Logitech__SpaceNavigator.bpf.c

// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2025 Curran Muhlberger
 */

#include "vmlinux.h"
#include "hid_bpf.h"
#include "hid_bpf_helpers.h"
#include <bpf/bpf_tracing.h>

#define VID_LOGITECH 0x046D
#define PID_SPACENAVIGATOR 0xC626

HID_BPF_CONFIG(
	HID_DEVICE(BUS_USB, HID_GROUP_ANY, VID_LOGITECH, PID_SPACENAVIGATOR)
);

/*
 * The 3Dconnexion SpaceNavigator 3D Mouse is a multi-axis controller with 6
 * axes (grouped as X,Y,Z and Rx,Ry,Rz).  Axis data is absolute, but the report
 * descriptor erroneously declares it to be relative.  We fix the report
 * descriptor to mark both axis collections as absolute.
 *
 * The kernel attempted to fix this in commit 24985cf68612 (HID: support
 * Logitech/3DConnexion SpaceTraveler and SpaceNavigator), but the descriptor
 * data offsets are incorrect for at least some SpaceNavigator units.
 */

SEC(HID_BPF_RDESC_FIXUP)
int BPF_PROG(hid_fix_rdesc, struct hid_bpf_ctx *hctx)
{
	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */);

	if (!data)
		return 0; /* EPERM check */

	/* Offset of Input item in X,Y,Z and Rx,Ry,Rz collections for all known
	 * firmware variants.
	 * - 2009 model: X,Y,Z @ 32-33, Rx,Ry,Rz @ 49-50 (fixup originally
	 *   applied in kernel)
	 * - 2016 model (size==228): X,Y,Z @ 36-37, Rx,Ry,Rz @ 53-54
	 *
	 * The descriptor size of the 2009 model is not known, and there is evidence
	 * for at least two other variants (with sizes 202 & 217) besides the 2016
	 * model, so we try all known offsets regardless of descriptor size.
	 */
	const u8 offsets[] = {32, 36, 49, 53};

	for (size_t idx = 0; idx < ARRAY_SIZE(offsets); idx++) {
		u8 offset = offsets[idx];

		/* if Input (Data,Var,Rel) , make it Input (Data,Var,Abs) */
		if (data[offset] == 0x81 && data[offset + 1] == 0x06)
			data[offset + 1] = 0x02;
	}

	return 0;
}

HID_BPF_OPS(logitech_spacenavigator) = {
	.hid_rdesc_fixup = (void *)hid_fix_rdesc,
};

SEC("syscall")
int probe(struct hid_bpf_probe_args *ctx)
{
	/* Ensure report descriptor size matches one of the known variants. */
	if (ctx->rdesc_size != 202 &&
	    ctx->rdesc_size != 217 &&
	    ctx->rdesc_size != 228) {
		ctx->retval = -EINVAL;
		return 0;
	}

	/* Check whether the kernel has already applied the fix. */
	if ((ctx->rdesc[32] == 0x81 && ctx->rdesc[33] == 0x02 &&
	     ctx->rdesc[49] == 0x81 && ctx->rdesc[50] == 0x02) ||
	    (ctx->rdesc[36] == 0x81 && ctx->rdesc[37] == 0x02 &&
	     ctx->rdesc[53] == 0x81 && ctx->rdesc[54] == 0x02))
		ctx->retval = -EINVAL;
	else
		ctx->retval = 0;

	return 0;
}

char _license[] SEC("license") = "GPL";