ANDROID: exec_domains: Disable request_module() call for personalities

(cherry pick from commit a9ac1262ce80c287562e604f3bb24f232fcb686e)

With Android M, Android environments use a separate execution
domain for 32bit processes.
See:
https://android-review.googlesource.com/#/c/122131/

This results in systems that use kernel modules to see selinux
audit noise like:
  type=1400 audit(28.989:15): avc: denied { module_request } for
  pid=1622 comm="app_process32" kmod="personality-8"
  scontext=u:r:zygote:s0 tcontext=u:r:kernel:s0 tclass=system

While using kernel modules is unadvised, some systems do require
them.

Thus to avoid developers adding sepolicy exceptions to allow for
request_module calls, this patch disables the logic which tries
to call request_module for the 32bit personality (ie:
personality-8), which doesn't actually exist.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Change-Id: I32774083340e0f928d0e3bb4295517218e23c66c

kernel/exec_domain.c

@@ -68,7 +68,14 @@ lookup_exec_domain(unsigned int personality)
 				goto out;
 	}
 
-#ifdef CONFIG_MODULES
+/*
+ * Disable the request_module here to avoid trying to
+ * load the personality-8 module, which  doesn't exist,
+ * and results in selinux audit noise.
+ * Disabling this here avoids folks adding module_request
+ * to their sepolicy, which is maybe too generous
+ */
+#if 0
 	read_unlock(&exec_domains_lock);
 	request_module("personality-%d", pers);
 	read_lock(&exec_domains_lock);