[Xense-devel] Re: [Xen-devel] ACM ternary ops?

[Michael LeMay <lemaymd@xxxxxxxxxxx>]

Reiner,

Thank you for that detailed explanation, it's great to hear that you'll 
be integrating additional networking hooks into ACM.  Are they currently 
available in any public repositories?  After this discussion, I've 
decided that the appropriate approach to my problem would be to add more 
networking hooks as well, although I haven't yet determined exactly 
where I will need them.  I would hate to recreate your work or conflict 
with it.
Since you asked what exactly I'm looking for, I'll try to explain it 
briefly here.  I'd like to have a general network access control 
architecture at the hypervisor level, that can control network 
communications to and from any domU.  It shouldn't matter whether the 
communications are intended for other VMs on the same machine, or some 
external host.  Originally, I had wanted to have some control over which 
IP addresses the domU's are permitted to communicate with.  However, 
after this discussion, I can see that a better approach would be to 
restrict the communications from all VMs such that they are unable to 
make any connections, but simply route connections through a designated 
VM that enforces an appropriate network policy from userspace or using 
iptables, etc.
-- Michael

Reiner Sailer wrote:
> > ------------------------------
> >
> > Message: 4
> > Date: Tue, 30 May 2006 08:52:48 -0400
> > From: Michael LeMay <lemaymd@xxxxxxxxxxx>
> > Subject: [Xen-devel] ACM ternary ops?
> > To: xen-devel@xxxxxxxxxxxxxxxxxxx
> > Message-ID: <447C4020.4020008@xxxxxxxxxxx>
> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> >
> > Hello all,
> >
> > I am interested in adding support for user-defined mandatory network
> > access control policies to the existing ACM policy framework.  The most
> > logical way to do this would be to add more hooks to handle networking
> > and then define another policy module, like chinese wall and type
> > enforcement.  However, it doesn't feel right to add a "ternary_ops"
> > structure that is invoked after "secondary_ops".  Is there any
> > reasonable justification for not including a link in each ops structure
> > that points to the next policy module in the chain?  Essentially, I'd
> > like to convert the current n-pointer structure to the following
> > linked-list structure:
> >
> > acm_primary_ops -> acm_secondary_ops -> acm_ternary_ops -> ... -> NULL
> >
> Hi Michael,
>
> to be able to answer more (than I do below) to your point, I need to 
> know what "user-defined" policy do you aim to enforce? Is it a 
> finer-grained operating system policy (based on OS structures, such as 
> IP address or similar things etc.)?
> If it is an operating system policy, then the policy should be 
> implemented, decided, enforced, and managed in the operating system 
> (e.g., IP tables, SELinux,...) and probably not in the hypervisor. The 
> major focus of the ACM hypervisor security module is to keep the 
> hypervisor code as small as possible and robust, and the hypervisor 
> security guarantees easy to understand. --> only integrate what needs 
> to be there. Higher layer security can and should be handled in the 
> higher layers (OS, Middleware, Apps.).
> Regarding hypervisor ACM network enforcement: We are currently 
> integrating network packet policy enforcement into the Dom0 netback 
> interface to control local network traffic (enforcing the simple 
> type-enforcement policy based on acm labels of sending/receiving 
> domain). In this case, we don't need new policies but integrate the 
> existing acm_getdecision hypervisor call into the netback code to 
> decide if a packet is passed or discarded between virtual network 
> interfaces. This solutions appears to be a good fit for local traffic 
> because the virtual network resource is part of the hypervisor 
> environment and because the network policy is based on hypervisor 
> structures: domains (not IP...). Other enforcement is be needed to 
> guard external packets and such controls (at least our prototypes) use 
> OS-level security, such as SELinux.
> >Is there any
> > reasonable justification for not including a link in each ops structure
> > that points to the next policy module in the chain?
>
> Every policy layer operating on the same hooks might keep internal 
> state information, which must be rolled back if an access is denied by 
> a policy component called "later" for the same hook. The chinese wall 
> and the simple type enforcement policy components were chosen to build 
> a hypervisor policy because they complete each other (one controls 
> which domains can start on a system, the other controls how started 
> domains can share information/communicate) and because they offer a 
> good abstraction (workload = Doms + resources) based on which security 
> guarantees are understood.
> Running more than two policy components at the same time would require 
> to show that you really need all these policies active at the same 
> time. Otherwise, it seems more appropriate to define a new hypervisor 
> policy that can be configured instead of the existing ones (assuming 
> this new policy belongs into the hypervisor layer).
> Greetings
> Reiner 
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