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[Xen-devel] [PATCH 2/2] flask: create unified "flask=" boot parameter



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

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

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@xxxxxxxxxx>
Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---
 docs/man/xl.pod.1                |  4 ++--
 docs/misc/xsm-flask.txt          | 48 +++++++++++++++++++---------------------
 xen/xsm/flask/flask_op.c         | 34 ++++++++++++++++++++++++----
 xen/xsm/flask/hooks.c            | 22 ++++++++++--------
 xen/xsm/flask/include/security.h |  8 ++++++-
 5 files changed, 75 insertions(+), 41 deletions(-)

diff --git a/docs/man/xl.pod.1 b/docs/man/xl.pod.1
index 6b89ba8..48b8f98 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/xsm-flask.txt b/docs/misc/xsm-flask.txt
index 9559028..efe8d50 100644
--- a/docs/misc/xsm-flask.txt
+++ b/docs/misc/xsm-flask.txt
@@ -400,28 +400,26 @@ 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.
+The xen command line accepts these values for the "flask=" parameter:
+
+ * permissive [default]
+     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".
+ * force or enforcing
+     This requires a security policy to be provided by the bootloader and will
+     enable enforcing prior to the creation of domain 0.  If a valid policy is
+     not provided, the hypervisor will not continue booting.
+ * late
+     This disabled 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" or similar commands.  Once a
+     policy is loaded, FLASK will run in enforcing mode unless "xl setenforce"
+     has disabled this.
+ * 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 be used to
+     switch to this mode after boot, but there is no way to re-enable FLASK
+     once the dummy module is loaded.
diff --git a/xen/xsm/flask/flask_op.c b/xen/xsm/flask/flask_op.c
index 0e89360..8db9b1e 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);
+int __read_mostly flask_bootparam = FLASK_BOOTPARAM_DEFAULT;
+static void parse_flask_param(char *s);
+custom_param("flask", parse_flask_param);
 
-int flask_enabled = 1;
-integer_param("flask_enabled", flask_enabled);
+int __read_mostly flask_enforcing = 0;
+integer_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, "force") || !strcmp(s, "enforcing") )
+    {
+        flask_enforcing = 1;
+        flask_bootparam = FLASK_BOOTPARAM_FORCE;
+    }
+    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
+        panic("Invalid value specified for flask= boot parameter");
+}
+
 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..00c8843 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -1628,28 +1628,32 @@ static struct xsm_operations flask_ops = {
 
 static __init void flask_init(void)
 {
-    int ret = 0;
+    int ret = -ENOENT;
 
-    if ( !flask_enabled )
+    if ( flask_bootparam == FLASK_BOOTPARAM_DISABLED )
     {
-        printk("Flask:  Disabled at boot.\n");
+        printk(XENLOG_INFO "Flask:  Disabled at boot.\n");
         return;
     }
 
-    printk("Flask:  Initializing.\n");
-
     avc_init();
 
     original_ops = xsm_ops;
     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_FORCE )
+        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/security.h b/xen/xsm/flask/include/security.h
index dea0143..bd2a4bc 100644
--- a/xen/xsm/flask/include/security.h
+++ b/xen/xsm/flask/include/security.h
@@ -35,7 +35,13 @@
 #define POLICYDB_VERSION_MIN   POLICYDB_VERSION_BASE
 #define POLICYDB_VERSION_MAX   POLICYDB_VERSION_BOUNDARY
 
-extern int flask_enabled;
+#define FLASK_BOOTPARAM_DEFAULT    0
+#define FLASK_BOOTPARAM_PERMISSIVE 0
+#define FLASK_BOOTPARAM_FORCE      1
+#define FLASK_BOOTPARAM_LATELOAD   2
+#define FLASK_BOOTPARAM_DISABLED   3
+
+extern int flask_bootparam;
 extern int flask_mls_enabled;
 
 int security_load_policy(void * data, size_t len);
-- 
2.1.0


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