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

[Stas Sergeev]

09.03.2017 04:15, Ricardo Neri ÐÐÑÐÑ:
> 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.
But isn't SLDT&friends just throw UD in v86?
How does UMIP affect this? How does your patch affect
this?