The current tc-bpf@ingress reads and writes the __sk_buff->tstamp as a (rcv) timestamp which currently could either be 0 (not available) or ktime_get_real(). This patch is to backward compatible with the (rcv) timestamp expectation at ingress. If the skb->tstamp has the delivery_time, the bpf insn rewrite will read 0 for tc-bpf running at ingress as it is not available. When writing at ingress, it will also clear the skb->mono_delivery_time bit. /* BPF_READ: a = __sk_buff->tstamp */ if (!skb->tc_at_ingress || !skb->mono_delivery_time) a = skb->tstamp; else a = 0 /* BPF_WRITE: __sk_buff->tstamp = a */ if (skb->tc_at_ingress) skb->mono_delivery_time = 0; skb->tstamp = a; [ A note on the BPF_CGROUP_INET_INGRESS which can also access skb->tstamp. At that point, the skb is delivered locally and skb_clear_delivery_time() has already been done, so the skb->tstamp will only have the (rcv) timestamp. ] If the tc-bpf@egress writes 0 to skb->tstamp, the skb->mono_delivery_time has to be cleared also. It could be done together during convert_ctx_access(). However, the latter patch will also expose the skb->mono_delivery_time bit as __sk_buff->delivery_time_type. Changing the delivery_time_type in the background may surprise the user, e.g. the 2nd read on __sk_buff->delivery_time_type may need a READ_ONCE() to avoid compiler optimization. Thus, in expecting the needs in the latter patch, this patch does a check on !skb->tstamp after running the tc-bpf and clears the skb->mono_delivery_time bit if needed. The earlier discussion on v4 [0]. The bpf insn rewrite requires the skb's mono_delivery_time bit and tc_at_ingress bit. They are moved up in sk_buff so that bpf rewrite can be done at a fixed offset. tc_skip_classify is moved together with tc_at_ingress. To get one bit for mono_delivery_time, csum_not_inet is moved down and this bit is currently used by sctp. [0]: https://lore.kernel.org/bpf/20220217015043.khqwqklx45c4m4se@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ Signed-off-by: Martin KaFai Lau <kafai@xxxxxx> --- include/linux/skbuff.h | 18 +++++++---- net/core/filter.c | 71 ++++++++++++++++++++++++++++++++++++------ net/sched/act_bpf.c | 2 ++ net/sched/cls_bpf.c | 2 ++ 4 files changed, 77 insertions(+), 16 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 4b5b926a81f2..5445860e1ba6 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -941,8 +941,12 @@ struct sk_buff { __u8 vlan_present:1; /* See PKT_VLAN_PRESENT_BIT */ __u8 csum_complete_sw:1; __u8 csum_level:2; - __u8 csum_not_inet:1; __u8 dst_pending_confirm:1; + __u8 mono_delivery_time:1; +#ifdef CONFIG_NET_CLS_ACT + __u8 tc_skip_classify:1; + __u8 tc_at_ingress:1; +#endif #ifdef CONFIG_IPV6_NDISC_NODETYPE __u8 ndisc_nodetype:2; #endif @@ -953,10 +957,6 @@ struct sk_buff { #ifdef CONFIG_NET_SWITCHDEV __u8 offload_fwd_mark:1; __u8 offload_l3_fwd_mark:1; -#endif -#ifdef CONFIG_NET_CLS_ACT - __u8 tc_skip_classify:1; - __u8 tc_at_ingress:1; #endif __u8 redirected:1; #ifdef CONFIG_NET_REDIRECT @@ -969,7 +969,7 @@ struct sk_buff { __u8 decrypted:1; #endif __u8 slow_gro:1; - __u8 mono_delivery_time:1; + __u8 csum_not_inet:1; #ifdef CONFIG_NET_SCHED __u16 tc_index; /* traffic control index */ @@ -1047,10 +1047,16 @@ struct sk_buff { /* if you move pkt_vlan_present around you also must adapt these constants */ #ifdef __BIG_ENDIAN_BITFIELD #define PKT_VLAN_PRESENT_BIT 7 +#define TC_AT_INGRESS_MASK (1 << 0) +#define SKB_MONO_DELIVERY_TIME_MASK (1 << 2) #else #define PKT_VLAN_PRESENT_BIT 0 +#define TC_AT_INGRESS_MASK (1 << 7) +#define SKB_MONO_DELIVERY_TIME_MASK (1 << 5) #endif #define PKT_VLAN_PRESENT_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset) +#define TC_AT_INGRESS_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset) +#define SKB_MONO_DELIVERY_TIME_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset) #ifdef __KERNEL__ /* diff --git a/net/core/filter.c b/net/core/filter.c index cfcf9b4d1ec2..5072733743e9 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -8859,6 +8859,65 @@ static struct bpf_insn *bpf_convert_shinfo_access(const struct bpf_insn *si, return insn; } +static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_insn *si, + struct bpf_insn *insn) +{ + __u8 value_reg = si->dst_reg; + __u8 skb_reg = si->src_reg; + +#ifdef CONFIG_NET_CLS_ACT + __u8 tmp_reg = BPF_REG_AX; + + *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, TC_AT_INGRESS_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, + SKB_MONO_DELIVERY_TIME_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. */ + *insn++ = BPF_MOV64_IMM(value_reg, 0); + *insn++ = BPF_JMP_A(1); +#endif + + *insn++ = BPF_LDX_MEM(BPF_DW, value_reg, skb_reg, + offsetof(struct sk_buff, tstamp)); + return insn; +} + +static struct bpf_insn *bpf_convert_tstamp_write(const struct bpf_insn *si, + struct bpf_insn *insn) +{ + __u8 value_reg = si->src_reg; + __u8 skb_reg = si->dst_reg; + +#ifdef CONFIG_NET_CLS_ACT + __u8 tmp_reg = BPF_REG_AX; + + *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, TC_AT_INGRESS_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, + SKB_MONO_DELIVERY_TIME_OFFSET); + *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, + ~SKB_MONO_DELIVERY_TIME_MASK); + *insn++ = BPF_STX_MEM(BPF_B, skb_reg, tmp_reg, + SKB_MONO_DELIVERY_TIME_OFFSET); +#endif + + /* skb->tstamp = tstamp */ + *insn++ = BPF_STX_MEM(BPF_DW, skb_reg, value_reg, + offsetof(struct sk_buff, tstamp)); + return insn; +} + static u32 bpf_convert_ctx_access(enum bpf_access_type type, const struct bpf_insn *si, struct bpf_insn *insn_buf, @@ -9167,17 +9226,9 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type, BUILD_BUG_ON(sizeof_field(struct sk_buff, tstamp) != 8); if (type == BPF_WRITE) - *insn++ = BPF_STX_MEM(BPF_DW, - si->dst_reg, si->src_reg, - bpf_target_off(struct sk_buff, - tstamp, 8, - target_size)); + insn = bpf_convert_tstamp_write(si, insn); else - *insn++ = BPF_LDX_MEM(BPF_DW, - si->dst_reg, si->src_reg, - bpf_target_off(struct sk_buff, - tstamp, 8, - target_size)); + insn = bpf_convert_tstamp_read(si, insn); break; case offsetof(struct __sk_buff, gso_segs): diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c index a77d8908e737..fea2d78b9ddc 100644 --- a/net/sched/act_bpf.c +++ b/net/sched/act_bpf.c @@ -53,6 +53,8 @@ static int tcf_bpf_act(struct sk_buff *skb, const struct tc_action *act, bpf_compute_data_pointers(skb); filter_res = bpf_prog_run(filter, skb); } + if (unlikely(!skb->tstamp && skb->mono_delivery_time)) + skb->mono_delivery_time = 0; if (skb_sk_is_prefetched(skb) && filter_res != TC_ACT_OK) skb_orphan(skb); diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c index df19a847829e..c85b85a192bf 100644 --- a/net/sched/cls_bpf.c +++ b/net/sched/cls_bpf.c @@ -102,6 +102,8 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp, bpf_compute_data_pointers(skb); filter_res = bpf_prog_run(prog->filter, skb); } + if (unlikely(!skb->tstamp && skb->mono_delivery_time)) + skb->mono_delivery_time = 0; if (prog->exts_integrated) { res->class = 0; -- 2.30.2
