| From 20eeec43347ca38d5bcca3a3a56d15f4b76b0c6b Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Thu, 17 Jun 2021 23:14:04 -0700 |
| Subject: bpf: Fix libelf endian handling in resolv_btfids |
| |
| From: Tony Ambardar <tony.ambardar@gmail.com> |
| |
| [ Upstream commit 61e8aeda9398925f8c6fc290585bdd9727d154c4 ] |
| |
| 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 |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| tools/bpf/resolve_btfids/main.c | 3 +++ |
| 1 file changed, 3 insertions(+) |
| |
| diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c |
| index d636643ddd35..f32c059fbfb4 100644 |
| --- a/tools/bpf/resolve_btfids/main.c |
| +++ b/tools/bpf/resolve_btfids/main.c |
| @@ -649,6 +649,9 @@ 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); |
| -- |
| 2.30.2 |
| |