linux-kernel - Re: [PATCH v4 2/4] serial: 8250: introduce serial8250_discard

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: <3a24d3ab-9567-4a0c-b904-4225ab4c489b@kernel.org>
Date: Fri, 25 Apr 2025 08:48:54 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Yunhui Cui <cuiyunhui@...edance.com>, arnd@...db.de,
 andriy.shevchenko@...ux.intel.com, benjamin.larsson@...exis.eu,
 gregkh@...uxfoundation.org, heikki.krogerus@...ux.intel.com,
 ilpo.jarvinen@...ux.intel.com, jkeeping@...usicbrands.com,
 john.ogness@...utronix.de, linux-kernel@...r.kernel.org,
 linux-serial@...r.kernel.org, markus.mayer@...aro.org,
 matt.porter@...aro.org, namcao@...utronix.de, paulmck@...nel.org,
 pmladek@...e.com, schnelle@...ux.ibm.com, sunilvl@...tanamicro.com,
 tim.kryger@...aro.org
Subject: Re: [PATCH v4 2/4] serial: 8250: introduce serial8250_discard_data()

On 25. 04. 25, 8:24, Yunhui Cui wrote:
> To prevent triggering PSLVERR, it is necessary to check whether the
> UART_LSR_DR bit of UART_LSR is set before reading UART_RX.
> Ensure atomicity of UART_LSR and UART_RX, put serial8250_discard_data()
> under port->lock.
> 
> Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
> ---
>   drivers/tty/serial/8250/8250.h      | 15 +++++++++++
>   drivers/tty/serial/8250/8250_port.c | 42 ++++++++++++++---------------
>   2 files changed, 36 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index b861585ca02a..5a106cf88207 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -162,6 +162,21 @@ static inline u16 serial_lsr_in(struct uart_8250_port *up)
>   	return lsr;
>   }
>   
> +/*
> + * To avoid PSLVERR, check UART_LSR_DR in UART_LSR before
> + * reading UART_RX.
> + */
> +static inline unsigned int serial8250_discard_data(struct uart_8250_port *up)
> +{
> +	u16 lsr;

Is lsr really 16-bit?

> +
> +	lsr = serial_in(up, UART_LSR);
> +	if (lsr & UART_LSR_DR)
> +		return serial_in(up, UART_RX);

Why does a discard function return a value at all?

> +
> +	return 0;
> +}
> +
>   /*
>    * For the 16C950
>    */
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index a913135d5217..802ac50357c0 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
...
> @@ -2137,25 +2136,21 @@ static void wait_for_xmitr(struct uart_8250_port *up, int bits)
>   static int serial8250_get_poll_char(struct uart_port *port)
>   {
>   	struct uart_8250_port *up = up_to_u8250p(port);
> -	int status;
> +	int status = NO_POLL_CHAR;
>   	u16 lsr;
>   
>   	serial8250_rpm_get(up);
>   
> +	uart_port_lock_irqsave(port, &flags);
>   	lsr = serial_port_in(port, UART_LSR);
> -
> -	if (!(lsr & UART_LSR_DR)) {
> -		status = NO_POLL_CHAR;
> -		goto out;
> -	}
> -
> -	status = serial_port_in(port, UART_RX);
> +	if ((lsr & UART_LSR_DR))

Too many parentheses.

> +		status = serial_port_in(port, UART_RX);
> +	uart_port_unlock_irqrestore(port, flags);

thanks,
-- 
js
suse labs