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@kernel.org Cc: stable@vger.kernel.org
From an RCU perspective:
Reviewed-by: Paul E. McKenney paulmck@kernel.org
Reviewed-by: Joel Fernandes (Google) joel@joelfernandes.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