From: Song Liu <song@kernel.org>
To: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
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>, Jonathan Corbet <corbet@lwn.net>,
Tero Kristo <tero.kristo@linux.intel.com>,
open list <linux-kernel@vger.kernel.org>,
"open list:HID CORE LAYER" <linux-input@vger.kernel.org>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
linux-kselftest@vger.kernel.org,
Linux Doc Mailing List <linux-doc@vger.kernel.org>
Subject: Re: [PATCH bpf-next v3 17/17] Documentation: add HID-BPF docs
Date: Fri, 18 Mar 2022 11:05:37 -0700 [thread overview]
Message-ID: <CAPhsuW77u64mxxLxp3B99cvu8NbqgNv1oW5Ffv0yn-k=YBw6GQ@mail.gmail.com> (raw)
In-Reply-To: <20220318161528.1531164-18-benjamin.tissoires@redhat.com>
On Fri, Mar 18, 2022 at 9:22 AM Benjamin Tissoires
<benjamin.tissoires@redhat.com> wrote:
>
> Gives a primer on HID-BPF.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
>
> ---
>
> new in v3
> ---
> Documentation/hid/hid-bpf.rst | 444 ++++++++++++++++++++++++++++++++++
> Documentation/hid/index.rst | 1 +
> include/uapi/linux/bpf_hid.h | 54 ++++-
> 3 files changed, 492 insertions(+), 7 deletions(-)
> create mode 100644 Documentation/hid/hid-bpf.rst
>
> diff --git a/Documentation/hid/hid-bpf.rst b/Documentation/hid/hid-bpf.rst
> new file mode 100644
> index 000000000000..0bf0d937b0e1
> --- /dev/null
> +++ b/Documentation/hid/hid-bpf.rst
> @@ -0,0 +1,444 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=======
> +HID-BPF
> +=======
> +
> +HID is a standard protocol for input devices and it can greatly make use
> +of the eBPF capabilities to speed up development and add new capabilities
> +to the existing HID interfaces.
> +
> +.. contents::
> + :local:
> + :depth: 2
> +
> +
> +When (and why) using HID-BPF
> +============================
> +
> +We can enumerate several use cases for when using HID-BPF is better than
> +using a standard kernel driver fix.
> +
> +dead zone of a joystick
> +-----------------------
> +
> +Assuming you have a joystick that is getting older, it is common to see it
> +wobbling around its neutral point. This is usually filtered at the application
> +level by adding a *dead zone* for this specific axis.
> +
> +With HID-BPF, we can put the filtering of this dead zone in the kernel directly
> +so we don't wake up userspace when nothing else is happening on the input
> +controller.
> +
> +Of course, given that this dead zone is device specific, we can not create a
nit: s/can not/cannot
There are a few more "can not" below.
[...]
> +firewall
> +--------
> +
> +What if we want to prevent other users to access a specific feature of a
> +device? (think a possibly bonker firmware update entry popint)
nit: point
> +
> +With eBPF, we can intercept any HID command emitted to the device and
> +validate it or not.
> +
> +This also allows to sync the state between the userspace and the
> +kernel/bpf program because we can intercept any incoming command.
> +
[...]
> +
> +The main idea behind HID-BPF is that it works at an array of bytes level.
> +Thus, all of the parsing of the HID report and the HID report descriptor
> +must be implemented in the userspace component that loads the eBPF
> +program.
> +
> +For example, in the dead zone joystick from above, knowing which fields
> +in the data stream needs to be set to ``0`` needs to be computed by userspace.
> +
> +A corrolar of this is that HID-BPF doesn't know about the other subsystems
nit: corollary?
> +available in the kernel. *You can not directly emit input event through the
> +input API from eBPF*.
> +
> +When a BPF program need to emit input events, it needs to talk HID, and rely
> +on the HID kernel processing to translate the HID data into input events.
> +
> +Available types of programs
> +===========================
[...]
> +
> +``BPF_HID_RDESC_FIXUP``
> +~~~~~~~~~~~~~~~~~~~~~~~
> +
> +Last, the ``BPF_HID_RDESC_FIXUP`` program works in the similar maneer than
nit: manner.
> +``.report_fixup`` of ``struct hid_driver``.
> +
[...]
next prev parent reply other threads:[~2022-03-18 18:05 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-18 16:15 [PATCH bpf-next v3 00/17] Introduce eBPF support for HID devices Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 01/17] bpf: add new is_sys_admin_prog_type() helper Benjamin Tissoires
2022-03-18 18:07 ` Song Liu
2022-03-18 16:15 ` [PATCH bpf-next v3 02/17] bpf: introduce hid program type Benjamin Tissoires
2022-03-18 20:48 ` Song Liu
2022-03-21 16:07 ` Benjamin Tissoires
2022-03-21 21:51 ` Song Liu
2022-03-22 11:06 ` Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 03/17] bpf/verifier: prevent non GPL programs to be loaded against HID Benjamin Tissoires
2022-03-18 20:51 ` Song Liu
2022-03-18 16:15 ` [PATCH bpf-next v3 04/17] libbpf: add HID program type and API Benjamin Tissoires
2022-03-18 20:53 ` Song Liu
2022-03-18 16:15 ` [PATCH bpf-next v3 05/17] HID: hook up with bpf Benjamin Tissoires
2022-03-18 21:02 ` Song Liu
2022-03-18 21:04 ` Song Liu
2022-03-18 16:15 ` [PATCH bpf-next v3 06/17] HID: allow to change the report descriptor from an eBPF program Benjamin Tissoires
2022-03-18 21:10 ` Song Liu
2022-03-21 16:20 ` Benjamin Tissoires
2022-03-21 22:03 ` Song Liu
2022-03-22 22:51 ` Alexei Starovoitov
2022-03-23 16:08 ` Benjamin Tissoires
2022-03-25 17:00 ` Andrii Nakryiko
2022-03-28 6:56 ` Benjamin Tissoires
2022-03-28 21:35 ` Andrii Nakryiko
2022-03-29 13:53 ` Benjamin Tissoires
2022-04-01 13:21 ` Benjamin Tissoires
2022-03-30 21:27 ` Alexei Starovoitov
2022-03-18 16:15 ` [PATCH bpf-next v3 07/17] selftests/bpf: add tests for the HID-bpf initial implementation Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 08/17] selftests/bpf: add report descriptor fixup tests Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 09/17] selftests/bpf: Add a test for BPF_F_INSERT_HEAD Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 10/17] selftests/bpf: add test for user call of HID bpf programs Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 11/17] samples/bpf: add new hid_mouse example Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 12/17] bpf/hid: add more HID helpers Benjamin Tissoires
2022-03-18 21:19 ` Song Liu
2022-03-21 16:24 ` Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 13/17] HID: bpf: implement hid_bpf_get|set_bits Benjamin Tissoires
2022-03-18 21:20 ` Song Liu
2022-03-18 16:15 ` [PATCH bpf-next v3 14/17] HID: add implementation of bpf_hid_raw_request Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 15/17] selftests/bpf: add tests for hid_{get|set}_bits helpers Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 16/17] selftests/bpf: add tests for bpf_hid_hw_request Benjamin Tissoires
2022-03-18 16:15 ` [PATCH bpf-next v3 17/17] Documentation: add HID-BPF docs Benjamin Tissoires
2022-03-18 18:05 ` Song Liu [this message]
2022-03-29 13:04 ` [PATCH bpf-next v3 00/17] Introduce eBPF support for HID devices Tero Kristo
2022-04-01 9:37 ` Benjamin Tissoires
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