linux-hardening - [PATCH v2 2/6] sched: Add wrapper for get

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Date:   Wed, 29 Sep 2021 15:02:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        kernel test robot <oliver.sang@...el.com>,
        Vito Caputo <vcaputo@...garu.com>,
        Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Anand K Mistry <amistry@...gle.com>,
        "Kenta.Tada@...y.com" <Kenta.Tada@...y.com>,
        Alexey Gladkov <legion@...nel.org>,
        Michael Weiß <michael.weiss@...ec.fraunhofer.de>,
        Michal Hocko <mhocko@...e.com>, Helge Deller <deller@....de>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        "Tobin C. Harding" <me@...in.cc>,
        Tycho Andersen <tycho@...ho.pizza>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mark Rutland <mark.rutland@....com>,
        Jens Axboe <axboe@...nel.dk>,
        Stefan Metzmacher <metze@...ba.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Ohhoon Kwon <ohoono.kwon@...sung.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        YiFei Zhu <yifeifz2@...inois.edu>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-hardening@...r.kernel.org, x86@...nel.org
Subject: [PATCH v2 2/6] sched: Add wrapper for get_wchan() to keep task blocked

Having a stable wchan means the process must be blocked and for it to
stay that way while performing stack unwinding.

Cc: Ingo Molnar <mingo@...hat.com>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/sched.h |  1 +
 kernel/sched/core.c   | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 39039ce8ac4c..0c8185089e20 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2137,6 +2137,7 @@ static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
 #endif /* CONFIG_SMP */
 
 extern bool sched_task_on_rq(struct task_struct *p);
+extern unsigned long sched_task_get_wchan(struct task_struct *p);
 
 /*
  * In order to reduce various lock holder preemption latencies provide an
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1bba4128a3e6..4a30455e1ff5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1962,6 +1962,22 @@ bool sched_task_on_rq(struct task_struct *p)
 	return task_on_rq_queued(p);
 }
 
+unsigned long sched_task_get_wchan(struct task_struct *p)
+{
+	unsigned int state;
+	unsigned long ip = 0;
+
+	/* Only get wchan if task is blocked and we can keep it that way. */
+	raw_spin_lock_irq(&p->pi_lock);
+	state = READ_ONCE(p->__state);
+	smp_rmb(); /* see try_to_wake_up() */
+	if (state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq)
+		ip = get_wchan(p);
+	raw_spin_unlock_irq(&p->pi_lock);
+
+	return ip;
+}
+
 static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 {
 	if (!(flags & ENQUEUE_NOCLOCK))
-- 
2.30.2