From 6d4126d2d4cfc188eb5d87a0b308988bf7efa230 Mon Sep 17 00:00:00 2001 From: Tony Ambardar Date: Thu, 17 Jun 2021 23:14:04 -0700 Subject: [PATCH] bpf: Fix libelf endian handling in resolv_btfids BugLink: https://bugs.launchpad.net/bugs/1938340 [ 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 Signed-off-by: Daniel Borkmann Acked-by: Jiri Olsa Cc: Frank Eigler Cc: Mark Wielaard Cc: Jiri Olsa Cc: Yonghong Song 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 Signed-off-by: Kamal Mostafa Signed-off-by: Stefan Bader --- 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 80d966cfcaa1..7ce4558a932f 100644 --- a/tools/bpf/resolve_btfids/main.c +++ b/tools/bpf/resolve_btfids/main.c @@ -656,6 +656,9 @@ 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); -- 2.39.5