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Date: Sat, 7 Mar 2020 02:47:02 -0500 From: Joel Fernandes <joel@...lfernandes.org> To: "Paul E. McKenney" <paulmck@...nel.org> Cc: Masami Hiramatsu <mhiramat@...nel.org>, Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, gregkh@...uxfoundation.org, gustavo@...eddedor.com, tglx@...utronix.de, josh@...htriplett.org, mathieu.desnoyers@...icios.com, jiangshanlai@...il.com, stable@...r.kernel.org Subject: Re: [PATCH] x86/kprobes: Prohibit probing on rcu_nmi_exit() and ist_exit() On Fri, Mar 06, 2020 at 07:28:31PM -0800, Paul E. McKenney wrote: > On Sat, Mar 07, 2020 at 12:02:12PM +0900, Masami Hiramatsu wrote: > > Prohibit probing on rcu_nmi_exit() and ist_exit() which > > are called from do_int3()'s kprobe path after kprobe_int3_handler(). > > > > The commit c13324a505c7 ("x86/kprobes: Prohibit probing on > > functions before kprobe_int3_handler()") tried to fix similar > > issue, but it only marks the functions before kprobe_int3_handler() > > in do_int3(). > > > > If we put a kprobe on rcu_nmi_exit() or ist_exit(), the kprobes > > will detect reentrance. However, it only skips the kprobe handler, > > exits from do_int3() and hits ist_exit() and rcu_nmi_exit() again. > > Thus, it causes another int3 exception and finally we will get > > the kernel panic with "Unrecoverable kprobe detected." error message. > > > > This is reproducible by the following commands. > > > > / # echo 0 > /proc/sys/debug/kprobes-optimization > > / # echo p vfs_read > /sys/kernel/debug/tracing/kprobe_events > > / # echo p rcu_nmi_exit >> /sys/kernel/debug/tracing/kprobe_events > > / # echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable > > > > Fixes: c13324a505c7 ("x86/kprobes: Prohibit probing on functions before kprobe_int3_handler()") > > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org> > > Cc: stable@...r.kernel.org > > From an RCU perspective: > > Reviewed-by: Paul E. McKenney <paulmck@...nel.org> > Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org> thanks, - Joel > > --- > > arch/x86/kernel/traps.c | 1 + > > kernel/rcu/tree.c | 1 + > > 2 files changed, 2 insertions(+) > > > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > > index 6ef00eb6fbb9..c63fb7697794 100644 > > --- a/arch/x86/kernel/traps.c > > +++ b/arch/x86/kernel/traps.c > > @@ -115,6 +115,7 @@ void ist_exit(struct pt_regs *regs) > > if (!user_mode(regs)) > > rcu_nmi_exit(); > > } > > +NOKPROBE_SYMBOL(ist_exit); > > > > /** > > * ist_begin_non_atomic() - begin a non-atomic section in an IST exception > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index d91c9156fab2..c49ea0e919f9 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -670,6 +670,7 @@ void rcu_nmi_exit(void) > > { > > rcu_nmi_exit_common(false); > > } > > +NOKPROBE_SYMBOL(rcu_nmi_exit); > > > > /** > > * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle > >
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