Re: [PATCH 2/7] soc: aspeed: lpc-snoop: Don't disable channels that aren't enabled

[Jean Delvare <jdelvare@suse.de>]

On Fri, 11 Apr 2025 10:38:32 +0930, Andrew Jeffery wrote:
> Mitigate e.g. the following:
> 
>     # echo 1e789080.lpc-snoop > /sys/bus/platform/drivers/aspeed-lpc-snoop/unbind
>     ...
>     [  120.363594] Unable to handle kernel NULL pointer dereference at virtual address 00000004 when write
>     [  120.373866] [00000004] *pgd=00000000
>     [  120.377910] Internal error: Oops: 805 [#1] SMP ARM
>     [  120.383306] CPU: 1 UID: 0 PID: 315 Comm: sh Not tainted 6.15.0-rc1-00009-g926217bc7d7d-dirty #20 NONE
>     ...
>     [  120.679543] Call trace:
>     [  120.679559]  misc_deregister from aspeed_lpc_snoop_remove+0x84/0xac
>     [  120.692462]  aspeed_lpc_snoop_remove from platform_remove+0x28/0x38
>     [  120.700996]  platform_remove from device_release_driver_internal+0x188/0x200
>     ...
> 
> Fixes: 9f4f9ae81d0a ("drivers/misc: add Aspeed LPC snoop driver")
> Cc: stable@vger.kernel.org
> Cc: Jean Delvare <jdelvare@suse.de>
> Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
> ---
>  drivers/soc/aspeed/aspeed-lpc-snoop.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/soc/aspeed/aspeed-lpc-snoop.c b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> index bfa770ec51a889260d11c26e675f3320bf710a54..e9d9a8e60a6f062c0b53c9c02e5d73768453998d 100644
> --- a/drivers/soc/aspeed/aspeed-lpc-snoop.c
> +++ b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> @@ -58,6 +58,7 @@ struct aspeed_lpc_snoop_model_data {
>  };
>  
>  struct aspeed_lpc_snoop_channel {
> +	bool enabled;
>  	struct kfifo		fifo;
>  	wait_queue_head_t	wq;
>  	struct miscdevice	miscdev;
> @@ -190,6 +191,9 @@ static int aspeed_lpc_enable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
>  	const struct aspeed_lpc_snoop_model_data *model_data =
>  		of_device_get_match_data(dev);
>  
> +	if (lpc_snoop->chan[channel].enabled)
> +		return -EBUSY;

This isn't supposed to happen, right? WARN_ON() may be appropriate.

> +
>  	init_waitqueue_head(&lpc_snoop->chan[channel].wq);
>  	/* Create FIFO datastructure */
>  	rc = kfifo_alloc(&lpc_snoop->chan[channel].fifo,
> @@ -236,6 +240,8 @@ static int aspeed_lpc_enable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
>  		regmap_update_bits(lpc_snoop->regmap, HICRB,
>  				hicrb_en, hicrb_en);
>  
> +	lpc_snoop->chan[channel].enabled = true;
> +
>  	return 0;
>  
>  err_misc_deregister:
> @@ -248,6 +254,9 @@ static int aspeed_lpc_enable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
>  static void aspeed_lpc_disable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
>  				     int channel)
>  {
> +	if (!lpc_snoop->chan[channel].enabled)
> +		return;
> +
>  	switch (channel) {
>  	case 0:
>  		regmap_update_bits(lpc_snoop->regmap, HICR5,
> @@ -263,6 +272,8 @@ static void aspeed_lpc_disable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
>  		return;
>  	}
>  
> +	lpc_snoop->chan[channel].enabled = false;
> +	/* Consider improving safety wrt concurrent reader(s) */
>  	misc_deregister(&lpc_snoop->chan[channel].miscdev);
>  	kfifo_free(&lpc_snoop->chan[channel].fifo);
>  }
> 

Acked-by: Jean Delvare <jdelvare@suse.de>

-- 
Jean Delvare
SUSE L3 Support