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>

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index f44504d..c14ca1c 100644 (file)
--- 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,
 };
 

diff --git a/net/core/filter.c b/net/core/filter.c
index 54071cf..10c4a2f 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1729,6 +1729,23 @@ static const struct bpf_func_proto bpf_get_route_realm_proto = {
        .arg1_type      = ARG_PTR_TO_CTX,
 };
 
+static u64 bpf_get_hash_recalc(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+       /* If skb_clear_hash() was called due to mangling, we can
+        * trigger SW recalculation here. Later access to hash
+        * can then use the inline skb->hash via context directly
+        * instead of calling this helper again.
+        */
+       return skb_get_hash((struct sk_buff *) (unsigned long) r1);
+}
+
+static const struct bpf_func_proto bpf_get_hash_recalc_proto = {
+       .func           = bpf_get_hash_recalc,
+       .gpl_only       = false,
+       .ret_type       = RET_INTEGER,
+       .arg1_type      = ARG_PTR_TO_CTX,
+};
+
 static u64 bpf_skb_vlan_push(u64 r1, u64 r2, u64 vlan_tci, u64 r4, u64 r5)
 {
        struct sk_buff *skb = (struct sk_buff *) (long) r1;
@@ -2337,6 +2354,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
                return &bpf_redirect_proto;
        case BPF_FUNC_get_route_realm:
                return &bpf_get_route_realm_proto;
+       case BPF_FUNC_get_hash_recalc:
+               return &bpf_get_hash_recalc_proto;
        case BPF_FUNC_perf_event_output:
                return bpf_get_event_output_proto();
        case BPF_FUNC_get_smp_processor_id: