bpf: make programs see skb->data == L2 for ingress and egress

eBPF programs attached to ingress and egress qdiscs see inconsistent skb->data.
For ingress L2 header is already pulled, whereas for egress it's present.
This is known to program writers which are currently forced to use
BPF_LL_OFF workaround.
Since programs don't change skb internal pointers it is safe to do
pull/push right around invocation of the program and earlier taps and
later pt->func() will not be affected.
Multiple taps via packet_rcv(), tpacket_rcv() are doing the same trick
around run_filter/BPF_PROG_RUN even if skb_shared.

This fix finally allows programs to use optimized LD_ABS/IND instructions
without BPF_LL_OFF for higher performance.
tc ingress + cls_bpf + samples/bpf/tcbpf1_kern.o
       w/o JIT   w/JIT
before  20.5     23.6 Mpps
after   21.8     26.6 Mpps

Old programs with BPF_LL_OFF will still work as-is.

We can now undo most of the earlier workaround commit:
a166151cbe33 ("bpf: fix bpf helpers to use skb->mac_header relative offsets")

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/filter.c b/net/core/filter.c
index 09b2062eb5b83594291d6ab861b8c01765fd1dde..36a69e33d76ba05c54b95132c9c61fa2eca99f43 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1238,21 +1238,6 @@ int sk_attach_bpf(u32 ufd, struct sock *sk)
        return 0;
 }
 
-/**
- *     bpf_skb_clone_not_writable - is the header of a clone not writable
- *     @skb: buffer to check
- *     @len: length up to which to write, can be negative
- *
- *     Returns true if modifying the header part of the cloned buffer
- *     does require the data to be copied. I.e. this version works with
- *     negative lengths needed for eBPF case!
- */
-static bool bpf_skb_clone_unwritable(const struct sk_buff *skb, int len)
-{
-       return skb_header_cloned(skb) ||
-              (int) skb_headroom(skb) + len > skb->hdr_len;
-}
-
 #define BPF_RECOMPUTE_CSUM(flags)      ((flags) & 1)
 
 static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
@@ -1275,9 +1260,8 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
        if (unlikely((u32) offset > 0xffff || len > sizeof(buf)))
                return -EFAULT;
 
-       offset -= skb->data - skb_mac_header(skb);
        if (unlikely(skb_cloned(skb) &&
-                    bpf_skb_clone_unwritable(skb, offset + len)))
+                    !skb_clone_writable(skb, offset + len)))
                return -EFAULT;
 
        ptr = skb_header_pointer(skb, offset, len, buf);
@@ -1321,9 +1305,8 @@ static u64 bpf_l3_csum_replace(u64 r1, u64 r2, u64 from, u64 to, u64 flags)
        if (unlikely((u32) offset > 0xffff))
                return -EFAULT;
 
-       offset -= skb->data - skb_mac_header(skb);
        if (unlikely(skb_cloned(skb) &&
-                    bpf_skb_clone_unwritable(skb, offset + sizeof(sum))))
+                    !skb_clone_writable(skb, offset + sizeof(sum))))
                return -EFAULT;
 
        ptr = skb_header_pointer(skb, offset, sizeof(sum), &sum);
@@ -1369,9 +1352,8 @@ static u64 bpf_l4_csum_replace(u64 r1, u64 r2, u64 from, u64 to, u64 flags)
        if (unlikely((u32) offset > 0xffff))
                return -EFAULT;
 
-       offset -= skb->data - skb_mac_header(skb);
        if (unlikely(skb_cloned(skb) &&
-                    bpf_skb_clone_unwritable(skb, offset + sizeof(sum))))
+                    !skb_clone_writable(skb, offset + sizeof(sum))))
                return -EFAULT;
 
        ptr = skb_header_pointer(skb, offset, sizeof(sum), &sum);
@@ -1425,8 +1407,6 @@ static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)
        if (unlikely(!skb2))
                return -ENOMEM;
 
-       skb_push(skb2, skb2->data - skb_mac_header(skb2));
-
        if (BPF_IS_REDIRECT_INGRESS(flags))
                return dev_forward_skb(dev, skb2);
 

diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
index dc6a2d324bd8163841e7c9e6a0defebd87792ae5..1d56903fd4c79aa008c4c540aabd8b4c099e81a1 100644 (file)
--- a/net/sched/act_bpf.c
+++ b/net/sched/act_bpf.c
@@ -37,6 +37,7 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
 {
        struct tcf_bpf *prog = act->priv;
        int action, filter_res;
+       bool at_ingress = G_TC_AT(skb->tc_verd) & AT_INGRESS;
 
        if (unlikely(!skb_mac_header_was_set(skb)))
                return TC_ACT_UNSPEC;
@@ -48,7 +49,13 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
 
        /* Needed here for accessing maps. */
        rcu_read_lock();
-       filter_res = BPF_PROG_RUN(prog->filter, skb);
+       if (at_ingress) {
+               __skb_push(skb, skb->mac_len);
+               filter_res = BPF_PROG_RUN(prog->filter, skb);
+               __skb_pull(skb, skb->mac_len);
+       } else {
+               filter_res = BPF_PROG_RUN(prog->filter, skb);
+       }
        rcu_read_unlock();
 
        /* A BPF program may overwrite the default action opcode.

diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index 91bd9c19471d58218cb340a2a871c8fe0ac8cd34..c79ecfd36e0f028388ea5f96a64dbb23451b01b1 100644 (file)
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -64,6 +64,11 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 {
        struct cls_bpf_head *head = rcu_dereference_bh(tp->root);
        struct cls_bpf_prog *prog;
+#ifdef CONFIG_NET_CLS_ACT
+       bool at_ingress = G_TC_AT(skb->tc_verd) & AT_INGRESS;
+#else
+       bool at_ingress = false;
+#endif
        int ret = -1;
 
        if (unlikely(!skb_mac_header_was_set(skb)))
@@ -72,7 +77,16 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
        /* Needed here for accessing maps. */
        rcu_read_lock();
        list_for_each_entry_rcu(prog, &head->plist, link) {
-               int filter_res = BPF_PROG_RUN(prog->filter, skb);
+               int filter_res;
+
+               if (at_ingress) {
+                       /* It is safe to push/pull even if skb_shared() */
+                       __skb_push(skb, skb->mac_len);
+                       filter_res = BPF_PROG_RUN(prog->filter, skb);
+                       __skb_pull(skb, skb->mac_len);
+               } else {
+                       filter_res = BPF_PROG_RUN(prog->filter, skb);
+               }
 
                if (filter_res == 0)
                        continue;

diff --git a/samples/bpf/tcbpf1_kern.c b/samples/bpf/tcbpf1_kern.c
index 7c27710f82968e640ff02c54fb29d2cbb56cb356..9bfb2eb34563d0158dae21c97c1b37d640e8d62a 100644 (file)
--- a/samples/bpf/tcbpf1_kern.c
+++ b/samples/bpf/tcbpf1_kern.c
@@ -21,7 +21,7 @@ static inline void set_dst_mac(struct __sk_buff *skb, char *mac)
 
 static inline void set_ip_tos(struct __sk_buff *skb, __u8 new_tos)
 {
-       __u8 old_tos = load_byte(skb, BPF_LL_OFF + TOS_OFF);
+       __u8 old_tos = load_byte(skb, TOS_OFF);
 
        bpf_l3_csum_replace(skb, IP_CSUM_OFF, htons(old_tos), htons(new_tos), 2);
        bpf_skb_store_bytes(skb, TOS_OFF, &new_tos, sizeof(new_tos), 0);
@@ -34,7 +34,7 @@ static inline void set_ip_tos(struct __sk_buff *skb, __u8 new_tos)
 
 static inline void set_tcp_ip_src(struct __sk_buff *skb, __u32 new_ip)
 {
-       __u32 old_ip = _htonl(load_word(skb, BPF_LL_OFF + IP_SRC_OFF));
+       __u32 old_ip = _htonl(load_word(skb, IP_SRC_OFF));
 
        bpf_l4_csum_replace(skb, TCP_CSUM_OFF, old_ip, new_ip, IS_PSEUDO | sizeof(new_ip));
        bpf_l3_csum_replace(skb, IP_CSUM_OFF, old_ip, new_ip, sizeof(new_ip));
@@ -44,7 +44,7 @@ static inline void set_tcp_ip_src(struct __sk_buff *skb, __u32 new_ip)
 #define TCP_DPORT_OFF (ETH_HLEN + sizeof(struct iphdr) + offsetof(struct tcphdr, dest))
 static inline void set_tcp_dest_port(struct __sk_buff *skb, __u16 new_port)
 {
-       __u16 old_port = htons(load_half(skb, BPF_LL_OFF + TCP_DPORT_OFF));
+       __u16 old_port = htons(load_half(skb, TCP_DPORT_OFF));
 
        bpf_l4_csum_replace(skb, TCP_CSUM_OFF, old_port, new_port, sizeof(new_port));
        bpf_skb_store_bytes(skb, TCP_DPORT_OFF, &new_port, sizeof(new_port), 0);
@@ -53,7 +53,7 @@ static inline void set_tcp_dest_port(struct __sk_buff *skb, __u16 new_port)
 SEC("classifier")
 int bpf_prog1(struct __sk_buff *skb)
 {
-       __u8 proto = load_byte(skb, BPF_LL_OFF + ETH_HLEN + offsetof(struct iphdr, protocol));
+       __u8 proto = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol));
        long *value;
 
        if (proto == IPPROTO_TCP) {