[PATCH net-next 15/24] net: Use nested-BH locking for XDP redirect.

[Sebastian Andrzej Siewior]

The per-CPU variables used during bpf_prog_run_xdp() invocation and
later during xdp_do_redirect() rely on disabled BH for their protection.
Without locking in local_bh_disable() on PREEMPT_RT these data structure
require explicit locking.

This is a follow-up on the previous change which introduced
bpf_run_lock.redirect_lock and uses it now within drivers.

The simple way is to acquire the lock before bpf_prog_run_xdp() is
invoked and hold it until the end of function.
This does not always work because some drivers (cpsw, atlantic) invoke
xdp_do_flush() in the same context.
Acquiring the lock in bpf_prog_run_xdp() and dropping in
xdp_do_redirect() (without touching drivers) does not work because not
all driver, which use bpf_prog_run_xdp(), do support XDP_REDIRECT (and
invoke xdp_do_redirect()).

Ideally the minimal locking scope would be bpf_prog_run_xdp() +
xdp_do_redirect() and everything else (error recovery, DMA unmapping,
free/ alloc of memory, …) would happen outside of the locked section.

Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Cc: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Cc: Hao Luo <haoluo@xxxxxxxxxx>
Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
Cc: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Jiri Pirko <jiri@xxxxxxxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
Cc: Ronak Doshi <doshir@xxxxxxxxxx>
Cc: Song Liu <song@xxxxxxxxxx>
Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: VMware PV-Drivers Reviewers <pv-drivers@xxxxxxxxxx>
Cc: Yonghong Song <yonghong.song@xxxxxxxxx>
Cc: bpf@xxxxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 drivers/net/vmxnet3/vmxnet3_xdp.c |  1 +
 kernel/bpf/cpumap.c               |  2 ++
 net/bpf/test_run.c                | 11 ++++++++---
 net/core/dev.c                    |  3 +++
 net/core/filter.c                 |  1 +
 net/core/lwt_bpf.c                |  2 ++
 net/sched/cls_api.c               |  2 ++
 7 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/net/vmxnet3/vmxnet3_xdp.c b/drivers/net/vmxnet3/vmxnet3_xdp.c
index 80ddaff759d47..18bce98fd2e31 100644
--- a/drivers/net/vmxnet3/vmxnet3_xdp.c
+++ b/drivers/net/vmxnet3/vmxnet3_xdp.c
@@ -257,6 +257,7 @@ vmxnet3_run_xdp(struct vmxnet3_rx_queue *rq, struct xdp_buff *xdp,
 	u32 act;
 
 	rq->stats.xdp_packets++;
+	guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
 	act = bpf_prog_run_xdp(prog, xdp);
 	page = virt_to_page(xdp->data_hard_start);
 
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 8a0bb80fe48a3..c26d49bb78679 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -144,6 +144,7 @@ static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu,
 	int err;
 
 	list_for_each_entry_safe(skb, tmp, listp, list) {
+		guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
 		act = bpf_prog_run_generic_xdp(skb, &xdp, rcpu->prog);
 		switch (act) {
 		case XDP_PASS:
@@ -182,6 +183,7 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
 	struct xdp_buff xdp;
 	int i, nframes = 0;
 
+	guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
 	xdp_set_return_frame_no_direct();
 	xdp.rxq = &rxq;
 
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index c9fdcc5cdce10..db8f7eb35c6ca 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -293,6 +293,7 @@ static int xdp_test_run_batch(struct xdp_test_data *xdp, struct bpf_prog *prog,
 	batch_sz = min_t(u32, repeat, xdp->batch_size);
 
 	local_bh_disable();
+	local_lock_nested_bh(&bpf_run_lock.redirect_lock);
 	xdp_set_return_frame_no_direct();
 
 	for (i = 0; i < batch_sz; i++) {
@@ -348,6 +349,9 @@ static int xdp_test_run_batch(struct xdp_test_data *xdp, struct bpf_prog *prog,
 	}
 
 out:
+	xdp_clear_return_frame_no_direct();
+	local_unlock_nested_bh(&bpf_run_lock.redirect_lock);
+
 	if (redirect)
 		xdp_do_flush();
 	if (nframes) {
@@ -356,7 +360,6 @@ static int xdp_test_run_batch(struct xdp_test_data *xdp, struct bpf_prog *prog,
 			err = ret;
 	}
 
-	xdp_clear_return_frame_no_direct();
 	local_bh_enable();
 	return err;
 }
@@ -417,10 +420,12 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat,
 	do {
 		run_ctx.prog_item = &item;
 		local_bh_disable();
-		if (xdp)
+		if (xdp) {
+			guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
 			*retval = bpf_prog_run_xdp(prog, ctx);
-		else
+		} else {
 			*retval = bpf_prog_run(prog, ctx);
+		}
 		local_bh_enable();
 	} while (bpf_test_timer_continue(&t, 1, repeat, &ret, time));
 	bpf_reset_run_ctx(old_ctx);
diff --git a/net/core/dev.c b/net/core/dev.c
index 5a0f6da7b3ae5..5ba7509e88752 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3993,6 +3993,7 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
 		*pt_prev = NULL;
 	}
 
+	guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
 	qdisc_skb_cb(skb)->pkt_len = skb->len;
 	tcx_set_ingress(skb, true);
 
@@ -4045,6 +4046,7 @@ sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
 	if (!entry)
 		return skb;
 
+	guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
 	/* qdisc_skb_cb(skb)->pkt_len & tcx_set_ingress() was
 	 * already set by the caller.
 	 */
@@ -5008,6 +5010,7 @@ int do_xdp_generic(struct bpf_prog *xdp_prog, struct sk_buff *skb)
 		u32 act;
 		int err;
 
+		guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
 		act = netif_receive_generic_xdp(skb, &xdp, xdp_prog);
 		if (act != XDP_PASS) {
 			switch (act) {
diff --git a/net/core/filter.c b/net/core/filter.c
index 7c9653734fb60..72a7812f933a1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4241,6 +4241,7 @@ static const struct bpf_func_proto bpf_xdp_adjust_meta_proto = {
  */
 void xdp_do_flush(void)
 {
+	guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
 	__dev_flush();
 	__cpu_map_flush();
 	__xsk_map_flush();
diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c
index a94943681e5aa..74b88e897a7e3 100644
--- a/net/core/lwt_bpf.c
+++ b/net/core/lwt_bpf.c
@@ -44,6 +44,7 @@ static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
 	 * BPF prog and skb_do_redirect().
 	 */
 	local_bh_disable();
+	local_lock_nested_bh(&bpf_run_lock.redirect_lock);
 	bpf_compute_data_pointers(skb);
 	ret = bpf_prog_run_save_cb(lwt->prog, skb);
 
@@ -76,6 +77,7 @@ static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
 		break;
 	}
 
+	local_unlock_nested_bh(&bpf_run_lock.redirect_lock);
 	local_bh_enable();
 
 	return ret;
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 1976bd1639863..da61b99bc558f 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -23,6 +23,7 @@
 #include <linux/jhash.h>
 #include <linux/rculist.h>
 #include <linux/rhashtable.h>
+#include <linux/bpf.h>
 #include <net/net_namespace.h>
 #include <net/sock.h>
 #include <net/netlink.h>
@@ -3925,6 +3926,7 @@ struct sk_buff *tcf_qevent_handle(struct tcf_qevent *qe, struct Qdisc *sch, stru
 
 	fl = rcu_dereference_bh(qe->filter_chain);
 
+	guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
 	switch (tcf_classify(skb, NULL, fl, &cl_res, false)) {
 	case TC_ACT_SHOT:
 		qdisc_qstats_drop(sch);
-- 
2.43.0