Date:   Wed, 21 Sep 2022 14:31:59 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Johnothan King <johnothanking@...tonmail.com>
Cc:     "Daniel J. Ogorchock" <djogorchock@...il.com>,
        Jiri Kosina <jikos@...nel.org>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] HID: nintendo: check analog user calibration for plausibility

On Wed, Sep 21, 2022 at 12:53 PM Johnothan King
<johnothanking@...tonmail.com> wrote:
>
> For my v4 patch I'll just change the check back to using >=. The
> signedness of the min, max and center values will probably need some
> sort of fix, but that's out of the scope of this patch.

Yeah, no worries. The signedness issue was more a FYI, in case you
ever need signed integers from that function. I hope we won't have the
case here and that we are actually having unsigned integers in the
data.

Cheers,
Benjamin

>
> - Johnothan King
>
> ------- Original Message -------
> On Wednesday, September 21st, 2022 at 1:34 AM, Benjamin Tissoires <benjamin.tissoires@...hat.com> wrote:
>
>
> > 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@...h.de
> > > Signed-off-by: Johnothan King johnothanking@...tonmail.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
>

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