This series adds support attaching freplace BPF programs to multiple targets. This is needed to support incremental attachment of multiple XDP programs using the libxdp dispatcher model. The first patch fixes an issue that came up in review: The verifier will currently allow MODIFY_RETURN tracing functions to attach to other BPF programs, even though it is pretty clear from the commit messages introducing the functionality that this was not the intention. This patch is included in the series because the subsequent refactoring patches touch the same code. The next three patches are refactoring patches: Patch 2 is a trivial change to the logging in the verifier, split out to make the subsequent refactor easier to read. Patch 3 refactors check_attach_btf_id() so that the checks on program and target compatibility can be reused when attaching to a secondary location. Patch 4 moves prog_aux->linked_prog and the trampoline to be embedded in bpf_tracing_link on attach, and freed by the link release logic, and introduces a mutex to protect the writing of the pointers in prog->aux. Based on these refactorings, it becomes pretty straight-forward to support multiple-attach for freplace programs (patch 5). This is simply a matter of creating a second bpf_tracing_link if a target is supplied. However, for API consistency with other types of link attach, this option is added to the BPF_LINK_CREATE API instead of extending bpf_raw_tracepoint_open(). Patch 6 is a port of Jiri Olsa's patch to support fentry/fexit on freplace programs. His approach of getting the target type from the target program reference no longer works after we've gotten rid of linked_prog (because the bpf_tracing_link reference disappears on attach). Instead, we used the saved reference to the target prog type that is also used to verify compatibility on secondary freplace attachment. Patches 7 is the accompanying libbpf update, and patches 8-11 are selftests: patch 8 tests for the multi-freplace functionality itself; patch 9 is Jiri's previous selftest for the fentry-to-freplace fix; patch 10 is a test for the change introduced in patch 1, blocking MODIFY_RETURN functions from attaching to other BPF programs; and finally, patch 11 removes MODIFY_RETURN functions from the benchmark and test_overhead programs in selftests, as these were never supposed to work in the first place. With this series, libxdp and xdp-tools can successfully attach multiple programs one at a time. To play with this, use the 'freplace-multi-attach' branch of xdp-tools: $ git clone --recurse-submodules --branch freplace-multi-attach https://github.com/xdp-project/xdp-tools $ cd xdp-tools/xdp-loader $ make $ sudo ./xdp-loader load veth0 ../lib/testing/xdp_drop.o $ sudo ./xdp-loader load veth0 ../lib/testing/xdp_pass.o $ sudo ./xdp-loader status The series is also available here: https://git.kernel.org/pub/scm/linux/kernel/git/toke/linux.git/log/?h=bpf-freplace-multi-attach-alt-08 Changelog: v8: - Add a separate error message when trying to attach FMOD_REPLACE to tgt_prog - Better error messages in bpf_program__attach_freplace() - Don't lock mutex when setting tgt_* pointers in prog create and verifier - Remove fmod_ret programs from benchmarks in selftests (new patch 11) - Fix a few other nits in selftests v7: - Add back missing ptype == prog->type check in link_create() - Use tracing_bpf_link_attach() instead of separate freplace_bpf_link_attach() - Don't break attachment of bpf_iters in libbpf (by clobbering link_create.iter_info) v6: - Rebase to latest bpf-next - Simplify logic in bpf_tracing_prog_attach() - Don't create a new attach_type for link_create(), disambiguate on prog->type instead - Use raw_tracepoint_open() in libbpf bpf_program__attach_ftrace() if called with NULL target - Switch bpf_program__attach_ftrace() to take function name as parameter instead of btf_id - Add a patch disallowing MODIFY_RETURN programs from attaching to other BPF programs, and an accompanying selftest (patches 1 and 10) v5: - Fix typo in inline function definition of bpf_trampoline_get() - Don't put bpf_tracing_link in prog->aux, use a mutex to protect tgt_prog and trampoline instead, and move them to the link on attach. - Restore Jiri as author of the last selftest patch v4: - Cleanup the refactored check_attach_btf_id() to make the logic easier to follow - Fix cleanup paths for bpf_tracing_link - Use xchg() for removing the bpf_tracing_link from prog->aux and restore on (some) failures - Use BPF_LINK_CREATE operation to create link with target instead of extending raw_tracepoint_open - Fold update of tools/ UAPI header into main patch - Update arg dereference patch to use skeletons and set_attach_target() v3: - Get rid of prog_aux->linked_prog entirely in favour of a bpf_tracing_link - Incorporate Jiri's fix for attaching fentry to freplace programs v2: - Drop the log arguments from bpf_raw_tracepoint_open - Fix kbot errors - Rebase to latest bpf-next --- Jiri Olsa (1): selftests/bpf: Adding test for arg dereference in extension trace Toke Høiland-Jørgensen (10): bpf: disallow attaching modify_return tracing functions to other BPF programs bpf: change logging calls from verbose() to bpf_log() and use log pointer bpf: verifier: refactor check_attach_btf_id() bpf: move prog->aux->linked_prog and trampoline into bpf_link on attach bpf: support attaching freplace programs to multiple attach points bpf: Fix context type resolving for extension programs libbpf: add support for freplace attachment in bpf_link_create selftests: add test for multiple attachments of freplace program selftests: Add selftest for disallowing modify_return attachment to freplace selftests: Remove fmod_ret from benchmarks and test_overhead include/linux/bpf.h | 26 +- include/linux/bpf_verifier.h | 14 +- include/uapi/linux/bpf.h | 9 +- kernel/bpf/btf.c | 21 +- kernel/bpf/core.c | 9 +- kernel/bpf/syscall.c | 135 ++++++++-- kernel/bpf/trampoline.c | 32 ++- kernel/bpf/verifier.c | 250 ++++++++++-------- tools/include/uapi/linux/bpf.h | 9 +- tools/lib/bpf/bpf.c | 18 +- tools/lib/bpf/bpf.h | 3 +- tools/lib/bpf/libbpf.c | 44 ++- tools/lib/bpf/libbpf.h | 3 + tools/lib/bpf/libbpf.map | 1 + tools/testing/selftests/bpf/bench.c | 5 - .../selftests/bpf/benchs/bench_rename.c | 17 -- .../selftests/bpf/benchs/bench_trigger.c | 17 -- .../selftests/bpf/prog_tests/fexit_bpf2bpf.c | 212 ++++++++++++--- .../selftests/bpf/prog_tests/test_overhead.c | 14 +- .../selftests/bpf/prog_tests/trace_ext.c | 111 ++++++++ .../selftests/bpf/progs/fmod_ret_freplace.c | 14 + .../bpf/progs/freplace_get_constant.c | 15 ++ .../selftests/bpf/progs/test_overhead.c | 6 - .../selftests/bpf/progs/test_trace_ext.c | 18 ++ .../bpf/progs/test_trace_ext_tracing.c | 25 ++ .../selftests/bpf/progs/trigger_bench.c | 7 - 26 files changed, 771 insertions(+), 264 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/trace_ext.c create mode 100644 tools/testing/selftests/bpf/progs/fmod_ret_freplace.c create mode 100644 tools/testing/selftests/bpf/progs/freplace_get_constant.c create mode 100644 tools/testing/selftests/bpf/progs/test_trace_ext.c create mode 100644 tools/testing/selftests/bpf/progs/test_trace_ext_tracing.c
