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-rw-r--r--samples/bpf/xdp2skb_meta_kern.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/samples/bpf/xdp2skb_meta_kern.c b/samples/bpf/xdp2skb_meta_kern.c
index 12e1024069c2..0c12048ac79f 100644
--- a/samples/bpf/xdp2skb_meta_kern.c
+++ b/samples/bpf/xdp2skb_meta_kern.c
@@ -35,15 +35,17 @@ int _xdp_mark(struct xdp_md *ctx)
void *data, *data_end;
int ret;
- /* Reserve space in-front data pointer for our meta info.
+ /* Reserve space in-front of data pointer for our meta info.
* (Notice drivers not supporting data_meta will fail here!)
*/
ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(*meta));
if (ret < 0)
return XDP_ABORTED;
- /* For some unknown reason, these ctx pointers must be read
- * after bpf_xdp_adjust_meta, else verifier will reject prog.
+ /* Notice: Kernel-side verifier requires that loading of
+ * ctx->data MUST happen _after_ helper bpf_xdp_adjust_meta(),
+ * as pkt-data pointers are invalidated. Helpers that require
+ * this are determined/marked by bpf_helper_changes_pkt_data()
*/
data = (void *)(unsigned long)ctx->data;