From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH] KVM: x86: Disallow hypercalls for guest callers in rings
 > 0
Date: Mon, 03 Aug 2009 17:24:37 +0300
Message-ID: <4A76F325.7020309@redhat.com>
References: <4A76EA7B.4080509@siemens.com> <4A76EE85.1090404@codemonkey.ws>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-15; format=flowed
Content-Transfer-Encoding: 7bit
Cc: Jan Kiszka <jan.kiszka@siemens.com>,
	kvm-devel <kvm@vger.kernel.org>
To: Anthony Liguori <anthony@codemonkey.ws>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx2.redhat.com ([66.187.237.31]:40222 "EHLO mx2.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S932186AbZHCO6I (ORCPT <rfc822;kvm@vger.kernel.org>);
	Mon, 3 Aug 2009 10:58:08 -0400
In-Reply-To: <4A76EE85.1090404@codemonkey.ws>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On 08/03/2009 05:04 PM, Anthony Liguori wrote:
>
> Actually, VT mandates that vmcalls can only be done from CPL=0.
>

That's exactly how I misremembered it.  However the docs say

IF not in VMX operation
     THEN #UD;
ELSIF in VMX non-root operation
     THEN VM exit;
ELSIF (RFLAGS.VM = 1) OR (IA32_EFER.LMA = 1 and CS.L = 0)
     THEN #UD;
ELSIF CPL > 0
     THEN #GP(0);

So CPL > 0 is only enforced on VMCALL from the hypervisor, not the guest 
(tip: don't ask what VMCALL in the hypervisor means).


> SVM allows hypercalls from CPL>0 unfortunately.

Yeah.

-- 
error compiling committee.c: too many arguments to function