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Date: Mon, 18 Mar 2024 11:14:13 +0800
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Subject: Re: [PATCH stable 5.10] serial: sc16is7xx: convert from _raw_ to
 _noinc_ regmap functions for FIFO
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From: Gong Ruiqi <gongruiqi1@huawei.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby
	<jirislaby@kernel.org>, Hugo Villeneuve <hvilleneuve@dimonoff.com>
CC: Jon Ringle <jringle@gridpoint.com>, <linux-serial@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, Wang Weiyang <wangweiyang2@huawei.com>,
	<stable@vger.kernel.org>
References: <20240318025259.1412353-1-gongruiqi1@huawei.com>
In-Reply-To: <20240318025259.1412353-1-gongruiqi1@huawei.com>
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Oops. + Cc stable@vger.kernel.org

On 2024/03/18 10:52, GONG, Ruiqi wrote:
> From: Hugo Villeneuve <hvilleneuve@dimonoff.com>
> 
> commit dbf4ab821804df071c8b566d9813083125e6d97b upstream.
> 
> The SC16IS7XX IC supports a burst mode to access the FIFOs where the
> initial register address is sent ($00), followed by all the FIFO data
> without having to resend the register address each time. In this mode, the
> IC doesn't increment the register address for each R/W byte.
> 
> The regmap_raw_read() and regmap_raw_write() are functions which can
> perform IO over multiple registers. They are currently used to read/write
> from/to the FIFO, and although they operate correctly in this burst mode on
> the SPI bus, they would corrupt the regmap cache if it was not disabled
> manually. The reason is that when the R/W size is more than 1 byte, these
> functions assume that the register address is incremented and handle the
> cache accordingly.
> 
> Convert FIFO R/W functions to use the regmap _noinc_ versions in order to
> remove the manual cache control which was a workaround when using the
> _raw_ versions. FIFO registers are properly declared as volatile so
> cache will not be used/updated for FIFO accesses.
> 
> Fixes: dfeae619d781 ("serial: sc16is7xx")
> Cc:  <stable@vger.kernel.org>
> Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
> Link: https://lore.kernel.org/r/20231211171353.2901416-6-hugo@hugovil.com
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Hugo Villeneuve <hvilleneuve@dimonoff.com>
> Signed-off-by: GONG, Ruiqi <gongruiqi1@huawei.com>
> ---
> 
> The mainline commit dbf4ab821804 ("serial: sc16is7xx: convert from _raw_
> to _noinc_ regmap functions for FIFO") by Hugo has been assigned to be
> CVE-2023-52488, but for stable branches lower than 6.1 there's no
> official backport.
> 
> I made up this backport patch for 5.10, and its correctness has been
> confirmed in previous communication with Hugo. Let's publicize it and
> merge it into upstream.
> 
>  drivers/tty/serial/sc16is7xx.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> index 31e0c5c3ddea..29f05db0d49b 100644
> --- a/drivers/tty/serial/sc16is7xx.c
> +++ b/drivers/tty/serial/sc16is7xx.c
> @@ -376,9 +376,7 @@ static void sc16is7xx_fifo_read(struct uart_port *port, unsigned int rxlen)
>  	const u8 line = sc16is7xx_line(port);
>  	u8 addr = (SC16IS7XX_RHR_REG << SC16IS7XX_REG_SHIFT) | line;
>  
> -	regcache_cache_bypass(s->regmap, true);
> -	regmap_raw_read(s->regmap, addr, s->buf, rxlen);
> -	regcache_cache_bypass(s->regmap, false);
> +	regmap_noinc_read(s->regmap, addr, s->buf, rxlen);
>  }
>  
>  static void sc16is7xx_fifo_write(struct uart_port *port, u8 to_send)
> @@ -394,9 +392,7 @@ static void sc16is7xx_fifo_write(struct uart_port *port, u8 to_send)
>  	if (unlikely(!to_send))
>  		return;
>  
> -	regcache_cache_bypass(s->regmap, true);
> -	regmap_raw_write(s->regmap, addr, s->buf, to_send);
> -	regcache_cache_bypass(s->regmap, false);
> +	regmap_noinc_write(s->regmap, addr, s->buf, to_send);
>  }
>  
>  static void sc16is7xx_port_update(struct uart_port *port, u8 reg,
> @@ -489,6 +485,11 @@ static bool sc16is7xx_regmap_precious(struct device *dev, unsigned int reg)
>  	return false;
>  }
>  
> +static bool sc16is7xx_regmap_noinc(struct device *dev, unsigned int reg)
> +{
> +	return reg == SC16IS7XX_RHR_REG;
> +}
> +
>  static int sc16is7xx_set_baud(struct uart_port *port, int baud)
>  {
>  	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
> @@ -1439,6 +1440,8 @@ static struct regmap_config regcfg = {
>  	.cache_type = REGCACHE_RBTREE,
>  	.volatile_reg = sc16is7xx_regmap_volatile,
>  	.precious_reg = sc16is7xx_regmap_precious,
> +	.writeable_noinc_reg = sc16is7xx_regmap_noinc,
> +	.readable_noinc_reg = sc16is7xx_regmap_noinc,
>  };
>  
>  #ifdef CONFIG_SERIAL_SC16IS7XX_SPI