Apply strict SELinux checking of PROT_EXEC on mmap/mprotect calls.

If checkreqprot == 1, SELinux only checks the protection flags passed
by the application, even if the kernel internally adds PROT_EXEC for
READ_IMPLIES_EXEC personality flags.  Switch to checkreqprot == 0
to check the final protection flags applied by the kernel.

Change-Id: Ic39242bbbd104fc9a1bcf2cd2ded7ce1aeadfac4
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

rootdir/init.rc

@@ -13,6 +13,9 @@ on early-init
     # Set init and its forked children's oom_adj.
     write /proc/1/oom_adj -16
 
+    # Apply strict SELinux checking of PROT_EXEC on mmap/mprotect calls.
+    write /sys/fs/selinux/checkreqprot 0
+
     # Set the security context for the init process.
     # This should occur before anything else (e.g. ueventd) is started.
     setcon u:r:init:s0