# 简要简要

由于安卓做了很多安全限制，但在物联网应用中需要更方便的调用设备 gpio，uart,can，WiFi 等底层硬件接口，所以需要编译root版本的Android系统，这样更能灵活开发所需求中的功能

# 修改步骤

1. 需要编译userdebug版本
2. 关闭selinux，在此目录 device/rockchip/common 找到以下文件修改

```bash
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 3706d7b7..8099919f 100755
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -59,7 +59,7 @@ BOARD_BOOT_HEADER_VERSION ?= 2
BOARD_MKBOOTIMG_ARGS :=
BOARD_PREBUILT_DTBOIMAGE ?= $(TARGET_DEVICE_DIR)/dtbo.img
BOARD_ROCKCHIP_VIRTUAL_AB_ENABLE ?= false
-BOARD_SELINUX_ENFORCING ?= true
+BOARD_SELINUX_ENFORCING ?= false
```

3. 修改su.cpp，注释用户组权限检测
   system/extras/su/su.cpp

```cpp
diff --git a/su/su.cpp b/su/su.cpp
index 1a1ab6bf..af3d2a68 100644
--- a/su/su.cpp
+++ b/su/su.cpp
@@ -80,8 +80,8 @@ void extract_uidgids(const char* uidgids, uid_t* uid, gid_t*
gid, gid_t* gids, i
}
int main(int argc, char** argv) {
- uid_t current_uid = getuid();
- if (current_uid != AID_ROOT && current_uid != AID_SHELL) error(1, 0, "not
allowed");
+ //uid_t current_uid = getuid();
+ //if (current_uid != AID_ROOT && current_uid != AID_SHELL) error(1, 0, "not
allowed");
// Handle -h and --help.
++argv;
```

4. 给 su 文件默认授予 root 权限
   system/core/libcutils/fs_config.cpp

```cpp
diff --git a/libcutils/fs_config.cpp b/libcutils/fs_config.cpp
index 5805a4d19..92e93e76f 100644
--- a/libcutils/fs_config.cpp
+++ b/libcutils/fs_config.cpp
@@ -188,7 +188,7 @@ static const struct fs_path_config android_files[] = {
// the following two files are INTENTIONALLY set-uid, but they
// are NOT included on user builds.
{ 06755, AID_ROOT, AID_ROOT, 0, "system/xbin/procmem" },
- { 04750, AID_ROOT, AID_SHELL, 0, "system/xbin/su" },
+ { 06755, AID_ROOT, AID_SHELL, 0, "system/xbin/su" },
// the following files have enhanced capabilities and ARE included
// in user builds.
```

修改 frameworks/base/core/jni/com_android_internal_os_Zygote.cpp

```cpp
diff --git a/core/jni/com_android_internal_os_Zygote.cpp
b/core/jni/com_android_internal_os_Zygote.cpp
index 9eede83e21e5..694eec2a40ac 100644
--- a/core/jni/com_android_internal_os_Zygote.cpp
+++ b/core/jni/com_android_internal_os_Zygote.cpp
@@ -656,6 +656,7 @@ static void EnableKeepCapabilities(fail_fn_t fail_fn) {
}
static void DropCapabilitiesBoundingSet(fail_fn_t fail_fn) {
+/*
for (int i = 0; prctl(PR_CAPBSET_READ, i, 0, 0, 0) >= 0; i++) {;
if (prctl(PR_CAPBSET_DROP, i, 0, 0, 0) == -1) {
if (errno == EINVAL) {
@@ -666,6 +667,7 @@ static void DropCapabilitiesBoundingSet(fail_fn_t fail_fn) {
}
}
}
+ */
}
```

修改 kernel/security/commoncap.c

```c
diff --git a/security/commoncap.c b/security/commoncap.c
index f86557a8e43f6..19124dd6239a1 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -1147,12 +1147,12 @@ int cap_task_setnice(struct task_struct *p, int nice)
static int cap_prctl_drop(unsigned long cap)
{
struct cred *new;
-
+/*
if (!ns_capable(current_user_ns(), CAP_SETPCAP))
return -EPERM;
if (!cap_valid(cap))
return -EINVAL;
-
+*/
new = prepare_creds();
if (!new)
return -ENOMEM;
```