libct/int: add exec benchmark

This is a benchmark which checks how fast we can execute /bin/true
inside a container.

Results from my machine are below. As you can see, in default setup
about 70% of exec time is spent for CVE-2019-5736 (copying runc binary),
and using either RUNC_DMZ=true or memfd-bind helps a lot.

This can also be used for profiling (using -test.cpuprofile option).

=== Default setup ===

[kir@kir-tp1 integration]$ sudo ./integration.test -test.run xxx -test.v -test.benchtime 5s -test.count 5 -test.bench . .
goos: linux
goarch: amd64
pkg: github.com/opencontainers/runc/libcontainer/integration
cpu: 12th Gen Intel(R) Core(TM) i7-12800H
BenchmarkExecTrue
BenchmarkExecTrue-20    	     327	  24475677 ns/op
BenchmarkExecTrue-20    	     244	  25242718 ns/op
BenchmarkExecTrue-20    	     232	  26187174 ns/op
BenchmarkExecTrue-20    	     237	  26780030 ns/op
BenchmarkExecTrue-20    	     318	  18487219 ns/op
PASS

=== With DMZ enabled ===

[kir@kir-tp1 integration]$ sudo -E RUNC_DMZ=true ./integration.test -test.run xxx -test.v -test.benchtime 5s -test.count 5 -test.bench . .
goos: linux
goarch: amd64
pkg: github.com/opencontainers/runc/libcontainer/integration
cpu: 12th Gen Intel(R) Core(TM) i7-12800H
BenchmarkExecTrue
BenchmarkExecTrue-20    	     694	   8263744 ns/op
BenchmarkExecTrue-20    	     778	   8483228 ns/op
BenchmarkExecTrue-20    	     784	   8456018 ns/op
BenchmarkExecTrue-20    	     732	   8160239 ns/op
BenchmarkExecTrue-20    	     769	   8236972 ns/op
PASS

=== With memfd-bind ===

[kir@kir-tp1 integration]$ sudo systemctl start  memfd-bind@$(systemd-escape -p $PWD/integration.test)
[kir@kir-tp1 integration]$ sudo ./integration.test -test.run xxx -test.v -test.benchtime 5s -test.count 5 -test.bench . .
goos: linux
goarch: amd64
pkg: github.com/opencontainers/runc/libcontainer/integration
cpu: 12th Gen Intel(R) Core(TM) i7-12800H
BenchmarkExecTrue
BenchmarkExecTrue-20    	     800	   7538839 ns/op
BenchmarkExecTrue-20    	     717	   7424755 ns/op
BenchmarkExecTrue-20    	     848	   7747787 ns/op
BenchmarkExecTrue-20    	     800	   7668740 ns/op
BenchmarkExecTrue-20    	     751	   7304373 ns/op
PASS

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/integration/bench_test.go

@@ -0,0 +1,51 @@
+package integration
+
+import (
+	"os"
+	"testing"
+
+	"github.com/opencontainers/runc/libcontainer"
+)
+
+func BenchmarkExecTrue(b *testing.B) {
+	config := newTemplateConfig(b, nil)
+	container, err := newContainer(b, config)
+	ok(b, err)
+	defer destroyContainer(container)
+
+	// Execute a first process in the container
+	stdinR, stdinW, err := os.Pipe()
+	ok(b, err)
+	process := &libcontainer.Process{
+		Cwd:   "/",
+		Args:  []string{"cat"},
+		Env:   standardEnvironment,
+		Stdin: stdinR,
+		Init:  true,
+	}
+	err = container.Run(process)
+	_ = stdinR.Close()
+	defer func() {
+		_ = stdinW.Close()
+		if _, err := process.Wait(); err != nil {
+			b.Log(err)
+		}
+	}()
+	ok(b, err)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		exec := &libcontainer.Process{
+			Cwd:      "/",
+			Args:     []string{"/bin/true"},
+			Env:      standardEnvironment,
+			LogLevel: "0", // Minimize forwardChildLogs involvement.
+		}
+		err := container.Run(exec)
+		if err != nil {
+			b.Fatal("exec failed:", err)
+		}
+		waitProcess(exec, b)
+	}
+	b.StopTimer()
+}