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

From: Song Liu <song@kernel.org>
To: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: Jiri Kosina <jikos@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>, Shuah Khan <shuah@kernel.org>,
	Dave Marchevsky <davemarchevsky@fb.com>,
	Joe Stringer <joe@cilium.io>,
	Tero Kristo <tero.kristo@linux.intel.com>,
	open list <linux-kernel@vger.kernel.org>,
	linux-input@vger.kernel.org, Networking <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf-next v1 2/6] HID: bpf: allow to change the report descriptor from an eBPF program
Date: Fri, 25 Feb 2022 23:25:13 -0800	[thread overview]
Message-ID: <CAPhsuW6m-HpfKLke1b7ni1j5Je3b3J0fa+MfJNnq2C9baOry1A@mail.gmail.com> (raw)
In-Reply-To: <20220224110828.2168231-3-benjamin.tissoires@redhat.com>

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