libbpf: Fix relocation of kfunc ksym in ld_imm64 insn.
void *p = kfunc; -> generates ld_imm64 insn.
kfunc() -> generates bpf_call insn.
libbpf patches bpf_call insn correctly while only btf_id part of ld_imm64 is
set in the former case. Which means that pointers to kfuncs in modules are not
patched correctly and the verifier rejects load of such programs due to btf_id
being out of range. Fix libbpf to patch ld_imm64 for kfunc.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230317201920.62030-3-alexei.starovoitov@gmail.com
diff --git a/src/libbpf.c b/src/libbpf.c
index a557718..4c34fbd 100644
--- a/src/libbpf.c
+++ b/src/libbpf.c
@@ -7533,6 +7533,12 @@
ext->is_set = true;
ext->ksym.kernel_btf_id = kfunc_id;
ext->ksym.btf_fd_idx = mod_btf ? mod_btf->fd_array_idx : 0;
+ /* Also set kernel_btf_obj_fd to make sure that bpf_object__relocate_data()
+ * populates FD into ld_imm64 insn when it's used to point to kfunc.
+ * {kernel_btf_id, btf_fd_idx} -> fixup bpf_call.
+ * {kernel_btf_id, kernel_btf_obj_fd} -> fixup ld_imm64.
+ */
+ ext->ksym.kernel_btf_obj_fd = mod_btf ? mod_btf->fd : 0;
pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n",
ext->name, kfunc_id);
