Re: [RFC PATCH 3/3] Prevent user from writing to IBT bitmap.

[Yu-cheng Yu]

On Sat, 2019-06-29 at 16:44 -0700, Andy Lutomirski wrote:
> On Fri, Jun 28, 2019 at 12:50 PM Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:
> > 
> > The IBT bitmap is visiable from user-mode, but not writable.
> > 
> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> > 
> > ---
> >  arch/x86/mm/fault.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index 59f4f66e4f2e..231196abb62e 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -1454,6 +1454,13 @@ void do_user_addr_fault(struct pt_regs *regs,
> >          * we can handle it..
> >          */
> >  good_area:
> > +#define USER_MODE_WRITE (FAULT_FLAG_WRITE | FAULT_FLAG_USER)
> > +       if (((flags & USER_MODE_WRITE)  == USER_MODE_WRITE) &&
> > +           (vma->vm_flags & VM_IBT)) {
> > +               bad_area_access_error(regs, hw_error_code, address, vma);
> > +               return;
> > +       }
> > +
> 
> Just make the VMA have VM_WRITE and VM_MAYWRITE clear.  No new code
> like this should be required.

Ok, I will work on that.

Thanks,
Yu-cheng