1 // SPDX-License-Identifier: GPL-2.0-only
2 /* Copyright (c) 2024 Kumar Swarnam Iyer (kumar.s.iyer65@gmail.com)
3 */
4
5 #include "vmlinux.h"
6 #include "hid_bpf.h"
7 #include "hid_bpf_helpers.h"
8 #include <bpf/bpf_tracing.h>
9
10 #define VID_THRUSTMASTER 0x044F
11 #define PID_TCA_YOKE_BOEING 0x0409
12
13 HID_BPF_CONFIG(
14 HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_THRUSTMASTER, PID_TCA_YOKE_BOEING)
15 );
16
17 /* The original HID descriptor of the Thrustmaster TCA Yoke Boeing joystick contains
18 * an Input field that shows up as an axis, ABS_MISC in Linux. But it is not possible
19 * to assign an actual physical control to this axis as they're all taken up. There
20 * are 2 vendor-defined inputs where the Input type appears to be defined wrongly.
21 * This bpf attempts to fix this by changing the Inputs so that it doesn't show up in
22 * Linux at all.
23 * This version is the short version fix that only changes 2 fields in the descriptor
24 * instead of the whole report descriptor.
25 * For reference, this is the original report descriptor:
26 *
27 * 0x05, 0x01, // Usage Page (Generic Desktop) 0
28 * 0x09, 0x04, // Usage (Joystick) 2
29 * 0xa1, 0x01, // Collection (Application) 4
30 * 0x85, 0x01, // Report ID (1) 6
31 * 0x09, 0x39, // Usage (Hat switch) 8
32 * 0x15, 0x00, // Logical Minimum (0) 10
33 * 0x25, 0x07, // Logical Maximum (7) 12
34 * 0x35, 0x00, // Physical Minimum (0) 14
35 * 0x46, 0x3b, 0x01, // Physical Maximum (315) 16
36 * 0x65, 0x14, // Unit (EnglishRotation: deg) 19
37 * 0x75, 0x04, // Report Size (4) 21
38 * 0x95, 0x01, // Report Count (1) 23
39 * 0x81, 0x42, // Input (Data,Var,Abs,Null) 25
40 * 0x65, 0x00, // Unit (None) 27
41 * 0x05, 0x09, // Usage Page (Button) 29
42 * 0x19, 0x01, // Usage Minimum (1) 31
43 * 0x29, 0x12, // Usage Maximum (18) 33
44 * 0x15, 0x00, // Logical Minimum (0) 35
45 * 0x25, 0x01, // Logical Maximum (1) 37
46 * 0x75, 0x01, // Report Size (1) 39
47 * 0x95, 0x12, // Report Count (18) 41
48 * 0x81, 0x02, // Input (Data,Var,Abs) 43
49 * 0x95, 0x02, // Report Count (2) 45
50 * 0x81, 0x03, // Input (Cnst,Var,Abs) 47
51 * 0x05, 0x01, // Usage Page (Generic Desktop) 49
52 * 0x09, 0x31, // Usage (Y) 51
53 * 0x09, 0x30, // Usage (X) 53
54 * 0x09, 0x32, // Usage (Z) 55
55 * 0x09, 0x34, // Usage (Ry) 57
56 * 0x09, 0x33, // Usage (Rx) 59
57 * 0x09, 0x35, // Usage (Rz) 61
58 * 0x15, 0x00, // Logical Minimum (0) 63
59 * 0x27, 0xff, 0xff, 0x00, 0x00, // Logical Maximum (65535) 65
60 * 0x75, 0x10, // Report Size (16) 70
61 * 0x95, 0x06, // Report Count (6) 72
62 * 0x81, 0x02, // Input (Data,Var,Abs) 74
63 * 0x06, 0xf0, 0xff, // Usage Page (Vendor Usage Page 0xfff0) 76
64 * 0x09, 0x59, // Usage (Vendor Usage 0x59) 79
65 * 0x15, 0x00, // Logical Minimum (0) 81
66 * 0x26, 0xff, 0x00, // Logical Maximum (255) 83
67 * 0x75, 0x08, // Report Size (8) 86
68 * 0x95, 0x01, // Report Count (1) 88
69 * 0x81, 0x02, // Input (Data,Var,Abs) 90 --> Needs to be changed
70 * 0x09, 0x51, // Usage (Vendor Usage 0x51) 92
71 * 0x15, 0x00, // Logical Minimum (0) 94
72 * 0x26, 0xff, 0x00, // Logical Maximum (255) 96
73 * 0x75, 0x08, // Report Size (8) 99
74 * 0x95, 0x20, // Report Count (32) 101 --> Needs to be changed
75 * 0x81, 0x02, // Input (Data,Var,Abs) 103
76 * 0x09, 0x50, // Usage (Vendor Usage 0x50) 105
77 * 0x15, 0x00, // Logical Minimum (0) 107
78 * 0x26, 0xff, 0x00, // Logical Maximum (255) 109
79 * 0x75, 0x08, // Report Size (8) 112
80 * 0x95, 0x0f, // Report Count (15) 114
81 * 0x81, 0x03, // Input (Cnst,Var,Abs) 116
82 * 0x09, 0x47, // Usage (Vendor Usage 0x47) 118
83 * 0x85, 0xf2, // Report ID (242) 120
84 * 0x15, 0x00, // Logical Minimum (0) 122
85 * 0x26, 0xff, 0x00, // Logical Maximum (255) 124
86 * 0x75, 0x08, // Report Size (8) 127
87 * 0x95, 0x3f, // Report Count (63) 129
88 * 0xb1, 0x02, // Feature (Data,Var,Abs) 131
89 * 0x09, 0x48, // Usage (Vendor Usage 0x48) 133
90 * 0x85, 0xf3, // Report ID (243) 135
91 * 0x15, 0x00, // Logical Minimum (0) 137
92 * 0x26, 0xff, 0x00, // Logical Maximum (255) 139
93 * 0x75, 0x08, // Report Size (8) 142
94 * 0x95, 0x3f, // Report Count (63) 144
95 * 0xb1, 0x02, // Feature (Data,Var,Abs) 146
96 * 0xc0, // End Collection 148
97 */
98
SEC(HID_BPF_RDESC_FIXUP)99 SEC(HID_BPF_RDESC_FIXUP)
100 int BPF_PROG(hid_fix_rdesc_tca_yoke, struct hid_bpf_ctx *hctx)
101 {
102 const int expected_length = 148;
103
104 if (hctx->size != expected_length)
105 return 0;
106
107 __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, HID_MAX_DESCRIPTOR_SIZE /* size */);
108
109 if (!data)
110 return 0; /* EPERM */
111
112 /* Safety check, our probe() should take care of this though */
113 if (data[1] != 0x01 /* Generic Desktop */ || data[3] != 0x04 /* Joystick */)
114 return 0;
115
116 /* The report descriptor sets incorrect Input items in 2 places, resulting in a
117 * non-existing axis showing up.
118 * This change sets the correct Input which prevents the axis from showing up in Linux.
119 */
120
121 if (data[90] == 0x81 && /* Input */
122 data[103] == 0x81) { /* Input */
123 data[91] = 0x03; /* Input set to 0x03 Constant, Variable Absolute */
124 data[104] = 0x03; /* Input set to 0X03 Constant, Variable Absolute */
125 }
126
127 return 0;
128 }
129
130 HID_BPF_OPS(tca_yoke) = {
131 .hid_rdesc_fixup = (void *)hid_fix_rdesc_tca_yoke,
132 };
133
134 SEC("syscall")
probe(struct hid_bpf_probe_args * ctx)135 int probe(struct hid_bpf_probe_args *ctx)
136 {
137 /* ensure the kernel isn't fixed already */
138 if (ctx->rdesc[91] != 0x02) /* Input for 0x59 Usage type has changed */
139 ctx->retval = -EINVAL;
140
141 return 0;
142 }
143
144 char _license[] SEC("license") = "GPL";
145