1// SPDX-License-Identifier: GPL-2.0
  2
  3#include "vmlinux.h"
  4#include <bpf/bpf_helpers.h>
  5#include <bpf/bpf_tracing.h>
  6#include "hid_bpf_helpers.h"
  7
  8SEC("fmod_ret/hid_bpf_device_event")
  9int BPF_PROG(hid_y_event, struct hid_bpf_ctx *hctx)
 10{
 11	s16 y;
 12	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 9 /* size */);
 13
 14	if (!data)
 15		return 0; /* EPERM check */
 16
 17	bpf_printk("event: size: %d", hctx->size);
 18	bpf_printk("incoming event: %02x %02x %02x",
 19		   data[0],
 20		   data[1],
 21		   data[2]);
 22	bpf_printk("                %02x %02x %02x",
 23		   data[3],
 24		   data[4],
 25		   data[5]);
 26	bpf_printk("                %02x %02x %02x",
 27		   data[6],
 28		   data[7],
 29		   data[8]);
 30
 31	y = data[3] | (data[4] << 8);
 32
 33	y = -y;
 34
 35	data[3] = y & 0xFF;
 36	data[4] = (y >> 8) & 0xFF;
 37
 38	bpf_printk("modified event: %02x %02x %02x",
 39		   data[0],
 40		   data[1],
 41		   data[2]);
 42	bpf_printk("                %02x %02x %02x",
 43		   data[3],
 44		   data[4],
 45		   data[5]);
 46	bpf_printk("                %02x %02x %02x",
 47		   data[6],
 48		   data[7],
 49		   data[8]);
 50
 51	return 0;
 52}
 53
 54SEC("fmod_ret/hid_bpf_device_event")
 55int BPF_PROG(hid_x_event, struct hid_bpf_ctx *hctx)
 56{
 57	s16 x;
 58	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 9 /* size */);
 59
 60	if (!data)
 61		return 0; /* EPERM check */
 62
 63	x = data[1] | (data[2] << 8);
 64
 65	x = -x;
 66
 67	data[1] = x & 0xFF;
 68	data[2] = (x >> 8) & 0xFF;
 69	return 0;
 70}
 71
 72SEC("fmod_ret/hid_bpf_rdesc_fixup")
 73int BPF_PROG(hid_rdesc_fixup, struct hid_bpf_ctx *hctx)
 74{
 75	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */);
 76
 77	if (!data)
 78		return 0; /* EPERM check */
 79
 80	bpf_printk("rdesc: %02x %02x %02x",
 81		   data[0],
 82		   data[1],
 83		   data[2]);
 84	bpf_printk("       %02x %02x %02x",
 85		   data[3],
 86		   data[4],
 87		   data[5]);
 88	bpf_printk("       %02x %02x %02x ...",
 89		   data[6],
 90		   data[7],
 91		   data[8]);
 92
 93	/*
 94	 * The original report descriptor contains:
 95	 *
 96	 * 0x05, 0x01,                    //   Usage Page (Generic Desktop)      30
 97	 * 0x16, 0x01, 0x80,              //   Logical Minimum (-32767)          32
 98	 * 0x26, 0xff, 0x7f,              //   Logical Maximum (32767)           35
 99	 * 0x09, 0x30,                    //   Usage (X)                         38
100	 * 0x09, 0x31,                    //   Usage (Y)                         40
101	 *
102	 * So byte 39 contains Usage X and byte 41 Usage Y.
103	 *
104	 * We simply swap the axes here.
105	 */
106	data[39] = 0x31;
107	data[41] = 0x30;
108
109	return 0;
110}
111
112char _license[] SEC("license") = "GPL";