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 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") 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