Hello,
On 2022/11/8 9:22, Andrii Nakryiko wrote:
On Mon, Nov 7, 2022 at 1:23 AM Yang Jihong <yangjihong1@xxxxxxxxxx> wrote:
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@xxxxxxxxxx>
---
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.
+ */
Nope, this is only for BPF UAPI context types like __sk_buff (right
now). fentry/fexit/raw_tp_btf programs traversing kernel types and
following pointers actually need this to work correctly. Don't do
this.
Distinguishing BPF UAPI context from kernel type requires some work.
According to current situation, the solution of patch2 is relatively simple.
Thanks,
Yang
