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authorTony Ambardar <tony.ambardar@gmail.com>2021-06-18 08:14:04 +0200
committerDaniel Borkmann <daniel@iogearbox.net>2021-06-18 17:01:00 +0200
commit61e8aeda9398925f8c6fc290585bdd9727d154c4 (patch)
treedc02e803383740f13fff7aaab5ff6d4c3c734641 /tools/bpf
parentxsk: Fix broken Tx ring validation (diff)
downloadlinux-61e8aeda9398925f8c6fc290585bdd9727d154c4.tar.xz
linux-61e8aeda9398925f8c6fc290585bdd9727d154c4.zip
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.c3
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);