linux-hardening - Re: [PATCH 6/7] arch: __get_wchan || STACKTRACE

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Message-ID: <20211014184125.4qu7lih6uwvx35qs@treble>
Date:   Thu, 14 Oct 2021 11:41:25 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>, keescook@...omium.org,
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Subject: Re: [PATCH 6/7] arch: __get_wchan || STACKTRACE_SUPPORT

On Thu, Oct 14, 2021 at 07:07:38PM +0100, Mark Rutland wrote:
> On Fri, Oct 08, 2021 at 09:17:07AM -0700, Josh Poimboeuf wrote:
> > On Fri, Oct 08, 2021 at 03:45:59PM +0200, Peter Zijlstra wrote:
> > > > stack_trace_save_tsk() *shouldn't* skip anything unless we've explicitly
> > > > told it to via skipnr, because I'd expect that
> > > 
> > > It's what most archs happen to do today and is what
> > > stack_trace_save_tsk() as implemented using arch_stack_walk() does.
> > > Which is I think the closest to canonical we have.
> 
> Ah; and arch_stack_walk() itself shouldn't skip anything, which gives
> the consistent low-level semantic I wanted.
> 
> > It *is* confusing though.  Even if 'nosched' may be the normally
> > desired behavior, stack_trace_save_tsk() should probably be named
> > stack_trace_save_tsk_nosched().
> 
> I agree that'd be less confusing!
> 
> Josh, am I right in my understanding that the reliable stacktrace
> functions *shouldn't* skip sched functions, or should those similarly
> gain a _nosched suffix?

Correct, the reliable variants need to see the entire call stack and
therefore they shouldn't skip sched functions.

-- 
Josh