Commit 539de932 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Daniel Borkmann
Browse files

bpf: Simplify insn rewrite on BPF_READ __sk_buff->tstamp 



The skb->tc_at_ingress and skb->mono_delivery_time are at the same
byte offset.  Thus, only one BPF_LDX_MEM(BPF_B) is needed
and both bits can be tested together.

/* BPF_READ: a = __sk_buff->tstamp */
if (skb->tc_at_ingress && skb->mono_delivery_time)
	a = 0;
else
	a = skb->tstamp;

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/20220309090456.3711530-1-kafai@fb.com
parent 3b5d4ddf

net/core/filter.c

+11 −10
Original line number Diff line number Diff line
@@ -8956,21 +8956,22 @@ static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_prog *prog, 
	__u8 skb_reg = si->src_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, read skb->tstamp as is if delivery_time_access is true.

	 */

	if (!prog->delivery_time_access) {

		/* AX is needed because src_reg and dst_reg could be the same */

		__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, 5);

		/* @ingress, read __sk_buff->tstamp as the (rcv) timestamp,

		 * so check 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_JMP32_IMM(BPF_JEQ, tmp_reg, 0, 2);

		/* skb->mono_delivery_time is set, read 0 as the (rcv) timestamp. */

					TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK);

		*insn++ = BPF_JMP32_IMM(BPF_JNE, tmp_reg,

					TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK, 2);

		/* skb->tc_at_ingress && skb->mono_delivery_time,

		 * read 0 as the (rcv) timestamp.

		 */

		*insn++ = BPF_MOV64_IMM(value_reg, 0);

		*insn++ = BPF_JMP_A(1);

	}