On Tue, 2 Apr 2019, Andy Lutomirski wrote:
> > On Apr 2, 2019, at 1:29 PM, Thomas Gleixner <t...@linutronix.de> wrote:
> >>> How about a much better fix: make the DB stack be the same size as all
> >>> the others and just have 4 of them (DB0, DB1, DB2, and DB3. After all,
> >>> overflowing from one debug stack into another is just as much of a bug as
> >>> overflowing into a different IST stack.
> >>
> >> That makes sense.
> >
> > Except that we just have two not four.
> >
> > It needs some tweaking of the ist_shift stuff in entry_64.S but that's not
> > rocket science. Famous last words....
> >
>
> The ist_shift mess should probably be in C, but that’s a big can of
> worms. That being said, why do we have it at all? Once upon a time, we’d
> do ICEBP from user mode (or a legit breakpoint), then send a signal and
> hit a data breakpoint, and we’d recurse. But we don’t run user debug
> handlers on the IST stack at all anymore.
>
> Maybe we can convince ourselves it’s safe?
Maybe. Need to think about it for a while.
Thanks,
tglx
