From Debian policy 0.2.20091117-2

Label /etc/gdm/Xsession, /etc/gdm/PostSession/* and /etc/gdm/PreSession/*
as xsession_exec_t.

Index: policy/modules/services/xserver.fc
===================================================================
--- policy/modules/services/xserver.fc.orig
+++ policy/modules/services/xserver.fc
@@ -28,10 +28,9 @@
 /etc/X11/wdm/Xstartup.*	--	gen_context(system_u:object_r:xsession_exec_t,s0)
 /etc/X11/Xsession[^/]*	--	gen_context(system_u:object_r:xsession_exec_t,s0)
 
-ifdef(`distro_redhat',`
+/etc/gdm/Xsession	--	gen_context(system_u:object_r:xsession_exec_t,s0)
 /etc/gdm/PostSession/.*	--	gen_context(system_u:object_r:xsession_exec_t,s0)
 /etc/gdm/PreSession/.*	--	gen_context(system_u:object_r:xsession_exec_t,s0)
-')
 
 #
 # /opt