[PATCH bpf v2 3/5] libbpf: Skip adjust mem size for load pointer in 32-bit arch in CO_RE

Yang Jihong
2022-11-07T09:24:14Z

bpf_core_patch_insn modifies load's mem size from 8 bytes to 4 bytes.
As a result, the bpf check fails, we need to skip adjust mem size to fit
the verifier.

Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
---
tools/lib/bpf/libbpf.c | 34 +++++++++++++++++++++++++++++-----
1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 184ce1684dcd..e1c21b631a0b 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5634,6 +5634,28 @@ static int bpf_core_resolve_relo(struct bpf_program *prog,
targ_res);
}

+static bool
+bpf_core_patch_insn_skip(const struct btf *local_btf, const struct bpf_insn *insn,
+ const struct bpf_core_relo_res *res)
+{
+ __u8 class;
+ const struct btf_type *orig_t;
+
+ class = BPF_CLASS(insn->code);
+ orig_t = btf_type_by_id(local_btf, res->orig_type_id);
+
+ /*
+ * verifier has to see a load of a pointer as a 8-byte load,
+ * CO_RE should not screws up access, bpf_core_patch_insn modifies
+ * load's mem size from 8 bytes to 4 bytes in 32-bit arch,
+ * so we skip adjust mem size.
+ */
+ if (class == BPF_LDX && btf_is_ptr(orig_t))
+ return true;
+
+ return false;
+}
+
static int
bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
{
@@ -5730,11 +5752,13 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
goto out;
}

- err = bpf_core_patch_insn(prog->name, insn, insn_idx, rec, i, &targ_res);
- if (err) {
- pr_warn("prog '%s': relo #%d: failed to patch insn #%u: %d\n",
- prog->name, i, insn_idx, err);
- goto out;
+ if (!bpf_core_patch_insn_skip(obj->btf, insn, &targ_res)) {
+ err = bpf_core_patch_insn(prog->name, insn, insn_idx, rec, i, &targ_res);
+ if (err) {
+ pr_warn("prog '%s': relo #%d: failed to patch insn #%u: %d\n",
+ prog->name, i, insn_idx, err);
+ goto out;
+ }
}
}
}
--
2.30.GIT