Re: [RFC PATCH 0/5] x86/hw_breakpoint: protects more cpu entry data

[Lai Jiangshan]

On Mon, May 25, 2020 at 11:27 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Mon, May 25, 2020 at 02:50:57PM +0000, Lai Jiangshan wrote:
> > Hello
> >
> > The patchset is based on (tag: entry-v9-the-rest, tglx-devel/x86/entry).
> > And it is complement of 3ea11ac991d
> > ("x86/hw_breakpoint: Prevent data breakpoints on cpu_entry_area").
> >
> > After reading the code, we can see that more data needs to be protected
> > against hw_breakpoint, otherwise it may cause
> > dangerous/recursive/unwanted #DB.
> >
> >
> > Lai Jiangshan (5):
> >   x86/hw_breakpoint: add within_area() to check data breakpoints
> >   x86/hw_breakpoint: Prevent data breakpoints on direct GDT
> >   x86/hw_breakpoint: Prevent data breakpoints on per_cpu cpu_tss_rw
>
> I think we can actually get rid of that #DB IST stack frobbing, also see
> patches linked below.

Hi, Peter

I reviewed that patchset before. It is all what I want, but it still
didn't remove IST-shifting. I remove it in V2.

>
> >   x86/hw_breakpoint: Prevent data breakpoints on user_pcid_flush_mask
>
> Should we disallow the full structure just to be sure?

Sure, just did it as you suggested, thanks!

>
> >   x86/hw_breakpoint: Prevent data breakpoints on debug_idt_table
>
> That's going away, see:

Yes, so I added a note in the patch, saying "Please drop this patch
when Peter's work to remove debug_idt_table is merged."

I directly drop the patch in V2.

Thank you.
Lai


>
> https://lkml.kernel.org/r/20200522204738.645043059@xxxxxxxxxxxxx
>
> But yes, nice!
>