nfc: Add KCOV annotations

Add remote KCOV annotations for NFC processing that is done
in background threads. This enables efficient coverage-guided
fuzzing of the NFC subsystem.

The intention is to add annotations to background threads that
process skb's that were allocated in syscall context
(thus have a KCOV handle associated with the current fuzz test).
This includes nci_recv_frame() that is called by the virtual nci
driver in the syscall context.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Bongsu Jeon <bongsu.jeon@samsung.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/nfc/rawsock.c b/net/nfc/rawsock.c
index 8dd5697..5125392 100644
--- a/net/nfc/rawsock.c
+++ b/net/nfc/rawsock.c
@@ -12,6 +12,7 @@
 #include <net/tcp_states.h>
 #include <linux/nfc.h>
 #include <linux/export.h>
+#include <linux/kcov.h>
 
 #include "nfc.h"
 
@@ -189,6 +190,7 @@ static void rawsock_tx_work(struct work_struct *work)
 	}
 
 	skb = skb_dequeue(&sk->sk_write_queue);
+	kcov_remote_start_common(skb_get_kcov_handle(skb));
 
 	sock_hold(sk);
 	rc = nfc_data_exchange(dev, target_idx, skb,
@@ -197,6 +199,7 @@ static void rawsock_tx_work(struct work_struct *work)
 		rawsock_report_error(sk, rc);
 		sock_put(sk);
 	}
+	kcov_remote_stop();
 }
 
 static int rawsock_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)