From 78d60dae9a0c9f09aa3d6477c94047df2fe6f7b0 Mon Sep 17 00:00:00 2001
From: Paul Geurts <paul_geurts@live.nl>
Date: Fri, 24 Nov 2023 14:11:10 +0100
Subject: [PATCH] serial: imx: fix tx statemachine deadlock
Git-commit: 78d60dae9a0c9f09aa3d6477c94047df2fe6f7b0
Patch-mainline: v6.8-rc1
References: git-fixes bsc#1220364 CVE-2023-52456
When using the serial port as RS485 port, the tx statemachine is used to
control the RTS pin to drive the RS485 transceiver TX_EN pin. When the
TTY port is closed in the middle of a transmission (for instance during
userland application crash), imx_uart_shutdown disables the interface
and disables the Transmission Complete interrupt. afer that,
imx_uart_stop_tx bails on an incomplete transmission, to be retriggered
by the TC interrupt. This interrupt is disabled and therefore the tx
statemachine never transitions out of SEND. The statemachine is in
deadlock now, and the TX_EN remains low, making the interface useless.
imx_uart_stop_tx now checks for incomplete transmission AND whether TC
interrupts are enabled before bailing to be retriggered. This makes sure
the state machine handling is reached, and is properly set to
WAIT_AFTER_SEND.
Fixes: cb1a60923609 ("serial: imx: implement rts delaying for rs485")
Signed-off-by: Paul Geurts <paul_geurts@live.nl>
Tested-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Tested-by: Eberhard Stoll <eberhard.stoll@gmx.de>
Link: https://lore.kernel.org/r/AM0PR09MB26758F651BC1B742EB45775995B8A@AM0PR09MB2675.eurprd09.prod.outlook.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
drivers/tty/serial/imx.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 52dd8a6b8760..e7e952bb7bb8 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -415,13 +415,13 @@ static void imx_uart_stop_tx(struct uart_port *port)
ucr1 = imx_uart_readl(sport, UCR1);
imx_uart_writel(sport, ucr1 & ~UCR1_TRDYEN, UCR1);
+ ucr4 = imx_uart_readl(sport, UCR4);
usr2 = imx_uart_readl(sport, USR2);
- if (!(usr2 & USR2_TXDC)) {
+ if ((!(usr2 & USR2_TXDC)) && (ucr4 & UCR4_TCEN)) {
/* The shifter is still busy, so retry once TC triggers */
return;
}
- ucr4 = imx_uart_readl(sport, UCR4);
ucr4 &= ~UCR4_TCEN;
imx_uart_writel(sport, ucr4, UCR4);
--
2.35.3