linux-kernel - Re: umip: AMD Ryzen 3900X, pagefault after emulate SLDT/SIDT instruction

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Date:   Sat, 23 May 2020 04:21:33 +0200
From:   andi@...much.email
To:     Brendan Shanks <bshanks@...eweavers.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Babu Moger <Babu.Moger@....com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Jason Yan <yanaijie@...wei.com>, linux-kernel@...r.kernel.org
Subject: Re: umip: AMD Ryzen 3900X, pagefault after emulate SLDT/SIDT
 instruction

On 11:56 19.05.20, Brendan Shanks wrote:
> The problem is that the kernel does not emulate/spoof the SLDT instruction, only SGDT, SIDT, and SMSW.
> SLDT and STR weren't thought to be commonly used, so emulation/spoofing wasn’t added.
> In the last few months I have seen reports of one or two (32-bit) Windows games that use SLDT though.
> Can you share more information about the application you’re running?

This is basically the "minimal" reproducer for the issue I've been
observed (as by the previously linked article):

https://gist.githubusercontent.com/andir/071981717460242a1df2e0fc20836fdc/raw/0c31877aa7ee59146596fe68934f9cecb5c998ae/test.c