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

On Tue, Aug 28, 2018 at 1:04 AM Andy Lutomirski luto@kernel.org 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?