Re: [PATCH v2 1/7] sysfs/cpu: Add "Unknown" vulnerability state

[Jeremy Linton]

Hi,

On 01/03/2019 10:37 AM, Dave Martin wrote:
> On Wed, Jan 02, 2019 at 06:49:15PM -0600, Jeremy Linton wrote:
> > There is a lot of variation in the Arm ecosystem. Because of this,
> > there exist possible cases where the kernel cannot authoritatively
> > determine if a machine is vulnerable.
> >
> > Rather than guess the vulnerability status in cases where
> > the mitigation is disabled or the firmware isn't responding
> > correctly, we need to display an "Unknown" state.
> >
> > Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
> > ---
> >   Documentation/ABI/testing/sysfs-devices-system-cpu | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > index 9605dbd4b5b5..876103fddfa4 100644
> > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > @@ -495,6 +495,7 @@ Description:	Information about CPU vulnerabilities
> >   		"Not affected"	  CPU is not affected by the vulnerability
> >   		"Vulnerable"	  CPU is affected and no mitigation in effect
> >   		"Mitigation: $M"  CPU is affected and mitigation $M is in effect
> > +		"Unknown"    	  The kernel is unable to make a determination
>
> Do some of the "Unknown" cases arise from the vulnerability detection
> code being compiled out of the kernel?

Yes,

> I wonder whether at least the detection support should be mandatory.
> sysfs is not very useful as a standard vulnerability reporting interface
> unless we make best efforts to always populate it with real information. >
>
> Also, does "Unknown" convey anything beyond what is indicated by the
> sysfs entry being omitted altogether?

I'm not sure about this one. I tend to think the "unknown" case 
encourages users that really want an answer to dig deeper and call their 
hardware/os/whoever to get an answer. I would tend to think that if the 
entry is missing it would tend to encourage the behavior that Greg KH 
mentions where the user assumes "hey the system doesn't have a sysfs 
entry for $VUNLERABILITY, that probably means that its not possible on 
the architecture".