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

On Wed, May 05, 2021 at 01:48:21PM -0500, Madhavan T. Venkataraman wrote:

On 5/5/21 11:46 AM, Mark Brown wrote:

quoted

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.

I could do something like this:

unwind_frame()
{
	int	i;
	...

	for (i = 0; i < MAX_CHECKS; i++) {
		if (!check_frame(tsk, frame))
			break;
	}

I think that could work, yes.  Have to see the actual code (and other
people's opinions!).

If this is acceptable, then the only question is - what should be the value of
MAX_CHECKS (I will rename it to something more appropriate)?

I'd expect something like 10 to be way more than we'd ever need, or we
could define it down to the 2 checks we expect to be possible ATM to be
conservative.  I'm tempted to be permissive if we have sufficient other
checks but I'm not 100% sure on that.