[F][PATCH 1/1] serial: imx: Introduce timeout when waiting on transmitter empty

[Yuxuan Luo]

From: Esben Haabendal <esben at geanix.com>

By waiting at most 1 second for USR2_TXDC to be set, we avoid a potential
deadlock.

In case of the timeout, there is not much we can do, so we simply ignore
the transmitter state and optimistically try to continue.

Signed-off-by: Esben Haabendal <esben at geanix.com>
Acked-by: Marc Kleine-Budde <mkl at pengutronix.de>
Link: https://lore.kernel.org/r/919647898c337a46604edcabaf13d42d80c0915d.1712837613.git.esben@geanix.com
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(backported from commit e533e4c62e9993e62e947ae9bbec34e4c7ae81c2)
[yuxuan.luo: read_poll_timeout_atomic() function is not introduced until
57a29df34146 (“iopoll: Introduce read_poll_timeout_atomic macro”),
however, readx_poll_timeout_atomic() can be used interchangeably.
]
CVE-2024-40967
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 drivers/tty/serial/imx.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 80cb72350ceaa..990d58fdeec61 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -30,6 +30,7 @@
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/dma-mapping.h>
 
 #include <asm/irq.h>
@@ -1939,7 +1940,7 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
 {
 	struct imx_port *sport = imx_uart_ports[co->index];
 	struct imx_port_ucrs old_ucr;
-	unsigned int ucr1;
+	unsigned int ucr1, usr2;
 	unsigned long flags = 0;
 	int locked = 1;
 
@@ -1971,8 +1972,8 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
 	 *	Finally, wait for transmitter to become empty
 	 *	and restore UCR1/2/3
 	 */
-	while (!(imx_uart_readl(sport, USR2) & USR2_TXDC));
-
+	readx_poll_timeout_atomic(imx_uart_readl, usr2, usr2 & USR2_TXDC,
+				 0, USEC_PER_SEC, false, sport, USR2);
 	imx_uart_ucrs_restore(sport, &old_ucr);
 
 	if (locked)
-- 
2.43.0