linux-kernel - Re: [PATCH v8 12/28] x86/insn-eval: Add utility functions to get segment selector

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170927114713.wbee7ze2ud2ekvbw@pd.tnic>
Date:   Wed, 27 Sep 2017 13:47:13 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
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, 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 v8 12/28] x86/insn-eval: Add utility functions to get
 segment selector

On Tue, Sep 26, 2017 at 09:21:44PM -0700, Ricardo Neri wrote:
> This is true except when we don't have an insn at all (well, it may be
> non-NULL but it will only contain garbage). The case to which I am
> referring is when we begin decoding our instruction. The first step is
> to copy_from_user the instruction and populate insn. For this we must
> calculate the linear address from where we copy using CS and rIP.

Where do we do that?

> Furthermore, in this only case we don't need to look at insn at all as
> the only register involved is rIP no segment override prefixes are
> allowed.

In any case, as it is now it sounds convoluted: you may or may not
have an insn, and yet you call get_overridden_seg_reg() on it but you
don't really need segment overrides because you only need CS and rIP
initially.

Sounds to me like this initial parsing should be done separately from
this function...

> I only used "(E)" (i.e., not the "(R|)" part) as these utility
> functions will deal mostly with protected mode, unless FS or GS are
> used in long mode.

eIP or rIP is simply much easier to type and parse. Those brackets, not
really.

> I only check for a NULL insn when needed (i.e., the contents of the
> instruction could change the used segment register).

... and those if (!insn) tests sprinkled around simply make the code
unreadable and if we can get rid of them, we should.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--