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serial: kgdboc: Fix NMI-safety problems from keyboard reset code

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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 <liu.yeC@h3c.com>
Closes: https://lore.kernel.org/all/20240228025602.3087748-1-liu.yeC@h3c.com/
Cc: stable@vger.kernel.org
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240424-kgdboc_fix_schedule_work-v2-1-50f5a490aec5@linaro.org
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
This commit is contained in:
Daniel Thompson 2024-04-24 15:21:41 +01:00
parent 64d504cfcd
commit b2aba15ad6
1 changed files with 29 additions and 1 deletions
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30
drivers/tty/serial/kgdboc.c
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@ -19,6 +19,7 @@
#include <linux/console.h>
#include <linux/vt_kern.h>
#include <linux/input.h>
#include <linux/irq_work.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/serial_core.h>
@ -48,6 +49,25 @@ static struct kgdb_io kgdboc_earlycon_io_ops;
static int (*earlycon_orig_exit)(struct console *con);
#endif /* IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */
/*
* 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,
@ -99,10 +119,17 @@ 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)
@ -133,6 +160,7 @@ 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 */