From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tim Deegan <tim@xen.org>
Subject: Re: [PATCH 21/22] libxc: range checks in
	xc_dom_p2m_host and _guest
Date: Wed, 12 Jun 2013 19:26:17 +0100
Message-ID: <20130612182617.GA45409@ocelot.phlegethon.org>
References: <1370974865-19554-1-git-send-email-ian.jackson@eu.citrix.com>
	<1370974865-19554-22-git-send-email-ian.jackson@eu.citrix.com>
	<CAFLBxZZhXQ6CWOCGWnwzaGuBdHgjFykoQsZDcchhkoAeSJvp5Q@mail.gmail.com>
	<20920.40058.635699.510629@mariner.uk.xensource.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
Content-Disposition: inline
In-Reply-To: <20920.40058.635699.510629@mariner.uk.xensource.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>, Andrew Cooper <andrew.cooper3@citrix.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, mattjd@gmail.com, security@xen.org
List-Id: xen-devel@lists.xenproject.org

At 17:06 +0100 on 12 Jun (1371056778), Ian Jackson wrote:
> George Dunlap writes ("Re: [Xen-devel] [PATCH 21/22] libxc: range checks in xc_dom_p2m_host and _guest"):
> > On Tue, Jun 11, 2013 at 7:21 PM, Ian Jackson <ian.jackson@eu.citrix.com> wrote:
> > > These functions take guest pfns and look them up in the p2m.  They did
> > > no range checking.
> > >
> > > However, some callers, notably xc_dom_boot.c:setup_hypercall_page want
> > > to pass untrusted guest-supplied value(s).  It is most convenient to
> > > detect this here and return INVALID_MFN.
> > >
> > > This is part of the fix to a security issue, XSA-55.
> > >
> > > Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
> > > Cc: Tim Deegan <tim@xen.org>
> > 
> > I've taken a look at where things get returned here, and it seems like
> > they should all be OK with INVALID_MFN.
> 
> Good.  Does that mean that we should promote the check to be done in
> the shadow_enabled case too ?

No - did my last reply to this get lost?  The check is not needed for
shadow-translated guests as Xen will refuse any invalid mapping requests
anyway -- AFAICS the check just protects the array access.

For HVM guests, adding this check would be incorrect, as they can have
pfns > tot-pages.

Tim.