linux-kernel - Re: [PATCHv2 0/6] efi: detect erroneous firmware IRQ manipulation

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Message-ID: <20160425111923.GS2829@codeblueprint.co.uk>
Date:	Mon, 25 Apr 2016 12:19:23 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Laszlo Ersek <lersek@...hat.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	"hpa@...or.com" <hpa@...or.com>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCHv2 0/6] efi: detect erroneous firmware IRQ manipulation

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.