linux-kernel - Re: [PATCH v4 0/12] ptrace: cleaning up ptrace

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Message-ID: <87h762z5js.fsf@email.froward.int.ebiederm.org>
Date:   Fri, 06 May 2022 16:59:03 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, rjw@...ysocki.net, oleg@...hat.com,
        mingo@...nel.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
        bigeasy@...utronix.de, Will Deacon <will@...nel.org>,
        tj@...nel.org, linux-pm@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        linux-um@...ts.infradead.org, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org, Jann Horn <jannh@...gle.com>,
        linux-ia64@...r.kernel.org, Robert O'Callahan <roc@...nos.co>,
        Kyle Huey <khuey@...nos.co>
Subject: Re: [PATCH v4 0/12] ptrace: cleaning up ptrace_stop

Kees Cook <keescook@...omium.org> writes:

> On Thu, May 05, 2022 at 01:25:57PM -0500, Eric W. Biederman wrote:
>> The states TASK_STOPPED and TASK_TRACE are special in they can not
>> handle spurious wake-ups.  This plus actively depending upon and
>> changing the value of tsk->__state causes problems for PREEMPT_RT and
>> Peter's freezer rewrite.
>> 
>> There are a lot of details we have to get right to sort out the
>> technical challenges and this is my parred back version of the changes
>> that contains just those problems I see good solutions to that I believe
>> are ready.
>> 
>> A couple of issues have been pointed but I think this parred back set of
>> changes is still on the right track.  The biggest change in v4 is the
>> split of "ptrace: Admit ptrace_stop can generate spuriuos SIGTRAPs" into
>> two patches because the dependency I thought exited between two
>> different changes did not exist.  The rest of the changes are minor
>> tweaks to "ptrace: Admit ptrace_stop can generate spuriuos SIGTRAPs";
>> removing an always true branch, and adding an early  test to see if the
>> ptracer had gone, before TASK_TRAPPING was set.
>> 
>> This set of changes should support Peter's freezer rewrite, and with the
>> addition of changing wait_task_inactive(TASK_TRACED) to be
>> wait_task_inactive(0) in ptrace_check_attach I don't think there are any
>> races or issues to be concerned about from the ptrace side.
>> 
>> More work is needed to support PREEMPT_RT, but these changes get things
>> closer.
>> 
>> This set of changes continues to look like it will provide a firm
>> foundation for solving the PREEMPT_RT and freezer challenges.
>
> One of the more sensitive projects to changes around ptrace is rr
> (Robert and Kyle added to CC). I ran rr's selftests before/after this
> series and saw no changes. My failures remained the same; I assume
> they're due to missing CPU features (pkeys) or build configs (bpf), etc:
>
> 99% tests passed, 19 tests failed out of 2777
>
> Total Test time (real) = 773.40 sec
>
> The following tests FAILED:
>          42 - bpf_map (Failed)
>          43 - bpf_map-no-syscallbuf (Failed)
>         414 - netfilter (Failed)
>         415 - netfilter-no-syscallbuf (Failed)
>         454 - x86/pkeys (Failed)
>         455 - x86/pkeys-no-syscallbuf (Failed)
>         1152 - ttyname (Failed)
>         1153 - ttyname-no-syscallbuf (Failed)
>         1430 - bpf_map-32 (Failed)
>         1431 - bpf_map-32-no-syscallbuf (Failed)
>         1502 - detach_sigkill-32 (Failed)
>         1802 - netfilter-32 (Failed)
>         1803 - netfilter-32-no-syscallbuf (Failed)
>         1842 - x86/pkeys-32 (Failed)
>         1843 - x86/pkeys-32-no-syscallbuf (Failed)
>         2316 - crash_in_function-32 (Failed)
>         2317 - crash_in_function-32-no-syscallbuf (Failed)
>         2540 - ttyname-32 (Failed)
>         2541 - ttyname-32-no-syscallbuf (Failed)
>
> So, I guess:
>
> Tested-by: Kees Cook <keescook@...omium.org>
>
> :)

Thank you.  I was thinking it would be good to add the rr folks to the
discussion.

Eric