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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrXNRHyB2NhpVAzgEh+UBFYD+uFrVJioFPwiO+dqQ9E1ww@mail.gmail.com>
Date:   Thu, 9 Mar 2017 18:39:38 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Stas Sergeev <stsp@...t.ru>
Cc:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Liang Z Li <liang.z.li@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        Alexandre Julliard <julliard@...ehq.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, linux-msdos@...r.kernel.org,
        wine-devel@...ehq.org
Subject: Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention

On Thu, Mar 9, 2017 at 2:10 PM, Stas Sergeev <stsp@...t.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@...t.ru> wrote:
>>>>
>>>> 08.03.2017 19:06, Andy Lutomirski пишет:
>>>>>
>>>>> On Wed, Mar 8, 2017 at 6:08 AM, Stas Sergeev <stsp@...t.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?  The behavior should be the same with and without
your patches applied.  The exception is #UD, not #GP, so maybe your
code just never executes in the vm86 case.

--Andy