There is an ongoing discussion on the choice of flag we want to care about here. Therefore, please don't pull this patch until we reach an agreement.
Thanks, Mathieu ----- On Sep 13, 2019, at 11:12 AM, Mathieu Desnoyers [email protected] wrote: > 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, making the rseq > registration point to the wrong TLS. > > Suggested-by: "H . Peter Anvin" <[email protected]> > Signed-off-by: Mathieu Desnoyers <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Peter Zijlstra (Intel) <[email protected]> > Cc: "Paul E. McKenney" <[email protected]> > Cc: Boqun Feng <[email protected]> > Cc: "H . Peter Anvin" <[email protected]> > Cc: Paul Turner <[email protected]> > Cc: Dmitry Vyukov <[email protected]> > Cc: [email protected] > Cc: <[email protected]> > --- > 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..76bf55b5cccf 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_SETTLS set. > */ > static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) > { > - if (clone_flags & CLONE_THREAD) { > + if (clone_flags & CLONE_SETTLS) { > t->rseq = NULL; > t->rseq_sig = 0; > t->rseq_event_mask = 0; > -- > 2.17.1 -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
