[PATCH v5] x86: Disallow GOT memory access beyond its GOT slot

[H.J. Lu]

On Wed, Feb 12, 2025 at 6:57 PM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 11.02.2025 22:47, H.J. Lu wrote:
> > --- a/gas/config/tc-i386.c
> > +++ b/gas/config/tc-i386.c
> > @@ -453,6 +453,9 @@ struct _i386_insn
> >      /* Compressed disp8*N attribute.  */
> >      unsigned int memshift;
> >
> > +    /* Memory size for instructions with compressed disp8.  */
> > +    unsigned int memsize;
>
> What an effort to implement something people won't be able to rely on,
> in both the positive and negative directions. You now even need a new
> state field.
>
> > @@ -8811,9 +8814,17 @@ check_VecOperands (const insn_template *t)
> >        && pp.disp_encoding <= disp_encoding_8bit)
> >      {
> >        if (i.broadcast.type || i.broadcast.bytes)
> > -     i.memshift = t->opcode_modifier.broadcast - 1;
> > +     {
> > +       i.memshift = t->opcode_modifier.broadcast - 1;
> > +       /* Remember memory size.  */
> > +       i.memsize = 1 << i.memshift;
> > +     }
> >        else if (t->opcode_modifier.disp8memshift != DISP8_SHIFT_VL)
> > -     i.memshift = t->opcode_modifier.disp8memshift;
> > +     {
> > +       i.memshift = t->opcode_modifier.disp8memshift;
> > +       /* Remember memory size.  */
> > +       i.memsize = 1 << i.memshift;
> > +     }
> >        else
> >       {
> >         const i386_operand_type *type = NULL, *fallback = NULL;
> > @@ -8856,6 +8867,9 @@ check_VecOperands (const insn_template *t)
> >               i.memshift = 4;
> >           }
> >
> > +       /* Remember memory size.  */
> > +       i.memsize = 1 << i.memshift;
> > +
> >         /* For the check in fits_in_disp8().  */
> >         if (i.memshift == 0)
> >           i.memshift = -1;
>
> Note how in particular in process_suffix() we save/restore i.memshift,
> to cover for check_VecOperands() possibly updating the field. I expect
> i.memsize would now also need saving/restoring (at least) there.
>

A testcase?

-- 
H.J.