Reported by linux-next:
After merging the hid tree, today's linux-next build (x86_64 allmodconfig)
failed like this:

x86_64-linux-gnu-ld: vmlinux.o: in function `hid_bpf_input_report':
(.text+0x1c75181): undefined reference to `hid_input_report'

Caused by commit 9be50ac30a83 ("HID: bpf: allow to inject HID event
from BPF")

I just forgot to put the indirection in place.

Link: https://lore.kernel.org/linux-kernel/20240411105131.7830f966@canb.auug.org.au/
Fixes: 9be50ac30a83 ("HID: bpf: allow to inject HID event from BPF")
Link: https://lore.kernel.org/r/20240411-fix-hid-bpf-v1-1-4ae913031a8c@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

Export the sleepable kfuncs we have on HID-BPF in tracing bpf programs,
but with the condition of being used in a sleepable context.
This allows to use the bpf_timer when used in a sleepable context
through bpf_timer_set_sleepable_cb() and initiate work from a device event.

Link: https://lore.kernel.org/r/20240315-b4-hid-bpf-new-funcs-v4-7-079c282469d3@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

It can be interesting to inject events from BPF as if the event were
to come from the device.
For example, some multitouch devices do not all the time send a proximity
out event, and we might want to send it for the physical device.

Compared to uhid, we can now inject events on any physical device, not
just uhid virtual ones.

Link: https://lore.kernel.org/r/20240315-b4-hid-bpf-new-funcs-v4-5-079c282469d3@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

We currently only export hid_hw_raw_request() as a BPF kfunc.
However, some devices require an explicit write on the Output Report
instead of the use of the control channel.

So also export hid_hw_output_report to BPF

Link: https://lore.kernel.org/r/20240315-b4-hid-bpf-new-funcs-v4-2-079c282469d3@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

No code change, just move down the hid_bpf_get_data() kfunc definition
so we have only one block of __bpf_kfunc_start/end_defs()

Link: https://lore.kernel.org/r/20240315-b4-hid-bpf-new-funcs-v4-1-079c282469d3@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

Daniel Borkmann says:

====================
pull-request: bpf-next 2024-02-29

We've added 119 non-merge commits during the last 32 day(s) which contain
a total of 150 files changed, 3589 insertions(+), 995 deletions(-).

The main changes are:

1) Extend the BPF verifier to enable static subprog calls in spin lock
   critical sections, from Kumar Kartikeya Dwivedi.

2) Fix confusing and incorrect inference of PTR_TO_CTX argument type
   in BPF global subprogs, from Andrii Nakryiko.

3) Larger batch of riscv BPF JIT improvements and enabling inlining
   of the bpf_kptr_xchg() for RV64, from Pu Lehui.

4) Allow skeleton users to change the values of the fields in struct_ops
   maps at runtime, from Kui-Feng Lee.

5) Extend the verifier's capabilities of tracking scalars when they
   are spilled to stack, especially when the spill or fill is narrowing,
   from Maxim Mikityanskiy & Eduard Zingerman.

6) Various BPF selftest improvements to fix errors under gcc BPF backend,
   from Jose E. Marchesi.

7) Avoid module loading failure when the module trying to register
   a struct_ops has its BTF section stripped, from Geliang Tang.

8) Annotate all kfuncs in .BTF_ids section which eventually allows
   for automatic kfunc prototype generation from bpftool, from Daniel Xu.

9) Several updates to the instruction-set.rst IETF standardization
   document, from Dave Thaler.

10) Shrink the size of struct bpf_map resp. bpf_array,
    from Alexei Starovoitov.

11) Initial small subset of BPF verifier prepwork for sleepable bpf_timer,
    from Benjamin Tissoires.

12) Fix bpftool to be more portable to musl libc by using POSIX's
    basename(), from Arnaldo Carvalho de Melo.

13) Add libbpf support to gcc in CORE macro definitions,
    from Cupertino Miranda.

14) Remove a duplicate type check in perf_event_bpf_event,
    from Florian Lehner.

15) Fix bpf_spin_{un,}lock BPF helpers to actually annotate them
    with notrace correctly, from Yonghong Song.

16) Replace the deprecated bpf_lpm_trie_key 0-length array with flexible
    array to fix build warnings, from Kees Cook.

17) Fix resolve_btfids cross-compilation to non host-native endianness,
    from Viktor Malik.

* tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: (119 commits)
  selftests/bpf: Test if shadow types work correctly.
  bpftool: Add an example for struct_ops map and shadow type.
  bpftool: Generated shadow variables for struct_ops maps.
  libbpf: Convert st_ops->data to shadow type.
  libbpf: Set btf_value_type_id of struct bpf_map for struct_ops.
  bpf: Replace bpf_lpm_trie_key 0-length array with flexible array
  bpf, arm64: use bpf_prog_pack for memory management
  arm64: patching: implement text_poke API
  bpf, arm64: support exceptions
  arm64: stacktrace: Implement arch_bpf_stack_walk() for the BPF JIT
  bpf: add is_async_callback_calling_insn() helper
  bpf: introduce in_sleepable() helper
  bpf: allow more maps in sleepable bpf programs
  selftests/bpf: Test case for lacking CFI stub functions.
  bpf: Check cfi_stubs before registering a struct_ops type.
  bpf: Clarify batch lookup/lookup_and_delete semantics
  bpf, docs: specify which BPF_ABS and BPF_IND fields were zero
  bpf, docs: Fix typos in instruction-set.rst
  selftests/bpf: update tcp_custom_syncookie to use scalar packet offset
  bpf: Shrink size of struct bpf_map/bpf_array.
  ...
====================

Link: https://lore.kernel.org/r/20240301001625.8800-1-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

This commit marks kfuncs as such inside the .BTF_ids section. The upshot
of these annotations is that we'll be able to automatically generate
kfunc prototypes for downstream users. The process is as follows:

1. In source, use BTF_KFUNCS_START/END macro pair to mark kfuncs
2. During build, pahole injects into BTF a "bpf_kfunc" BTF_DECL_TAG for
   each function inside BTF_KFUNCS sets
3. At runtime, vmlinux or module BTF is made available in sysfs
4. At runtime, bpftool (or similar) can look at provided BTF and
   generate appropriate prototypes for functions with "bpf_kfunc" tag

To ensure future kfunc are similarly tagged, we now also return error
inside kfunc registration for untagged kfuncs. For vmlinux kfuncs,
we also WARN(), as initcall machinery does not handle errors.

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Acked-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/e55150ceecbf0a5d961e608941165c0bee7bc943.1706491398.git.dxu@dxuuu.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Follow the docs at Documentation/bpf/kfuncs.rst:
- declare the function with `__bpf_kfunc`
- disables missing prototype warnings, which allows to remove them from
  include/linux/hid-bpf.h

Removing the prototypes is not an issue because we currently have to
redeclare them when writing the BPF program. They will eventually be
generated by bpftool directly AFAIU.

Link: https://lore.kernel.org/r/20240124-b4-hid-bpf-fixes-v2-3-052520b1e5e6@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

Turns out that I got my reference counts wrong and each successful
bus_find_device() actually calls get_device(), and we need to manually
call put_device().

Ensure each bus_find_device() gets a matching put_device() when releasing
the bpf programs and fix all the error paths.

Cc: <stable@vger.kernel.org>
Fixes: f5c27da4e3c8 ("HID: initial BPF implementation")
Link: https://lore.kernel.org/r/20240124-b4-hid-bpf-fixes-v2-2-052520b1e5e6@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

When the kfunc hid_bpf_attach_prog() is called, we called twice fdget():
one for fetching the type of the bpf program, and one for actually
attaching the program to the device.

The problem is that between those two calls, we have no guarantees that
the prog_fd is still the same file descriptor for the given program.

Solve this by calling bpf_prog_get() earlier, and use this to fetch the
program type.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/bpf/CAO-hwJJ8vh8JD3-P43L-_CLNmPx0hWj44aom0O838vfP4=_1CA@mail.gmail.com/T/#t
Cc: <stable@vger.kernel.org>
Fixes: f5c27da4e3c8 ("HID: initial BPF implementation")
Link: https://lore.kernel.org/r/20240124-b4-hid-bpf-fixes-v2-1-052520b1e5e6@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>