[PATCH v5] flask: create unified "flask=" boot parameter

* [PATCH v5] flask: create unified "flask=" boot parameter
@ 2015-03-09 17:02 Daniel De Graaf
  2015-03-09 17:31 ` Andrew Cooper
  0 siblings, 1 reply; 2+ messages in thread
From: Daniel De Graaf @ 2015-03-09 17:02 UTC (permalink / raw)
  To: xen-devel
  Cc: andrew.cooper3, Daniel De Graaf, julien.grall, wei.liu2, ian.campbell

This unifies the flask_enforcing and flask_enabled boot parameters into
a single parameter with additional states.  Defined options are:

 enforcing - require policy to be loaded at boot time and enforce it
 permissive - a missing or broken policy does not panic
 disabled - revert to dummy (no XSM) policy.  Was flask_enabled=0
 late - bootloader policy is not used; later loadpolicy is enforcing

The default mode remains "permissive" and the flask_enforcing boot
parameter is retained for compatibility.  If flask_enforcing=1 is
specified and flask= is not, the bootloader policy will be loaded in
enforcing mode if present, but errors will disable access controls until
a successful loadpolicy instead of causing a panic at boot.

Suggested-by: Julien Grall <julien.grall@linaro.org>
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
---
Changes from v4:
 - Use enum and bool_t for parameter globals
 - Remove duplication of flask=force/enforcing
 - Move panic out of command line parsing so it is visible

---
 docs/man/xl.pod.1                   |  4 ++--
 docs/misc/xen-command-line.markdown | 30 +++++++++++++++++++++++++-----
 docs/misc/xsm-flask.txt             | 29 -----------------------------
 xen/xsm/flask/flask_op.c            | 34 ++++++++++++++++++++++++++++++----
 xen/xsm/flask/hooks.c               | 32 +++++++++++++++++++++++---------
 xen/xsm/flask/include/avc.h         |  2 +-
 xen/xsm/flask/include/security.h    | 10 +++++++++-
 7 files changed, 90 insertions(+), 51 deletions(-)

diff --git a/docs/man/xl.pod.1 b/docs/man/xl.pod.1
index cd80ffc..198ee2b 100644
--- a/docs/man/xl.pod.1
+++ b/docs/man/xl.pod.1
@@ -1441,8 +1441,8 @@ Determine if the FLASK security module is loaded and enforcing its policy.
 =item B<setenforce> I<1|0|Enforcing|Permissive>
 
 Enable or disable enforcing of the FLASK access controls. The default is
-permissive and can be changed using the flask_enforcing option on the
-hypervisor's command line.
+permissive, but this can be changed to enforcing by specifying "flask=enforcing"
+or "flask=late" on the hypervisor's command line.
 
 =item B<loadpolicy> I<policy-file>
 
diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index e125212..5044da1 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -638,11 +638,31 @@ hardware domain is architecture dependent.
 Note that specifying zero as domU value means zero, while for dom0 it means
 to use the default.
 
-### flask\_enabled
-> `= <integer>`
-
-### flask\_enforcing
-> `= <integer>`
+### flask
+> `= permissive | enforcing | late | disabled`
+
+> Default: `permissive`
+
+Specify how the FLASK security server should be configured.  This option is only
+available if the hypervisor was compiled with XSM support (which can be enabled
+by setting XSM\_ENABLE = y in .config).
+
+* `permissive`: This is intended for development and is not suitable for use
+  with untrusted guests.  If a policy is provided by the bootloader, it will be
+  loaded; errors will be reported to the ring buffer but will not prevent
+  booting.  The policy can be changed to enforcing mode using "xl setenforce".
+* `enforcing`: This requires a security policy to be provided by the bootloader
+  and will enter enforcing mode prior to the creation of domain 0.  If a valid
+  policy is not provided, the hypervisor will not continue booting.
+* `late`: This disables loading of the security policy from the bootloader.
+  FLASK will be enabled but will not enforce access controls until a policy is
+  loaded by a domain using "xl loadpolicy".  Once a policy is loaded, FLASK will
+  run in enforcing mode unless "xl setenforce" has changed that setting.
+* `disabled`: This causes the XSM framework to revert to the dummy module.  The
+  dummy module provides the same security policy as is used when compiling the
+  hypervisor without support for XSM.  The xsm\_op hypercall can also be used to
+  switch to this mode after boot, but there is no way to re-enable FLASK once
+  the dummy module is loaded.
 
 ### font
 > `= <height>` where height is `8x8 | 8x14 | 8x16`
diff --git a/docs/misc/xsm-flask.txt b/docs/misc/xsm-flask.txt
index 9559028..ab05913 100644
--- a/docs/misc/xsm-flask.txt
+++ b/docs/misc/xsm-flask.txt
@@ -396,32 +396,3 @@ the ranges being denied to more easily determine what resources are required.
 When running in permissive mode, only the first denial of a given
 source/destination is printed to the log, so labeling devices using this method
 may require multiple passes to find all required ranges.
-
-Additional notes on XSM:FLASK
------------------------------
-
-1) xen command line parameters
-
-	a) flask_enforcing
-	
-	The default value for flask_enforcing is '0'.  This parameter causes the 
-	platform to boot in permissive mode which means that the policy is loaded 
-	but not enforced.  This mode is often helpful for developing new systems 
-	and policies as the policy violations are reported on the xen console and 
-	may be viewed in dom0 through 'xl dmesg'.
-	
-	To boot the platform into enforcing mode, which means that the policy is
-	loaded and enforced, append 'flask_enforcing=1' on the grub line.
-	
-	This parameter may also be changed through the flask hypercall.
-	
-	b) flask_enabled
-	
-	The default value for flask_enabled is '1'.  This parameter causes the
-	platform to enable the FLASK security module under the XSM framework.
-	The parameter may be enabled/disabled only once per boot.  If the parameter
-	is set to '0', only a reboot can re-enable flask.  When flask_enabled is '0'
-	the DUMMY module is enforced.
-
-	This parameter may also be changed through the flask hypercall.  But may
-	only be performed once per boot.
diff --git a/xen/xsm/flask/flask_op.c b/xen/xsm/flask/flask_op.c
index 0e89360..84c7fec 100644
--- a/xen/xsm/flask/flask_op.c
+++ b/xen/xsm/flask/flask_op.c
@@ -24,11 +24,12 @@
 #define _copy_to_guest copy_to_guest
 #define _copy_from_guest copy_from_guest
 
-int flask_enforcing = 0;
-integer_param("flask_enforcing", flask_enforcing);
+enum flask_bootparam_t __read_mostly flask_bootparam = FLASK_BOOTPARAM_PERMISSIVE;
+static void parse_flask_param(char *s);
+custom_param("flask", parse_flask_param);
 
-int flask_enabled = 1;
-integer_param("flask_enabled", flask_enabled);
+bool_t __read_mostly flask_enforcing = 0;
+boolean_param("flask_enforcing", flask_enforcing);
 
 #define MAX_POLICY_SIZE 0x4000000
 
@@ -60,6 +61,26 @@ extern int ss_initialized;
 
 extern struct xsm_operations *original_ops;
 
+static void __init parse_flask_param(char *s)
+{
+    if ( !strcmp(s, "enforcing") )
+    {
+        flask_enforcing = 1;
+        flask_bootparam = FLASK_BOOTPARAM_ENFORCING;
+    }
+    else if ( !strcmp(s, "late") )
+    {
+        flask_enforcing = 1;
+        flask_bootparam = FLASK_BOOTPARAM_LATELOAD;
+    }
+    else if ( !strcmp(s, "disabled") )
+        flask_bootparam = FLASK_BOOTPARAM_DISABLED;
+    else if ( !strcmp(s, "permissive") )
+        flask_bootparam = FLASK_BOOTPARAM_PERMISSIVE;
+    else
+        flask_bootparam = FLASK_BOOTPARAM_INVALID;
+}
+
 static int domain_has_security(struct domain *d, u32 perms)
 {
     struct domain_security_struct *dsec;
@@ -502,6 +523,7 @@ static int flask_security_load(struct xen_flask_load *load)
 {
     int ret;
     void *buf = NULL;
+    bool_t is_reload = ss_initialized;
 
     ret = domain_has_security(current->domain, SECURITY__LOAD_POLICY);
     if ( ret )
@@ -526,6 +548,10 @@ static int flask_security_load(struct xen_flask_load *load)
     if ( ret )
         goto out;
 
+    if ( !is_reload )
+        printk(XENLOG_INFO "Flask: Policy loaded, continuing in %s mode.\n",
+            flask_enforcing ? "enforcing" : "permissive");
+
     xfree(bool_pending_values);
     bool_pending_values = NULL;
     ret = 0;
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index dad5deb..05dafed 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -1628,15 +1628,23 @@ static struct xsm_operations flask_ops = {
 
 static __init void flask_init(void)
 {
-    int ret = 0;
+    int ret = -ENOENT;
 
-    if ( !flask_enabled )
+    switch ( flask_bootparam )
     {
-        printk("Flask:  Disabled at boot.\n");
+    case FLASK_BOOTPARAM_DISABLED:
+        printk(XENLOG_INFO "Flask: Disabled at boot.\n");
         return;
-    }
 
-    printk("Flask:  Initializing.\n");
+    case FLASK_BOOTPARAM_PERMISSIVE:
+    case FLASK_BOOTPARAM_ENFORCING:
+    case FLASK_BOOTPARAM_LATELOAD:
+        break;
+
+    case FLASK_BOOTPARAM_INVALID:
+    default:
+        panic("Flask: Invalid value for flask= boot parameter.\n");
+    }
 
     avc_init();
 
@@ -1644,12 +1652,18 @@ static __init void flask_init(void)
     if ( register_xsm(&flask_ops) )
         panic("Flask: Unable to register with XSM");
 
-    ret = security_load_policy(policy_buffer, policy_size);
+    if ( policy_size && flask_bootparam != FLASK_BOOTPARAM_LATELOAD )
+        ret = security_load_policy(policy_buffer, policy_size);
+
+    if ( ret && flask_bootparam == FLASK_BOOTPARAM_ENFORCING )
+        panic("Unable to load FLASK policy");
 
-    if ( flask_enforcing )
-        printk("Flask:  Starting in enforcing mode.\n");
+    if ( ret )
+        printk(XENLOG_INFO "Flask:  Access controls disabled until policy is loaded.\n");
+    else if ( flask_enforcing )
+        printk(XENLOG_INFO "Flask:  Starting in enforcing mode.\n");
     else
-        printk("Flask:  Starting in permissive mode.\n");
+        printk(XENLOG_INFO "Flask:  Starting in permissive mode.\n");
 }
 
 xsm_initcall(flask_init);
diff --git a/xen/xsm/flask/include/avc.h b/xen/xsm/flask/include/avc.h
index a00a6eb..c7a99fc 100644
--- a/xen/xsm/flask/include/avc.h
+++ b/xen/xsm/flask/include/avc.h
@@ -17,7 +17,7 @@
 #include "av_permissions.h"
 #include "security.h"
 
-extern int flask_enforcing;
+extern bool_t flask_enforcing;
 
 /*
  * An entry in the AVC.
diff --git a/xen/xsm/flask/include/security.h b/xen/xsm/flask/include/security.h
index dea0143..d07bae0 100644
--- a/xen/xsm/flask/include/security.h
+++ b/xen/xsm/flask/include/security.h
@@ -35,7 +35,15 @@
 #define POLICYDB_VERSION_MIN   POLICYDB_VERSION_BASE
 #define POLICYDB_VERSION_MAX   POLICYDB_VERSION_BOUNDARY
 
-extern int flask_enabled;
+enum flask_bootparam_t {
+    FLASK_BOOTPARAM_PERMISSIVE,
+    FLASK_BOOTPARAM_ENFORCING,
+    FLASK_BOOTPARAM_LATELOAD,
+    FLASK_BOOTPARAM_DISABLED,
+    FLASK_BOOTPARAM_INVALID,
+};
+
+extern enum flask_bootparam_t flask_bootparam;
 extern int flask_mls_enabled;
 
 int security_load_policy(void * data, size_t len);
-- 
2.1.0

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