[PATCH v4 net-next 5/8] bpf: Keep the (rcv) timestamp behavior for the existing tc-bpf@ingress

[Martin KaFai Lau <kafai@fb.com>]

The current tc-bpf@ingress reads and writes the __sk_buff->tstamp
as a (rcv) timestamp.  This patch is to backward compatible with the
(rcv) timestamp expectation when the skb->tstamp has a mono delivery_time.

If needed, the patch first saves the mono delivery_time.  Depending on
the static key "netstamp_needed_key", it then resets the skb->tstamp to
either 0 or ktime_get_real() before running the tc-bpf@ingress.  After
the tc-bpf prog returns, if the (rcv) timestamp in skb->tstamp has not
been changed, it will restore the earlier saved mono delivery_time.

The current logic to run tc-bpf@ingress is refactored to a new
bpf_prog_run_at_ingress() function and shared between cls_bpf and act_bpf.
The above new delivery_time save/restore logic is also done together in
this function.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
---
 include/linux/filter.h | 28 ++++++++++++++++++++++++++++
 net/sched/act_bpf.c    |  5 +----
 net/sched/cls_bpf.c    |  6 +-----
 3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index d23e999dc032..e43e1701a80e 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -699,6 +699,34 @@ static inline void bpf_compute_data_pointers(struct sk_buff *skb)
 	cb->data_end  = skb->data + skb_headlen(skb);
 }
 
+static __always_inline u32 bpf_prog_run_at_ingress(const struct bpf_prog *prog,
+						   struct sk_buff *skb)
+{
+	ktime_t tstamp, saved_mono_dtime = 0;
+	int filter_res;
+
+	if (unlikely(skb->mono_delivery_time)) {
+		saved_mono_dtime = skb->tstamp;
+		skb->mono_delivery_time = 0;
+		if (static_branch_unlikely(&netstamp_needed_key))
+			skb->tstamp = tstamp = ktime_get_real();
+		else
+			skb->tstamp = tstamp = 0;
+	}
+
+	/* It is safe to push/pull even if skb_shared() */
+	__skb_push(skb, skb->mac_len);
+	bpf_compute_data_pointers(skb);
+	filter_res = bpf_prog_run(prog, skb);
+	__skb_pull(skb, skb->mac_len);
+
+	/* __sk_buff->tstamp was not changed, restore the delivery_time */
+	if (unlikely(saved_mono_dtime) && skb_tstamp(skb) == tstamp)
+		skb_set_delivery_time(skb, saved_mono_dtime, true);
+
+	return filter_res;
+}
+
 /* Similar to bpf_compute_data_pointers(), except that save orginal
  * data in cb->data and cb->meta_data for restore.
  */
diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
index a77d8908e737..14c3bd0a5088 100644
--- a/net/sched/act_bpf.c
+++ b/net/sched/act_bpf.c
@@ -45,10 +45,7 @@ static int tcf_bpf_act(struct sk_buff *skb, const struct tc_action *act,
 
 	filter = rcu_dereference(prog->filter);
 	if (at_ingress) {
-		__skb_push(skb, skb->mac_len);
-		bpf_compute_data_pointers(skb);
-		filter_res = bpf_prog_run(filter, skb);
-		__skb_pull(skb, skb->mac_len);
+		filter_res = bpf_prog_run_at_ingress(filter, skb);
 	} else {
 		bpf_compute_data_pointers(skb);
 		filter_res = bpf_prog_run(filter, skb);
diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index df19a847829e..036b2e1f74af 100644
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -93,11 +93,7 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 		if (tc_skip_sw(prog->gen_flags)) {
 			filter_res = prog->exts_integrated ? TC_ACT_UNSPEC : 0;
 		} else if (at_ingress) {
-			/* It is safe to push/pull even if skb_shared() */
-			__skb_push(skb, skb->mac_len);
-			bpf_compute_data_pointers(skb);
-			filter_res = bpf_prog_run(prog->filter, skb);
-			__skb_pull(skb, skb->mac_len);
+			filter_res = bpf_prog_run_at_ingress(prog->filter, skb);
 		} else {
 			bpf_compute_data_pointers(skb);
 			filter_res = bpf_prog_run(prog->filter, skb);
-- 
2.30.2