Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap()

[Andy Lutomirski]

On Wed, Mar 29, 2017 at 11:15 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> Based on PaX's x86 pax_{open,close}_kernel() implementation, this
> allows HAVE_ARCH_RARE_WRITE to work on x86.
>

> +
> +static __always_inline unsigned long __arch_rare_write_begin(void)
> +{
> +       unsigned long cr0;
> +
> +       preempt_disable();

This looks wrong.  DEBUG_LOCKS_WARN_ON(!irqs_disabled()) would work,
as would local_irq_disable().  There's no way that just disabling
preemption is enough.

(Also, how does this interact with perf nmis?)

--Andy