Re: [PATCH v3] HID: nintendo: check analog user calibration for plausibility

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

Hi Johnothan,

On Sep 21 2022, Johnothan King wrote:
> Arne Wendt writes:
>   Cheap clone controllers may (falsely) report as having a user
>   calibration for the analog sticks in place, but return
>   wrong/impossible values for the actual calibration data.
>   In the present case at mine, the controller reports having a
>   user calibration in place and successfully executes the read
>   commands. The reported user calibration however is
>   min = center = max = 0.
> 
>   This pull request addresses problems of this kind by checking the
>   provided user calibration-data for plausibility (min < center < max)
>   and falling back to the default values if implausible.
> 
> I'll note that I was experiencing a crash because of this bug when using
> the GuliKit KingKong 2 controller. The crash manifests as a divide by
> zero error in the kernel logs:
> kernel: divide error: 0000 [#1] PREEMPT SMP NOPTI
> 
> Changes in v2:
>  - Move the plausibility check to joycon_read_stick_calibration() and
>    have that function return -EINVAL if the check fails.
>  - In the plausibility check, change >= to ==. hid_field_extract() never
>    returns a negative value, so a scenario involving min > center or
>    center > max is impossible.

I am not so sure this is a great idea. I agree this is correct, but it
definitely requires some processing from my brain and double
verifications in the code that this is correct.

The problem is that all of the values are declared as s32.
hid_field_extract() returns a u32, yes, but I haven't checked the report
descriptor if that value can be a negative one. What needs to be done,
if the logical min value is negative is that we should call hid_snto32()
to convert into a proper s32 (I doubt you have to do it but I am putting
it here for completeness).

So basically, you are blindly converting a u32 into a s32 and do not
take rollover into account.

Given that this function is only called at probe time where timing is
not the biggest of our concerns, I would simply leave the more human
friendy with obvious failures cases with >= and <=.


Second note: please move all "Changes in v*" below the first '---' and
before the file stats. This way they will be stripped out when applying
the patch. People who want to see the changes can always follow the lore
link that should be applied to the commit when this patch gets applied.

>  - To reduce code duplication, move the code for setting default
>    calibration values into a single function called
>    joycon_use_default_calibration().
> 
> Changes in v3:
>  - Unbreak warning string to conform to coding style.
>  - Change joycon_use_default_calibration() to accept a struct hid_device
>    pointer instead of a struct joycon_ctlr pointer.
> 
> Link: https://github.com/nicman23/dkms-hid-nintendo/pull/25
> Link: https://github.com/DanielOgorchock/linux/issues/36
> Co-authored-by: Arne Wendt <arne.wendt@tuhh.de>
> Signed-off-by: Johnothan King <johnothanking@protonmail.com>
> ---
>  drivers/hid/hid-nintendo.c | 55 +++++++++++++++++++++-----------------
>  1 file changed, 30 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/hid/hid-nintendo.c b/drivers/hid/hid-nintendo.c
> index 6028af3c3aae..f25b7b19e9a4 100644
> --- a/drivers/hid/hid-nintendo.c
> +++ b/drivers/hid/hid-nintendo.c
> @@ -760,12 +760,31 @@ static int joycon_read_stick_calibration(struct joycon_ctlr *ctlr, u16 cal_addr,
>  	cal_y->max = cal_y->center + y_max_above;
>  	cal_y->min = cal_y->center - y_min_below;
>  
> -	return 0;
> +	/* check if values are plausible */
> +	if (cal_x->min == cal_x->center || cal_x->center == cal_x->max ||
> +	    cal_y->min == cal_y->center || cal_y->center == cal_y->max)
> +		ret = -EINVAL;
> +
> +	return ret;
>  }
>  
>  static const u16 DFLT_STICK_CAL_CEN = 2000;
>  static const u16 DFLT_STICK_CAL_MAX = 3500;
>  static const u16 DFLT_STICK_CAL_MIN = 500;
> +static void joycon_use_default_calibration(struct hid_device *hdev,
> +					   struct joycon_stick_cal *cal_x,
> +					   struct joycon_stick_cal *cal_y,
> +					   const char *stick, int ret)
> +{
> +	hid_warn(hdev,
> +		 "Failed to read %s stick cal, using defaults; e=%d\n", stick,
> +		 ret);

nitpick: why not putting the format string on the line above and leave
"stick" and "ret in the second line? It should be OK for checkpatch and
will be less weird to have "ret" on its line all by itself.

> +
> +	cal_x->center = cal_y->center = DFLT_STICK_CAL_CEN;
> +	cal_x->max = cal_y->max = DFLT_STICK_CAL_MAX;
> +	cal_x->min = cal_y->min = DFLT_STICK_CAL_MIN;
> +}
> +
>  static int joycon_request_calibration(struct joycon_ctlr *ctlr)
>  {
>  	u16 left_stick_addr = JC_CAL_FCT_DATA_LEFT_ADDR;
> @@ -793,38 +812,24 @@ static int joycon_request_calibration(struct joycon_ctlr *ctlr)
>  					    &ctlr->left_stick_cal_x,
>  					    &ctlr->left_stick_cal_y,
>  					    true);
> -	if (ret) {
> -		hid_warn(ctlr->hdev,
> -			 "Failed to read left stick cal, using dflts; e=%d\n",
> -			 ret);
> -
> -		ctlr->left_stick_cal_x.center = DFLT_STICK_CAL_CEN;
> -		ctlr->left_stick_cal_x.max = DFLT_STICK_CAL_MAX;
> -		ctlr->left_stick_cal_x.min = DFLT_STICK_CAL_MIN;
>  
> -		ctlr->left_stick_cal_y.center = DFLT_STICK_CAL_CEN;
> -		ctlr->left_stick_cal_y.max = DFLT_STICK_CAL_MAX;
> -		ctlr->left_stick_cal_y.min = DFLT_STICK_CAL_MIN;
> -	}
> +	if (ret)
> +		joycon_use_default_calibration(ctlr->hdev,
> +					       &ctlr->left_stick_cal_x,
> +					       &ctlr->left_stick_cal_y,
> +					       "left", ret);
>  
>  	/* read the right stick calibration data */
>  	ret = joycon_read_stick_calibration(ctlr, right_stick_addr,
>  					    &ctlr->right_stick_cal_x,
>  					    &ctlr->right_stick_cal_y,
>  					    false);
> -	if (ret) {
> -		hid_warn(ctlr->hdev,
> -			 "Failed to read right stick cal, using dflts; e=%d\n",
> -			 ret);
> -
> -		ctlr->right_stick_cal_x.center = DFLT_STICK_CAL_CEN;
> -		ctlr->right_stick_cal_x.max = DFLT_STICK_CAL_MAX;
> -		ctlr->right_stick_cal_x.min = DFLT_STICK_CAL_MIN;
>  
> -		ctlr->right_stick_cal_y.center = DFLT_STICK_CAL_CEN;
> -		ctlr->right_stick_cal_y.max = DFLT_STICK_CAL_MAX;
> -		ctlr->right_stick_cal_y.min = DFLT_STICK_CAL_MIN;
> -	}
> +	if (ret)
> +		joycon_use_default_calibration(ctlr->hdev,
> +					       &ctlr->right_stick_cal_x,
> +					       &ctlr->right_stick_cal_y,
> +					       "right", ret);
>  
>  	hid_dbg(ctlr->hdev, "calibration:\n"
>  			    "l_x_c=%d l_x_max=%d l_x_min=%d\n"
> -- 
> 2.37.3
> 
> 

Cheers,
Benjamin