From 90b81ac174111790dd7af5a018e0b03b8bfbbbe9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20=C5=BBenczykowski?= <maze@google.com>
Date: Sun, 7 Mar 2021 06:48:26 -0800
Subject: [PATCH] ebpf offload - beginnings of xdp implementation
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Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I6956e78bd325b63dc6dc813440f9f80c29aada36
---
 Tethering/bpf_progs/offload.c | 50 ++++++++++++++++++++++++++++++++---
 1 file changed, 46 insertions(+), 4 deletions(-)

diff --git a/Tethering/bpf_progs/offload.c b/Tethering/bpf_progs/offload.c
index 4ca1b5735a..7f9754d896 100644
--- a/Tethering/bpf_progs/offload.c
+++ b/Tethering/bpf_progs/offload.c
@@ -755,27 +755,69 @@ DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_upstream4_ether$stub", AID_ROOT, AID
 DEFINE_BPF_MAP_GRW(tether_xdp_devmap, DEVMAP_HASH, uint32_t, uint32_t, 64,
                    AID_NETWORK_STACK)
 
+static inline __always_inline int do_xdp_forward6(struct xdp_md *ctx, const bool is_ethernet,
+        const bool downstream) {
+    return XDP_PASS;
+}
+
+static inline __always_inline int do_xdp_forward4(struct xdp_md *ctx, const bool is_ethernet,
+        const bool downstream) {
+    return XDP_PASS;
+}
+
+static inline __always_inline int do_xdp_forward_ether(struct xdp_md *ctx, const bool downstream) {
+    const void* data = (void*)(long)ctx->data;
+    const void* data_end = (void*)(long)ctx->data_end;
+    const struct ethhdr* eth = data;
+
+    // Make sure we actually have an ethernet header
+    if ((void*)(eth + 1) > data_end) return XDP_PASS;
+
+    if (eth->h_proto == htons(ETH_P_IPV6))
+        return do_xdp_forward6(ctx, /* is_ethernet */ true, downstream);
+    if (eth->h_proto == htons(ETH_P_IP))
+        return do_xdp_forward4(ctx, /* is_ethernet */ true, downstream);
+
+    // Anything else we don't know how to handle...
+    return XDP_PASS;
+}
+
+static inline __always_inline int do_xdp_forward_rawip(struct xdp_md *ctx, const bool downstream) {
+    const void* data = (void*)(long)ctx->data;
+    const void* data_end = (void*)(long)ctx->data_end;
+
+    // The top nibble of both IPv4 and IPv6 headers is the IP version.
+    if (data_end - data < 1) return XDP_PASS;
+    const uint8_t v = (*(uint8_t*)data) >> 4;
+
+    if (v == 6) return do_xdp_forward6(ctx, /* is_ethernet */ false, downstream);
+    if (v == 4) return do_xdp_forward4(ctx, /* is_ethernet */ false, downstream);
+
+    // Anything else we don't know how to handle...
+    return XDP_PASS;
+}
+
 #define DEFINE_XDP_PROG(str, func) \
     DEFINE_BPF_PROG_KVER(str, AID_ROOT, AID_NETWORK_STACK, func, KVER(5, 9, 0))(struct xdp_md *ctx)
 
 DEFINE_XDP_PROG("xdp/tether_downstream_ether",
                  xdp_tether_downstream_ether) {
-    return XDP_PASS;
+    return do_xdp_forward_ether(ctx, /* downstream */ true);
 }
 
 DEFINE_XDP_PROG("xdp/tether_downstream_rawip",
                  xdp_tether_downstream_rawip) {
-    return XDP_PASS;
+    return do_xdp_forward_rawip(ctx, /* downstream */ true);
 }
 
 DEFINE_XDP_PROG("xdp/tether_upstream_ether",
                  xdp_tether_upstream_ether) {
-    return XDP_PASS;
+    return do_xdp_forward_ether(ctx, /* downstream */ false);
 }
 
 DEFINE_XDP_PROG("xdp/tether_upstream_rawip",
                  xdp_tether_upstream_rawip) {
-    return XDP_PASS;
+    return do_xdp_forward_rawip(ctx, /* downstream */ false);
 }
 
 LICENSE("Apache 2.0");