From: Martin KaFai Lau <kafai@fb.com>
Date: Wed, 2 Mar 2022 11:56:28 -0800
Subject: bpf: Keep the (rcv) timestamp behavior for the existing
tc-bpf@ingress
Patch-mainline: v5.18-rc1
Git-commit: 7449197d600d30d038b1ce6285ab4747096eac7f
References: jsc#PED-1377
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@kafai-mbp.dhcp.thefacebook.com/
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
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(-)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -844,8 +844,12 @@ 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
@@ -857,10 +861,6 @@ struct sk_buff {
__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
__u8 from_ingress:1;
@@ -869,7 +869,7 @@ 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 */
@@ -949,10 +949,16 @@ 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__
/*
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8859,6 +8859,65 @@ static struct bpf_insn *bpf_convert_shin
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 b
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):
--- a/net/sched/act_bpf.c
+++ b/net/sched/act_bpf.c
@@ -53,6 +53,8 @@ static int tcf_bpf_act(struct sk_buff *s
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);
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -102,6 +102,8 @@ static int cls_bpf_classify(struct sk_bu
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;