samples/hid/hid_mouse.bpf.c

   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
   8 SEC("fmod_ret/hid_bpf_device_event")
   9 int 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
  54 SEC("fmod_ret/hid_bpf_device_event")
  55 int 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
  72 SEC("fmod_ret/hid_bpf_rdesc_fixup")
  73 int 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
 112 char _license[] SEC("license") = "GPL";