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

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Date:   Thu, 05 May 2022 13:25:57 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     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>,
        Kees Cook <keescook@...omium.org>, linux-ia64@...r.kernel.org
Subject: [PATCH v4 0/12] ptrace: cleaning up ptrace_stop

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.

Eric W. Biederman (11):
      signal: Rename send_signal send_signal_locked
      signal: Replace __group_send_sig_info with send_signal_locked
      ptrace/um: Replace PT_DTRACE with TIF_SINGLESTEP
      ptrace/xtensa: Replace PT_SINGLESTEP with TIF_SINGLESTEP
      ptrace: Remove arch_ptrace_attach
      signal: Use lockdep_assert_held instead of assert_spin_locked
      ptrace: Reimplement PTRACE_KILL by always sending SIGKILL
      ptrace: Document that wait_task_inactive can't fail
      ptrace: Admit ptrace_stop can generate spuriuos SIGTRAPs
      ptrace: Don't change __state
      ptrace: Always take siglock in ptrace_resume

Peter Zijlstra (1):
      sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state

 arch/ia64/include/asm/ptrace.h    |   4 --
 arch/ia64/kernel/ptrace.c         |  57 ----------------
 arch/um/include/asm/thread_info.h |   2 +
 arch/um/kernel/exec.c             |   2 +-
 arch/um/kernel/process.c          |   2 +-
 arch/um/kernel/ptrace.c           |   8 +--
 arch/um/kernel/signal.c           |   4 +-
 arch/x86/kernel/step.c            |   3 +-
 arch/xtensa/kernel/ptrace.c       |   4 +-
 arch/xtensa/kernel/signal.c       |   4 +-
 drivers/tty/tty_jobctrl.c         |   4 +-
 include/linux/ptrace.h            |   7 --
 include/linux/sched.h             |  10 ++-
 include/linux/sched/jobctl.h      |   8 +++
 include/linux/sched/signal.h      |  20 ++++--
 include/linux/signal.h            |   3 +-
 kernel/ptrace.c                   |  87 ++++++++---------------
 kernel/sched/core.c               |   5 +-
 kernel/signal.c                   | 140 +++++++++++++++++---------------------
 kernel/time/posix-cpu-timers.c    |   6 +-
 20 files changed, 140 insertions(+), 240 deletions(-)

Eric