On Wed, Mar 29, 2017 at 6:41 PM, Kees Cook <keesc...@chromium.org> wrote:
> On Wed, Mar 29, 2017 at 3:38 PM, Andy Lutomirski <l...@amacapital.net> wrote:
>> On Wed, Mar 29, 2017 at 11:15 AM, Kees Cook <keesc...@chromium.org> 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...
>
Sorry for the very slow response.
preempt_disable() isn't strong enough to prevent interrupts, and an
interrupt here would run with WP off, causing unknown havoc. I tend
to think that the caller should be responsible for turning off
interrupts.
--Andy
