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- From a9355b201d160aa777d1480911c9ee5c7deeb88b Mon Sep 17 00:00:00 2001
- From: Tony Ambardar <tony.ambardar@gmail.com>
- Date: Thu, 17 Jun 2021 23:14:04 -0700
- Subject: [PATCH] bpf: Fix libelf endian handling in resolv_btfids
- [ 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);
- --
- 2.55.0
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