From: Alexei Starovoitov <ast@xxxxxxxxxx>
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@xxxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a557718401e4..4c34fbd7b5be 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7533,6 +7533,12 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
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);
--
2.34.1
