diff options
114 files changed, 6443 insertions, 1579 deletions
diff --git a/Documentation/hid/hid-bpf.rst b/Documentation/hid/hid-bpf.rst index 0765b3298ecf..5939eeafb361 100644 --- a/Documentation/hid/hid-bpf.rst +++ b/Documentation/hid/hid-bpf.rst @@ -129,19 +129,37 @@ When a BPF program needs to emit input events, it needs to talk with the HID protocol, and rely on the HID kernel processing to translate the HID data into input events. +In-tree HID-BPF programs and ``udev-hid-bpf`` +============================================= + +Official device fixes are shipped in the kernel tree as source in the +``drivers/hid/bpf/progs`` directory. This allows to add selftests to them in +``tools/testing/selftests/hid``. + +However, the compilation of these objects is not part of a regular kernel compilation +given that they need an external tool to be loaded. This tool is currently +`udev-hid-bpf <https://libevdev.pages.freedesktop.org/udev-hid-bpf/index.html>`_. + +For convenience, that external repository duplicates the files from here in +``drivers/hid/bpf/progs`` into its own ``src/bpf/stable`` directory. This allows +distributions to not have to pull the entire kernel source tree to ship and package +those HID-BPF fixes. ``udev-hid-bpf`` also has capabilities of handling multiple +objects files depending on the kernel the user is running. + Available types of programs =========================== -HID-BPF is built "on top" of BPF, meaning that we use tracing method to +HID-BPF is built "on top" of BPF, meaning that we use bpf struct_ops method to declare our programs. HID-BPF has the following attachment types available: -1. event processing/filtering with ``SEC("fmod_ret/hid_bpf_device_event")`` in libbpf +1. event processing/filtering with ``SEC("struct_ops/hid_device_event")`` in libbpf 2. actions coming from userspace with ``SEC("syscall")`` in libbpf -3. change of the report descriptor with ``SEC("fmod_ret/hid_bpf_rdesc_fixup")`` in libbpf +3. change of the report descriptor with ``SEC("struct_ops/hid_rdesc_fixup")`` or + ``SEC("struct_ops.s/hid_rdesc_fixup")`` in libbpf -A ``hid_bpf_device_event`` is calling a BPF program when an event is received from +A ``hid_device_event`` is calling a BPF program when an event is received from the device. Thus we are in IRQ context and can act on the data or notify userspace. And given that we are in IRQ context, we can not talk back to the device. @@ -149,37 +167,42 @@ A ``syscall`` means that userspace called the syscall ``BPF_PROG_RUN`` facility. This time, we can do any operations allowed by HID-BPF, and talking to the device is allowed. -Last, ``hid_bpf_rdesc_fixup`` is different from the others as there can be only one +Last, ``hid_rdesc_fixup`` is different from the others as there can be only one BPF program of this type. This is called on ``probe`` from the driver and allows to -change the report descriptor from the BPF program. Once a ``hid_bpf_rdesc_fixup`` +change the report descriptor from the BPF program. Once a ``hid_rdesc_fixup`` program has been loaded, it is not possible to overwrite it unless the program which inserted it allows us by pinning the program and closing all of its fds pointing to it. +Note that ``hid_rdesc_fixup`` can be declared as sleepable (``SEC("struct_ops.s/hid_rdesc_fixup")``). + + Developer API: ============== -User API data structures available in programs: ------------------------------------------------ +Available ``struct_ops`` for HID-BPF: +------------------------------------- .. kernel-doc:: include/linux/hid_bpf.h + :identifiers: hid_bpf_ops -Available tracing functions to attach a HID-BPF program: --------------------------------------------------------- -.. kernel-doc:: drivers/hid/bpf/hid_bpf_dispatch.c - :functions: hid_bpf_device_event hid_bpf_rdesc_fixup +User API data structures available in programs: +----------------------------------------------- -Available API that can be used in all HID-BPF programs: -------------------------------------------------------- +.. kernel-doc:: include/linux/hid_bpf.h + :identifiers: hid_bpf_ctx + +Available API that can be used in all HID-BPF struct_ops programs: +------------------------------------------------------------------ .. kernel-doc:: drivers/hid/bpf/hid_bpf_dispatch.c - :functions: hid_bpf_get_data + :identifiers: hid_bpf_get_data -Available API that can be used in syscall HID-BPF programs: ------------------------------------------------------------ +Available API that can be used in syscall HID-BPF programs or in sleepable HID-BPF struct_ops programs: +------------------------------------------------------------------------------------------------------- .. kernel-doc:: drivers/hid/bpf/hid_bpf_dispatch.c - :functions: hid_bpf_attach_prog hid_bpf_hw_request hid_bpf_hw_output_report hid_bpf_input_report hid_bpf_allocate_context hid_bpf_release_context + :identifiers: hid_bpf_hw_request hid_bpf_hw_output_report hid_bpf_input_report hid_bpf_try_input_report hid_bpf_allocate_context hid_bpf_release_context General overview of a HID-BPF program ===================================== @@ -222,20 +245,21 @@ This allows the following: Effect of a HID-BPF program --------------------------- -For all HID-BPF attachment types except for :c:func:`hid_bpf_rdesc_fixup`, several eBPF -programs can be attached to the same device. +For all HID-BPF attachment types except for :c:func:`hid_rdesc_fixup`, several eBPF +programs can be attached to the same device. If a HID-BPF struct_ops has a +:c:func:`hid_rdesc_fixup` while another is already attached to the device, the +kernel will return `-EINVAL` when attaching the struct_ops. -Unless ``HID_BPF_FLAG_INSERT_HEAD`` is added to the flags while attaching the -program, the new program is appended at the end of the list. -``HID_BPF_FLAG_INSERT_HEAD`` will insert the new program at the beginning of the -list which is useful for e.g. tracing where we need to get the unprocessed events -from the device. +Unless ``BPF_F_BEFORE`` is added to the flags while attaching the program, the new +program is appended at the end of the list. +``BPF_F_BEFORE`` will insert the new program at the beginning of the list which is +useful for e.g. tracing where we need to get the unprocessed events from the device. -Note that if there are multiple programs using the ``HID_BPF_FLAG_INSERT_HEAD`` flag, +Note that if there are multiple programs using the ``BPF_F_BEFORE`` flag, only the most recently loaded one is actually the first in the list. -``SEC("fmod_ret/hid_bpf_device_event")`` -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +``SEC("struct_ops/hid_device_event")`` +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Whenever a matching event is raised, the eBPF programs are called one after the other and are working on the same data buffer. @@ -258,17 +282,17 @@ with, userspace needs to refer to the device by its unique system id (the last 4 in the sysfs path: ``/sys/bus/hid/devices/xxxx:yyyy:zzzz:0000``). To retrieve a context associated with the device, the program must call -:c:func:`hid_bpf_allocate_context` and must release it with :c:func:`hid_bpf_release_context` +hid_bpf_allocate_context() and must release it with hid_bpf_release_context() before returning. Once the context is retrieved, one can also request a pointer to kernel memory with -:c:func:`hid_bpf_get_data`. This memory is big enough to support all input/output/feature +hid_bpf_get_data(). This memory is big enough to support all input/output/feature reports of the given device. -``SEC("fmod_ret/hid_bpf_rdesc_fixup")`` -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +``SEC("struct_ops/hid_rdesc_fixup")`` +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -The ``hid_bpf_rdesc_fixup`` program works in a similar manner to -``.report_fixup`` of ``struct hid_driver``. +The ``hid_rdesc_fixup`` program works in a similar manner to ``.report_fixup`` +of ``struct hid_driver``. When the device is probed, the kernel sets the data buffer of the context with the content of the report descriptor. The memory associated with that buffer is @@ -277,33 +301,31 @@ content of the report descriptor. The memory associated with that buffer is The eBPF program can modify the data buffer at-will and the kernel uses the mod |