[PARISC] only make executable areas executable

Currently parisc has the whole kernel marked as RWX, meaning any
kernel page at all is eligible to be executed.  This can cause a
theoretical problem on systems with combined I/D TLB because the act
of referencing a page causes a TLB insertion with an executable bit.
This TLB entry may be used by the CPU as the basis for speculating the
page into the I-Cache.  If this speculated page is subsequently used
for a user process, there is the possibility we will get a stale
I-cache line picked up as the binary executes.

As a point of good practise, only mark actual kernel text pages as
executable.  The same has to be done for init_text pages, but they're
converted to data pages (and the I-Cache flushed) when the init memory
is released.

Signed-off-by: James Bottomley <James.Bottomley@suse.de>

arch/parisc/kernel/entry.S

@@ -692,6 +692,9 @@ ENTRY(fault_vector_11)
 END(fault_vector_11)
 
 #endif
+	/* Fault vector is separately protected and *must* be on its own page */
+	.align		PAGE_SIZE
+ENTRY(end_fault_vector)
 
 	.import		handle_interruption,code
 	.import		do_cpu_irq_mask,code