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

From: Jeremy Linton
Date: Thu Jan 03 2019 - 15:32:51 EST


On 01/03/2019 01:30 PM, Stefan Wahren wrote:
Hi Jeremy,

Jeremy Linton <jeremy.linton@xxxxxxx> hat am 3. Januar 2019 um 17:46 geschrieben:


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.

i applied your patch series on linux-next-20190103. On my Raspberry Pi 3B+ (defconfig) i'm getting this from sysfs:

l1tf:Not affected
meltdown:Not affected
spectre_v1:Mitigation: __user pointer sanitization

AFAIK it has 4 Cortex-A53 cores (no PSCI firmware), so shouldn't be affected.

So, for spec_store_bypass, as you noted your getting hit by the lack of psci/smccc to report the ssb state, and this patch is just reflecting that.

In the case of spectrev2 it may be correct to blame this patch set because its displaying "unknown" since your core isn't in the black list, and your core isn't new enough to have the csv2 bit indicating its not vulnerable. In this case if we do away with the unknown state, we should probably depend entirely on the black list and simply display "Not affected" if the core isn't listed. (meaning we may report cores not affected when they are missing from the blacklist).

How can this be fixed?

For ssb, the correct answer is probably fix the firmware, but given the situation, its likely this kind of machine is going to force an additional MIDR list to report the state correctly. Maybe Will or someone can chime in here?

For spectrev2, wait for another version of this patch.