Re: [RFC][PATCH v2 11/21] x86/pti: Extend PTI user mappings

[Alexandre Chartre]

On 11/16/20 8:48 PM, Andy Lutomirski wrote:
> On Mon, Nov 16, 2020 at 6:49 AM Alexandre Chartre
> <alexandre.chartre@xxxxxxxxxx> wrote:
> > Extend PTI user mappings so that more kernel entry code can be executed
> > with the user page-table. To do so, we need to map syscall and interrupt
> > entry code, per cpu offsets (__per_cpu_offset, which is used some in
> > entry code), the stack canary, and the PTI stack (which is defined per
> > task).
>
> Does anything unmap the PTI stack?  Mapping is easy, and unmapping
> could be a pretty big mess.

No, there's no unmap. The mapping exists as long as the task page-table
does (i.e. as long as the task mm exits). I assume that the task stack
and mm are freed at the same time but that's not something I have checked.

alex.