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

From: Nadav Amit
Date: Wed Aug 29 2018 - 14:56:14 EST

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:

> +
> + WARN_ON_ONCE(!loaded_mm);
> +#endif

Will be changed to VM_WARN_ON_ONCE() in the two instances.