kprobes: support kretprobe blacklist

Introduce architecture dependent kretprobe blacklists to prohibit users
from inserting return probes on the function in which kprobes can be
inserted but kretprobes can not.

This patch also removes "__kprobes" mark from "__switch_to" on x86_64 and
registers "__switch_to" to the blacklist on x86-64, because that mark is to
prohibit user from inserting only kretprobe.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/avr32/kernel/kprobes.c

@@ -22,6 +22,8 @@ DEFINE_PER_CPU(struct kprobe *, current_kprobe);
 static unsigned long kprobe_status;
 static struct pt_regs jprobe_saved_regs;
 
+struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
+
 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 {
 	int ret = 0;