Commit 16137b09 authored by Cong Wang's avatar Cong Wang Committed by Alexei Starovoitov
Browse files

bpf: Compute data_end dynamically with JIT code 



Currently, we compute ->data_end with a compile-time constant
offset of skb. But as Jakub pointed out, we can actually compute
it in eBPF JIT code at run-time, so that we can competely get
rid of ->data_end. This is similar to skb_shinfo(skb) computation
in bpf_convert_shinfo_access().

Suggested-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: default avatarCong Wang <cong.wang@bytedance.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Acked-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20210223184934.6054-4-xiyou.wangcong@gmail.com
parent 5a685cd9

include/net/tcp.h

+0 −6
Original line number Diff line number Diff line
@@ -886,18 +886,12 @@ struct tcp_skb_cb { 
		struct {

			__u32 flags;

			struct sock *sk_redir;

			void *data_end;

		} bpf;

	};

};



#define TCP_SKB_CB(__skb)	((struct tcp_skb_cb *)&((__skb)->cb[0]))



static inline void bpf_compute_data_end_sk_skb(struct sk_buff *skb)

{

	TCP_SKB_CB(skb)->bpf.data_end = skb->data + skb_headlen(skb);

}



static inline bool tcp_skb_bpf_ingress(const struct sk_buff *skb)

{

	return TCP_SKB_CB(skb)->bpf.flags & BPF_F_INGRESS;

net/core/filter.c

+28 −20
Original line number Diff line number Diff line
@@ -1863,10 +1863,7 @@ static const struct bpf_func_proto bpf_sk_fullsock_proto = { 
static inline int sk_skb_try_make_writable(struct sk_buff *skb,

					   unsigned int write_len)

{

	int err = __bpf_try_make_writable(skb, write_len);



	bpf_compute_data_end_sk_skb(skb);

	return err;

	return __bpf_try_make_writable(skb, write_len);

}



BPF_CALL_2(sk_skb_pull_data, struct sk_buff *, skb, u32, len)
@@ -3577,7 +3574,6 @@ BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, 
			return -ENOMEM;

		__skb_pull(skb, len_diff_abs);

	}

	bpf_compute_data_end_sk_skb(skb);

	if (tls_sw_has_ctx_rx(skb->sk)) {

		struct strp_msg *rxm = strp_msg(skb);
@@ -3742,10 +3738,7 @@ static const struct bpf_func_proto bpf_skb_change_tail_proto = { 
BPF_CALL_3(sk_skb_change_tail, struct sk_buff *, skb, u32, new_len,

	   u64, flags)

{

	int ret = __bpf_skb_change_tail(skb, new_len, flags);



	bpf_compute_data_end_sk_skb(skb);

	return ret;

	return __bpf_skb_change_tail(skb, new_len, flags);

}



static const struct bpf_func_proto sk_skb_change_tail_proto = {
@@ -3808,10 +3801,7 @@ static const struct bpf_func_proto bpf_skb_change_head_proto = { 
BPF_CALL_3(sk_skb_change_head, struct sk_buff *, skb, u32, head_room,

	   u64, flags)

{

	int ret = __bpf_skb_change_head(skb, head_room, flags);



	bpf_compute_data_end_sk_skb(skb);

	return ret;

	return __bpf_skb_change_head(skb, head_room, flags);

}



static const struct bpf_func_proto sk_skb_change_head_proto = {
@@ -9655,22 +9645,40 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type, 
	return insn - insn_buf;

}



/* data_end = skb->data + skb_headlen() */

static struct bpf_insn *bpf_convert_data_end_access(const struct bpf_insn *si,

						    struct bpf_insn *insn)

{

	/* si->dst_reg = skb->data */

	*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, data),

			      si->dst_reg, si->src_reg,

			      offsetof(struct sk_buff, data));

	/* AX = skb->len */

	*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, len),

			      BPF_REG_AX, si->src_reg,

			      offsetof(struct sk_buff, len));

	/* si->dst_reg = skb->data + skb->len */

	*insn++ = BPF_ALU64_REG(BPF_ADD, si->dst_reg, BPF_REG_AX);

	/* AX = skb->data_len */

	*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, data_len),

			      BPF_REG_AX, si->src_reg,

			      offsetof(struct sk_buff, data_len));

	/* si->dst_reg = skb->data + skb->len - skb->data_len */

	*insn++ = BPF_ALU64_REG(BPF_SUB, si->dst_reg, BPF_REG_AX);



	return insn;

}



static u32 sk_skb_convert_ctx_access(enum bpf_access_type type,

				     const struct bpf_insn *si,

				     struct bpf_insn *insn_buf,

				     struct bpf_prog *prog, u32 *target_size)

{

	struct bpf_insn *insn = insn_buf;

	int off;



	switch (si->off) {

	case offsetof(struct __sk_buff, data_end):

		off  = si->off;

		off -= offsetof(struct __sk_buff, data_end);

		off += offsetof(struct sk_buff, cb);

		off += offsetof(struct tcp_skb_cb, bpf.data_end);

		*insn++ = BPF_LDX_MEM(BPF_SIZEOF(void *), si->dst_reg,

				      si->src_reg, off);

		insn = bpf_convert_data_end_access(si, insn);

		break;

	default:

		return bpf_convert_ctx_access(type, si, insn_buf, prog,

net/core/skmsg.c

+0 −1
Original line number Diff line number Diff line
@@ -746,7 +746,6 @@ EXPORT_SYMBOL_GPL(sk_psock_msg_verdict); 
static int sk_psock_bpf_run(struct sk_psock *psock, struct bpf_prog *prog,

			    struct sk_buff *skb)

{

	bpf_compute_data_end_sk_skb(skb);

	return bpf_prog_run_pin_on_cpu(prog, skb);

}