From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention
Date: Sat, 01 Apr 2017 10:49:56 -0700
Message-ID: <201704011750.v31Ho5q2028383@mail.zytor.com>
References: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com> <79ba0fff-4c01-2bfa-06cb-5cfc98dd710c@list.ru> <CALCETrX4D13Q4LRxGrQzXQCWvaRpq7sG0ws8CpB_bM4rKQ4W_A@mail.gmail.com> <997ba581-ecfa-b773-a48e-85b92a439836@list.ru> <CALCETrX87_RyEscDLLscNaE33=FEpzW0JVphZaWoJSBL5VhN0w@mail.gmail.com> <1489022122.131264.33.camel@ranerica-desktop> <a9043b85-e44c-4070-1ecc-75f653539423@list.ru> <CALCETrXNRHyB2NhpVAzgEh+UBFYD+uFrVJioFPwiO+dqQ9E1ww@mail.gmail.com> <63231222-5b42-c8c9-02f0-0afbe702d8b5@list.ru> <1489190396.131264.47.camel@ranerica-desktop> <6331deea-e9b0-fcfe-b75d-8100f37a615a@list.ru> <1490658399.2647.14.camel@ranerica-desktop> <cc490254-9c0b-e55e-6228-ad5e1f365123@list.ru> <1490762284.2647.24.camel@ranerica-desktop> <2a9c7bfd-e85c-2673-d3b5-906fe7dd8db4@list.ru> <14908508
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To: Stas Sergeev <stsp@list.ru>, Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>, Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@suse.de>, Peter Zijlstra <peterz@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Brian Gerst <brgerst@gmail.com>, Chris Metcalf <cmetcalf@mellanox.com>, Dave Hansen <dave.hansen@linux.intel.com>, Paolo Bonzini <pbonzini@redhat.com>, Liang Z Li <liang.z.li@intel.com>, Masami Hiramatsu <mhiramat@kernel.org>, Huang Rui <ray.huang@amd.com>, Jiri Slaby <jslaby@suse.cz>, Jonathan Corbet <corbet@lwn.net>, "Michael S. Tsirkin" <mst@redhat.com>, Paul Gortmaker <paul.gortmaker@windriver.com>, Vlastimil Babka <vbabka@suse.cz>, Chen Yucong <slaoub@gmail.com>, Alexandre

<x86@kernel.org>,linux-msdos@vger.kernel.org,wine-devel@winehq.org
From: hpa@zytor.com
Message-ID: <3FD12652-AA83-4D73-9914-BBA089E58FFA@zytor.com>

On April 1, 2017 6:08:43 AM PDT, Stas Sergeev <stsp@list.ru> wrote:
>30.03.2017 08:14, Ricardo Neri пишет:
>>>>>>> You know the wine's
>>>>>>> requirements now - they are very small. And
>>>>>>> dosemu doesn't need anything at all but smsw.
>>>>>>> And even smsw is very rare.
>>>>>> But emulation is still needed for SMSW, right?
>>>>> Likely so.
>>>>> If you want, I can enable the logging of this command
>>>>> and see if it is used by some of the DOS programs I have.
>>>> It would be great if you could do that, if you don't mind.
>>> OK, scheduled to the week-end.
>>> I'll let you know.
>> Thanks!
>OK, done the testing.
>It appears smsw is used in v86 by windows-3.1 and dos4gw
>at the very least, and these are the "major" apps. So doing
>without a fixup in v86 will not go unnoticed. Unfortunately
>this also means that KVM-vm86 should be properly tested.
>I have also found a weird program that does SGDT under
>v86. This causes "ERROR: SGDT not implemented" under
>dosemu, but the prog still works fine as it obviously does
>not care about the results. This app can easily be broken
>of course, if that makes any sense (likely not).

Using SMSW to detect v86 mode is relatively common.  pushf hides the VM flag, but SMSW is available, providing the v86 virtualization hole.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.