Re: [RFC PATCH v3 2/4] arm64: Check the return PC against unreliable code sections

On Tue, May 04, 2021 at 02:32:35PM -0500, Madhavan T. Venkataraman wrote:

If you prefer, I could do something like this:

check_pc:
	if (!__kernel_text_address(frame->pc))
		frame->reliable = false;

	range = lookup_range(frame->pc);

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	if (tsk->ret_stack &&
		frame->pc == (unsigned long)return_to_handler) {
		...
		frame->pc = ret_stack->ret;
		frame->pc = ptrauth_strip_insn_pac(frame->pc);
		goto check_pc;
	}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

Is that acceptable?

I think that works even if it's hard to love the goto, might want some
defensiveness to ensure we can't somehow end up in an infinite loop with
a sufficiently badly formed stack.