linux-kernel - Re: [PATCH] x86/umip: Add emulation for 64-bit processes

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Date:   Mon, 09 Sep 2019 12:56:18 +0100
From:   hpa@...or.com
To:     Borislav Petkov <bp@...en8.de>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
CC:     Brendan Shanks <bshanks@...eweavers.com>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] x86/umip: Add emulation for 64-bit processes

On September 8, 2019 8:22:48 AM GMT+01:00, Borislav Petkov <bp@...en8.de> wrote:
>On Sat, Sep 07, 2019 at 02:26:10PM -0700, Ricardo Neri wrote:
>> > Wine users have encountered a number of 64-bit Windows games that
>use
>> > these instructions (particularly sgdt), and were crashing when run
>on
>> > UMIP-enabled systems.
>> 
>> Emulation support for 64-bit processes was not initially included
>> because no use cases had been identified.
>
>AFAIR, we said at the time that 64-bit doesn't need it because this is
>legacy software only and 64-bit will get fixed properly not to use
>those
>insns. I can probably guess how that went ...

I don't think Windows games was something we considered. However, needing to simulate these instructions is not a huge surprise. The important thing is that by simulating them, we can plug the leak of some very high value kernel information – mainly the GDT, IDT and TSS addresses.
-- 
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