bpf: add bpf_get_hash_recalc helper

If skb_clear_hash() was invoked due to mangling of relevant headers and
BPF program needs skb->hash later on, we can add a helper to trigger hash
recalculation via bpf_get_hash_recalc().

The helper will return the newly retrieved hash directly, but later access
can also be done via skb context again through skb->hash directly (inline)
without needing to call the helper once more.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index f44504d875e2..c14ca1cd6297 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -348,6 +348,15 @@ enum bpf_func_id {
          *    < 0 error
          */
         BPF_FUNC_skb_in_cgroup,
+
+        /**
+         * bpf_get_hash_recalc(skb)
+         * Retrieve and possibly recalculate skb->hash.
+         * @skb: pointer to skb
+         * Return: hash
+         */
+        BPF_FUNC_get_hash_recalc,
+
         __BPF_FUNC_MAX_ID,
 };