linux-kernel - Re: [PATCH 0/4] x86: enable User-Mode Instruction Prevention

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Date:   Tue, 8 Nov 2016 14:16:00 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-doc@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>, Brian Gerst <brgerst@...il.com>,
        Chen Yucong <slaoub@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        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>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH 0/4] x86: enable User-Mode Instruction Prevention

On Mon, Nov 07, 2016 at 10:12:09PM -0800, Ricardo Neri wrote:
> There is a caveat, however. Certain applications running in virtual-8086
> mode, such as DOSEMU[1] and Wine[2], want to utilize the SGDT, SIDT and
> SLDT instructions for legitimate reasons. In order to keep such
> applications working, UMIP must be disabled/enabled when entering/exiting
> virtual-8086 mode. 

Would it not be better to emulate these instructions for them? What way
we can verify they're not malicious.