kernel/drivers/tty/serial/kgdboc.c, branch linux-6.9.y

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

2024-05-25T14:30:55Z

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

tty: serial: kgdboc: fix mutex locking order for configure_kgdboc()

2023-01-16T15:44:53Z

Several mutexes are taken while setting up console serial ports. In particular, the tty_port->mutex and @console_mutex are taken: serial_pnp_probe serial8250_register_8250_port uart_add_one_port (locks tty_port->mutex) uart_configure_port register_console (locks @console_mutex) In order to synchronize kgdb's tty_find_polling_driver() with register_console(), commit 6193bc90849a ("tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()") takes the @console_mutex. However, this leads to the following call chain (with locking): platform_probe kgdboc_probe configure_kgdboc (locks @console_mutex) tty_find_polling_driver uart_poll_init (locks tty_port->mutex) uart_set_options This is clearly deadlock potential due to the reverse lock ordering. Since uart_set_options() requires holding @console_mutex in order to serialize early initialization of the serial-console lock, take the @console_mutex in uart_poll_init() instead of configure_kgdboc(). Since configure_kgdboc() was using @console_mutex for safe traversal of the console list, change it to use the SRCU iterator instead. Add comments to uart_set_options() kerneldoc mentioning that it requires holding @console_mutex (aka the console_list_lock). Fixes: 6193bc90849a ("tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()") Signed-off-by: John Ogness Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek [pmladek@suse.com: Export console_srcu_read_lock_is_held() to fix build kgdboc as a module.] Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20230112161213.1434854-1-john.ogness@linutronix.de

tty: serial: kgdboc: use console_list_lock to trap exit

2022-12-02T10:25:02Z

kgdboc_earlycon_init() uses the console_lock to ensure that no consoles are unregistered until the kgdboc_earlycon is setup. The console_list_lock should be used instead because list synchronization responsibility will be removed from the console_lock in a later change. Signed-off-by: John Ogness Reviewed-by: Daniel Thompson Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-39-john.ogness@linutronix.de

tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()

2022-12-02T10:25:02Z

Calling tty_find_polling_driver() can lead to uart_set_options() being called (via the poll_init() callback of tty_operations) to configure the uart. But uart_set_options() can also be called by register_console() (via the setup() callback of console). Take the console_list_lock to synchronize against register_console() and also use it for console list traversal. This also ensures the console list cannot change until the polling console has been chosen. Signed-off-by: John Ogness Reviewed-by: Daniel Thompson Reviewed-by: Petr Mladek Reviewed-by: Douglas Anderson Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-38-john.ogness@linutronix.de

tty: serial: kgdboc: use console_list_lock for list traversal

2022-12-02T10:25:02Z

configure_kgdboc() uses the console_lock for console list iteration. Use the console_list_lock instead because list synchronization responsibility will be removed from the console_lock in a later change. The SRCU iterator could have been used here, but a later change will relocate the locking of the console_list_lock to also provide synchronization against register_console(). Note, the console_lock is still needed to serialize the device() callback with other console operations. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Reviewed-by: Douglas Anderson Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-37-john.ogness@linutronix.de

tty: serial: kgdboc: use srcu console list iterator

2022-12-02T10:25:02Z

Use srcu console list iteration for safe console list traversal. Note that this is a preparatory change for when console_lock no longer provides synchronization for the console list. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Reviewed-by: Douglas Anderson Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-36-john.ogness@linutronix.de

tty: serial: kgdboc: document console_lock usage

2022-12-02T10:25:00Z

kgdboc_earlycon_init() uses the console_lock to ensure that no consoles are unregistered until the kgdboc_earlycon is setup. This is necessary because the trapping of the exit() callback assumes that the exit() callback is not called before the trap is setup. Explicitly document this non-typical console_lock usage. Signed-off-by: John Ogness Reviewed-by: Greg Kroah-Hartman Reviewed-by: Douglas Anderson Reviewed-by: Daniel Thompson Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-9-john.ogness@linutronix.de

serial: kgdboc: Lock console list in probe function

2022-12-02T10:24:59Z

Unprotected list walks are not necessarily safe. Signed-off-by: Thomas Gleixner Signed-off-by: John Ogness Reviewed-by: Greg Kroah-Hartman Reviewed-by: Douglas Anderson Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek Reviewed-by: Daniel Thompson Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-2-john.ogness@linutronix.de

serial: kgdboc: Fix typo in comment

2022-06-27T12:37:09Z

Delete the redundant word 'the'. Signed-off-by: Xiang wangx Link: https://lore.kernel.org/r/20220620104653.5451-1-wangxiang@cdjrlc.com Signed-off-by: Greg Kroah-Hartman

kgdboc: fix return value of __setup handler

2022-03-18T12:12:33Z

__setup() handlers should return 1 to obsolete_checksetup() in init/main.c to indicate that the boot option has been handled. A return of 0 causes the boot option/value to be listed as an Unknown kernel parameter and added to init's (limited) environment strings. So return 1 from kgdboc_option_setup(). Unknown kernel command line parameters "BOOT_IMAGE=/boot/bzImage-517rc7 kgdboc=kbd kgdbts=", will be passed to user space. Run /sbin/init as init process with arguments: /sbin/init with environment: HOME=/ TERM=linux BOOT_IMAGE=/boot/bzImage-517rc7 kgdboc=kbd kgdbts= Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru Fixes: 1bd54d851f50 ("kgdboc: Passing ekgdboc to command line causes panic") Fixes: f2d937f3bf00 ("consoles: polling support, kgdboc") Cc: He Zhe Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: kgdb-bugreport@lists.sourceforge.net Cc: Jason Wessel Cc: Daniel Thompson Cc: Douglas Anderson Cc: linux-serial@vger.kernel.org Reported-by: Igor Zhbanov Reviewed-by: Douglas Anderson Signed-off-by: Randy Dunlap Link: https://lore.kernel.org/r/20220309033018.17936-1-rdunlap@infradead.org Signed-off-by: Greg Kroah-Hartman