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

[Jeremy Linton <jeremy.linton@arm.com>]

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@arm.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Dave Hansen <dave.hansen@intel.com>
>> Cc: Borislav Petkov <bp@alien8.de>
>> Cc: David Woodhouse <dwmw@amazon.co.uk>
>> ---
>>   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".