Re: [Xense-devel] [PATCH] ACM: adding C-support for policy translation and labeling support for domains

[David Palmer <dwpalmer.xense@gmail.com>]

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Is it your experience that decision cache's aren't efficient? I thought the 
theory was that most access checks will be against the local cache in order 
to make calls to the security server infrequent. This is accomplished by the 
ACM responding to each decision request with a list of related decisions. As 
the cache is checked locally, it avoids the context switch and should 
perform well. By adding a method for the ACM to signal each object manager 
when to clear the cache, we're still able to support changing the policy. 
This could be provided by a standard static library and promoted as the 
accepted method for creating object managers and should be carefully 
optimized.

By suggesting that domains should make "informed decisions" rather than 
"blindly call the ACM", are you suggesting that you'll be making the Xen 
security policy that everyone else will abide by? To change the policy will 
require changing code in each "informed" domain that wasn't designed with 
that policy in mind. This would eventially make it very costly to change the 
policy in interesting and new ways. As long as the policy is obviously 
correct and accepted by everyone who will use Xen, then I suppose there 
isn't a problem.

Dave


On 8/31/05, Reiner Sailer <sailer@us.ibm.com> wrote:
> 
> 
> Hi Dave, 
> 
> we are introducing the get_ssid ACM command to allow ACM policy-specific 
> decisions 
> and enforcement in policy-aware domains. 
> 
> One can call back into the hypervisor for policy decisions having the 
> benefit you are 
> naming (transparency). However doing this for every IP packet, for 
> example, seems not efficient. 
> Consequently, you'll end up establishing decision cashes in the domains. 
> Then you have the same 
> problem as before (change in policy) without the performance benefit. If 
> transparency 
> (policy hiding) is the most important factor, then such a solution has 
> merit. Another benefit of 
> getting the whole ssid is that you can re-use this information for other 
> decisions since you get 
> all the types of a domain, not just a yes/no decision. 
> 
> Nothing speaks against having an optional "acm_decision" call that can be 
> used 
> by domains that don't want to make informed decisions but blindly call the 
> ACM 
> (hypervisor call++ overhead) each time they make a decisions. Such a call 
> might prove useful 
> where decisions are made very infrequently. For example, a virtual block 
> device domain owning a 
> hard drive and allowing other domains to mount certain logical partitions 
> might just ask the ACM for 
> a decision when deciding about accepting a mount-request from a domain to 
> a logical partition 
> (right now, the virtual block device domain is dom0 but this could be 
> refined in the future when other 
> domains can 'own' peripherals). 
> 
> Regards 
> Reiner 
> 
> xense-devel-bounces@lists.xensource.com wrote on 08/31/2005 07:11:44 PM:
> 
> > I'm not clear why the getssid() needs to be introduced. Isn't the 
> > problem better solved by introducing new object managers? With the 
> > getssid(), the code must know about the specific policy, making the 
> > policy less amenable to adjustment as problems are discovered. 
> > Wouldn't it be better for the domains to provide object managers? 
> > This would allow the STE policy to make statements about those new 
> > objects. The code can be policy neutral by strictly following the 
> > decisions of the security server. Wouldn't this make it easier to 
> > revoke policies and update them without having to change the code and 
> patch?
> > 
> > Dave
> > 
>  
> > On 8/18/05, Reiner Sailer <sailer@us.ibm.com> wrote: 
> > 
> > This patch: 
> > 
> > * adds a C-based security policy translation tool to Xen 
> > (secpol_xml2bin) and removes the current Java 
> > security policy translator (Java dependencies). The C-based tool 
> > integrates into the Xen source tree build 
> > and install (using gnome libxml2 for XML parsing). See install.txt. 
> > 
> > * introduces security labels and related tools. Users can now use 
> > semantic-rich label names to put security-tags 
> > on domains. See example.txt, policy.txt. 
> > 
> > * moves the security configuration (currently 
> > ACM_USE_SECURITY_POLICY) from xen/Rules.mk 
> > into a separate top-level Security.mk <http://Security.mk> file (it is 
> needed by the 
> > tools/security and xen/acm). 
> > 
> > Both xen/acm and tools/security are built during the Xen build 
> > process only if ACM_USE_SECURITY_POLICY 
> > is not ACM_NULL_POLICY (which is the default setting). 
> > 
> > Comments welcome! 
> > 
> > Note: We are currently preparing a patch that introduces a new ACM 
> > command (getssid) to retrieve the security types 
> > of a running domain. This command is enables domain-internal 
> > enforcement functions based on the ACM security policy. 
> > 
> > Thanks 
> > Reiner 
> > 
> > Signed-off-by Reiner Sailer <sailer@us.ibm.com> 
> > Signed-off by Stefan Berger <stefanb@us.ibm.com> 
> > Signed-off by Ray Valdez <rvaldez@us.ibm.com> 
> > 
> > 
> > _______________________________________________
> > Xense-devel mailing list
> > Xense-devel@lists.xensource.com 
> > http://lists.xensource.com/xense-devel
> > 
> > 
>  
> > _______________________________________________
> > Xense-devel mailing list
> > Xense-devel@lists.xensource.com
> > http://lists.xensource.com/xense-devel
>

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