From 512b9385201c7dec1b8d490711e9b578ae50525e Mon Sep 17 00:00:00 2001 From: Daniel Thompson Date: Wed, 24 Apr 2024 15:21:41 +0100 Subject: [PATCH] serial: kgdboc: Fix NMI-safety problems from keyboard reset code commit b2aba15ad6f908d1a620fd97f6af5620c3639742 upstream. Currently, when kdb is compiled with keyboard support, then we will use schedule_work() to provoke reset of the keyboard status. Unfortunately schedule_work() gets called from the kgdboc post-debug-exception handler. That risks deadlock since schedule_work() is not NMI-safe and, even on platforms where the NMI is not directly used for debugging, the debug trap can have NMI-like behaviour depending on where breakpoints are placed. Fix this by using the irq work system, which is NMI-safe, to defer the call to schedule_work() to a point when it is safe to call. Reported-by: Liuye Closes: https://lore.kernel.org/all/20240228025602.3087748-1-liu.yeC@h3c.com/ Cc: stable@vger.kernel.org Reviewed-by: Douglas Anderson Acked-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20240424-kgdboc_fix_schedule_work-v2-1-50f5a490aec5@linaro.org Signed-off-by: Daniel Thompson Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/kgdboc.c | 30 +++++++++++++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index 6e81d782d8a0..d837a585f114 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #define MAX_CONFIG_LEN 40 @@ -35,6 +36,25 @@ static int kgdboc_use_kms; /* 1 if we use kernel mode switching */ static struct tty_driver *kgdb_tty_driver; static int kgdb_tty_line; +/* + * When we leave the debug trap handler we need to reset the keyboard status + * (since the original keyboard state gets partially clobbered by kdb use of + * the keyboard). + * + * The path to deliver the reset is somewhat circuitous. + * + * To deliver the reset we register an input handler, reset the keyboard and + * then deregister the input handler. However, to get this done right, we do + * have to carefully manage the calling context because we can only register + * input handlers from task context. + * + * In particular we need to trigger the action from the debug trap handler with + * all its NMI and/or NMI-like oddities. To solve this the kgdboc trap exit code + * (the "post_exception" callback) uses irq_work_queue(), which is NMI-safe, to + * schedule a callback from a hardirq context. From there we have to defer the + * work again, this time using schedule_work(), to get a callback using the + * system workqueue, which runs in task context. + */ #ifdef CONFIG_KDB_KEYBOARD static int kgdboc_reset_connect(struct input_handler *handler, struct input_dev *dev, @@ -86,10 +106,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy) static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper); +static void kgdboc_queue_restore_input_helper(struct irq_work *unused) +{ + schedule_work(&kgdboc_restore_input_work); +} + +static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper); + static void kgdboc_restore_input(void) { if (likely(system_state == SYSTEM_RUNNING)) - schedule_work(&kgdboc_restore_input_work); + irq_work_queue(&kgdboc_restore_input_irq_work); } static int kgdboc_register_kbd(char **cptr) @@ -120,6 +147,7 @@ static void kgdboc_unregister_kbd(void) i--; } } + irq_work_sync(&kgdboc_restore_input_irq_work); flush_work(&kgdboc_restore_input_work); } #else /* ! CONFIG_KDB_KEYBOARD */