Allow FENTRY/FEXIT BPF programs to attach to other BPF programs of any type including their subprograms. This feature allows snooping on input and output packets in XDP, TC programs including their return values. In order to do that the verifier needs to track types not only of vmlinux, but types of other BPF programs as well. The verifier also needs to translate uapi/linux/bpf.h types used by networking programs into kernel internal BTF types used by FENTRY/FEXIT BPF programs. In some cases LLVM optimizations can remove arguments from BPF subprograms without adjusting BTF info that LLVM backend knows. When BTF info disagrees with actual types that the verifiers sees the BPF trampoline has to fallback to conservative and treat all arguments as u64. The FENTRY/FEXIT program can still attach to such subprograms, but it won't be able to recognize pointer types like 'struct sk_buff *' and it won't be able to pass them to bpf_skb_output() for dumping packets to user space. The FENTRY/FEXIT program would need to use bpf_probe_read_kernel() instead. The BPF_PROG_LOAD command is extended with attach_prog_fd field. When it's set to zero the attach_btf_id is one vmlinux BTF type ids. When attach_prog_fd points to previously loaded BPF program the attach_btf_id is BTF type id of main function or one of its subprograms.
Showing the changes to include/uapi/linux (1 of 8 files). Show all
Unified · Split
| @@ -425,6 +425,7 @@ union bpf_attr { · 424 unmodified lines | |||
| 425 | __aligned_u64 line_info; /* line info */ | 425 | __aligned_u64 line_info; /* line info */ |
| 426 | __u32 line_info_cnt; /* number of bpf_line_info records */ | 426 | __u32 line_info_cnt; /* number of bpf_line_info records */ |
| 427 | __u32 attach_btf_id; /* in-kernel BTF type id to attach to */ | 427 | __u32 attach_btf_id; /* in-kernel BTF type id to attach to */ |
| 428 | __u32 attach_prog_fd; /* 0 to attach to vmlinux */ | ||
| 428 | }; | 429 | }; |
| 429 | 430 | ||
| 430 | struct { /* anonymous struct used by BPF_OBJ_* commands */ | 431 | struct { /* anonymous struct used by BPF_OBJ_* commands */ |