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4fcac46c7e
Teach libbpf to not add BPF_F_MMAPABLE flag unnecessarily for ARRAY maps that are backing data sections, if such data sections don't expose any variables to user-space. Exposed variables are those that have STB_GLOBAL or STB_WEAK ELF binding and correspond to BTF VAR's BTF_VAR_GLOBAL_ALLOCATED linkage. The overall idea is that if some data section doesn't have any variable that is exposed through BPF skeleton, then there is no reason to make such BPF array mmapable. Making BPF array mmapable is not a free no-op action, because BPF verifier doesn't allow users to put special objects (such as BPF spin locks, RB tree nodes, linked list nodes, kptrs, etc; anything that has a sensitive internal state that should not be modified arbitrarily from user space) into mmapable arrays, as there is no way to prevent user space from corrupting such sensitive state through direct memory access through memory-mapped region. By making sure that libbpf doesn't add BPF_F_MMAPABLE flag to BPF array maps corresponding to data sections that only have static variables (which are not supposed to be visible to user space according to libbpf and BPF skeleton rules), users now can have spinlocks, kptrs, etc in either default .bss/.data sections or custom .data.* sections (assuming there are no global variables in such sections). The only possible hiccup with this approach is the need to use global variables during BPF static linking, even if it's not intended to be shared with user space through BPF skeleton. To allow such scenarios, extend libbpf's STV_HIDDEN ELF visibility attribute handling to variables. Libbpf is already treating global hidden BPF subprograms as static subprograms and adjusts BTF accordingly to make BPF verifier verify such subprograms as static subprograms with preserving entire BPF verifier state between subprog calls. This patch teaches libbpf to treat global hidden variables as static ones and adjust BTF information accordingly as well. This allows to share variables between multiple object files during static linking, but still keep them internal to BPF program and not get them exposed through BPF skeleton. Note, that if the user has some advanced scenario where they absolutely need BPF_F_MMAPABLE flag on .data/.bss/.rodata BPF array map despite only having static variables, they still can achieve this by forcing it through explicit bpf_map__set_map_flags() API. Acked-by: Stanislav Fomichev <sdf@google.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Acked-by: Dave Marchevsky <davemarchevsky@fb.com> Link: https://lore.kernel.org/r/20221019002816.359650-3-andrii@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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| .. | ||
| .gitignore | ||
| bpf_core_read.h | ||
| bpf_endian.h | ||
| bpf_gen_internal.h | ||
| bpf_helpers.h | ||
| bpf_prog_linfo.c | ||
| bpf_tracing.h | ||
| bpf.c | ||
| bpf.h | ||
| btf_dump.c | ||
| btf.c | ||
| btf.h | ||
| Build | ||
| gen_loader.c | ||
| hashmap.c | ||
| hashmap.h | ||
| libbpf_common.h | ||
| libbpf_errno.c | ||
| libbpf_internal.h | ||
| libbpf_legacy.h | ||
| libbpf_probes.c | ||
| libbpf_version.h | ||
| libbpf.c | ||
| libbpf.h | ||
| libbpf.map | ||
| libbpf.pc.template | ||
| linker.c | ||
| Makefile | ||
| netlink.c | ||
| nlattr.c | ||
| nlattr.h | ||
| relo_core.c | ||
| relo_core.h | ||
| ringbuf.c | ||
| skel_internal.h | ||
| str_error.c | ||
| str_error.h | ||
| strset.c | ||
| strset.h | ||
| usdt.bpf.h | ||
| usdt.c | ||