kprobes: Fix arch_prepare_kprobe to handle copy insn failures

Fix arch_prepare_kprobe() to handle failures in copy instruction
correctly. This fix is related to the previous fix: 8101376
which made __copy_instruction return an error result if failed,
but caller site was not updated to handle it. Thus, this is the
other half of the bugfix.

This fix is also related to the following bug-report:

   https://bugzilla.redhat.com/show_bug.cgi?id=910649

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Jonathan Lebon <jlebon@redhat.com>
Cc: Frank Ch. Eigler <fche@redhat.com>
Cc: systemtap@sourceware.org
Cc: yrl.pp-manager.tt@hitachi.com
Link: http://lkml.kernel.org/r/20130605031216.15285.2001.stgit@mhiramat-M0-7522
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/kprobes/core.c

@@ -365,10 +365,14 @@ int __kprobes __copy_instruction(u8 *dest, u8 *src)
 	return insn.length;
 }
 
-static void __kprobes arch_copy_kprobe(struct kprobe *p)
+static int __kprobes arch_copy_kprobe(struct kprobe *p)
 {
+	int ret;
+
 	/* Copy an instruction with recovering if other optprobe modifies it.*/
-	__copy_instruction(p->ainsn.insn, p->addr);
+	ret = __copy_instruction(p->ainsn.insn, p->addr);
+	if (!ret)
+		return -EINVAL;
 
 	/*
 	 * __copy_instruction can modify the displacement of the instruction,
@@ -384,6 +388,8 @@ static void __kprobes arch_copy_kprobe(struct kprobe *p)
 
 	/* Also, displacement change doesn't affect the first byte */
 	p->opcode = p->ainsn.insn[0];
+
+	return 0;
 }
 
 int __kprobes arch_prepare_kprobe(struct kprobe *p)
@@ -397,8 +403,8 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	p->ainsn.insn = get_insn_slot();
 	if (!p->ainsn.insn)
 		return -ENOMEM;
-	arch_copy_kprobe(p);
-	return 0;
+
+	return arch_copy_kprobe(p);
 }
 
 void __kprobes arch_arm_kprobe(struct kprobe *p)