linux-kernel - [GIT PULL] rseq fixes

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Date:   Sat, 18 Jan 2020 18:11:16 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [GIT PULL] rseq fixes

Linus,

Please pull the latest core-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-urgent-for-linus

   # HEAD: 463f550fb47bede3a5d7d5177f363a6c3b45d50b rseq: Unregister rseq for clone CLONE_VM

This tree contains two rseq bugfixes:

- CLONE_VM !CLONE_THREAD didn't work properly, the kernel would end up 
  corrupting the TLS of the parent. Technically a change in the ABI but the 
  previous behavior couldn't resonably have been relied on by applications 
  so this looks like a valid exception to the ABI rule.

- Make the RSEQ_FLAG_UNREGISTER ABI behavior consistent with the handling 
  of other flags. This is not thought to impact any applications either.

( Of course both are only one contrary regression report away from being 
  reverted. )

 Thanks,

	Ingo

------------------>
Mathieu Desnoyers (2):
      rseq: Reject unknown flags on rseq unregister
      rseq: Unregister rseq for clone CLONE_VM


 include/linux/sched.h | 4 ++--
 kernel/rseq.c         | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 467d26046416..716ad1d8d95e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1929,11 +1929,11 @@ 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_VM set.
  */
 static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags)
 {
-	if (clone_flags & CLONE_THREAD) {
+	if (clone_flags & CLONE_VM) {
 		t->rseq = NULL;
 		t->rseq_sig = 0;
 		t->rseq_event_mask = 0;
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 27c48eb7de40..a4f86a9d6937 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -310,6 +310,8 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
 	int ret;
 
 	if (flags & RSEQ_FLAG_UNREGISTER) {
+		if (flags & ~RSEQ_FLAG_UNREGISTER)
+			return -EINVAL;
 		/* Unregister rseq for current thread. */
 		if (current->rseq != rseq || !current->rseq)
 			return -EINVAL;