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In-Reply-To: <20170308003254.27833-22-ricardo.neri-calderon@linux.intel.com>
References: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com> <20170308003254.27833-22-ricardo.neri-calderon@linux.intel.com>
From: Andy Lutomirski <luto@amacapital.net>
Date: Wed, 8 Mar 2017 07:56:20 -0800
Message-ID: <CALCETrX8EAkDMYxx0QB-k1eZH51sMXDpXKHfZTo0hS-FE7weBg@mail.gmail.com>
Subject: Re: [v6 PATCH 21/21] selftests/x86: Add tests for User-Mode
 Instruction Prevention
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        "H. Peter Anvin" <hpa@zytor.com>, 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 Julliard <julliard@winehq.org>, Stas Sergeev <stsp@list.ru>,
        Fenghua Yu <fenghua.yu@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Shuah Khan <shuah@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, linux-msdos@vger.kernel.org,
        wine-devel@winehq.org
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On Tue, Mar 7, 2017 at 4:32 PM, Ricardo Neri
<ricardo.neri-calderon@linux.intel.com> wrote:
> Certain user space programs that run on virtual-8086 mode may utilize
> instructions protected by the User-Mode Instruction Prevention (UMIP)
> security feature present in new Intel processors: SGDT, SIDT and SMSW. In
> such a case, a general protection fault is issued if UMIP is enabled. When
> such a fault happens, the kernel catches it and emulates the results of
> these instructions with dummy values. The purpose of this new
> test is to verify whether the impacted instructions can be executed without
> causing such #GP. If no #GP exceptions occur, we expect to exit virtual-
> 8086 mode from INT 0x80.
>
> The instructions protected by UMIP are executed in representative use
> cases:
>  a) the memory address of the result is given in the form of a displacement
>     from the base of the data segment
>  b) the memory address of the result is given in a general purpose register
>  c) the result is stored directly in a general purpose register.
>
> Unfortunately, it is not possible to check the results against a set of
> expected values because no emulation will occur in systems that do not have
> the UMIP feature. Instead, results are printed for verification.

You could pre-initialize the result buffer to a bunch of non-matching
values (1, 2, 3, ...) and then check that all the invocations of the
same instruction gave the same value.

If you do this, maybe make it a follow-up patch -- see other email.