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

From: Mark Brown
Date: Thu May 06 2021 - 09:46:22 EST

On Wed, May 05, 2021 at 01:48:21PM -0500, Madhavan T. Venkataraman wrote:
> On 5/5/21 11:46 AM, Mark Brown wrote:

> > 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.

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