Re: [PATCH bpf-next v1 2/6] HID: bpf: allow to change the report descriptor from an eBPF program

Song Liu
2022-02-26T07:25:32Z

On Thu, Feb 24, 2022 at 3:09 AM Benjamin Tissoires
<benjamin.tissoires@redhat.com> wrote:
>
> The report descriptor is the dictionary of the HID protocol specific
> to the given device.
> Changing it is a common habit in the HID world, and making that feature
> accessible from eBPF allows to fix devices without having to install a
> new kernel.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

[...]

> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index 8fd79011f461..66d949d10b78 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -1213,10 +1213,16 @@ do { \
>
> #ifdef CONFIG_BPF
> u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *rd, int *size);
> +u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size);
> int hid_bpf_module_init(void);
> void hid_bpf_module_exit(void);
> #else
> static inline u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *rd, int *size) { return rd; }
> +static inline u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc,
> + unsigned int *size)
> +{
> + return kmemdup(rdesc, *size, GFP_KERNEL);
> +}
> static inline int hid_bpf_module_init(void) { return 0; }
> static inline void hid_bpf_module_exit(void) {}
> #endif
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 5978b92cacd3..a7a8d9cfcf24 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -999,6 +999,7 @@ enum bpf_attach_type {
> BPF_SK_REUSEPORT_SELECT_OR_MIGRATE,
> BPF_PERF_EVENT,
> BPF_HID_DEVICE_EVENT,
> + BPF_HID_RDESC_FIXUP,
> __MAX_BPF_ATTACH_TYPE
> };
>
> diff --git a/include/uapi/linux/bpf_hid.h b/include/uapi/linux/bpf_hid.h
> index 243ac45a253f..c0801d7174c3 100644
> --- a/include/uapi/linux/bpf_hid.h
> +++ b/include/uapi/linux/bpf_hid.h
> @@ -18,6 +18,7 @@ struct hid_device;
> enum hid_bpf_event {
> HID_BPF_UNDEF = 0,
> HID_BPF_DEVICE_EVENT,
> + HID_BPF_RDESC_FIXUP,
> };
>
> /* type is HID_BPF_DEVICE_EVENT */
> @@ -26,12 +27,19 @@ struct hid_bpf_ctx_device_event {
> unsigned long size;
> };
>
> +/* type is HID_BPF_RDESC_FIXUP */
> +struct hid_bpf_ctx_rdesc_fixup {
> + __u8 data[HID_BPF_MAX_BUFFER_SIZE];
> + unsigned long size;
> +};

This looks same as HID_BPF_DEVICE_EVENT, do we really need to
separate the two?

Thanks,
Song