kernel: 5.4: import wireguard backport

Rather than using the clunky, old, slower wireguard-linux-compat out of
tree module, this commit does a patch-by-patch backport of upstream's
wireguard to 5.4. This specific backport is in widespread use, being
part of SUSE's enterprise kernel, Oracle's enterprise kernel, Google's
Android kernel, Gentoo's distro kernel, and probably more I've forgotten
about. It's definately the "more proper" way of adding wireguard to a
kernel than the ugly compat.h hell of the wireguard-linux-compat repo.
And most importantly for OpenWRT, it allows using the same module
configuration code for 5.10 as for 5.4, with no need for bifurcation.

These patches are from the backport tree which is maintained in the
open here: https://git.zx2c4.com/wireguard-linux/log/?h=backport-5.4.y
I'll be sending PRs to update this as needed.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 88 insertions, 0 deletions

diff --git a/target/linux/generic/backport-5.4/080-wireguard-0102-wireguard-send-receive-use-explicit-unlikely-branch-.patch b/target/linux/generic/backport-5.4/080-wireguard-0102-wireguard-send-receive-use-explicit-unlikely-branch-.patch
new file mode 100644
index 0000000000..d8ea8908b9
--- /dev/null
+++ b/target/linux/generic/backport-5.4/080-wireguard-0102-wireguard-send-receive-use-explicit-unlikely-branch-.patch
@@ -0,0 +1,88 @@
+From 8df862b663b026d61b4c463caece77f1f127771f Mon Sep 17 00:00:00 2001
+From: "Jason A. Donenfeld" <Jason@zx2c4.com>
+Date: Wed, 6 May 2020 15:33:06 -0600
+Subject: [PATCH 102/124] wireguard: send/receive: use explicit unlikely branch
+ instead of implicit coalescing
+
+commit 243f2148937adc72bcaaa590d482d599c936efde upstream.
+
+It's very unlikely that send will become true. It's nearly always false
+between 0 and 120 seconds of a session, and in most cases becomes true
+only between 120 and 121 seconds before becoming false again. So,
+unlikely(send) is clearly the right option here.
+
+What happened before was that we had this complex boolean expression
+with multiple likely and unlikely clauses nested. Since this is
+evaluated left-to-right anyway, the whole thing got converted to
+unlikely. So, we can clean this up to better represent what's going on.
+
+The generated code is the same.
+
+Suggested-by: Sultan Alsawaf <sultan@kerneltoast.com>
+Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
+---
+ drivers/net/wireguard/receive.c | 13 ++++++-------
+ drivers/net/wireguard/send.c    | 15 ++++++---------
+ 2 files changed, 12 insertions(+), 16 deletions(-)
+
+--- a/drivers/net/wireguard/receive.c
++++ b/drivers/net/wireguard/receive.c
+@@ -226,21 +226,20 @@ void wg_packet_handshake_receive_worker(
+ static void keep_key_fresh(struct wg_peer *peer)
+ {
+ 	struct noise_keypair *keypair;
+-	bool send = false;
++	bool send;
+ 
+ 	if (peer->sent_lastminute_handshake)
+ 		return;
+ 
+ 	rcu_read_lock_bh();
+ 	keypair = rcu_dereference_bh(peer->keypairs.current_keypair);
+-	if (likely(keypair && READ_ONCE(keypair->sending.is_valid)) &&
+-	    keypair->i_am_the_initiator &&
+-	    unlikely(wg_birthdate_has_expired(keypair->sending.birthdate,
+-			REJECT_AFTER_TIME - KEEPALIVE_TIMEOUT - REKEY_TIMEOUT)))
+-		send = true;
++	send = keypair && READ_ONCE(keypair->sending.is_valid) &&
++	       keypair->i_am_the_initiator &&
++	       wg_birthdate_has_expired(keypair->sending.birthdate,
++			REJECT_AFTER_TIME - KEEPALIVE_TIMEOUT - REKEY_TIMEOUT);
+ 	rcu_read_unlock_bh();
+ 
+-	if (send) {
++	if (unlikely(send)) {
+ 		peer->sent_lastminute_handshake = true;
+ 		wg_packet_send_queued_handshake_initiation(peer, false);
+ 	}
+--- a/drivers/net/wireguard/send.c
++++ b/drivers/net/wireguard/send.c
+@@ -124,20 +124,17 @@ void wg_packet_send_handshake_cookie(str
+ static void keep_key_fresh(struct wg_peer *peer)
+ {
+ 	struct noise_keypair *keypair;
+-	bool send = false;
++	bool send;
+ 
+ 	rcu_read_lock_bh();
+ 	keypair = rcu_dereference_bh(peer->keypairs.current_keypair);
+-	if (likely(keypair && READ_ONCE(keypair->sending.is_valid)) &&
+-	    (unlikely(atomic64_read(&keypair->sending.counter.counter) >
+-		      REKEY_AFTER_MESSAGES) ||
+-	     (keypair->i_am_the_initiator &&
+-	      unlikely(wg_birthdate_has_expired(keypair->sending.birthdate,
+-						REKEY_AFTER_TIME)))))
+-		send = true;
++	send = keypair && READ_ONCE(keypair->sending.is_valid) &&
++	       (atomic64_read(&keypair->sending.counter.counter) > REKEY_AFTER_MESSAGES ||
++		(keypair->i_am_the_initiator &&
++		 wg_birthdate_has_expired(keypair->sending.birthdate, REKEY_AFTER_TIME)));
+ 	rcu_read_unlock_bh();
+ 
+-	if (send)
++	if (unlikely(send))
+ 		wg_packet_send_queued_handshake_initiation(peer, false);
+ }
+