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offload - begin ipv4 tethering implementation

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Test: atest, TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I0ad143be954d55d0ed39853031c7bd364378e1ec
This commit is contained in:
Maciej Żenczykowski
2021-01-24 21:01:29 -08:00
parent 18552e8fb3
commit c2b0146045
1 changed files with 186 additions and 8 deletions
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194
Tethering/bpf_progs/offload.c
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@@ -20,10 +20,17 @@
#include <linux/pkt_cls.h>
#include <linux/tcp.h>
// bionic kernel uapi linux/udp.h header is munged...
#define __kernel_udphdr udphdr
#include <linux/udp.h>
#include "bpf_helpers.h"
#include "bpf_net_helpers.h"
#include "netdbpf/bpf_shared.h"
// From kernel:include/net/ip.h
#define IP_DF 0x4000 // Flag: "Don't Fragment"
// Tethering stats, indexed by upstream interface.
DEFINE_BPF_MAP_GRW(tether_stats_map, HASH, TetherStatsKey, TetherStatsValue, 16, AID_NETWORK_STACK)
@@ -284,26 +291,197 @@ DEFINE_BPF_MAP_GRW(tether_downstream4_map, HASH, TetherDownstream4Key, TetherDow
DEFINE_BPF_MAP_GRW(tether_upstream4_map, HASH, TetherUpstream4Key, TetherUpstream4Value, 64,
AID_NETWORK_STACK)
DEFINE_BPF_PROG("schedcls/tether_downstream4_ether", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_downstream4_ether)
static inline __always_inline int do_forward4(struct __sk_buff* skb, const bool is_ethernet,
const bool downstream) {
const int l2_header_size = is_ethernet ? sizeof(struct ethhdr) : 0;
void* data = (void*)(long)skb->data;
const void* data_end = (void*)(long)skb->data_end;
struct ethhdr* eth = is_ethernet ? data : NULL; // used iff is_ethernet
struct iphdr* ip = is_ethernet ? (void*)(eth + 1) : data;
// Require ethernet dst mac address to be our unicast address.
if (is_ethernet && (skb->pkt_type != PACKET_HOST)) return TC_ACT_OK;
// Must be meta-ethernet IPv4 frame
if (skb->protocol != htons(ETH_P_IP)) return TC_ACT_OK;
// Must have (ethernet and) ipv4 header
if (data + l2_header_size + sizeof(*ip) > data_end) return TC_ACT_OK;
// Ethertype - if present - must be IPv4
if (is_ethernet && (eth->h_proto != htons(ETH_P_IP))) return TC_ACT_OK;
// IP version must be 4
if (ip->version != 4) return TC_ACT_OK;
// We cannot handle IP options, just standard 20 byte == 5 dword minimal IPv4 header
if (ip->ihl != 5) return TC_ACT_OK;
// Calculate the IPv4 one's complement checksum of the IPv4 header.
__wsum sum4 = 0;
for (int i = 0; i < sizeof(*ip) / sizeof(__u16); ++i) {
sum4 += ((__u16*)ip)[i];
}
// Note that sum4 is guaranteed to be non-zero by virtue of ip4->version == 4
sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse u32 into range 1 .. 0x1FFFE
sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse any potential carry into u16
// for a correct checksum we should get *a* zero, but sum4 must be positive, ie 0xFFFF
if (sum4 != 0xFFFF) return TC_ACT_OK;
// Minimum IPv4 total length is the size of the header
if (ntohs(ip->tot_len) < sizeof(*ip)) return TC_ACT_OK;
// We are incapable of dealing with IPv4 fragments
if (ip->frag_off & ~htons(IP_DF)) return TC_ACT_OK;
// Cannot decrement during forward if already zero or would be zero,
// Let the kernel's stack handle these cases and generate appropriate ICMP errors.
if (ip->ttl <= 1) return TC_ACT_OK;
const bool is_tcp = (ip->protocol == IPPROTO_TCP);
// We do not support anything besides TCP and UDP
if (!is_tcp && (ip->protocol != IPPROTO_UDP)) return TC_ACT_OK;
struct tcphdr* tcph = is_tcp ? (void*)(ip + 1) : NULL;
struct udphdr* udph = is_tcp ? NULL : (void*)(ip + 1);
if (is_tcp) {
// Make sure we can get at the tcp header
if (data + l2_header_size + sizeof(*ip) + sizeof(*tcph) > data_end) return TC_ACT_OK;
// If hardware offload is running and programming flows based on conntrack entries, try not
// to interfere with it, so do not offload TCP packets with any one of the SYN/FIN/RST flags
if (tcph->syn || tcph->fin || tcph->rst) return TC_ACT_OK;
} else { // UDP
// Make sure we can get at the udp header
if (data + l2_header_size + sizeof(*ip) + sizeof(*udph) > data_end) return TC_ACT_OK;
}
TetherDownstream4Key kd = {
.iif = skb->ifindex,
.l4Proto = ip->protocol,
.src4.s_addr = ip->saddr,
.dst4.s_addr = ip->daddr,
.srcPort = is_tcp ? tcph->source : udph->source,
.dstPort = is_tcp ? tcph->dest : udph->dest,
};
if (is_ethernet) for (int i = 0; i < ETH_ALEN; ++i) kd.dstMac[i] = eth->h_dest[i];
TetherUpstream4Key ku = {
.iif = skb->ifindex,
.l4Proto = ip->protocol,
.src4.s_addr = ip->saddr,
.dst4.s_addr = ip->daddr,
.srcPort = is_tcp ? tcph->source : udph->source,
.dstPort = is_tcp ? tcph->dest : udph->dest,
};
if (is_ethernet) for (int i = 0; i < ETH_ALEN; ++i) ku.dstMac[i] = eth->h_dest[i];
TetherDownstream4Value* vd = downstream ? bpf_tether_downstream4_map_lookup_elem(&kd) : NULL;
TetherUpstream4Value* vu = downstream ? NULL : bpf_tether_upstream4_map_lookup_elem(&ku);
// If we don't find any offload information then simply let the core stack handle it...
if (downstream && !vd) return TC_ACT_OK;
if (!downstream && !vu) return TC_ACT_OK;
uint32_t stat_and_limit_k = downstream ? skb->ifindex : vu->oif;
TetherStatsValue* stat_v = bpf_tether_stats_map_lookup_elem(&stat_and_limit_k);
// If we don't have anywhere to put stats, then abort...
if (!stat_v) return TC_ACT_OK;
uint64_t* limit_v = bpf_tether_limit_map_lookup_elem(&stat_and_limit_k);
// If we don't have a limit, then abort...
if (!limit_v) return TC_ACT_OK;
// Required IPv4 minimum mtu is 68, below that not clear what we should do, abort...
const int pmtu = downstream ? vd->pmtu : vu->pmtu;
if (pmtu < 68) return TC_ACT_OK;
// Approximate handling of TCP/IPv4 overhead for incoming LRO/GRO packets: default
// outbound path mtu of 1500 is not necessarily correct, but worst case we simply
// undercount, which is still better then not accounting for this overhead at all.
// Note: this really shouldn't be device/path mtu at all, but rather should be
// derived from this particular connection's mss (ie. from gro segment size).
// This would require a much newer kernel with newer ebpf accessors.
// (This is also blindly assuming 12 bytes of tcp timestamp option in tcp header)
uint64_t packets = 1;
uint64_t bytes = skb->len;
if (bytes > pmtu) {
const int tcp_overhead = sizeof(struct iphdr) + sizeof(struct tcphdr) + 12;
const int mss = pmtu - tcp_overhead;
const uint64_t payload = bytes - tcp_overhead;
packets = (payload + mss - 1) / mss;
bytes = tcp_overhead * packets + payload;
}
// Are we past the limit? If so, then abort...
// Note: will not overflow since u64 is 936 years even at 5Gbps.
// Do not drop here. Offload is just that, whenever we fail to handle
// a packet we let the core stack deal with things.
// (The core stack needs to handle limits correctly anyway,
// since we don't offload all traffic in both directions)
if (stat_v->rxBytes + stat_v->txBytes + bytes > *limit_v) return TC_ACT_OK;
// TODO: replace Errors with Packets once implemented
__sync_fetch_and_add(downstream ? &stat_v->rxErrors : &stat_v->txErrors, packets);
__sync_fetch_and_add(downstream ? &stat_v->rxBytes : &stat_v->txBytes, bytes);
// TODO: not actually implemented yet
return TC_ACT_OK;
}
// Real implementations for 5.9+ kernels
DEFINE_BPF_PROG_KVER("schedcls/tether_downstream4_ether$5_9", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_downstream4_ether_5_9, KVER(5, 9, 0))
(struct __sk_buff* skb) {
return do_forward4(skb, /* is_ethernet */ true, /* downstream */ true);
}
DEFINE_BPF_PROG_KVER("schedcls/tether_downstream4_rawip$5_9", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_downstream4_rawip_5_9, KVER(5, 9, 0))
(struct __sk_buff* skb) {
return do_forward4(skb, /* is_ethernet */ false, /* downstream */ true);
}
DEFINE_BPF_PROG_KVER("schedcls/tether_upstream4_ether$5_9", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_upstream4_ether_5_9, KVER(5, 9, 0))
(struct __sk_buff* skb) {
return do_forward4(skb, /* is_ethernet */ true, /* downstream */ false);
}
DEFINE_BPF_PROG_KVER("schedcls/tether_upstream4_rawip$5_9", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_upstream4_rawip_5_9, KVER(5, 9, 0))
(struct __sk_buff* skb) {
return do_forward4(skb, /* is_ethernet */ false, /* downstream */ false);
}
// Placeholder implementations for older pre-5.9 kernels
DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_downstream4_ether$stub", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_downstream4_ether_stub, KVER_NONE, KVER(5, 9, 0))
(struct __sk_buff* skb) {
return TC_ACT_OK;
}
DEFINE_BPF_PROG("schedcls/tether_downstream4_rawip", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_downstream4_rawip)
DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_downstream4_rawip$stub", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_downstream4_rawip_stub, KVER_NONE, KVER(5, 9, 0))
(struct __sk_buff* skb) {
return TC_ACT_OK;
}
DEFINE_BPF_PROG("schedcls/tether_upstream4_ether", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_upstream4_ether)
DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_upstream4_ether$stub", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_upstream4_ether_stub, KVER_NONE, KVER(5, 9, 0))
(struct __sk_buff* skb) {
return TC_ACT_OK;
}
DEFINE_BPF_PROG("schedcls/tether_upstream4_rawip", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_upstream4_rawip)
DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_upstream4_rawip$stub", AID_ROOT, AID_NETWORK_STACK,
sched_cls_tether_upstream4_rawip_stub, KVER_NONE, KVER(5, 9, 0))
(struct __sk_buff* skb) {
return TC_ACT_OK;
}