On 21 August 2017 at 16:59, Peter Zijlstra [off-list ref] wrote:

On Mon, Aug 21, 2017 at 08:23:10AM -0700, Andy Lutomirski wrote:

quoted

quoted

Ah, but only root can create per-cpu events or attach events to kernel
threads (with sensible paranoia levels).

But this may not need to be percpu.  If a non root user can trigger, say, an EFI variable read in their own thread context, boom.

I was going by the proposed: "everything EFI in a kthread" model. But
yes, if that's not done, then you're quite right.

How does this work in cases where we need to call into UEFI from
non-process context? Or at least from a context where current != EFI's
kthread. We have EFI pstore code, for instance, that records panic
data. Should we make an exception for those?

I'm happy to have a stab at implementing the EFI kthread, but I'd like
to get some of these details clarified first.