Re: [PATCH 3/6] hwmon: (k10temp) Check return value of amd_smn_read()

[Guenter Roeck <linux@roeck-us.net>]

On Tue, May 16, 2023 at 03:24:27PM -0500, Yazen Ghannam wrote:
> Check the return value of amd_smn_read() before saving a value. This
> ensures invalid values aren't saved or used.
> 
> There are three cases here with slightly different behavior.
> 
> 1) read_tempreg_nb_zen():
> 	This is a function pointer which does not include a return code.
> 	In this case, set the register value to 0 on failure. This
> 	enforces Read-as-Zero behavior.
> 
> 2) k10temp_read_temp():
> 	This function does have return codes, so return -EINVAL on a
> 	failed register read. Continued operation is not necessary,
> 	since there is no valid data from the register. Furthermore, if
> 	the register value was set to 0, then the following operation
> 	would underflow.
> 
> 3) k10temp_get_ccd_support():
> 	This function reads the same register from multiple CCD
> 	instances in a loop. And a bitmask is formed if a specific bit
> 	is set in each register instance. The loop should continue on a
> 	failed register read, skipping the bit check.
> 
> Furthermore, the __must_check attribute will be added to amd_smn_read().
> Therefore, this change is required to avoid compile-time warnings.
> 
> Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
> Cc: stable@vger.kernel.org
> ---
>  drivers/hwmon/k10temp.c | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/hwmon/k10temp.c b/drivers/hwmon/k10temp.c
> index 7b177b9fbb09..6ea1fa62b7c1 100644
> --- a/drivers/hwmon/k10temp.c
> +++ b/drivers/hwmon/k10temp.c
> @@ -145,8 +145,9 @@ static void read_tempreg_nb_f15(struct pci_dev *pdev, u32 *regval)
>  
>  static void read_tempreg_nb_zen(struct pci_dev *pdev, u32 *regval)
>  {
> -	amd_smn_read(amd_pci_dev_to_node_id(pdev),
> -		     ZEN_REPORTED_TEMP_CTRL_BASE, regval);
> +	if (amd_smn_read(amd_pci_dev_to_node_id(pdev),
> +			 ZEN_REPORTED_TEMP_CTRL_BASE, regval))
> +		*regval = 0;
>  }
>  
>  static long get_raw_temp(struct k10temp_data *data)
> @@ -213,9 +214,11 @@ static int k10temp_read_temp(struct device *dev, u32 attr, int channel,
>  				*val = 0;
>  			break;
>  		case 2 ... 13:		/* Tccd{1-12} */
> -			amd_smn_read(amd_pci_dev_to_node_id(data->pdev),
> -				     ZEN_CCD_TEMP(data->ccd_offset, channel - 2),
> -						  &regval);
> +			if (amd_smn_read(amd_pci_dev_to_node_id(data->pdev),
> +					 ZEN_CCD_TEMP(data->ccd_offset, channel - 2),
> +					 &regval))
> +				return -EINVAL;
> +

-EINVAL: Invalid Argument, supposed to be used for bad user input.
I don't see how that would apply here. amd_smn_read() returns
a valid error code. This error core should be returned to the caller,
or there needs to be an explanation why this is not appropriate.

>  			*val = (regval & ZEN_CCD_TEMP_MASK) * 125 - 49000;
>  			break;
>  		default:
> @@ -373,8 +376,10 @@ static void k10temp_get_ccd_support(struct pci_dev *pdev,
>  	int i;
>  
>  	for (i = 0; i < limit; i++) {
> -		amd_smn_read(amd_pci_dev_to_node_id(pdev),
> -			     ZEN_CCD_TEMP(data->ccd_offset, i), &regval);
> +		if (amd_smn_read(amd_pci_dev_to_node_id(pdev),
> +				 ZEN_CCD_TEMP(data->ccd_offset, i), &regval))
> +			continue;
> +
The reason for ignoring the error should be explained here.

>  		if (regval & ZEN_CCD_TEMP_VALID)
>  			data->show_temp |= BIT(TCCD_BIT(i));
>  	}
> -- 
> 2.34.1
>