Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S935579AbaDJN6F (ORCPT <rfc822;w@1wt.eu>);
	Thu, 10 Apr 2014 09:58:05 -0400
Received: from mail4.hitachi.co.jp ([133.145.228.5]:36709 "EHLO
	mail4.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S934020AbaDJN6D (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 10 Apr 2014 09:58:03 -0400
Message-ID: <5346A362.9010802@hitachi.com>
Date: Thu, 10 Apr 2014 22:57:54 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Organization: Hitachi, Ltd., Japan
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20120614 Thunderbird/13.0.1
MIME-Version: 1.0
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@elte.hu>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Anton Arapov <aarapov@redhat.com>, David Long <dave.long@linaro.org>,
        "Frank Ch. Eigler" <fche@redhat.com>,
        Jonathan Lebon <jlebon@redhat.com>, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 4/6] uprobes/x86: Emulate rip-relative call's
References: <20140406201628.GA507@redhat.com> <1396995963.5056.46.camel@oc7886638347.ibm.com.usor.ibm.com> <20140409154346.GB18486@redhat.com> <53469F95.1030709@redhat.com>
In-Reply-To: <53469F95.1030709@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

(2014/04/10 22:41), Denys Vlasenko wrote:
> On 04/09/2014 05:43 PM, Oleg Nesterov wrote:
>> On 04/08, Jim Keniston wrote:
>>>
>>> On Sun, 2014-04-06 at 22:16 +0200, Oleg Nesterov wrote:
>>>> 0xe8. Anything else?
>>>
>>> No, I think e8 is the only call instruction uprobes will see.
>>
>> Good.
> 
> There is this monstrosity, "16-bit override for branches" in 64-mode:
> 
> 66 e8 nn nn       callw   <offset16>
> 
> Nobody sane uses it because it truncates instruction pointer.

No problem, insn.c can handle that too. :)

Thank you,

> 
> Or rather, *I think* it should truncate it (i.e. zero-extend to full width),
> but conceivably some CPUs can be buggy wrt that:
> they can decide to modify only lower 16 bits of IP,
> or even they can decided to use signed <offset16> but apply it
> to full-width RIP.
> 
> AMD manuals are not clear on what exactly should happen.
> 
> I am sure no one sane uses this form of branch instructions
> in 32-bit and 64-bit code.
> 
> I don't think we should be trying to support it "correctly"
> (we can just let program crash with SIGILL or something),
> we only need to make sure we don't overlook its existence
> and thus are not tricked into touching or modifying unrelated data.
> 
> 
> Imagine that   66 e8 nn nn    bytes are exactly at the end of
> a page, and we wrongly assume that offset is 32-bit, not 16-bit.
> 
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/