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

From: Stas Sergeev
Date: Thu Mar 09 2017 - 17:10:21 EST

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
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