linux-kernel - Re: [PATCH 0/3] ptrace: Stop supporting SIGKILL for PTRACE_EVENT

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Date:   Sat, 16 Jul 2022 16:21:50 -0700
From:   Kyle Huey <khuey@...nos.co>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Keno Fischer <keno@...iacomputing.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        mingo@...nel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        "Robert O'Callahan" <roc@...nos.co>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 0/3] ptrace: Stop supporting SIGKILL for PTRACE_EVENT_EXIT

On Sat, Jul 16, 2022 at 2:31 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> "Eric W. Biederman" <ebiederm@...ssion.com> writes:
>
> > Keno Fischer <keno@...iacomputing.com> writes:
> >
> >> Hi Eric,
> >>
> >> On Fri, Jul 8, 2022 at 6:25 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> >>> > Recently I had a conversation where it was pointed out to me that
> >>> > SIGKILL sent to a tracee stropped in PTRACE_EVENT_EXIT is quite
> >>> > difficult for a tracer to handle.
> >>> >
> >>>
> >>> RR folks any comments?
> >>>
> >>> Did I properly understand what Keno Fischer was asking for when we
> >>> talked in person?
> >>
> >> Yes, this is indeed what I had in mind. I have not yet had the opportunity
> >> to try out your patch series (sorry), but from visual inspection, it does indeed
> >> do what I wanted, which is to make sure that a tracee stays in
> >> PTRACE_EVENT_EXIT for the tracer to inspect, even if there is another
> >> SIGKILL incoming simultaneously (since otherwise it may be impossible
> >> for the tracer to observe the PTRACE_EVENT_EXIT if two SIGKILLs
> >> come in rapid succession). I will try to take this series for a proper spin
> >> shortly.
> >
> > Thanks,
> >
> > I haven't yet figured out how to get the rr test suite to run
> > successfully.  Something about my test machine and lack of perf counters
> > seems to be causing problems.  So if you can perform the testing on your
> > side that would be fantastic.
>
> Ok.  I finally found a machine where I can run rr and the rr test suite.
>
> It looks like there are a couple of the rr 5.5.0 test that fail on
> Linus's lastest kernel simply because of changes in kernel behavior.  In
> particular clone_cleartid_coredump, and fcntl_rw_hints.  The
> clone_cleartid_coredump appears to fail because SIGSEGV no longer kills
> all processes that share an mm.  Which was a deliberate change.

Yeah, we changed to handle this in
https://github.com/rr-debugger/rr/commit/04bbacdbaba1cc496e92060014442bd1fd26b41d
and https://github.com/rr-debugger/rr/commit/1a3b389c2956e1844c0d07bf4297398bb6c561ea.

> With the lastest development version of rr, only detach_sigkill appears
> to be failing on Linus's latest.  That failure appears to be independent
> of the patches in question as well.  When run manually the
> detach_sigkill test succeeds so I am not quite certain what is going on,
> any thoughts?

If it fails before your changes I wouldn't worry about it too much,
there's been some other failures in that test lately.

- Kyle

> As for my patchset it looks like it does not cause any new test failures
> for rr so I will plan on getting it into linux-next shortly.
>
> Eric
>