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

[Kees Cook]

On Wed, Mar 29, 2017 at 3:38 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> 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?)

Do you mean preempt_disable() isn't strong enough here? I'm open to
suggestions. The goal would be to make sure nothing between _begin and
_end would get executed without interruption...

-Kees

-- 
Kees Cook
Pixel Security