Follow up fixes for kernel-side and libbpf-side logic around handling arg:ctx (__arg_ctx) tagged arguments of BPF global subprogs. Patch #1 adds libbpf feature detection of kernel-side __arg_ctx support to avoid unnecessary rewriting BTF types. With stricter kernel-side type enforcement this is now mandatory to avoid problems with using `struct bpf_user_pt_regs_t` instead of actual typedef. For __arg_ctx tagged arguments verifier is now ignoring superficial `bpf_user_pt_regs_t` typedef and resolves it down to the actual struct (pt_regs/user_pt_regs/etc, depending on architecture), but for old kernels without __arg_ctx support it's more backwards compatible for libbpf to use `struct bpf_user_pt_regs_t` rewrite which will work on wider range of kernels. So feature detection prevent libbpf accidentally breaking global subprogs on new kernels. We also adjust selftests to do similar feature detection (much simpler, but potentially breaking due to kernel source code refactoring, which is fine for selftests), and skip tests expecting libbpf's BTF type rewrites. Patch #2 is preparatory refactoring for patch #3 which adds type enforcement for arg:ctx tagged global subprog args. See the patch for specifics. Patch #4 adds many new cases to ensure type logic works as expected. Finally, patch #5 adds a relevant subset of kernel-side type checks to __arg_ctx cases that libbpf supports rewrite of. In libbpf's case, type violations are reported as warnings and BTF rewrite is not performed, which will eventually lead to BPF verifier complaining at program verification time. Good care was taken to avoid conflicts between bpf and bpf-next tree (which has few follow up refactorings in the same code area). Once trees converge some of the code will be moved around a bit (and some will be deleted), but with no change to functionality or general shape of the code. v1->v2: - add user_pt_regs and user_regs_struct support for PERF_EVENT (CI); - drop FEAT_ARG_CTX_TAG enum leftover from patch #1; - fix warning about default: without break in the switch (CI). Andrii Nakryiko (5): libbpf: feature-detect arg:ctx tag support in kernel bpf: extract bpf_ctx_convert_map logic and make it more reusable bpf: enforce types for __arg_ctx-tagged arguments in global subprogs selftests/bpf: add tests confirming type logic in kernel for __arg_ctx libbpf: warn on unexpected __arg_ctx type when rewriting BTF include/linux/btf.h | 2 +- kernel/bpf/btf.c | 217 +++++++++++++++--- tools/lib/bpf/libbpf.c | 142 +++++++++++- .../bpf/prog_tests/test_global_funcs.c | 13 ++ .../bpf/progs/verifier_global_subprogs.c | 164 ++++++++++++- 5 files changed, 499 insertions(+), 39 deletions(-) -- 2.34.1
