Re: [PATCH v4 0/12] ptrace: cleaning up ptrace_stop

Eric W. Biederman
2022-05-06T21:59:03Z

Kees Cook <keescook@chromium.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@chromium.org>
>
> :)

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

Eric