 25, 2016 at 11:51:53AM +0100, Matt Fleming wrote:
> > On Mon, 25 Apr, at 11:40:09AM, Mark Rutland wrote:
> > >
> > > It looks like irqs_disabled_flags() will do what you expect, and ignore
> > > everything but the interrupt flag.
> > >
> > > However, for ARM that will ignore the other exceptions we've seen FW
> > > erroneously unmask (e.g. FIQ), which is unfortunate, as fiddling with
> > > those is just as disastrous.
> >
> > Bah, right.
> >
> > > Would you be happy with an arch_efi_call_check_flags(before, after),
> > > instead? That way we can make the flags we check arch-specific.
> >
> > Could we just make the flag mask arch-specific instead of the call
> > since the rest of efi_call_virt_check_flags() is good?
>
> Yup, I meant that arch_efi_call_check_flags would only do the flag
> comparison, only replacing the bit currently in the WARN_ON_ONCE().
>
> > Something like this (uncompiled, untested, half-baked),
> >
> > ---
> >
> > diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
> > index c38b1cfc26e2..057d00bee7d6 100644
> > --- a/drivers/firmware/efi/runtime-wrappers.c
> > +++ b/drivers/firmware/efi/runtime-wrappers.c
> > @@ -25,9 +25,12 @@
> > static void efi_call_virt_check_flags(unsigned long flags, const char *call)
> > {
> > unsigned long cur_flags;
> > + bool mismatch;
> >
> > local_save_flags(cur_flags);
> > - if (!WARN_ON_ONCE(cur_flags != flags))
> > +
> > + mismatch = (cur_flags ^ flags) & ARCH_EFI_IRQ_FLAGS_MASK;
> > + if (!WARN_ON_ONCE(mismatch))
> > return;
>
> This style also works for me.

Cool. One thing that occurred to me after I sent it is that
technically we should either,

1) make 'mismatch' an int or
2) do mismatch = !!((cur_flags ^ flags) & ARCH_EFI_IRQ_FLAGS_MASK)

Either is fine with me, I just don't want to leave the implicit
conversion to C's type system.

> Should I respin patch 6 as a series doing the above?
>
> I assume that the first 5 patches are fine as-is.

Yep, they're fine. Sure, go ahead and respin patch 6.