From: Mark Kettenis <mark.kettenis@xs4all.nl>
Subject: Re: imt(4)/umt(4): finding HID report IDs
To: Ulf Brosziewski <ulf.brosziewski@t-online.de>
Cc: tech@openbsd.org
Date: Wed, 16 Jul 2025 00:07:22 +0200

> Date: Tue, 15 Jul 2025 23:08:29 +0200
> From: Ulf Brosziewski <ulf.brosziewski@t-online.de>
> 
> Anybody?

The same comment about "top-level usage" not being a thing in the spec
and being inconsistent with the existing comments applies here as well.

Otherwise this makes (some) sense to me.

> On 7/2/25 01:37, Ulf Brosziewski wrote:
> > The way imt(4) and umt(4) search for report IDs is broken.  Depending
> > on the structure and distribution of IDs in a report descriptor, it might
> > succeed, or fail with wrong ID values (as has been reported by Thomas
> > Dettbarn, see https://marc.info/?l=openbsd-tech&m=174841257723328&w=2 ).
> > 
> > The hid_*_collection functions only provide partial information, which,
> > in isolation, may be useless if you aren't lucky and deal with simple,
> > uniform descriptors.
> > 
> > The patch adds another helper function to hid.c, which permits searching
> > for several report items at once, and filters out "unknown" collections
> > (see the comment in the diff).  It doesn't put further constraints on the
> > search and the structure of the descriptor, but the heuristic might be
> > safe enough for most practical purposes.  However, my experience with the
> > real HID world is limited, comments and hints would be appreciated.
> > 
> > The patch moves the search for "PTP" reports to hidmt, and adapts imt
> > and umt accordingly.  Please note that it also contains a fix for another
> > bug in hidmt (see https://marc.info/?l=openbsd-tech&m=175101436027656&w=2 ).
> > It may be hidden by the faulty report search; that's why for tests, it
> > makes sense to combine the patches.
> > 
> > Tests, comments, and OKs would be welcome.
> > 
> > 
> > Index: dev/hid/hid.c
> > ===================================================================
> > RCS file: /cvs/src/sys/dev/hid/hid.c,v
> > retrieving revision 1.7
> > diff -u -p -r1.7 hid.c
> > --- dev/hid/hid.c	10 May 2024 10:49:10 -0000	1.7
> > +++ dev/hid/hid.c	1 Jul 2025 20:11:57 -0000
> > @@ -706,3 +706,70 @@ hid_get_id_of_collection(const void *des
> >  	hid_end_parse(hd);
> >  	return -1;
> >  }
> > +
> > +/*
> > + * Find the first report that contains each of the given "usages"
> > + * and belongs to a top-level collection with the 'top_usage' type.
> > + * The size of the 'usages' array must be in the range [1..32].
> > + *
> > + * If 'coll_usages' is NULL, the search will skip collections with
> > + * usages from vendor pages (0xFF00 - 0xFFFF).
> > + *
> > + * If 'coll_usages' is non-NULL, it must point to a 0-terminated
> > + * sequence of collection usages, and the search will skip collections
> > + * with usages not present in this set. (It isn't necessary to include
> > + * the top-level usage here).
> > + *
> > + * Return Values:
> > + *     -1:		No match
> > + *     0:		Success (single report without an ID)
> > + *     [1..255]:	Report ID
> > + */
> > +int
> > +hid_find_report(const void *desc, int len, enum hid_kind kind,
> > +    int32_t top_usage, int n_usages, int32_t *usages, int32_t *coll_usages)
> > +{
> > +	struct hid_data *hd;
> > +	struct hid_item h;
> > +	uint32_t matches;
> > +	int i, cur_id, skip;
> > +
> > +	hd = hid_start_parse(desc, len, hid_all);
> > +	for (cur_id = -1, skip = 0;  hid_get_item(hd, &h); ) {
> > +		if (cur_id != h.report_ID) {
> > +			matches = 0;
> > +			cur_id = h.report_ID;
> > +		}
> > +		if (h.kind == hid_collection) {
> > +			if (skip)
> > +				continue;
> > +			if (h.collevel == 1) {
> > +			       if (h.usage != top_usage)
> > +					skip = 1;
> > +			} else if (coll_usages != NULL) {
> > +				for (i = 0; coll_usages[i] != h.usage; i++)
> > +					if (coll_usages[i] == 0) {
> > +						skip = h.collevel;
> > +						break;
> > +					}
> > +			} else if (((h.usage >> 16) & 0xffff) >= 0xff00) {
> > +				skip = h.collevel;
> > +			}
> > +		} else if (h.kind == hid_endcollection) {
> > +			if (h.collevel < skip)
> > +				skip = 0;
> > +		}
> > +		if (h.kind != kind || skip)
> > +			continue;
> > +		for (i = 0; i < n_usages; i++)
> > +			if (h.usage == usages[i] && !(matches & (1 << i))) {
> > +				matches |= (1 << i);
> > +				if (matches != (1 << n_usages) - 1)
> > +					break;
> > +				hid_end_parse(hd);
> > +				return (h.report_ID);
> > +			}
> > +	}
> > +	hid_end_parse(hd);
> > +	return (-1);
> > +}
> > Index: dev/hid/hid.h
> > ===================================================================
> > RCS file: /cvs/src/sys/dev/hid/hid.h,v
> > retrieving revision 1.11
> > diff -u -p -r1.11 hid.h
> > --- dev/hid/hid.h	12 Aug 2023 20:47:06 -0000	1.11
> > +++ dev/hid/hid.h	1 Jul 2025 20:11:57 -0000
> > @@ -95,6 +95,8 @@ uint32_t hid_get_udata(const uint8_t *bu
> >  int	hid_is_collection(const void *, int, uint8_t, int32_t);
> >  struct hid_data *hid_get_collection_data(const void *, int, int32_t, uint32_t);
> >  int	hid_get_id_of_collection(const void *, int, int32_t, uint32_t);
> > +int	hid_find_report(const void *, int len, enum hid_kind, int32_t,
> > +	    int, int32_t *, int32_t *);
> > 
> >  #endif /* _KERNEL */
> > 
> > Index: dev/hid/hidmt.c
> > ===================================================================
> > RCS file: /cvs/src/sys/dev/hid/hidmt.c,v
> > retrieving revision 1.13
> > diff -u -p -r1.13 hidmt.c
> > --- dev/hid/hidmt.c	16 Oct 2022 20:17:08 -0000	1.13
> > +++ dev/hid/hidmt.c	1 Jul 2025 20:11:57 -0000
> > @@ -42,6 +42,9 @@
> >  #define DPRINTF(x)
> >  #endif
> > 
> > +#define IS_TOP_LEVEL_USAGE(u) ((((u) >> 16) & 0xffff) == HUP_BUTTON || \
> > +    (u) == HID_USAGE2(HUP_DIGITIZERS, HUD_CONTACTCOUNT))
> > +
> >  #define HID_UNIT_CM	0x11
> >  #define HID_UNIT_INCH	0x13
> > 
> > @@ -373,7 +376,7 @@ hidmt_input(struct hidmt *mt, uint8_t *d
> > 
> >  			bzero(&hc, sizeof(struct hidmt_contact));
> >  		}
> > -		else if (!firstu)
> > +		else if (!firstu && !IS_TOP_LEVEL_USAGE(hi->usage))
> >  			firstu = hi->usage;
> > 
> >  		switch (hi->usage) {
> > @@ -530,4 +533,41 @@ void
> >  hidmt_disable(struct hidmt *mt)
> >  {
> >  	mt->sc_enabled = 0;
> > +}
> > +
> > +int
> > +hidmt_find_winptp_reports(const void *desc, int len, int *input_rid,
> > +    int *config_rid, int *cap_rid)
> > +{
> > +	static int32_t ptp_collections[] = {
> > +		HID_USAGE2(HUP_DIGITIZERS, HUD_FINGER), 0
> > +	};
> > +	static int32_t input_usages[] = {
> > +		/* top-level */
> > +		HID_USAGE2(HUP_DIGITIZERS, HUD_CONTACTCOUNT),
> > +		/* contact-level */
> > +		HID_USAGE2(HUP_GENERIC_DESKTOP, HUG_X),
> > +		HID_USAGE2(HUP_GENERIC_DESKTOP, HUG_Y),
> > +		HID_USAGE2(HUP_DIGITIZERS, HUD_CONFIDENCE),
> > +		HID_USAGE2(HUP_DIGITIZERS, HUD_TIP_SWITCH),
> > +		HID_USAGE2(HUP_DIGITIZERS, HUD_CONTACTID),
> > +	};
> > +	static int32_t cfg_usages[] = {
> > +		HID_USAGE2(HUP_DIGITIZERS, HUD_INPUT_MODE),
> > +	};
> > +	static int32_t cap_usages[] = {
> > +		HID_USAGE2(HUP_DIGITIZERS, HUD_CONTACT_MAX),
> > +	};
> > +
> > +	*input_rid = hid_find_report(desc, len, hid_input,
> > +	    HID_USAGE2(HUP_DIGITIZERS, HUD_TOUCHPAD),
> > +	    nitems(input_usages), input_usages, ptp_collections);
> > +	*config_rid = hid_find_report(desc, len, hid_feature,
> > +	    HID_USAGE2(HUP_DIGITIZERS, HUD_CONFIG),
> > +	    nitems(cfg_usages), cfg_usages, ptp_collections);
> > +	*cap_rid = hid_find_report(desc, len, hid_feature,
> > +	    HID_USAGE2(HUP_DIGITIZERS, HUD_TOUCHPAD),
> > +	    nitems(cap_usages), cap_usages, ptp_collections);
> > +
> > +	return (*input_rid > 0 && *config_rid > 0 && *cap_rid > 0);
> >  }
> > Index: dev/hid/hidmtvar.h
> > ===================================================================
> > RCS file: /cvs/src/sys/dev/hid/hidmtvar.h,v
> > retrieving revision 1.8
> > diff -u -p -r1.8 hidmtvar.h
> > --- dev/hid/hidmtvar.h	8 Nov 2019 01:20:22 -0000	1.8
> > +++ dev/hid/hidmtvar.h	1 Jul 2025 20:11:57 -0000
> > @@ -77,3 +77,4 @@ int	hidmt_enable(struct hidmt *);
> >  void	hidmt_input(struct hidmt *, uint8_t *, u_int);
> >  int	hidmt_ioctl(struct hidmt *, u_long, caddr_t, int, struct proc *);
> >  int	hidmt_setup(struct device *, struct hidmt *, void *, int);
> > +int	hidmt_find_winptp_reports(const void *, int, int *, int *, int *);
> > Index: dev/i2c/imt.c
> > ===================================================================
> > RCS file: /cvs/src/sys/dev/i2c/imt.c,v
> > retrieving revision 1.6
> > diff -u -p -r1.6 imt.c
> > --- dev/i2c/imt.c	13 May 2024 01:15:50 -0000	1.6
> > +++ dev/i2c/imt.c	1 Jul 2025 20:11:57 -0000
> > @@ -56,8 +56,6 @@ const struct wsmouse_accessops imt_acces
> >  };
> > 
> >  int	imt_match(struct device *, void *, void *);
> > -int	imt_find_winptp_reports(struct ihidev_softc *, void *, int,
> > -	    struct imt_softc *);
> >  void	imt_attach(struct device *, struct device *, void *);
> >  int	imt_hidev_get_report(struct device *, int, int, void *, int);
> >  int	imt_hidev_set_report(struct device *, int, int, void *, int);
> > @@ -78,16 +76,17 @@ int
> >  imt_match(struct device *parent, void *match, void *aux)
> >  {
> >  	struct ihidev_attach_arg *iha = (struct ihidev_attach_arg *)aux;
> > -	struct imt_softc sc;
> > +	int input_rid, conf_rid, cap_rid;
> >  	int size;
> >  	void *desc;
> > 
> >  	if (iha->reportid == IHIDEV_CLAIM_MULTIPLEID) {
> >  		ihidev_get_report_desc(iha->parent, &desc, &size);
> > -		if (imt_find_winptp_reports(iha->parent, desc, size, &sc)) {
> > -			iha->claims[0] = sc.sc_rep_input;
> > -			iha->claims[1] = sc.sc_rep_config;
> > -			iha->claims[2] = sc.sc_rep_cap;
> > +		if (hidmt_find_winptp_reports(desc, size,
> > +		    &input_rid, &conf_rid, &cap_rid)) {
> > +			iha->claims[0] = input_rid;
> > +			iha->claims[1] = conf_rid;
> > +			iha->claims[2] = cap_rid;
> >  			iha->nclaims = 3;
> >  			return (IMATCH_DEVCLASS_DEVSUBCLASS);
> >  		}
> > @@ -96,49 +95,6 @@ imt_match(struct device *parent, void *m
> >  	return (IMATCH_NONE);
> >  }
> > 
> > -int
> > -imt_find_winptp_reports(struct ihidev_softc *parent, void *desc, int size,
> > -    struct imt_softc *sc)
> > -{
> > -	int repid;
> > -	int input = 0, conf = 0, cap = 0;
> > -
> > -	if (sc != NULL) {
> > -		sc->sc_rep_input = -1;
> > -		sc->sc_rep_config = -1;
> > -		sc->sc_rep_cap = -1;
> > -	}
> > -
> > -	for (repid = 0; repid < parent->sc_nrepid; repid++) {
> > -		if (hid_report_size(desc, size, hid_input, repid) == 0 &&
> > -		    hid_report_size(desc, size, hid_output, repid) == 0 &&
> > -		    hid_report_size(desc, size, hid_feature, repid) == 0)
> > -			continue;
> > -
> > -		if (hid_is_collection(desc, size, repid,
> > -		    HID_USAGE2(HUP_DIGITIZERS, HUD_TOUCHPAD))) {
> > -			input = 1;
> > -			if (sc != NULL && sc->sc_rep_input == -1)
> > -				sc->sc_rep_input = repid;
> > -		} else if (hid_is_collection(desc, size, repid,
> > -		    HID_USAGE2(HUP_DIGITIZERS, HUD_CONFIG))) {
> > -			conf = 1;
> > -			if (sc != NULL && sc->sc_rep_config == -1)
> > -				sc->sc_rep_config = repid;
> > -		}
> > -
> > -		/* capabilities report could be anywhere */
> > -		if (hid_locate(desc, size, HID_USAGE2(HUP_DIGITIZERS,
> > -		    HUD_CONTACT_MAX), repid, hid_feature, NULL, NULL)) {
> > -			cap = 1;
> > -			if (sc != NULL && sc->sc_rep_cap == -1)
> > -				sc->sc_rep_cap = repid;
> > -		}
> > -	}
> > -
> > -	return (conf && input && cap);
> > -}
> > -
> >  void
> >  imt_attach(struct device *parent, struct device *self, void *aux)
> >  {
> > @@ -152,7 +108,8 @@ imt_attach(struct device *parent, struct
> >  	sc->sc_hdev.sc_parent = iha->parent;
> > 
> >  	ihidev_get_report_desc(iha->parent, &desc, &size);
> > -	imt_find_winptp_reports(iha->parent, desc, size, sc);
> > +	hidmt_find_winptp_reports(desc, size, &sc->sc_rep_input,
> > +	    &sc->sc_rep_config, &sc->sc_rep_cap);
> > 
> >  	memset(mt, 0, sizeof(sc->sc_mt));
> > 
> > Index: dev/usb/umt.c
> > ===================================================================
> > RCS file: /cvs/src/sys/dev/usb/umt.c,v
> > retrieving revision 1.8
> > diff -u -p -r1.8 umt.c
> > --- dev/usb/umt.c	26 May 2024 20:06:27 -0000	1.8
> > +++ dev/usb/umt.c	1 Jul 2025 20:11:57 -0000
> > @@ -60,8 +60,6 @@ const struct wsmouse_accessops umt_acces
> >  };
> > 
> >  int	umt_match(struct device *, void *, void *);
> > -int	umt_find_winptp_reports(struct uhidev_softc *, void *, int, int *,
> > -	    int *, int *);
> >  void	umt_attach(struct device *, struct device *, void *);
> >  int	umt_hidev_get_report(struct device *, int, int, void *, int);
> >  int	umt_hidev_set_report(struct device *, int, int, void *, int);
> > @@ -88,7 +86,7 @@ umt_match(struct device *parent, void *m
> > 
> >  	if (UHIDEV_CLAIM_MULTIPLE_REPORTID(uha)) {
> >  		uhidev_get_report_desc(uha->parent, &desc, &size);
> > -		if (umt_find_winptp_reports(uha->parent, desc, size, &input,
> > +		if (hidmt_find_winptp_reports(desc, size, &input,
> >  		    &conf, &cap)) {
> >  			uha->claimed[input] = 1;
> >  			uha->claimed[conf] = 1;
> > @@ -100,50 +98,6 @@ umt_match(struct device *parent, void *m
> >  	return (UMATCH_NONE);
> >  }
> > 
> > -int
> > -umt_find_winptp_reports(struct uhidev_softc *parent, void *desc, int size,
> > -    int *input, int *config, int *cap)
> > -{
> > -	int repid;
> > -	int finput = 0, fconf = 0, fcap = 0;
> > -
> > -	if (input != NULL)
> > -		*input = -1;
> > -	if (config != NULL)
> > -		*config = -1;
> > -	if (cap != NULL)
> > -		*cap = -1;
> > -
> > -	for (repid = 0; repid < parent->sc_nrepid; repid++) {
> > -		if (hid_report_size(desc, size, hid_input, repid) == 0 &&
> > -		    hid_report_size(desc, size, hid_output, repid) == 0 &&
> > -		    hid_report_size(desc, size, hid_feature, repid) == 0)
> > -			continue;
> > -
> > -		if (hid_is_collection(desc, size, repid,
> > -		    HID_USAGE2(HUP_DIGITIZERS, HUD_TOUCHPAD))) {
> > -			finput = 1;
> > -			if (input != NULL && *input == -1)
> > -				*input = repid;
> > -		} else if (hid_is_collection(desc, size, repid,
> > -		    HID_USAGE2(HUP_DIGITIZERS, HUD_CONFIG))) {
> > -			fconf = 1;
> > -			if (config != NULL && *config == -1)
> > -				*config = repid;
> > -		}
> > -
> > -		/* capabilities report could be anywhere */
> > -		if (hid_locate(desc, size, HID_USAGE2(HUP_DIGITIZERS,
> > -		    HUD_CONTACT_MAX), repid, hid_feature, NULL, NULL)) {
> > -			fcap = 1;
> > -			if (cap != NULL && *cap == -1)
> > -				*cap = repid;
> > -		}
> > -	}
> > -
> > -	return (fconf && finput && fcap);
> > -}
> > -
> >  void
> >  umt_attach(struct device *parent, struct device *self, void *aux)
> >  {
> > @@ -163,7 +117,7 @@ umt_attach(struct device *parent, struct
> >  	sc->sc_quirks = usbd_get_quirks(sc->sc_hdev.sc_udev)->uq_flags;
> > 
> >  	uhidev_get_report_desc(uha->parent, &desc, &size);
> > -	umt_find_winptp_reports(uha->parent, desc, size, &sc->sc_rep_input,
> > +	hidmt_find_winptp_reports(desc, size, &sc->sc_rep_input,
> >  	    &sc->sc_rep_config, &sc->sc_rep_cap);
> > 
> >  	memset(mt, 0, sizeof(sc->sc_mt));
> > 
> 
>