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Message-Id: <20210213214421.226357-4-xiyou.wangcong@gmail.com>
Date: Sat, 13 Feb 2021 13:44:19 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: netdev@...r.kernel.org
Cc: bpf@...r.kernel.org, duanxiongchun@...edance.com,
wangdongdong.6@...edance.com, jiang.wang@...edance.com,
Cong Wang <cong.wang@...edance.com>,
Jakub Sitnicki <jakub@...udflare.com>,
John Fastabend <john.fastabend@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Lorenz Bauer <lmb@...udflare.com>
Subject: [Patch bpf-next v3 3/5] bpf: compute data_end dynamically with JIT code
From: Cong Wang <cong.wang@...edance.com>
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: Jakub Sitnicki <jakub@...udflare.com>
Cc: John Fastabend <john.fastabend@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Lorenz Bauer <lmb@...udflare.com>
Signed-off-by: Cong Wang <cong.wang@...edance.com>
---
include/net/tcp.h | 6 ------
net/core/filter.c | 48 +++++++++++++++++++++++++++--------------------
net/core/skmsg.c | 1 -
3 files changed, 28 insertions(+), 27 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 99fdbf03aeee..697712178eff 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -885,18 +885,12 @@ 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;
diff --git a/net/core/filter.c b/net/core/filter.c
index 7059cf604d94..38c4996e48bf 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -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 = {
@@ -9657,22 +9647,40 @@ 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,
diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index 7f400d044cda..2d8bbb3fd87c 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -744,7 +744,6 @@ 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);
}
--
2.25.1
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