powerpc/jprobes: Validate break handler invocation as being due to a jprobe_return()

void __used jprobe_return(void)

{

	asm volatile("trap" ::: "memory");

	asm volatile("jprobe_return_trap:\n"

		     "trap\n"

		     ::: "memory");

}

NOKPROBE_SYMBOL(jprobe_return);

static void __used jprobe_return_end(void)

{

}

NOKPROBE_SYMBOL(jprobe_return_end);

int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)

{

	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	/*

	 * FIXME - we should ideally be validating that we got here 'cos

	 * of the "trap" in jprobe_return() above, before restoring the

	 * saved regs...

	 */

	if (regs->nip != ppc_kallsyms_lookup_name("jprobe_return_trap")) {

		pr_debug("longjmp_break_handler NIP (0x%lx) does not match jprobe_return_trap (0x%lx)\n",

				regs->nip, ppc_kallsyms_lookup_name("jprobe_return_trap"));

		return 0;

	}

	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));

	/* It's OK to start function graph tracing again */

	unpause_graph_tracing();