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

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Message-ID: <87pmi4ycdu.fsf@email.froward.int.ebiederm.org>
Date:   Sat, 16 Jul 2022 16:29:49 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Keno Fischer <keno@...iacomputing.com>
Cc:     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>, Kyle Huey <khuey@...nos.co>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 0/3] ptrace: Stop supporting SIGKILL for PTRACE_EVENT_EXIT

"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.

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?

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