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. Patch 1 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 this refactoring (and previously applied patches), it becomes pretty straight-forward to support multiple-attach for freplace programs (patch 2). 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 3 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. Patch 4 is the accompanying libbpf update, and patches 5-7 are selftests: patch 5 tests for the multi-freplace functionality itself; patch 6 is Jiri's previous selftest for the fentry-to-freplace fix; patch 7 is a test for the change introduced in the previously-applied patches, blocking MODIFY_RETURN functions from attaching to other BPF programs. 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-10 Changelog: v10: - Dial back the s/tgt_/dst_/ replacement a bit - Fix smatch warning (from ktest robot) - Rebase to bpf-next, drop already-applied patches v9: - Clarify commit message of patch 3 - Add new struct bpf_attach_target_info for returning from bpf_check_attach_target() and passing to bpf_trampoline_get() - Move trampoline key computation into a helper - Make sure we don't break bpffs debug umh - Add some comment blocks explaining the logic flow in bpf_tracing_prog_attach() - s/tgt_/dst_/ in prog->aux, and for local variables using those members - Always drop dst_trampoline and dst_prog from prog->aux on first attach - Don't remove syscall fmod_ret test from selftest benchmarks - Add saved_ prefix to dst_{prog,attach}_type members in prog_aux - Drop prog argument from check_attach_modify_return() - Add comment about possible NULL of tr_link->tgt_prog on link_release() 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 (6): 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 include/linux/bpf.h | 2 + include/uapi/linux/bpf.h | 9 +- kernel/bpf/btf.c | 9 +- kernel/bpf/syscall.c | 132 +++++++++-- kernel/bpf/verifier.c | 10 + 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 + .../selftests/bpf/prog_tests/fexit_bpf2bpf.c | 212 +++++++++++++++--- .../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_trace_ext.c | 18 ++ .../bpf/progs/test_trace_ext_tracing.c | 25 +++ 17 files changed, 573 insertions(+), 62 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
