Commit 9d90db97 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Daniel Borkmann
Browse files

bpf: Simplify insn rewrite on BPF_WRITE __sk_buff->tstamp 



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: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220309090502.3711982-1-kafai@fb.com
parent 539de932

net/core/filter.c

+14 −12
Original line number Diff line number Diff line
@@ -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;