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ebpf offload - add support for tethering of ipv4 udp

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Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I6229e33cb219e9acd14f5b880cfa2ea0a34442f4
This commit is contained in:
Maciej Żenczykowski
2021-02-16 17:27:34 -08:00
parent 2c0edb112f
commit e4a726a5c6
2 changed files with 44 additions and 8 deletions
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1
Tethering/bpf_progs/bpf_tethering.h
View File

@@ -44,6 +44,7 @@
ERR(SHORT_L4_HEADER) \
ERR(SHORT_TCP_HEADER) \
ERR(SHORT_UDP_HEADER) \
ERR(UDP_CSUM_ZERO) \
ERR(TRUNCATED_IPV4) \
ERR(_MAX)

51
Tethering/bpf_progs/offload.c
View File

@@ -428,6 +428,36 @@ static inline __always_inline int do_forward4(struct __sk_buff* skb, const bool
} else { // UDP
// Make sure we can get at the udp header
if (data + l2_header_size + sizeof(*ip) + sizeof(*udph) > data_end) PUNT(SHORT_UDP_HEADER);
// Skip handling of CHECKSUM_COMPLETE packets with udp checksum zero due to need for
// additional updating of skb->csum (this could be fixed up manually with more effort).
//
// Note that the in-kernel implementation of 'int64_t bpf_csum_update(skb, u32 csum)' is:
// if (skb->ip_summed == CHECKSUM_COMPLETE)
// return (skb->csum = csum_add(skb->csum, csum));
// else
// return -ENOTSUPP;
//
// So this will punt any CHECKSUM_COMPLETE packet with a zero UDP checksum,
// and leave all other packets unaffected (since it just at most adds zero to skb->csum).
//
// In practice this should almost never trigger because most nics do not generate
// CHECKSUM_COMPLETE packets on receive - especially so for nics/drivers on a phone.
//
// Additionally since we're forwarding, in most cases the value of the skb->csum field
// shouldn't matter (it's not used by physical nic egress).
//
// It only matters if we're ingressing through a CHECKSUM_COMPLETE capable nic
// and egressing through a virtual interface looping back to the kernel itself
// (ie. something like veth) where the CHECKSUM_COMPLETE/skb->csum can get reused
// on ingress.
//
// If we were in the kernel we'd simply probably call
// void skb_checksum_complete_unset(struct sk_buff *skb) {
// if (skb->ip_summed == CHECKSUM_COMPLETE) skb->ip_summed = CHECKSUM_NONE;
// }
// here instead. Perhaps there should be a bpf helper for that?
if (!udph->check && (bpf_csum_update(skb, 0) >= 0)) PUNT(UDP_CSUM_ZERO);
}
Tether4Key k = {
@@ -486,8 +516,6 @@ static inline __always_inline int do_forward4(struct __sk_buff* skb, const bool
// since we don't offload all traffic in both directions)
if (stat_v->rxBytes + stat_v->txBytes + bytes > *limit_v) PUNT(LIMIT_REACHED);
if (!is_tcp) PUNT(NON_TCP); // TEMP HACK: will remove once UDP is supported.
if (!is_ethernet) {
// Try to inject an ethernet header, and simply return if we fail.
// We do this even if TX interface is RAWIP and thus does not need an ethernet header,
@@ -520,26 +548,33 @@ static inline __always_inline int do_forward4(struct __sk_buff* skb, const bool
// For a rawip tx interface it will simply be a bunch of zeroes and later stripped.
*eth = v->macHeader;
const int l4_offs_csum = is_tcp ? ETH_IP4_TCP_OFFSET(check) : ETH_IP4_UDP_OFFSET(check);
const int sz4 = sizeof(__be32);
// UDP 0 is special and stored as FFFF (this flag also causes a csum of 0 to be unmodified)
const int l4_flags = is_tcp ? 0 : BPF_F_MARK_MANGLED_0;
const __be32 old_daddr = k.dst4.s_addr;
const __be32 old_saddr = k.src4.s_addr;
const __be32 new_daddr = v->dst46.s6_addr32[3];
const __be32 new_saddr = v->src46.s6_addr32[3];
bpf_l4_csum_replace(skb, ETH_IP4_TCP_OFFSET(check), old_daddr, new_daddr, sz4 | BPF_F_PSEUDO_HDR);
bpf_l4_csum_replace(skb, l4_offs_csum, old_daddr, new_daddr, sz4 | BPF_F_PSEUDO_HDR | l4_flags);
bpf_l3_csum_replace(skb, ETH_IP4_OFFSET(check), old_daddr, new_daddr, sz4);
bpf_skb_store_bytes(skb, ETH_IP4_OFFSET(daddr), &new_daddr, sz4, 0);
bpf_l4_csum_replace(skb, ETH_IP4_TCP_OFFSET(check), old_saddr, new_saddr, sz4 | BPF_F_PSEUDO_HDR);
bpf_l4_csum_replace(skb, l4_offs_csum, old_saddr, new_saddr, sz4 | BPF_F_PSEUDO_HDR | l4_flags);
bpf_l3_csum_replace(skb, ETH_IP4_OFFSET(check), old_saddr, new_saddr, sz4);
bpf_skb_store_bytes(skb, ETH_IP4_OFFSET(saddr), &new_saddr, sz4, 0);
const int sz2 = sizeof(__be16);
bpf_l4_csum_replace(skb, ETH_IP4_TCP_OFFSET(check), k.srcPort, v->srcPort, sz2);
bpf_skb_store_bytes(skb, ETH_IP4_TCP_OFFSET(source), &v->srcPort, sz2, 0);
// The offsets for TCP and UDP ports: source (u16 @ L4 offset 0) & dest (u16 @ L4 offset 2) are
// actually the same, so the compiler should just optimize them both down to a constant.
bpf_l4_csum_replace(skb, l4_offs_csum, k.srcPort, v->srcPort, sz2 | l4_flags);
bpf_skb_store_bytes(skb, is_tcp ? ETH_IP4_TCP_OFFSET(source) : ETH_IP4_UDP_OFFSET(source),
&v->srcPort, sz2, 0);
bpf_l4_csum_replace(skb, ETH_IP4_TCP_OFFSET(check), k.dstPort, v->dstPort, sz2);
bpf_skb_store_bytes(skb, ETH_IP4_TCP_OFFSET(dest), &v->dstPort, sz2, 0);
bpf_l4_csum_replace(skb, l4_offs_csum, k.dstPort, v->dstPort, sz2 | l4_flags);
bpf_skb_store_bytes(skb, is_tcp ? ETH_IP4_TCP_OFFSET(dest) : ETH_IP4_UDP_OFFSET(dest),
&v->dstPort, sz2, 0);
// TEMP HACK: lack of TTL decrement