Re: [PATCH] x86/nmi: Fix some races in NMI uaccess

From: Jann Horn
Date: Mon Aug 27 2018 - 19:12:41 EST

On Tue, Aug 28, 2018 at 1:04 AM Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> In NMI context, we might be in the middle of context switching or in
> the middle of switch_mm_irqs_off(). In either case, CR3 might not
> match current->mm, which could cause copy_from_user_nmi() and
> friends to read the wrong memory.
> Fix it by adding a new nmi_uaccess_okay() helper and checking it in
> copy_from_user_nmi() and in __copy_from_user_nmi()'s callers.

What about eBPF probes (which I think can be attached to kprobe points
/ tracepoints / perf events) that perform userspace reads / userspace
writes / kernel reads? Can those run in NMI context, and if so, do
they also need special handling?