1 // SPDX-License-Identifier: GPL-2.0 2 /* Copyright (c) 2024 Tatsuyuki Ishi 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_HOLTEK 0x04D9 11 #define PID_MD770 0x0339 12 #define RDESC_SIZE 203 13 14 HID_BPF_CONFIG( 15 HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_HOLTEK, PID_MD770) 16 ); 17 18 /* 19 * The Mistel MD770 keyboard reports the first 6 simultaneous key presses 20 * through the first interface, and anything beyond that through a second 21 * interface. Unfortunately, the second interface's report descriptor has an 22 * error, causing events to be malformed and ignored. This HID-BPF driver 23 * fixes the descriptor to allow NKRO to work again. 24 * 25 * For reference, this is the original report descriptor: 26 * 27 * 0x05, 0x01, // Usage Page (Generic Desktop) 0 28 * 0x09, 0x80, // Usage (System Control) 2 29 * 0xa1, 0x01, // Collection (Application) 4 30 * 0x85, 0x01, // Report ID (1) 6 31 * 0x19, 0x81, // Usage Minimum (129) 8 32 * 0x29, 0x83, // Usage Maximum (131) 10 33 * 0x15, 0x00, // Logical Minimum (0) 12 34 * 0x25, 0x01, // Logical Maximum (1) 14 35 * 0x95, 0x03, // Report Count (3) 16 36 * 0x75, 0x01, // Report Size (1) 18 37 * 0x81, 0x02, // Input (Data,Var,Abs) 20 38 * 0x95, 0x01, // Report Count (1) 22 39 * 0x75, 0x05, // Report Size (5) 24 40 * 0x81, 0x01, // Input (Cnst,Arr,Abs) 26 41 * 0xc0, // End Collection 28 42 * 0x05, 0x0c, // Usage Page (Consumer Devices) 29 43 * 0x09, 0x01, // Usage (Consumer Control) 31 44 * 0xa1, 0x01, // Collection (Application) 33 45 * 0x85, 0x02, // Report ID (2) 35 46 * 0x15, 0x00, // Logical Minimum (0) 37 47 * 0x25, 0x01, // Logical Maximum (1) 39 48 * 0x95, 0x12, // Report Count (18) 41 49 * 0x75, 0x01, // Report Size (1) 43 50 * 0x0a, 0x83, 0x01, // Usage (AL Consumer Control Config) 45 51 * 0x0a, 0x8a, 0x01, // Usage (AL Email Reader) 48 52 * 0x0a, 0x92, 0x01, // Usage (AL Calculator) 51 53 * 0x0a, 0x94, 0x01, // Usage (AL Local Machine Browser) 54 54 * 0x09, 0xcd, // Usage (Play/Pause) 57 55 * 0x09, 0xb7, // Usage (Stop) 59 56 * 0x09, 0xb6, // Usage (Scan Previous Track) 61 57 * 0x09, 0xb5, // Usage (Scan Next Track) 63 58 * 0x09, 0xe2, // Usage (Mute) 65 59 * 0x09, 0xea, // Usage (Volume Down) 67 60 * 0x09, 0xe9, // Usage (Volume Up) 69 61 * 0x0a, 0x21, 0x02, // Usage (AC Search) 71 62 * 0x0a, 0x23, 0x02, // Usage (AC Home) 74 63 * 0x0a, 0x24, 0x02, // Usage (AC Back) 77 64 * 0x0a, 0x25, 0x02, // Usage (AC Forward) 80 65 * 0x0a, 0x26, 0x02, // Usage (AC Stop) 83 66 * 0x0a, 0x27, 0x02, // Usage (AC Refresh) 86 67 * 0x0a, 0x2a, 0x02, // Usage (AC Bookmarks) 89 68 * 0x81, 0x02, // Input (Data,Var,Abs) 92 69 * 0x95, 0x01, // Report Count (1) 94 70 * 0x75, 0x0e, // Report Size (14) 96 71 * 0x81, 0x01, // Input (Cnst,Arr,Abs) 98 72 * 0xc0, // End Collection 100 73 * 0x05, 0x01, // Usage Page (Generic Desktop) 101 74 * 0x09, 0x02, // Usage (Mouse) 103 75 * 0xa1, 0x01, // Collection (Application) 105 76 * 0x09, 0x01, // Usage (Pointer) 107 77 * 0xa1, 0x00, // Collection (Physical) 109 78 * 0x85, 0x03, // Report ID (3) 111 79 * 0x05, 0x09, // Usage Page (Button) 113 80 * 0x19, 0x01, // Usage Minimum (1) 115 81 * 0x29, 0x08, // Usage Maximum (8) 117 82 * 0x15, 0x00, // Logical Minimum (0) 119 83 * 0x25, 0x01, // Logical Maximum (1) 121 84 * 0x75, 0x01, // Report Size (1) 123 85 * 0x95, 0x08, // Report Count (8) 125 86 * 0x81, 0x02, // Input (Data,Var,Abs) 127 87 * 0x05, 0x01, // Usage Page (Generic Desktop) 129 88 * 0x09, 0x30, // Usage (X) 131 89 * 0x09, 0x31, // Usage (Y) 133 90 * 0x16, 0x01, 0x80, // Logical Minimum (-32767) 135 91 * 0x26, 0xff, 0x7f, // Logical Maximum (32767) 138 92 * 0x75, 0x10, // Report Size (16) 141 93 * 0x95, 0x02, // Report Count (2) 143 94 * 0x81, 0x06, // Input (Data,Var,Rel) 145 95 * 0x09, 0x38, // Usage (Wheel) 147 96 * 0x15, 0x81, // Logical Minimum (-127) 149 97 * 0x25, 0x7f, // Logical Maximum (127) 151 98 * 0x75, 0x08, // Report Size (8) 153 99 * 0x95, 0x01, // Report Count (1) 155 100 * 0x81, 0x06, // Input (Data,Var,Rel) 157 101 * 0x05, 0x0c, // Usage Page (Consumer Devices) 159 102 * 0x0a, 0x38, 0x02, // Usage (AC Pan) 161 103 * 0x95, 0x01, // Report Count (1) 164 104 * 0x81, 0x06, // Input (Data,Var,Rel) 166 105 * 0xc0, // End Collection 168 106 * 0xc0, // End Collection 169 107 * 0x05, 0x01, // Usage Page (Generic Desktop) 170 108 * 0x09, 0x06, // Usage (Keyboard) 172 109 * 0xa1, 0x01, // Collection (Application) 174 110 * 0x85, 0x04, // Report ID (4) 176 111 * 0x05, 0x07, // Usage Page (Keyboard) 178 112 * 0x95, 0x01, // Report Count (1) 180 113 * 0x75, 0x08, // Report Size (8) 182 114 * 0x81, 0x03, // Input (Cnst,Var,Abs) 184 115 * 0x95, 0xe8, // Report Count (232) 186 116 * 0x75, 0x01, // Report Size (1) 188 117 * 0x15, 0x00, // Logical Minimum (0) 190 118 * 0x25, 0x01, // Logical Maximum (1) 192 119 * 0x05, 0x07, // Usage Page (Keyboard) 194 120 * 0x19, 0x00, // Usage Minimum (0) 196 121 * 0x29, 0xe7, // Usage Maximum (231) 198 122 * 0x81, 0x00, // Input (Data,Arr,Abs) 200 <- change to 0x81, 0x02 (Data,Var,Abs) 123 * 0xc0, // End Collection 202 124 */ 125 126 SEC(HID_BPF_RDESC_FIXUP) 127 int BPF_PROG(hid_rdesc_fixup_mistel_md770, struct hid_bpf_ctx *hctx) 128 { 129 __u8 *data = hid_bpf_get_data(hctx, 0, HID_MAX_DESCRIPTOR_SIZE); 130 131 if (!data) 132 return 0; /* EPERM check */ 133 134 if (data[201] == 0x00) 135 data[201] = 0x02; 136 137 return 0; 138 } 139 140 HID_BPF_OPS(mistel_md770) = { 141 .hid_rdesc_fixup = (void *)hid_rdesc_fixup_mistel_md770, 142 }; 143 144 SEC("syscall") 145 int probe(struct hid_bpf_probe_args *ctx) 146 { 147 ctx->retval = ctx->rdesc_size != RDESC_SIZE; 148 if (ctx->retval) 149 ctx->retval = -EINVAL; 150 151 return 0; 152 } 153 154 char _license[] SEC("license") = "GPL"; 155