linux-kernel - [PATCH 1/6] serial: 8250: Protect LCR write in shutdown

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20260123172739.13410-2-ilpo.jarvinen@linux.intel.com>
Date: Fri, 23 Jan 2026 19:27:34 +0200
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	linux-serial@...r.kernel.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	qianfan Zhao <qianfanguijin@....com>,
	Adriana Nicolae <adriana@...sta.com>,
	linux-kernel@...r.kernel.org
Cc: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	"Bandal, Shankar" <shankar.bandal@...el.com>,
	"Murthy, Shanth" <shanth.murthy@...el.com>
Subject: [PATCH 1/6] serial: 8250: Protect LCR write in shutdown

The 8250_dw driver needs to potentially perform very complex operations
during LCR writes because its BUSY handling prevents updates to LCR
while UART is BUSY (which is not fully under our control without those
complex operations). Thus, LCR writes should occur under port's lock.

Move LCR write under port's lock in serial8250_do_shutdown(). Also
split the LCR RMW so that the logic is on a separate line for clarity.

Tested-by: "Bandal, Shankar" <shankar.bandal@...el.com>
Tested-by: "Murthy, Shanth" <shanth.murthy@...el.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
---
 drivers/tty/serial/8250/8250_port.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 719faf92aa8a..f7a3c5555204 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2350,6 +2350,7 @@ static int serial8250_startup(struct uart_port *port)
 void serial8250_do_shutdown(struct uart_port *port)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
+	u32 lcr;
 
 	serial8250_rpm_get(up);
 	/*
@@ -2376,13 +2377,13 @@ void serial8250_do_shutdown(struct uart_port *port)
 			port->mctrl &= ~TIOCM_OUT2;
 
 		serial8250_set_mctrl(port, port->mctrl);
+
+		/* Disable break condition */
+		lcr = serial_port_in(port, UART_LCR);
+		lcr &= ~UART_LCR_SBC;
+		serial_port_out(port, UART_LCR, lcr);
 	}
 
-	/*
-	 * Disable break condition and FIFOs
-	 */
-	serial_port_out(port, UART_LCR,
-			serial_port_in(port, UART_LCR) & ~UART_LCR_SBC);
 	serial8250_clear_fifos(up);
 
 	rsa_disable(up);
-- 
2.39.5