Commit e84cc7b8 authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by Yongqiang Liu
Browse files

serial: 8250: Fix serial8250_tx_empty() race with DMA Tx 

stable inclusion
from stable-v4.19.283
commit 3f9cab5766daa1c1e5b389cd12b6e717ce95852f
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7BZ5U


CVE: NA

--------------------------------

There's a potential race before THRE/TEMT deasserts when DMA Tx is
starting up (or the next batch of continuous Tx is being submitted).
This can lead to misdetecting Tx empty condition.

It is entirely normal for THRE/TEMT to be set for some time after the
DMA Tx had been setup in serial8250_tx_dma(). As Tx side is definitely
not empty at that point, it seems incorrect for serial8250_tx_empty()
claim Tx is empty.

Fix the race by also checking in serial8250_tx_empty() whether there's
DMA Tx active.

Note: This fix only addresses in-kernel race mainly to make using
TCSADRAIN/FLUSH robust. Userspace can still cause other races but they
seem userspace concurrency control problems.

Fixes: 9ee4b83e ("serial: 8250: Add support for dmaengine")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230317113318.31327-3-ilpo.jarvinen@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 146a37e0)
Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarYongqiang Liu <liuyongqiang13@huawei.com>
parent 5195a946

drivers/tty/serial/8250/8250.h

+12 −0
Original line number Diff line number Diff line
@@ -217,6 +217,13 @@ extern int serial8250_rx_dma(struct uart_8250_port *); 
extern void serial8250_rx_dma_flush(struct uart_8250_port *);

extern int serial8250_request_dma(struct uart_8250_port *);

extern void serial8250_release_dma(struct uart_8250_port *);



static inline bool serial8250_tx_dma_running(struct uart_8250_port *p)

{

	struct uart_8250_dma *dma = p->dma;



	return dma && dma->tx_running;

}

#else

static inline int serial8250_tx_dma(struct uart_8250_port *p)

{
@@ -232,6 +239,11 @@ static inline int serial8250_request_dma(struct uart_8250_port *p) 
	return -1;

}

static inline void serial8250_release_dma(struct uart_8250_port *p) { }



static inline bool serial8250_tx_dma_running(struct uart_8250_port *p)

{

	return false;

}

#endif



static inline int ns16550a_goto_highspeed(struct uart_8250_port *up)

drivers/tty/serial/8250/8250_port.c

+9 −3
Original line number Diff line number Diff line
@@ -1962,19 +1962,25 @@ static int serial8250_tx_threshold_handle_irq(struct uart_port *port) 
static unsigned int serial8250_tx_empty(struct uart_port *port)

{

	struct uart_8250_port *up = up_to_u8250p(port);

	unsigned int result = 0;

	unsigned long flags;

	unsigned int lsr;



	serial8250_rpm_get(up);



	spin_lock_irqsave(&port->lock, flags);

	if (!serial8250_tx_dma_running(up)) {

		lsr = serial_port_in(port, UART_LSR);

		up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;



		if ((lsr & BOTH_EMPTY) == BOTH_EMPTY)

			result = TIOCSER_TEMT;

	}

	spin_unlock_irqrestore(&port->lock, flags);



	serial8250_rpm_put(up);



	return (lsr & BOTH_EMPTY) == BOTH_EMPTY ? TIOCSER_TEMT : 0;

	return result;

}



unsigned int serial8250_do_get_mctrl(struct uart_port *port)