Re: [PATCH v19 08/25] x86/mm: Introduce _PAGE_COW

[Dave Hansen]

On 2/4/21 12:19 PM, Kees Cook wrote:
>> (e) A page where the processor observed a Write=1 PTE, started a write, set
>>     Dirty=1, but then observed a Write=0 PTE.  That's possible today, but
>>     will not happen on processors that support shadow stack.
> What happens for "e" with/without CET? It sounds like direct writes to
> such pages will be (correctly) rejected by the MMU?

A page fault would be generated regardless of CET support.

If CET were not around, the fault would be reported as a present, write
fault.

If this happened and CET were around (which shouldn't happen in
practice, it means we have a hardware issue) a page fault exception is
generated.  Yu-cheng, I'm not sure there's enough debugging around to
tell us if this happens.  Would we even notice?