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bpf: Simplify insn rewrite on BPF_WRITE __sk_buff->tstamp

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BPF_JMP32_IMM(BPF_JSET) is used to save a BPF_ALU32_IMM(BPF_AND).

The skb->tc_at_ingress and skb->mono_delivery_time are at the same
offset, so only one BPF_LDX_MEM(BPF_B) is needed.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220309090502.3711982-1-kafai@fb.com
This commit is contained in:
Martin KaFai Lau 2022-03-09 01:05:02 -08:00 committed by Daniel Borkmann
parent 539de9328e
commit 9d90db97e4
1 changed files with 14 additions and 12 deletions
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26
net/core/filter.c
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@ -8990,25 +8990,27 @@ static struct bpf_insn *bpf_convert_tstamp_write(const struct bpf_prog *prog,
__u8 skb_reg = si->dst_reg;
#ifdef CONFIG_NET_CLS_ACT
/* If the delivery_time_type is read,
* the bpf prog is aware the tstamp could have delivery time.
* Thus, write skb->tstamp as is if delivery_time_access is true.
* Otherwise, writing at ingress will have to clear the
* mono_delivery_time bit also.
*/
if (!prog->delivery_time_access) {
__u8 tmp_reg = BPF_REG_AX;
*insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, PKT_VLAN_PRESENT_OFFSET);
*insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, TC_AT_INGRESS_MASK);
*insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0, 3);
/* Writing __sk_buff->tstamp at ingress as the (rcv) timestamp.
* Clear the skb->mono_delivery_time.
*/
*insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg,
PKT_VLAN_PRESENT_OFFSET);
*insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg,
~SKB_MONO_DELIVERY_TIME_MASK);
*insn++ = BPF_STX_MEM(BPF_B, skb_reg, tmp_reg,
PKT_VLAN_PRESENT_OFFSET);
/* Writing __sk_buff->tstamp as ingress, goto <clear> */
*insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg, TC_AT_INGRESS_MASK, 1);
/* goto <store> */
*insn++ = BPF_JMP_A(2);
/* <clear>: mono_delivery_time */
*insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, ~SKB_MONO_DELIVERY_TIME_MASK);
*insn++ = BPF_STX_MEM(BPF_B, skb_reg, tmp_reg, PKT_VLAN_PRESENT_OFFSET);
}
#endif
/* skb->tstamp = tstamp */
/* <store>: skb->tstamp = tstamp */
*insn++ = BPF_STX_MEM(BPF_DW, skb_reg, value_reg,
offsetof(struct sk_buff, tstamp));
return insn;