linux-kernel - Re: [v3 PATCH 00/10] x86: Enable User-Mode Instruction Prevention

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Date:   Wed, 25 Jan 2017 21:51:16 -0800
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Liang Z Li <liang.z.li@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        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>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        Alexandre Julliard <julliard@...ehq.org>,
        Fenghua Yu <fenghua.yu@...el.com>, Stas Sergeev <stsp@...t.ru>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-msdos@...r.kernel.org, wine-devel@...ehq.org
Subject: Re: [v3 PATCH 00/10] x86: Enable User-Mode Instruction Prevention

Hi Peter,
On Wed, 2017-01-25 at 12:34 -0800, H. Peter Anvin wrote:
> On 01/25/17 12:23, Ricardo Neri wrote:
> >  * SMSW returns the value with which the CR0 register is programmed in
> >    head_32/64.S at boot time. This is, the following bits are enabed:
> >    CR0.0 for Protection Enable, CR.1 for Monitor Coprocessor, CR.4 for
> >    Extension Type, which will always be 1 in recent processors with UMIP;
> >    CR.5 for Numeric Error, CR0.16 for Write Protect, CR0.18 for Alignment
> >    Mask. Additionally, in x86_64, CR0.31 for Paging is set.
> 
> SMSW only returns CR0[15:0], so the reference here to CR0[31:16] seems odd.

I checked again the latest version (from Dec 2016) of the Intel Software
Development Manual. The documentation for SMSW states the following:

SMSW r16 operand size 16, store CR0[15:0] in r16
SMSW r32 operand size 32, zero-extend CR0[31:0], and store in r32
SMSW r64 operand size 64, zero-extend CR0[63:0], and store in r64

When the operand is a memory location, yes, it only returns CR0[15:0]

Also, in the tests that I ran I wrote the result of SMSW to a 64-bit
register. I get 0x80050033. It seems to me that it does write as many
bits as the register operand can hold.

Am I missing something?

Thanks and BR,
Ricardo
> 
> 	-hpa
> 
>