[v6,02/10] xsm: remove the ability to disable flask

Commit Message

Daniel P. Smith Sept. 10, 2021, 8:12 p.m. UTC

On Linux when SELinux is put into permissive mode the descretionary access
controls are still in place. Whereas for Xen when the enforcing state of flask
is set to permissive, all operations for all domains would succeed, i.e. it
does not fall back to the default access controls. To provide a means to mimic
a similar but not equivalent behavior, a flask op is present to allow a
one-time switch back to the default access controls, aka the "dummy policy".

While this may be desirable for an OS, Xen is a hypervisor and should not allow
the switching of which security policy framework is being enforced after boot.
This patch removes the flask op to enforce the desired XSM usage model
requiring a reboot of Xen to change the XSM policy module in use.

Signed-off-by: Daniel P. Smith <[e-mail]>
Acked-by: Andrew Cooper <[e-mail]>
---
 xen/include/public/xsm/flask_op.h |  2 +-
 xen/xsm/flask/flask_op.c          | 30 ------------------------------
 2 files changed, 1 insertion(+), 31 deletions(-)

Patch

diff --git a/xen/include/public/xsm/flask_op.h b/xen/include/public/xsm/flask_op.h
index 16af7bc22f..b41dd6dac8 100644
--- a/xen/include/public/xsm/flask_op.h
+++ b/xen/include/public/xsm/flask_op.h
@@ -188,7 +188,7 @@  struct xen_flask_op {
 #define FLASK_SETBOOL           12
 #define FLASK_COMMITBOOLS       13
 #define FLASK_MLS               14
-#define FLASK_DISABLE           15
+#define FLASK_DISABLE           15 /* No longer implemented */
 #define FLASK_GETAVC_THRESHOLD  16
 #define FLASK_SETAVC_THRESHOLD  17
 #define FLASK_AVC_HASHSTATS     18
diff --git a/xen/xsm/flask/flask_op.c b/xen/xsm/flask/flask_op.c
index 01e52138a1..f41c025391 100644
--- a/xen/xsm/flask/flask_op.c
+++ b/xen/xsm/flask/flask_op.c
@@ -223,32 +223,6 @@  static int flask_security_sid(struct xen_flask_sid_context *arg)
 
 #ifndef COMPAT
 
-static int flask_disable(void)
-{
-    static int flask_disabled = 0;
-
-    if ( ss_initialized )
-    {
-        /* Not permitted after initial policy load. */
-        return -EINVAL;
-    }
-
-    if ( flask_disabled )
-    {
-        /* Only do this once. */
-        return -EINVAL;
-    }
-
-    printk("Flask:  Disabled at runtime.\n");
-
-    flask_disabled = 1;
-
-    /* Reset xsm_ops to the original module. */
-    xsm_ops = &dummy_xsm_ops;
-
-    return 0;
-}
-
 static int flask_security_setavc_threshold(struct xen_flask_setavc_threshold *arg)
 {
     int rv = 0;
@@ -698,10 +672,6 @@  ret_t do_flask_op(XEN_GUEST_HANDLE_PARAM(xsm_op_t) u_flask_op)
         rv = flask_mls_enabled;
         break;    
 
-    case FLASK_DISABLE:
-        rv = flask_disable();
-        break;
-
     case FLASK_GETAVC_THRESHOLD:
         rv = avc_cache_threshold;
         break;