My last posting cut the main part of the mail. So here is the complete
posting:
Hi,
as a follow-up to the posting of the sHype patches for Xen from Tue/We
this week
[http://lists.xensource.com/archives/html/xen-devel/2005-03/msg01371.html],
you''ll find attached the promised draft Readme for the courageous ones
to
get
a little exposure to sHype at a small example.
I am posting this right before being away-from-email until April 11th.
Please be patient when waiting for any replies to your responses.
Hope you find it helpful. Feedback and corrections welcome.
Reiner
============= README ========Copyright: IBM Corporation (C)
03/31/05
Author: Reiner Sailer
This document is a very short introduction into the sHype security
architecture
implementation and how it is perceived by users. It is a very preliminary
draft
for the courageous ones to get "their feet wet" with the architecture
and
to be
able to give feedback (via the xen-devel mailing list).
Install:
goto xeno-unstable.bk (user --dry-run option if you want to test the patch
only)
patch -p1 -g0 < *sparse.diff
patch -p1 -g0 < *tools.diff
patch -p1 -g0 < *xen.diff
(no rejects, probably some line offsets)
make uninstall; make mrproper; make; ./install.sh should install the
default
sHype into Xen (rebuild your initrd images if necessary). Reboot.
Debug output: there are two triggers for debug output:
a) General sHype debug:
xeno-unstable.bk/xen/include/public/acm.h
undefine ACM_DEBUG to switch this debug off
b) sHype enforcement hook trace: This prints a small trace for each
enforcement
hook that is executed. The trigger is in
xeno-unstable.bk/xen/include/acm/acm_hooks.h
undefine ACM_TRACE_MODE to switch this debug off
1. The default NULL policy
***************************
When you apply the patches and startup xen, you should at first not notice
any
difference because the default policy is the "NULL" policy, which as
the
name
implies does not enforce anything.
However, when you try
[root@laptop policy]# xm list
Name Id Mem(MB) CPU State Time(s) Console SSID-REF
Domain-0 0 620 0 r---- 25.6 s:00/p:00
You might detect a new parameter "SSID-REF" displayed for domains.
This
parameter describes the subject security identifier reference of the
domain. It
is set in the domain configuration for manually created domains and is
fixed to
00/00 for DOM0 (see DOM0 ssidref definition in xen/include/public/acm.h).
The item that defines the ssidref in a domain configuration is:
ssidref = 0x12345678
Where ssidref is interpreted as a 32bit number, where the lower 16bits
become
the ssidref for the primary policy and the higher 16bits become the
ssidref for
the secondary policy. sHype currently supports two policies but this is an
implementation decision and can be extended if necessary.
This reference defines the security information of a domain. The meaning
of the
SSID-REF depends on the policy, so we explain it when we explain the real
policies.
To display the currently enforced policy, use the policy tool under xeno-
unstable.bk/tools/policy: policy_tool getpolicy. You should see output
like the
one below.
[root@laptop policy]#./policy_tool getpolicy
Policy dump:
===========Magic = 1debc.
PolVer = aaaa0000.
Len = 14.
Primary = NULL policy (c=0, off=14).
Secondary = NULL policy (c=0, off=14).
No primary policy (NULL).
No secondary policy (NULL).
Policy dump End.
Since this is a dump of a binary policy, it''s not pretty. The important
parts
are the "Primary" and "Secondary" policy fields set to
"NULL policy".
sHype
currently allows to set two independent policies; thus the two SSID-REF
parts
shown in ''xm list''. Right here: primary policy only means this
policy is
checked first, the secondary policy is checked if the primary results in
"permitted access". The result of the combined policy is
"permitted" if
both
policies return permitted (NULL policy always returns permitted). The
result is
"denied" if at least one of the policies returns "denied".
Look into xeno-
unstable.bk/xen/include/acm/acm_hooks.h for the general hook structure
integrating the policy decisions (if you like, you won''t need it for
the
rest
of the Readme file).
2. Setting Chinese Wall and Simple Type Enforcement policies:
*************************************************************
We''ll get fast to the point. However, in order to understand what we
are
doing,
we must at least understand the purpose of the policies that we are going
to
enforce. The two policies presented here are just examples and the
implementation encourages adding new policies easily.
2.1. Chinese Wall policy: "decides whether a domain can be started based
on
this domain''s ssidref and the ssidrefs of the currently running
domains".
Generally, the Chinese wall policy allows specifying certain types (or
classes
or categories, whatever the preferred word) that conflict; we usually
assign a
type to a workload and the set of types of those workloads running in a
domain
make up the type set for this domain. Each domain is assigned a set of
types
through its SSID-REF (we register Chinese Wall as primary policy, so the
ssidref used for determining the Chinese Wall types is the one annotated
with
"p:" in xm list) since each SSID-REF points at a set of types.
We''ll see
how
SSIDREFs are represented in Xen later when we will look at the policy. (A
good
read for Chinese Wall is: Brewer/Nash The Chinese Wall Security Policy
1989.)
So let''s assume the Chinese Wall policy we are running distinguishes 10
types:
t0 ... t9. Let us assume further that each SSID-REF points to a set that
includes exactly one type (attached to domains that run workloads of a
single
type). SSID-REF 0 points to {t0}, ssidref 1 points to {t1} ... 9 points to
{t9}. [This is actually the example policy we are going to push into xen
later]
Now the Chinese Wall policy allows you to define "Conflict type sets"
and
it
guarantees that of any conflict set at most one type is "running" at
any
time.
As an example, we have defined 2 conflict set: {t2, t3} and {t0, t5, t6}.
Specifying these conflict sets, sHype ensures that at most one type of
each set
is running (either t2 or t3 but not both; either t0 or t5 or t6 but not
multiple of them).
The effect is that administrators can define which workload types cannot
run
simultaneously on a single Xen system. This is useful to limit the covert
timing channels between such payloads or to ensure that payloads don''t
interfere with each other through existing resource dependencies.
2.2. Simple Type Enforcement (ste) policy: "decides whether two domains
can
share data, e.g., setup event channels or grant tables to each other,
based on
the two domains'' ssidref. This, as the name says, is a simple policy.
Think of
each type as of a single color. Each domain has one or more colors, i.e.,
the
domains ssid for the ste policy points to a set that has set one or
multiple
types. Let us assume in our example policy we differentiate 5 colors
(types)
and define 5 different ssids referenced by ssidref=0..4. Each ssid shall
have
exactly one type set, i.e., describes a uni-color. Only ssid(0) has all
types
set, i.e., has all defined colors.
Sharing is enforced by the ste policy by requiring that two domains that
want
to establish an event channel or grant pages to each other must have a
common
color. Currently all domains communicate through DOM0 by default; i.e.,
Domain0
will necessarily have all colors to be able to create domains (thus, we
will
assign ssidref(0) to Domain0 in our example below.
More complex mandatory access control policies governing sharing will
follow;
such policies are more sophisticated than the "color" scheme above by
allowing
more flexible (and complex :_) access control decisions than "share a
color" or
"don''t share a color" and will be able to express
finer-grained policies.
2.3 Binary Policy:
In the future, we will have a policy tool that takes as input a more
humane
policy description, using types such as development, home-banking,
donated-
Grid, CorpA-Payload ... and translates the respective policy into what we
see
today as the binary policy using 1s and 0s and sets of them. For now, we
must
live with the binary policy when working with sHype.
2.4 Exemplary use of a real sHype policy on Xen. To activate a real
policy,
edit the file (yes, this will soon be a compile option):
xeno-unstable.bk/xen/include/public/acm.h
Change: #define ACM_USE_SECURITY_POLICY ACM_NULL_POLICY
To : #define ACM_USE_SECURITY_POLICY
ACM_CHINESE_WALL_AND_SIMPLE_TYPE_ENFORCEMENT_POLICY
cd xeno-unstable.bk
make mrproper
make uninstall (manually remove /etc/xen.old if necessary)
make
./install.sh (recreate your kernel initrd''s if necessary)
Reboot into new xen.gz
After booting, check out ''xm dmesg''; should show somewhere in
the middle:
(XEN) acm_init: Enforcing Primary CHINESE WALL policy, Secondary SIMPLE
TYPE
ENFORCEMENT policy.
Even though you can activate those policies in any combination and also
independently, the policy tool currently only supports setting the policy
for
the above combination.
Now look at the minimal startup policy with:
xeno-unstable.bk/tools/policytool getpolicy
You should see something like:
[root@laptop policy]# ./policy_tool getpolicy
Policy dump:
===========Magic = 1debc.
PolVer = aaaa0000.
Len = 36.
Primary = CHINESE WALL policy (c=1, off=14).
Secondary = SIMPLE TYPE ENFORCEMENT policy (c=2, off=2c).
Chinese Wall policy:
===================Max Types = 1.
Max Ssidrefs = 1.
Max ConfSets = 1.
Ssidrefs Off = 10.
Conflicts Off = 12.
Runing T. Off = 14.
C. Agg. Off = 16.
SSID To CHWALL-Type matrix:
ssidref 0: 00
Confict Sets:
c-set 0: 00
Running
Types: 00
Conflict
Aggregate Set: 00
Simple Type Enforcement policy:
==============================Max Types = 1.
Max Ssidrefs = 1.
Ssidrefs Off = 8.
SSID To STE-Type matrix:
ssidref 0: 01
Policy dump End.
This is a minimal policy (of little use), except it will disable starting
any
domain that does not have ssidref set to 0x0. The Chinese Wall policy has
nothing to enforce and the ste policy only knows one type, which is set
for the
only defined ssidref.
Setting a new Security Policy:
******************************
The policy tool with all its current limitations has one usable example
policy
compiled-in. Please try at this time to use the setpolicy command:
xeno-unstable.bk/tools/policy/policy_tool setpolicy
You should see a dump of the policy you are setting. It should say at the
very
end:
Policy successfully set.
Now try to dump the currently enforced policy, which is the policy we have
just
set and the dynamic security state information of this policy
(<<< ... some additional explanations)
[root@laptop policy]# ./policy_tool getpolicy
Policy dump:
===========Magic = 1debc.
PolVer = aaaa0000.
Len = 112.
Primary = CHINESE WALL policy (c=1, off=14).
Secondary = SIMPLE TYPE ENFORCEMENT policy (c=2, off=d8).
Chinese Wall policy:
===================Max Types = a.
Max Ssidrefs = 5.
Max ConfSets = 2.
Ssidrefs Off = 10.
Conflicts Off = 74.
Runing T. Off = 9c.
C. Agg. Off = b0.
SSID To CHWALL-Type matrix:
ssidref 0: 01 00 00 00 00 00 00 00 00 00 <<< type0 is set for
ssidref0
ssidref 1: 00 01 00 00 00 00 00 00 00 00
ssidref 2: 00 00 01 00 00 00 00 00 00 00
ssidref 3: 00 00 00 01 00 00 00 00 00 00
ssidref 4: 00 00 00 00 01 00 00 00 00 00 <<< type4 is set for
ssidref4
<<< types 5-9 are unused
Confict Sets:
c-set 0: 00 00 01 01 00 00 00 00 00 00 <<< type2 and type3 never
run together
c-set 1: 01 00 00 00 00 01 01 00 00 00 <<< only one of types 0,
5
or 6
<<< can run
simultaneously
Running
Types: 01 00 00 00 00 00 00 00 00 00 <<< ref-count for types
of
running domains
Conflict
Aggregate Set: 00 00 00 00 00 01 01 00 00 00 <<< aggregated set of
types
that
<<< cannot run because
they
<<< are in conflict set 1
and
<<< (domain 0 is running
w
t0)
Simple Type Enforcement policy:
==============================Max Types = 5.
Max Ssidrefs = 5.
Ssidrefs Off = 8.
SSID To STE-Type matrix:
ssidref 0: 01 01 01 01 01 <<< ssidref0 points to a
set
that
<<< has all types set
(colors)
ssidref 1: 00 01 00 00 00 <<< ssidref1 has color1
set
ssidref 2: 00 00 01 00 00 <<< ...
ssidref 3: 00 00 00 01 00
ssidref 4: 00 00 00 00 01
Policy dump End.
This is a small example policy with which we will demonstrate the
enforcement.
Starting Domains with policy enforcement
=======================================Now let us play with this policy.
Define 3 or 4 domain configurations. I use the following config using a
ramdisk
only and about 8MBytes of memory for each DomU (test purposes):
#-------configuration xmsec1-------------------------
kernel = "/boot/vmlinuz-2.6.11-xenU"
ramdisk="/boot/U1_ramdisk.img"
#security reference identifier
ssidref= 0x00010001
memory = 10
name = "xmsec1"
cpu = -1 # leave to Xen to pick
# Number of network interfaces. Default is 1.
nics=1
dhcp="dhcp"
#-----------------------------------------------------
xmsec2 and xmsec3 look the same except for the name and the ssidref line.
Use
your domain config file and add "ssidref = 0x00010001" to the first
(xmsec1),
"ssidref= 0x00020002" to the second (call it xmsec2), and
"ssidref=0x00030003"
to the third (we will call this one xmsec3).
First start xmsec1: xm create -c xmsec1 (succeeds)
Then
[root@laptop policy]# xm list
Name Id Mem(MB) CPU State Time(s) Console SSID-REF
Domain-0 0 620 0 r---- 42.3 s:00/p:00
xmnosec 1 9 0 -b--- 0.3 9601 s:00/p:05
xmsec1 2 9 0 -b--- 0.2 9602 s:01/p:01
Shows a new domain xmsec1 running with primary (here: chinese wall)
ssidref 1
and secondary (here: simple type enforcement) ssidref 1. The ssidrefs are
independent and can differ for a domain.
[root@laptop policy]# ./policy_tool getpolicy
Policy dump:
===========Magic = 1debc.
PolVer = aaaa0000.
Len = 112.
Primary = CHINESE WALL policy (c=1, off=14).
Secondary = SIMPLE TYPE ENFORCEMENT policy (c=2, off=d8).
Chinese Wall policy:
===================Max Types = a.
Max Ssidrefs = 5.
Max ConfSets = 2.
Ssidrefs Off = 10.
Conflicts Off = 74.
Runing T. Off = 9c.
C. Agg. Off = b0.
SSID To CHWALL-Type matrix:
ssidref 0: 01 00 00 00 00 00 00 00 00 00
ssidref 1: 00 01 00 00 00 00 00 00 00 00
ssidref 2: 00 00 01 00 00 00 00 00 00 00
ssidref 3: 00 00 00 01 00 00 00 00 00 00
ssidref 4: 00 00 00 00 01 00 00 00 00 00
Confict Sets:
c-set 0: 00 00 01 01 00 00 00 00 00 00
c-set 1: 01 00 00 00 00 01 01 00 00 00 <<< t1 is not part of
any
c-set
Running
Types: 01 01 00 00 00 00 00 00 00 00 <<< xmsec1 has ssidref
1->type1
^^ <<< ref-count at
position 1
incr
Conflict
Aggregate Set: 00 00 00 00 00 01 01 00 00 00 <<< domain 1 was allowed
to
<<< start since type 1
was
not
<<< in conflict with
running
<<< types
Simple Type Enforcement policy:
==============================Max Types = 5.
Max Ssidrefs = 5.
Ssidrefs Off = 8.
SSID To STE-Type matrix:
ssidref 0: 01 01 01 01 01 <<< the ste policy does not
maintain; we
ssidref 1: 00 01 00 00 00 <-- <<< see that domain xmsec1
has ste
ssidref 2: 00 00 01 00 00 <<< ssidref1->type1 and has
this
type in
ssidref 3: 00 00 00 01 00 <<< common with dom0
ssidref 4: 00 00 00 00 01
Policy dump End.
Look at sHype output in xen dmesg:
[root@laptop xen]# xm dmesg
.
.
[somewhere near the very end]
(XEN) chwall_init_domain_ssid: determined chwall_ssidref to 1.
(XEN) ste_init_domain_ssid.
(XEN) ste_init_domain_ssid: determined ste_ssidref to 1.
(XEN) acm_init_domain_ssid: Instantiated individual ssid for domain 0x01.
(XEN) chwall_post_domain_create.
(XEN) ste_pre_eventchannel_interdomain.
(XEN) ste_pre_eventchannel_interdomain: (evtchn 0 --> 1) common type #01.
(XEN) shype_authorize_domops.
(XEN) ste_pre_eventchannel_interdomain.
(XEN) ste_pre_eventchannel_interdomain: (evtchn 0 --> 1) common type #01.
(XEN) ste_pre_eventchannel_interdomain.
(XEN) ste_pre_eventchannel_interdomain: (evtchn 0 --> 1) common type #01.
You can see that the chinese wall policy does not complain and that the
ste
policy makes three access control decisions for three event-channels setup
between domain 0 and the new domain 1. Each time, the two domains share
the
type1 and setting up the eventchannel is permitted.
Starting up a second domain xmsec2:
[root@laptop xen]# xm create -c xmsec2
Using config file "xmsec2".
Started domain xmsec2, console on port 9602
************ REMOTE CONSOLE: CTRL-] TO QUIT ********
Linux version 2.6.11-xenU (root@laptop.home.org) (gcc version 3.4.2
20041017
(Red Hat 3.4.2-6.fc3)) #1 Wed Mar 30 13:14:31 EST 2005
.
.
.
[root@laptop policy]# xm list
Name Id Mem(MB) CPU State Time(s) Console SSID-REF
Domain-0 0 620 0 r---- 71.7 s:00/p:00
xmsec1 1 9 0 -b--- 0.3 9601 s:01/p:01
xmsec2 2 7 0 -b--- 0.3 9602 s:02/p:02 <<
our domain runs both policies with ssidref 2
[root@laptop policy]# ./policy_tool getpolicy
Policy dump:
===========Magic = 1debc.
PolVer = aaaa0000.
Len = 112.
Primary = CHINESE WALL policy (c=1, off=14).
Secondary = SIMPLE TYPE ENFORCEMENT policy (c=2, off=d8).
Chinese Wall policy:
===================Max Types = a.
Max Ssidrefs = 5.
Max ConfSets = 2.
Ssidrefs Off = 10.
Conflicts Off = 74.
Runing T. Off = 9c.
C. Agg. Off = b0.
SSID To CHWALL-Type matrix:
ssidref 0: 01 00 00 00 00 00 00 00 00 00
ssidref 1: 00 01 00 00 00 00 00 00 00 00
ssidref 2: 00 00 01 00 00 00 00 00 00 00 <<< our domain has type
2
set
ssidref 3: 00 00 00 01 00 00 00 00 00 00
ssidref 4: 00 00 00 00 01 00 00 00 00 00
Confict Sets:
c-set 0: 00 00 01 01 00 00 00 00 00 00 <<< t2 is in c-set0 with
type 3
c-set 1: 01 00 00 00 00 01 01 00 00 00
Running
Types: 01 01 01 00 00 00 00 00 00 00 <<< t2 is running since
the
^^ <<< current aggregate
conflict
<<< set (see above) does
not
<<< include type 2
Conflict
Aggregate Set: 00 00 00 01 00 01 01 00 00 00 <<< type 3 is added to
the
<<< conflict aggregate
Simple Type Enforcement policy:
==============================Max Types = 5.
Max Ssidrefs = 5.
Ssidrefs Off = 8.
SSID To STE-Type matrix:
ssidref 0: 01 01 01 01 01
ssidref 1: 00 01 00 00 00
ssidref 2: 00 00 01 00 00
ssidref 3: 00 00 00 01 00
ssidref 4: 00 00 00 00 01
Policy dump End.
The sHype xen dmesg output looks similar to the one above when starting
the
first domain.
Now we start xmsec3 and it has ssidref3. Thus, it tries to run as type3
which
conflicts with running type2 (from xmsec2). As expected, creating this
domain
fails for security policy enforcement reasons.
[root@laptop xen]# xm create -c xmsec3
Using config file "xmsec3".
Error: Error creating domain: (22, ''Invalid argument'')
[root@laptop xen]#
[root@laptop xen]# xm dmesg
.
.
[somewhere near the very end]
(XEN) chwall_pre_domain_create.
(XEN) chwall_pre_domain_create: CHINESE WALL CONFLICT in type 03.
xmsec3 ssidref3 points to type3, which is in the current conflict
aggregate
set. This domain cannot start until domain xmsec2 is destroyed, at which
time
the aggregate conflict set is reduced and type3 is excluded from it. Then,
xmsec3 can start. Of course, afterwards, xmsec2 cannot be restarted. Try
it.
====================end-of readme=============
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