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

From: Jeremy Linton
Date: Thu Jan 03 2019 - 11:46:59 EST


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?


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".