From: Yunhui Cui <cuiyunhui@bytedance.com> stable inclusion from stable-v6.6.103 commit cb7b3633ed749db8e56f475f43c960652cbd6882 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/ICWO1S CVE: CVE-2025-39724 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit 7f8fdd4dbffc05982b96caf586f77a014b2a9353 upstream. When the PSLVERR_RESP_EN parameter is set to 1, the device generates an error response if an attempt is made to read an empty RBR (Receive Buffer Register) while the FIFO is enabled. In serial8250_do_startup(), calling serial_port_out(port, UART_LCR, UART_LCR_WLEN8) triggers dw8250_check_lcr(), which invokes dw8250_force_idle() and serial8250_clear_and_reinit_fifos(). The latter function enables the FIFO via serial_out(p, UART_FCR, p->fcr). Execution proceeds to the serial_port_in(port, UART_RX). This satisfies the PSLVERR trigger condition. When another CPU (e.g., using printk()) is accessing the UART (UART is busy), the current CPU fails the check (value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR) in dw8250_check_lcr(), causing it to enter dw8250_force_idle(). Put serial_port_out(port, UART_LCR, UART_LCR_WLEN8) under the port->lock to fix this issue. Panic backtrace: [ 0.442336] Oops - unknown exception [#1] [ 0.442343] epc : dw8250_serial_in32+0x1e/0x4a [ 0.442351] ra : serial8250_do_startup+0x2c8/0x88e ... [ 0.442416] console_on_rootfs+0x26/0x70 Fixes: c49436b657d0 ("serial: 8250_dw: Improve unwritable LCR workaround") Link: https://lore.kernel.org/all/84cydt5peu.fsf@jogness.linutronix.de/T/ Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com> Reviewed-by: John Ogness <john.ogness@linutronix.de> Cc: stable <stable@kernel.org> Link: https://lore.kernel.org/r/20250723023322.464-2-cuiyunhui@bytedance.com [ Applied fix to serial8250_do_startup() instead of serial8250_initialize() ] Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Yi Yang <yiyang13@huawei.com> --- drivers/tty/serial/8250/8250_port.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index d5ad6cae6b65..23aed9e89e30 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2375,9 +2375,8 @@ int serial8250_do_startup(struct uart_port *port) /* * Now, initialize the UART */ - serial_port_out(port, UART_LCR, UART_LCR_WLEN8); - spin_lock_irqsave(&port->lock, flags); + serial_port_out(port, UART_LCR, UART_LCR_WLEN8); if (up->port.flags & UPF_FOURPORT) { if (!up->port.irq) up->port.mctrl |= TIOCM_OUT1; -- 2.25.1