From 9a789fcfe8605417f7a1a970355f5efa4fe88c64 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Tue, 19 Jun 2018 09:32:30 -0400 Subject: rseq/cleanup: Do not abort rseq c.s. in child on fork() Considering that we explicitly forbid system calls in rseq critical sections, it is not valid to issue a fork or clone system call within a rseq critical section, so rseq_fork() is not required to restart an active rseq c.s. in the child process. Signed-off-by: Mathieu Desnoyers Cc: Andrew Morton Cc: Andy Lutomirski Cc: Ben Maurer Cc: Boqun Feng Cc: Catalin Marinas Cc: Chris Lameter Cc: Dave Watson Cc: Joel Fernandes Cc: Josh Triplett Cc: Linus Torvalds Cc: Michael Kerrisk Cc: Paul E . McKenney Cc: Paul Turner Cc: Peter Zijlstra Cc: Russell King Cc: Shuah Khan Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Will Deacon Cc: linux-api@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Link: https://lore.kernel.org/lkml/20180619133230.4087-4-mathieu.desnoyers@efficios.com Signed-off-by: Ingo Molnar --- include/linux/sched.h | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'include/linux') diff --git a/include/linux/sched.h b/include/linux/sched.h index 87bf02d93a27..c1882643d455 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1831,9 +1831,7 @@ 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. In - * case a parent fork() in the middle of a restartable sequence, set the - * resume notifier to force the child to retry. + * child inherits. Only applies when forking a process, not a thread. */ static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) { @@ -1847,7 +1845,6 @@ static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) t->rseq_len = current->rseq_len; t->rseq_sig = current->rseq_sig; t->rseq_event_mask = current->rseq_event_mask; - rseq_preempt(t); } } -- cgit v1.2.3 From 784e0300fe9fe4aa81bd7df9d59e138f56bb605b Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 22 Jun 2018 11:45:07 +0100 Subject: rseq: Avoid infinite recursion when delivering SIGSEGV When delivering a signal to a task that is using rseq, we call into __rseq_handle_notify_resume() so that the registers pushed in the sigframe are updated to reflect the state of the restartable sequence (for example, ensuring that the signal returns to the abort handler if necessary). However, if the rseq management fails due to an unrecoverable fault when accessing userspace or certain combinations of RSEQ_CS_* flags, then we will attempt to deliver a SIGSEGV. This has the potential for infinite recursion if the rseq code continuously fails on signal delivery. Avoid this problem by using force_sigsegv() instead of force_sig(), which is explicitly designed to reset the SEGV handler to SIG_DFL in the case of a recursive fault. In doing so, remove rseq_signal_deliver() from the internal rseq API and have an optional struct ksignal * parameter to rseq_handle_notify_resume() instead. Signed-off-by: Will Deacon Signed-off-by: Thomas Gleixner Acked-by: Mathieu Desnoyers Cc: peterz@infradead.org Cc: paulmck@linux.vnet.ibm.com Cc: boqun.feng@gmail.com Link: https://lkml.kernel.org/r/1529664307-983-1-git-send-email-will.deacon@arm.com --- include/linux/sched.h | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) (limited to 'include/linux') diff --git a/include/linux/sched.h b/include/linux/sched.h index c1882643d455..9256118bd40c 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1799,20 +1799,22 @@ static inline void rseq_set_notify_resume(struct task_struct *t) set_tsk_thread_flag(t, TIF_NOTIFY_RESUME); } -void __rseq_handle_notify_resume(struct pt_regs *regs); +void __rseq_handle_notify_resume(struct ksignal *sig, struct pt_regs *regs); -static inline void rseq_handle_notify_resume(struct pt_regs *regs) +static inline void rseq_handle_notify_resume(struct ksignal *ksig, + struct pt_regs *regs) { if (current->rseq) - __rseq_handle_notify_resume(regs); + __rseq_handle_notify_resume(ksig, regs); } -static inline void rseq_signal_deliver(struct pt_regs *regs) +static inline void rseq_signal_deliver(struct ksignal *ksig, + struct pt_regs *regs) { preempt_disable(); __set_bit(RSEQ_EVENT_SIGNAL_BIT, ¤t->rseq_event_mask); preempt_enable(); - rseq_handle_notify_resume(regs); + rseq_handle_notify_resume(ksig, regs); } /* rseq_preempt() requires preemption to be disabled. */ @@ -1861,10 +1863,12 @@ static inline void rseq_execve(struct task_struct *t) static inline void rseq_set_notify_resume(struct task_struct *t) { } -static inline void rseq_handle_notify_resume(struct pt_regs *regs) +static inline void rseq_handle_notify_resume(struct ksignal *ksig, + struct pt_regs *regs) { } -static inline void rseq_signal_deliver(struct pt_regs *regs) +static inline void rseq_signal_deliver(struct ksignal *ksig, + struct pt_regs *regs) { } static inline void rseq_preempt(struct task_struct *t) -- cgit v1.2.3