pkg/build: build Android kernel and embed in Cuttlefish image

Android uses some config files (specified with the BUILD_CONFIG
environment variable) to configure kernel builds. KASan configurations
already exist.

We want to mount the image, install a new Cuttlefish emulator binary
(using fetch_cvd) and copy over the kernel that we've built.

1 files changed, 67 insertions, 0 deletions

diff --git a/pkg/build/android_linux.go b/pkg/build/android_linux.go
new file mode 100644
index 000000000..a6e4e086c
--- /dev/null
+++ b/pkg/build/android_linux.go
@@ -0,0 +1,67 @@
+// Copyright 2022 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package build
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"time"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/google/syzkaller/pkg/osutil"
+)
+
+// buildCuttlefishImage mounts a disk image, fetches and installs a Cuttlefish emulator binary,
+// and copies in the required kernel artifacts.
+func buildCuttlefishImage(params Params, bzImage, vmlinux, initramfs string) error {
+	tempDir, err := ioutil.TempDir("", "syz-build")
+	if err != nil {
+		return err
+	}
+	defer os.RemoveAll(tempDir)
+	imageFile := filepath.Join(tempDir, "image")
+	if err := osutil.CopyFile(params.UserspaceDir, imageFile); err != nil {
+		return err
+	}
+	loop, loopFile, err := linuxSetupLoop(imageFile)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		unix.IoctlGetInt(loop, unix.LOOP_CLR_FD)
+		unix.Close(loop)
+	}()
+	mountDir := filepath.Join(tempDir, "mnt")
+	if err := osutil.MkdirAll(mountDir); err != nil {
+		return err
+	}
+	if err := tryMount(loopFile+"p1", mountDir); err != nil {
+		return fmt.Errorf("mount(%vp1, %v) failed: %v", loopFile, mountDir, err)
+	}
+	defer unix.Unmount(mountDir, 0)
+
+	imageHomeDir := filepath.Join(mountDir, "root")
+	if _, err := osutil.RunCmd(time.Hour, imageHomeDir, "./fetchcvd"); err != nil {
+		return fmt.Errorf("run fetch_cvd: %s", err)
+	}
+
+	if err := osutil.CopyFile(bzImage, filepath.Join(imageHomeDir, "bzImage")); err != nil {
+		return err
+	}
+	if err := osutil.CopyFile(vmlinux, filepath.Join(imageHomeDir, "vmlinux")); err != nil {
+		return err
+	}
+	if err := osutil.CopyFile(initramfs, filepath.Join(imageHomeDir, "initramfs.img")); err != nil {
+		return err
+	}
+
+	if err := unix.Unmount(mountDir, 0); err != nil {
+		return err
+	}
+
+	return osutil.CopyFile(imageFile, filepath.Join(params.OutputDir, "image"))
+}