On Wed, 2024-01-17 at 14:33 -0800, Andrii Nakryiko wrote: > 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). I've read through patch-set and it seem to be ok, checks match behavior described in patch #3 description. Reviewed-by: Eduard Zingerman <eddyz87@xxxxxxxxx> [...]
