This is a note to let you know that I've just added the patch titled

kprobes/x86: Disable preemption in ftrace-based jprobes

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: kprobes-x86-disable-preemption-in-ftrace-based-jprobes.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Wed Dec 6 16:43:17 CET 2017

From: Masami Hiramatsu mhiramat@kernel.org Date: Tue, 19 Sep 2017 19:01:40 +0900 Subject: kprobes/x86: Disable preemption in ftrace-based jprobes

From: Masami Hiramatsu mhiramat@kernel.org

[ Upstream commit 5bb4fc2d8641219732eb2bb654206775a4219aca ]

Disable preemption in ftrace-based jprobe handlers as described in Documentation/kprobes.txt:

"Probe handlers are run with preemption disabled."

This will fix jprobes behavior when CONFIG_PREEMPT=y.

Signed-off-by: Masami Hiramatsu mhiramat@kernel.org Cc: Alexei Starovoitov ast@fb.com Cc: Alexei Starovoitov ast@kernel.org Cc: Ananth N Mavinakayanahalli ananth@linux.vnet.ibm.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Paul E . McKenney paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Steven Rostedt rostedt@goodmis.org Cc: Thomas Gleixner tglx@linutronix.de Link: http://lkml.kernel.org/r/150581530024.32348.9863783558598926771.stgit@devbox Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/kprobes/ftrace.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-)

--- a/arch/x86/kernel/kprobes/ftrace.c +++ b/arch/x86/kernel/kprobes/ftrace.c @@ -26,7 +26,7 @@ #include "common.h"

static nokprobe_inline -int __skip_singlestep(struct kprobe *p, struct pt_regs *regs, +void __skip_singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb, unsigned long orig_ip) { /* @@ -41,20 +41,21 @@ int __skip_singlestep(struct kprobe *p, __this_cpu_write(current_kprobe, NULL); if (orig_ip) regs->ip = orig_ip; - return 1; }

int skip_singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { - if (kprobe_ftrace(p)) - return __skip_singlestep(p, regs, kcb, 0); - else - return 0; + if (kprobe_ftrace(p)) { + __skip_singlestep(p, regs, kcb, 0); + preempt_enable_no_resched(); + return 1; + } + return 0; } NOKPROBE_SYMBOL(skip_singlestep);

-/* Ftrace callback handler for kprobes */ +/* Ftrace callback handler for kprobes -- called under preepmt disabed */ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, struct ftrace_ops *ops, struct pt_regs *regs) { @@ -77,13 +78,17 @@ void kprobe_ftrace_handler(unsigned long /* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */ regs->ip = ip + sizeof(kprobe_opcode_t);

+ /* To emulate trap based kprobes, preempt_disable here */ + preempt_disable(); __this_cpu_write(current_kprobe, p); kcb->kprobe_status = KPROBE_HIT_ACTIVE; - if (!p->pre_handler || !p->pre_handler(p, regs)) + if (!p->pre_handler || !p->pre_handler(p, regs)) { __skip_singlestep(p, regs, kcb, orig_ip); + preempt_enable_no_resched(); + } /* * If pre_handler returns !0, it sets regs->ip and - * resets current kprobe. + * resets current kprobe, and keep preempt count +1. */ } end:

Patches currently in stable-queue which might be from mhiramat@kernel.org are

queue-4.4/kprobes-x86-disable-preemption-in-ftrace-based-jprobes.patch