Re: [PATCH v2] x86/nmi: Fix some races in NMI uaccess

[Thomas Gleixner]

On Wed, 29 Aug 2018, Nadav Amit wrote:
> at 8:47 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.
> > 
> > Cc: stable@xxxxxxxxxxxxxxx
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
> > Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > ---
> > 
> > Nadav, this is intended for your series.  Want to add it right
> > before the use_temporary_mm() stuff?
> 
> Sure. Thanks! I will apply the following small fix:
> 
> > +
> > +#ifdef CONFIG_DEBUG_VM
> > +	WARN_ON_ONCE(!loaded_mm);
> > +#endif
> 
> Will be changed to VM_WARN_ON_ONCE() in the two instances.

Unless I'm completely lost, this can just be applied to tip right
away. It's not depending on anything else.

Thanks,

	tglx