diff options
| author | Tony Ambardar <tony.ambardar@gmail.com> | 2021-06-17 23:14:04 -0700 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-06-18 17:01:00 +0200 |
| commit | 61e8aeda9398925f8c6fc290585bdd9727d154c4 (patch) | |
| tree | dc02e803383740f13fff7aaab5ff6d4c3c734641 /tools/bpf | |
| parent | f654fae47e83e56b454fbbfd0af0a4f232e356d6 (diff) | |
bpf: Fix libelf endian handling in resolv_btfids
The vmlinux ".BTF_ids" ELF section is declared in btf_ids.h to hold a list
of zero-filled BTF IDs, which is then patched at link-time with correct
values by resolv_btfids. The section is flagged as "allocable" to preclude
compression, but notably the section contents (BTF IDs) are untyped.
When patching the BTF IDs, resolve_btfids writes in host-native endianness
and relies on libelf for any required translation on reading and updating
vmlinux. However, since the type of the .BTF_ids section content defaults
to ELF_T_BYTE (i.e. unsigned char), no translation occurs. This results in
incorrect patched values when cross-compiling to non-native endianness,
and can manifest as kernel Oops and test failures which are difficult to
troubleshoot [1].
Explicitly set the type of patched data to ELF_T_WORD, the architecture-
neutral ELF type corresponding to the u32 BTF IDs. This enables libelf to
transparently perform any needed endian conversions.
Fixes: fbbb68de80a4 ("bpf: Add resolve_btfids tool to resolve BTF IDs in ELF object")
Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Frank Eigler <fche@redhat.com>
Cc: Mark Wielaard <mark@klomp.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/CAPGftE_eY-Zdi3wBcgDfkz_iOr1KF10n=9mJHm1_a_PykcsoeA@mail.gmail.com [1]
Link: https://lore.kernel.org/bpf/20210618061404.818569-1-Tony.Ambardar@gmail.com
Diffstat (limited to 'tools/bpf')
| -rw-r--r-- | tools/bpf/resolve_btfids/main.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c index 7550fd9c3188..3ad9301b0f00 100644 --- a/tools/bpf/resolve_btfids/main.c +++ b/tools/bpf/resolve_btfids/main.c @@ -655,6 +655,9 @@ static int symbols_patch(struct object *obj) if (sets_patch(obj)) return -1; + /* Set type to ensure endian translation occurs. */ + obj->efile.idlist->d_type = ELF_T_WORD; + elf_flagdata(obj->efile.idlist, ELF_C_SET, ELF_F_DIRTY); err = elf_update(obj->efile.elf, ELF_C_WRITE); |