Commit 3431205e authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

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:
a166151c ("bpf: fix bpf helpers to use skb->mac_header relative offsets")

Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Acked-by: default avatarJamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 98da81a4

net/core/filter.c

+3 −23
Original line number Diff line number Diff line
@@ -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);

net/sched/act_bpf.c

+8 −1
Original line number Diff line number Diff line
@@ -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();

	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.

net/sched/cls_bpf.c

+15 −1
Original line number Diff line number Diff line
@@ -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;

samples/bpf/tcbpf1_kern.c

+4 −4
Original line number Diff line number Diff line
@@ -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) {

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