From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH v12 1/9] x86: add generic resource (e.g. MSR) access hypercall Date: Fri, 4 Jul 2014 11:52:36 +0100 Message-ID: <53B68774.4060603@citrix.com> References: <53B67699.20608@citrix.com> <53B69E490200007800020A70@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <53B69E490200007800020A70@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich , Dongxiao Xu , xen-devel@lists.xen.org Cc: keir@xen.org, Ian.Campbell@citrix.com, George.Dunlap@eu.citrix.com, stefano.stabellini@eu.citrix.com, Ian.Jackson@eu.citrix.com, dgdegra@tycho.nsa.gov List-Id: xen-devel@lists.xenproject.org On 04/07/14 11:30, Jan Beulich wrote: >>>> On 04.07.14 at 11:40, wrote: >> On 04/07/14 09:34, Dongxiao Xu wrote: >>> Add a generic resource access hypercall for tool stack or other >>> components, e.g., accessing MSR, port I/O, etc. >>> >>> Signed-off-by: Dongxiao Xu >> This still permits a user of the hypercalls to play with EFER or >> SYSENTER_EIP, which obviously is a very bad thing. >> >> There needs to be a whitelist of permitted MSRs which can be accessed. > Hmm, I'm not sure. One particular purpose I see here is to allow the > tool stack (or Dom0) access to MSRs Xen may not know about (yet). > Furthermore, this being a platform op, only the hardware domain > should ever have access, and it certainly ought to know what it's > doing. So the sum of these two considerations is: If at all, we may > want a black list here. > > Jan > I don't think it is safe for the toolstack to ever be playing with MSRs which Xen is completely unaware of. There is no guarentee whatsoever that a new MSR which Xen is unaware of doesn't have security implications if the toolstack were to play with it. Adding entries to a whitelist is easy and could be considered a maintenance activity similar to keeping the model/stepping information up-to-date. ~Andrew