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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: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20210223184934.6054-4-xiyou.wangcong@gmail.com
This commit is contained in:
Cong Wang 2021-02-23 10:49:28 -08:00 committed by Alexei Starovoitov
parent 5a685cd94b
commit 16137b09a6
3 changed files with 28 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/net/tcp.h
View File

@ -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;

48
net/core/filter.c
View File

@ -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,

1
net/core/skmsg.c
View File

@ -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);
}