From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Paul Turner <pjt@google.com>
Cc: linux-kernel@vger.kernel.org,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
"Paul E. McKenney" <paulmck@linux.ibm.com>,
Boqun Feng <boqun.feng@gmail.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Dmitry Vyukov <dvyukov@google.com>,
linux-api@vger.kernel.org
Subject: [RFC PATCH 2/4] rseq: Fix: Unregister rseq for CLONE_TLS
Date: Tue, 10 Sep 2019 20:27:42 -0400 [thread overview]
Message-ID: <20190911002744.8690-2-mathieu.desnoyers@efficios.com> (raw)
In-Reply-To: <20190911002744.8690-1-mathieu.desnoyers@efficios.com>
It has been reported by Google that rseq is not behaving properly
with respect to clone when CLONE_VM is used without CLONE_THREAD.
It keeps the prior thread's rseq TLS registered when the TLS of the
thread has moved, so the kernel deals with the wrong TLS.
The approach of clearing the per task-struct rseq registration
on clone with CLONE_THREAD flag is incomplete. It does not cover
the use-case of clone with CLONE_VM set, but without CLONE_THREAD.
Looking more closely at each of the clone flags:
- CLONE_THREAD,
- CLONE_VM,
- CLONE_SETTLS.
It appears that the flag we really want to track is CLONE_SETTLS, which
moves the location of the TLS for the child, which makes the rseq
registration point to the wrong TLS.
Suggested-by: "H . Peter Anvin" <hpa@zytor.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Paul Turner <pjt@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: linux-api@vger.kernel.org
---
include/linux/sched.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9f51932bd543..deb4154dbf11 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1919,11 +1919,11 @@ static inline void rseq_migrate(struct task_struct *t)
/*
* If parent process has a registered restartable sequences area, the
- * child inherits. Only applies when forking a process, not a thread.
+ * child inherits. Unregister rseq for a clone with CLONE_TLS set.
*/
static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags)
{
- if (clone_flags & CLONE_THREAD) {
+ if (clone_flags & CLONE_TLS) {
t->rseq = NULL;
t->rseq_sig = 0;
t->rseq_event_mask = 0;
--
2.17.1
next prev parent reply other threads:[~2019-09-11 0:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-11 0:27 [RFC PATCH 1/4] rseq: Fix: Reject unknown flags on rseq unregister Mathieu Desnoyers
2019-09-11 0:27 ` Mathieu Desnoyers [this message]
2019-09-11 0:31 ` [RFC PATCH 2/4] rseq: Fix: Unregister rseq for CLONE_TLS Mathieu Desnoyers
2019-09-11 0:27 ` [RFC PATCH 3/4] rseq: Introduce unreg_clone_flags Mathieu Desnoyers
2019-09-13 14:26 ` Mathieu Desnoyers
2019-09-11 0:27 ` [RFC PATCH 4/4] rseq/selftests: Use RSEQ_FLAG_UNREG_CLONE_FLAGS Mathieu Desnoyers
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