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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Jun 07, 2016 at 03:39:59PM -0400, Daniel De Graaf wrote:
> 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.

Ah, stubdomains!

Could there be an s/utility domain/utility domain (stubdomains)/ ?

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

Yes pls. That way it is easier to do a grep and find what it can refere to.

> 
> >[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.

/me nods.
> 
> >.. 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.

Would it be better to rename 'default_role' to 'all_domains_access'
or such?

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

It may be good for other newbies (like me) to get a gently introduction
via reading patches/code?
> 
> >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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