linux-kernel - Re: [PATCH v9 17/29] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 101b

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Message-ID: <20171020180741.GC12298@voyager>
Date:   Fri, 20 Oct 2017 11:07:41 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        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>,
        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>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, ricardo.neri@...el.com,
        Adam Buchbinder <adam.buchbinder@...il.com>,
        Colin Ian King <colin.king@...onical.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Qiaowei Ren <qiaowei.ren@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v9 17/29] x86/insn-eval: Indicate a 32-bit displacement
 if ModRM.mod is 0 and ModRM.rm is 101b

On Fri, Oct 20, 2017 at 05:44:48PM +0200, Borislav Petkov wrote:
> On Tue, Oct 03, 2017 at 08:54:20PM -0700, Ricardo Neri wrote:
> > Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software
> > Developer's Manual volume 2A states that when ModRM.mod is zero and
> > ModRM.rm is 101b, a 32-bit displacement follows the ModRM byte. This means
> > that none of the registers are used in the computation of the effective
> > address. A return value of -EDOM indicates callers that they should not
> > use the value of registers when computing the effective address for the
> > instruction.
> > 
> > In long mode, the effective address is given by the 32-bit displacement
> > plus the location of the next instruction. In protected mode, only the
> > displacement is used.
> > 
> > The instruction decoder takes care of obtaining the displacement.
> > 
> > Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> > Cc: Adam Buchbinder <adam.buchbinder@...il.com>
> > Cc: Colin Ian King <colin.king@...onical.com>
> > Cc: Lorenzo Stoakes <lstoakes@...il.com>
> > Cc: Qiaowei Ren <qiaowei.ren@...el.com>
> > Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> > Cc: Masami Hiramatsu <mhiramat@...nel.org>
> > Cc: Adrian Hunter <adrian.hunter@...el.com>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Thomas Garnier <thgarnie@...gle.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Borislav Petkov <bp@...e.de>
> > Cc: Dmitry Vyukov <dvyukov@...gle.com>
> > Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
> > Cc: x86@...nel.org
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> > ---
> >  arch/x86/lib/insn-eval.c | 25 ++++++++++++++++++++++---
> >  1 file changed, 22 insertions(+), 3 deletions(-)
> 
> Reviewed-by: Borislav Petkov <bp@...e.de>

Thank you!

BR,
Ricardo