From 9d90db97e4d4537c82a5ee476b1c13553e487f28 Mon Sep 17 00:00:00 2001 From: Martin KaFai Lau Date: Wed, 9 Mar 2022 01:05:02 -0800 Subject: [PATCH] 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: Martin KaFai Lau Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20220309090502.3711982-1-kafai@fb.com --- net/core/filter.c | 26 ++++++++++++++------------ 1 file changed, 14 insertions(+), 12 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index 2c83d1f387045..f914e4b13b18a 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -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 */ + *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg, TC_AT_INGRESS_MASK, 1); + /* goto */ + *insn++ = BPF_JMP_A(2); + /* : 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 */ + /* : skb->tstamp = tstamp */ *insn++ = BPF_STX_MEM(BPF_DW, skb_reg, value_reg, offsetof(struct sk_buff, tstamp)); return insn; -- 2.30.2