Re: [Xen-devel] [PATCH 1/5] flask/policy: split into modules

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 06/07/2016 03:22 PM, Konrad Rzeszutek Wilk wrote:
> On Mon, May 23, 2016 at 11:05:29AM -0400, Daniel De Graaf wrote:
> > This makes it easier to enable or disable parts of the XSM policy.
> Hey Daniel,
>
> I am no expert on this so please take it with a grain of salt.
That can actually be helpful to spot documentation problems :)

> .. snip..
> > diff --git a/tools/flask/policy/modules/default_role.te 
> > b/tools/flask/policy/modules/default_role.te
> > new file mode 100644
> > index 0000000..74f870f
> > --- /dev/null
> > +++ b/tools/flask/policy/modules/default_role.te
> > @@ -0,0 +1,8 @@
> > +# Allow all domains to use system_r so that systems that are not using the
> > +# user/role separation feature will work properly.
> > +role system_r types domain_type;
> In the 'original' code it also had : xen_type :
>
> 266 role system_r types { xen_type domain_type };
>
> Is this change done on purpose? Reading the xen.te it describes the 'system_r' 
> as:
>  "The system role is used for utility domains and pseudo-domains                
> "
>
> which is .. confusing. What is an utility domain? Pseudo-domain?
Utility domains would be a domain that is not actually a part of a guest,
such as xenstore, vtpm-manager, and disaggregated components of dom0.

Pseudo-domain is the term used here to refer to DOMID_XEN and DOMID_IO.
Is there a better name for this?

> [Looking in the new xen.te I see that it has the same syntax]
> > +
> > +# The vm role is used as part of user separation.  Allow all domain types to 
> > use
> > +# this role except dom0.
> > +role vm_r;
> > +role vm_r types { domain_type -dom0_t };
> > diff --git a/tools/flask/policy/modules/dom0.te 
> > b/tools/flask/policy/modules/dom0.te
> > new file mode 100644
> > index 0000000..dd4d7dd
> > --- /dev/null
> > +++ b/tools/flask/policy/modules/dom0.te
> > @@ -0,0 +1,74 @@
> > +################################################################################
> > +#
> > +# Allow dom0 access to all sysctls, devices, and the security server.
> > +#
> > +# While this could be written more briefly using wildcards, the permissions are
> > +# listed out to make removing specific permissions simpler.
> > +#
> > +################################################################################
> > +allow dom0_t xen_t:xen {
> > +       settime tbufcontrol readconsole clearconsole perfcontrol mtrr_add
> > +       mtrr_del mtrr_read microcode physinfo quirk writeconsole readapic
> > +       writeapic privprofile nonprivprofile kexec firmware sleep frequency
> > +       getidle debug getcpuinfo heap pm_op mca_op lockprof cpupool_op tmem_op
> > +       tmem_control getscheduler setscheduler
> > +};
> > +allow dom0_t xen_t:xen2 {
> > +       resource_op psr_cmt_op psr_cat_op pmu_ctrl get_symbol
> > +       get_cpu_levelling_caps get_cpu_featureset xsplice_op
> Hehe. livepatch_op now :-)
I have a corrected series that also has some other pending hypervisor
patches, which I can post whenever the 4.8 merging window is fully
open.

> .. giant snip...
>
> > diff --git a/tools/flask/policy/modules/xen.te 
> > b/tools/flask/policy/modules/xen.te
> > new file mode 100644
> > index 0000000..f374dc5
> > --- /dev/null
> > +++ b/tools/flask/policy/modules/xen.te
> .. snip..
>
> > +################################################################################
> > +#
> > +# Roles
> > +#
> > +################################################################################
> > +
> > +# The object role (object_r) is used for devices, resources, and event 
> > channels;
> > +# it does not need to be defined here and should not be used for domains.
> > +
> > +# The system role is used for utility domains and pseudo-domains.  If roles are
> > +# not being used for separation, all domains can use the system role.
> > +role system_r;
> > +role system_r types { xen_type dom0_t };
> Right here it is back again.
>
> Is the 'default_role' neccessary then?
Specifying some role is necessary to create a valid security label
(which is a user:role:type tuple).

The line in xen.te only allows the pseudo-domains and dom0 to use
system_r; this is a useful minimum, if you are going to place any
actual guests in another role.  If you include default_role.te,
then this expands to allowing all domains to use system_r.

I could split the default_role extraction into a separate patch if
you think this explanation belongs in a commit message.

> I've looked at the original xen.te and them splitting out to individual and 
> there were no
> missing copy-n-paste (except the above 'default_role.te' which I am not
> clear about).
>
> Thanks!

--
Daniel De Graaf
National Security Agency

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