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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: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220309090456.3711530-1-kafai@fb.com
This commit is contained in:
Martin KaFai Lau 2022-03-09 01:04:56 -08:00 committed by Daniel Borkmann
parent 3b5d4ddf8f
commit 539de9328e
1 changed files with 11 additions and 10 deletions
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21
net/core/filter.c
View File

@ -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);
}