bpf: introduce bpf_skb_vlan_push/pop() helpers

Allow eBPF programs attached to TC qdiscs call skb_vlan_push/pop via
helper functions. These functions may change skb->data/hlen which are
cached by some JITs to improve performance of ld_abs/ld_ind instructions.
Therefore JITs need to recognize bpf_skb_vlan_push/pop() calls,
re-compute header len and re-cache skb->data/hlen back into cpu registers.
Note, skb->data/hlen are not directly accessible from the programs,
so any changes to skb->data done either by these helpers or by other
TC actions are safe.

eBPF JIT supported by three architectures:
- arm64 JIT is using bpf_load_pointer() without caching, so it's ok as-is.
- x64 JIT re-caches skb->data/hlen unconditionally after vlan_push/pop calls
  (experiments showed that conditional re-caching is slower).
- s390 JIT falls back to interpreter for now when bpf_skb_vlan_push() is present
  in the program (re-caching is tbd).

These helpers allow more scalable handling of vlan from the programs.
Instead of creating thousands of vlan netdevs on top of eth0 and attaching
TC+ingress+bpf to all of them, the program can be attached to eth0 directly
and manipulate vlans as necessary.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 48 insertions, 0 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 247450a5e387..50338071fac4 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1437,6 +1437,50 @@ static const struct bpf_func_proto bpf_get_cgroup_classid_proto = {
 	.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;
+	__be16 vlan_proto = (__force __be16) r2;
+
+	if (unlikely(vlan_proto != htons(ETH_P_8021Q) &&
+		     vlan_proto != htons(ETH_P_8021AD)))
+		vlan_proto = htons(ETH_P_8021Q);
+
+	return skb_vlan_push(skb, vlan_proto, vlan_tci);
+}
+
+const struct bpf_func_proto bpf_skb_vlan_push_proto = {
+	.func           = bpf_skb_vlan_push,
+	.gpl_only       = false,
+	.ret_type       = RET_INTEGER,
+	.arg1_type      = ARG_PTR_TO_CTX,
+	.arg2_type      = ARG_ANYTHING,
+	.arg3_type      = ARG_ANYTHING,
+};
+
+static u64 bpf_skb_vlan_pop(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+	struct sk_buff *skb = (struct sk_buff *) (long) r1;
+
+	return skb_vlan_pop(skb);
+}
+
+const struct bpf_func_proto bpf_skb_vlan_pop_proto = {
+	.func           = bpf_skb_vlan_pop,
+	.gpl_only       = false,
+	.ret_type       = RET_INTEGER,
+	.arg1_type      = ARG_PTR_TO_CTX,
+};
+
+bool bpf_helper_changes_skb_data(void *func)
+{
+	if (func == bpf_skb_vlan_push)
+		return true;
+	if (func == bpf_skb_vlan_pop)
+		return true;
+	return false;
+}
+
 static const struct bpf_func_proto *
 sk_filter_func_proto(enum bpf_func_id func_id)
 {
@@ -1476,6 +1520,10 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
 		return &bpf_clone_redirect_proto;
 	case BPF_FUNC_get_cgroup_classid:
 		return &bpf_get_cgroup_classid_proto;
+	case BPF_FUNC_skb_vlan_push:
+		return &bpf_skb_vlan_push_proto;
+	case BPF_FUNC_skb_vlan_pop:
+		return &bpf_skb_vlan_pop_proto;
 	default:
 		return sk_filter_func_proto(func_id);
 	}