Re: [PATCH RFC] Add support for core-wide protection of IRQ and softirq

[Peter Zijlstra]

On Sun, May 10, 2020 at 07:46:52PM -0400, Joel Fernandes (Google) wrote:
> With current core scheduling patchset, non-threaded IRQ and softirq
> victims can leak data from its hyperthread to a sibling hyperthread
> running an attacker.
> 
> For MDS, it is possible for the IRQ and softirq handlers to leak data to
> either host or guest attackers. For L1TF, it is possible to leak to
> guest attackers. There is no possible mitigation involving flushing of
> buffers to avoid this since the execution of attacker and victims happen
> concurrently on 2 or more HTs.
> 
> The solution in this patch is to monitor the outer-most core-wide
> irq_enter() and irq_exit() executed by any sibling. In between these
> two, we mark the core to be in a special core-wide IRQ state.

Another possible option is force_irqthreads :-) That would cure it
nicely.

Anyway, I'll go read this.