Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention

[Ricardo Neri]

On Wed, 2017-03-08 at 08:46 -0800, Andy Lutomirski wrote:
> On Wed, Mar 8, 2017 at 8:29 AM, Stas Sergeev <stsp@xxxxxxx> wrote:
> > 08.03.2017 19:06, Andy Lutomirski ÐÐÑÐÑ:
> >>
> >> On Wed, Mar 8, 2017 at 6:08 AM, Stas Sergeev <stsp@xxxxxxx> wrote:
> >>>
> >>> 08.03.2017 03:32, Ricardo Neri ÐÐÑÐÑ:
> >>>>
> >>>> These are the instructions covered by UMIP:
> >>>> * SGDT - Store Global Descriptor Table
> >>>> * SIDT - Store Interrupt Descriptor Table
> >>>> * SLDT - Store Local Descriptor Table
> >>>> * SMSW - Store Machine Status Word
> >>>> * STR - Store Task Register
> >>>>
> >>>> This patchset initially treated tasks running in virtual-8086
> mode as a
> >>>> special case. However, I received clarification that DOSEMU[8]
> does not
> >>>> support applications that use these instructions.
> >>
> >> Can you remind me what was special about it?  It looks like you
> still
> >> emulate them in v8086 mode.
> >
> > Indeed, sorry, I meant prot mode here. :)
> > So I wonder what was cited to be special about v86.

Initially my patches disabled UMIP on virtual-8086 instructions, without
regards of protected mode (i.e., UMIP was always enabled). I didn't have
emulation at the time. Then, I added emulation code that now covers
protected and virtual-8086 modes. I guess it is not special anymore.

Thanks and BR,
Ricardo