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

Stas Sergeev
2017-03-10T11:33:53Z

10.03.2017 05:39, Andy Lutomirski пишет:
> On Thu, Mar 9, 2017 at 2:10 PM, Stas Sergeev <stsp@list.ru> wrote:
>> 09.03.2017 04:15, Ricardo Neri пишет:
>>
>>> On Wed, 2017-03-08 at 08:46 -0800, Andy Lutomirski wrote:
>>>> On Wed, Mar 8, 2017 at 8:29 AM, Stas Sergeev <stsp@list.ru> wrote:
>>>>> 08.03.2017 19:06, Andy Lutomirski пишет:
>>>>>> On Wed, Mar 8, 2017 at 6:08 AM, Stas Sergeev <stsp@list.ru> wrote:
>>>>>>> 08.03.2017 03:32, Ricardo Neri пишет:
>>>>>>>> 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?
> Er, right. Ricardo, your code may need fixing. But don't you have a
> test case for this?
Why would you need one?
Or do you really want to allow these instructions
in v86 by the means of emulation? If so - this wasn't
clearly stated in the patch description, neither it was
properly discussed, it seems.