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>

1 files changed, 3 insertions, 23 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 09b2062eb5b8..36a69e33d76b 100644
--- 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);