Hi Benjamin,
I noticed a couple of issues with this series, but was able to fix/workaround them locally and got my USI program working with it.
1) You seem to be missing tools/include/uapi/linux/hid_bpf.h from index, I wasn't able to compile the selftests (or my own program) without adding this. It is included from tools/testing/selftests/bpf/prog_tests/hid.c: #include <linux/hid_bpf.h>
2) The limitation of needing to hardcode the size for hid_bpf_get_data() seems somewhat worrying, especially as the kernel side limits this to the ctx->allocated_size. I used a sufficiently large number for my purposes for now (256) which seems to work, but how should I handle my case where I basically need to read the whole input report and parse certain portions of it? How does the HID subsystem select the size of the ctx->allocated_size?
-Tero
On 18/05/2022 23:59, Benjamin Tissoires wrote:
Hi,
And here comes the v5 of the HID-BPF series.
I managed to achive the same functionalities than v3 this time. Handling per-device BPF program was "interesting" to say the least, but I don't know if we can have a generic BPF way of handling such situation.
The interesting bits is that now the BPF core changes are rather small, and I am mostly using existing facilities. I didn't managed to write selftests for the RET_PTR_TO_MEM kfunc, because I can not call kmalloc while in a SEC("tc") program to match what the other kfunc tests are doing. And AFAICT, the most interesting bits would be to implement verifier selftests, which are way out of my league, given that they are implemented as plain bytecode.
The logic is the following (see also the last patch for some more documentation):
- hid-bpf first preloads a BPF program in the kernel that does a few things:
- find out which attach_btf_id are associated with our trace points
- adds a bpf_tail_call() BPF program that I can use to "call" any other BPF program stored into a jump table
- monitors the releases of struct bpf_prog, and when there are no other users than us, detach the bpf progs from the HID devices
- users then declare their tracepoints and then call hid_bpf_attach_prog() in a SEC("syscall") program
- hid-bpf then calls multiple time the bpf_tail_call() program with a different index in the jump table whenever there is an event coming from a matching HID device
Note that I am tempted to pin an "attach_hid_program" in the bpffs so that users don't need to declare one, but I am afraid this will be one more API to handle, so maybe not.
I am also wondering if I should not strip out hid_bpf_jmp_table of most of its features and implement everything as a BPF program. This might remove the need to add the kernel light skeleton implementations of map modifications, and might also possibly be more re-usable for other subsystems. But every plan I do in my head involves a lot of back and forth between the kernel and BPF to achieve the same, which doesn't feel right. The tricky part is the RCU list of programs that is stored in each device and also the global state of the jump table. Anyway, something to look for in a next version if there is a push for it.
FWIW, patch 1 is something I'd like to get merged sooner. With 2 colleagues, we are also working on supporting the "revoke" functionality of a fd for USB and for hidraw. While hidraw can be emulated with the current features, we need the syscall kfuncs for USB, because when we revoke a USB access, we also need to kick out the user, and for that, we need to actually execute code in the kernel from a userspace event.
Anyway, happy reviewing.
Cheers, Benjamin
[Patch series based on commit 68084a136420 ("selftests/bpf: Fix building bpf selftests statically") in the bpf-next tree]
Benjamin Tissoires (17): bpf/btf: also allow kfunc in tracing and syscall programs bpf/verifier: allow kfunc to return an allocated mem bpf: prepare for more bpf syscall to be used from kernel and user space. libbpf: add map_get_fd_by_id and map_delete_elem in light skeleton HID: core: store the unique system identifier in hid_device HID: export hid_report_type to uapi HID: initial BPF implementation selftests/bpf: add tests for the HID-bpf initial implementation HID: bpf: allocate data memory for device_event BPF programs selftests/bpf/hid: add test to change the report size HID: bpf: introduce hid_hw_request() selftests/bpf: add tests for bpf_hid_hw_request HID: bpf: allow to change the report descriptor selftests/bpf: add report descriptor fixup tests samples/bpf: add new hid_mouse example selftests/bpf: Add a test for BPF_F_INSERT_HEAD Documentation: add HID-BPF docs
Documentation/hid/hid-bpf.rst | 528 ++++++++++ Documentation/hid/index.rst | 1 + drivers/hid/Kconfig | 2 + drivers/hid/Makefile | 2 + drivers/hid/bpf/Kconfig | 19 + drivers/hid/bpf/Makefile | 11 + drivers/hid/bpf/entrypoints/Makefile | 88 ++ drivers/hid/bpf/entrypoints/README | 4 + drivers/hid/bpf/entrypoints/entrypoints.bpf.c | 78 ++ .../hid/bpf/entrypoints/entrypoints.lskel.h | 782 ++++++++++++++ drivers/hid/bpf/hid_bpf_dispatch.c | 565 ++++++++++ drivers/hid/bpf/hid_bpf_dispatch.h | 28 + drivers/hid/bpf/hid_bpf_jmp_table.c | 587 +++++++++++ drivers/hid/hid-core.c | 43 +- include/linux/btf.h | 7 + include/linux/hid.h | 29 +- include/linux/hid_bpf.h | 144 +++ include/uapi/linux/hid.h | 12 + include/uapi/linux/hid_bpf.h | 25 + kernel/bpf/btf.c | 47 +- kernel/bpf/syscall.c | 10 +- kernel/bpf/verifier.c | 72 +- samples/bpf/.gitignore | 1 + samples/bpf/Makefile | 23 + samples/bpf/hid_mouse.bpf.c | 134 +++ samples/bpf/hid_mouse.c | 157 +++ tools/lib/bpf/skel_internal.h | 23 + tools/testing/selftests/bpf/config | 3 + tools/testing/selftests/bpf/prog_tests/hid.c | 990 ++++++++++++++++++ tools/testing/selftests/bpf/progs/hid.c | 222 ++++ 30 files changed, 4593 insertions(+), 44 deletions(-) create mode 100644 Documentation/hid/hid-bpf.rst create mode 100644 drivers/hid/bpf/Kconfig create mode 100644 drivers/hid/bpf/Makefile create mode 100644 drivers/hid/bpf/entrypoints/Makefile create mode 100644 drivers/hid/bpf/entrypoints/README create mode 100644 drivers/hid/bpf/entrypoints/entrypoints.bpf.c create mode 100644 drivers/hid/bpf/entrypoints/entrypoints.lskel.h create mode 100644 drivers/hid/bpf/hid_bpf_dispatch.c create mode 100644 drivers/hid/bpf/hid_bpf_dispatch.h create mode 100644 drivers/hid/bpf/hid_bpf_jmp_table.c create mode 100644 include/linux/hid_bpf.h create mode 100644 include/uapi/linux/hid_bpf.h create mode 100644 samples/bpf/hid_mouse.bpf.c create mode 100644 samples/bpf/hid_mouse.c create mode 100644 tools/testing/selftests/bpf/prog_tests/hid.c create mode 100644 tools/testing/selftests/bpf/progs/hid.c