linux-kernel - Re: [v6 PATCH 08/21] x86/insn-eval: Add utility function to get segment descriptor base address

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Date:   Wed, 26 Apr 2017 15:52:41 -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>,
        Alexandre Julliard <julliard@...ehq.org>,
        Stas Sergeev <stsp@...t.ru>, Fenghua Yu <fenghua.yu@...el.com>,
        "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,
        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: [v6 PATCH 08/21] x86/insn-eval: Add utility function to get
 segment descriptor base address

On Thu, 2017-04-20 at 10:25 +0200, Borislav Petkov wrote:
> > + * insn_get_seg_base() - Obtain base address contained in
> descriptor
> > + * @regs:    Set of registers containing the segment selector
> > + * @insn:    Instruction structure with selector override prefixes
> > + * @regoff:  Operand offset, in pt_regs, of which the selector is
> needed
> > + * @use_default_seg: Use the default segment instead of prefix
> overrides
> 
> I'm wondering whether you really need that bool or you can deduce this
> from pt_regs... I guess I'll see...

Probably insn_get_seg_base() itself can verify if there are segment
override prefixes in the struct insn. If yes, use them except for
specific cases such as CS.

On an unrelated note, I still have the problem of using DS vs ES for
string instructions. Perhaps instead of a use_default_seg flag, a
string_instruction flag that indicates how to determine the default
segment.

Thanks and BR,
Ricardo