add boringcrypto Makefile targets (#856)

This adds a few build targets to compile with `GOEXPERIMENT=boringcrypto`:

- `bin-boringcrypto`
- `release-boringcrypto`

It also adds a field to the intial start up log indicating if
boringcrypto is enabled in the binary.

Makefile

@@ -77,6 +77,8 @@ release-linux: $(ALL_LINUX:%=build/nebula-%.tar.gz)
 
 release-freebsd: build/nebula-freebsd-amd64.tar.gz
 
+release-boringcrypto: build/nebula-linux-$(shell go env GOARCH)-boringcrypto.tar.gz
+
 BUILD_ARGS = -trimpath
 
 bin-windows: build/windows-amd64/nebula.exe build/windows-amd64/nebula-cert.exe
@@ -91,6 +93,9 @@ bin-darwin: build/darwin-amd64/nebula build/darwin-amd64/nebula-cert
 bin-freebsd: build/freebsd-amd64/nebula build/freebsd-amd64/nebula-cert
 	mv $? .
 
+bin-boringcrypto: build/linux-$(shell go env GOARCH)-boringcrypto/nebula build/linux-$(shell go env GOARCH)-boringcrypto/nebula-cert
+	mv $? .
+
 bin:
 	go build $(BUILD_ARGS) -ldflags "$(LDFLAGS)" -o ./nebula${NEBULA_CMD_SUFFIX} ${NEBULA_CMD_PATH}
 	go build $(BUILD_ARGS) -ldflags "$(LDFLAGS)" -o ./nebula-cert${NEBULA_CMD_SUFFIX} ./cmd/nebula-cert
@@ -105,6 +110,10 @@ build/linux-mips-%: GOENV += GOMIPS=$(word 3, $(subst -, ,$*))
 # Build an extra small binary for mips-softfloat
 build/linux-mips-softfloat/%: LDFLAGS += -s -w
 
+# boringcrypto
+build/linux-amd64-boringcrypto/%: GOENV += GOEXPERIMENT=boringcrypto CGO_ENABLED=1
+build/linux-arm64-boringcrypto/%: GOENV += GOEXPERIMENT=boringcrypto CGO_ENABLED=1
+
 build/%/nebula: .FORCE
 	GOOS=$(firstword $(subst -, , $*)) \
 		GOARCH=$(word 2, $(subst -, ,$*)) $(GOENV) \

boring.go

@@ -0,0 +1,8 @@
+//go:build boringcrypto
+// +build boringcrypto
+
+package nebula
+
+import "crypto/boring"
+
+var boringEnabled = boring.Enabled

interface.go

@@ -204,6 +204,7 @@ func (f *Interface) activate() {
 
 	f.l.WithField("interface", f.inside.Name()).WithField("network", f.inside.Cidr().String()).
 		WithField("build", f.version).WithField("udpAddr", addr).
+		WithField("boringcrypto", boringEnabled()).
 		Info("Nebula interface is active")
 
 	metrics.GetOrRegisterGauge("routines", nil).Update(int64(f.routines))

notboring.go

@@ -0,0 +1,6 @@
+//go:build !boringcrypto
+// +build !boringcrypto
+
+package nebula
+
+var boringEnabled = func() bool { return false }

stats.go

@@ -7,6 +7,7 @@ import (
 	"net"
 	"net/http"
 	"runtime"
+	"strconv"
 	"time"
 
 	graphite "github.com/cyberdelia/go-metrics-graphite"
@@ -107,6 +108,7 @@ func startPrometheusStats(l *logrus.Logger, i time.Duration, c *config.C, buildV
 		ConstLabels: prometheus.Labels{
 			"version":      buildVersion,
 			"goversion":    runtime.Version(),
+			"boringcrypto": strconv.FormatBool(boringEnabled()),
 		},
 	})
 	pr.MustRegister(g)