aosp启动流程2-SetupSelinux

Android aosp启动流程2-SetupSelinux

参考：
https://www.it610.com/article/1304931662924124160.htm
https://blog.csdn.net/pepsimaxin/article/details/107284563
https://juejin.cn/post/6844903946151002125
上一篇：
http://www.gaohaiyan.com/4021.html#FirstStageMain

system/core/init/selinux.cpp

main –> FirstStageMain –> SetupSelinux –> SecondStageMain
main –> SetupSelinux –> SecondStageMain

部分操作和FirstStageMain是一样的，做一些Linux的设定操作。最后都是前往SecondStageMain。
●挂载boot.img的更新
●注册回调，用来设置需要写入kmsg的selinux日志
●加载SELinux规则配置文件
●通过init进入second_stage

#include "selinux.h"
#include <android/api-level.h>
#include <fcntl.h>
#include <linux/audit.h>
#include <linux/netlink.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>
#include <android-base/chrono_utils.h>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/parseint.h>
#include <android-base/strings.h>
#include <android-base/unique_fd.h>
#include <fs_avb/fs_avb.h>
#include <fs_mgr.h>
#include <libgsi/libgsi.h>
#include <libsnapshot/snapshot.h>
#include <selinux/android.h>
#include "block_dev_initializer.h"
#include "debug_ramdisk.h"
#include "reboot_utils.h"
#include "util.h"

using namespace std::string_literals;

using android::base::ParseInt;
using android::base::Timer;
using android::base::unique_fd;
using android::fs_mgr::AvbHandle;
using android::snapshot::SnapshotManager;

namespace android {
namespace init {

namespace {

enum EnforcingStatus { SELINUX_PERMISSIVE, SELINUX_ENFORCING };

EnforcingStatus StatusFromCmdline() {
    //  略
}
bool IsEnforcing() {
    //  略
}
bool ForkExecveAndWaitForCompletion(const char* filename, char* const argv[]) {
    //  略
}
bool ReadFirstLine(const char* file, std::string* line) {
    //  略
}
bool FindPrecompiledSplitPolicy(std::string* file) {
    //  略
}
bool GetVendorMappingVersion(std::string* plat_vers) {
    //  略
}
constexpr const char plat_policy_cil_file[] = "/system/etc/selinux/plat_sepolicy.cil";

bool IsSplitPolicyDevice() {
    //  略
}
bool LoadSplitPolicy() {
    //  略
}
bool LoadMonolithicPolicy() {
    //  略
}
bool LoadPolicy() {
    //  略
}
void SelinuxInitialize() {
    //  略
}
constexpr size_t kKlogMessageSize = 1024;

void SelinuxAvcLog(char* buf, size_t buf_len) {
    //  略
}
}  // namespace

void SelinuxRestoreContext() {
    //  略
}
int SelinuxKlogCallback(int type, const char* fmt, ...) {
    //  略
}
void SelinuxSetupKernelLogging() {
    //  略
}
int SelinuxGetVendorAndroidVersion() {
    //  略
}
// This is for R(指Android 11，api 30) system.img/system_ext.img to work on old vendor.img as system_ext.img is introduced in R. 
// We mount system_ext in second stage init because the first-stage init in boot.img won't be updated in the system-only OTA scenario.
// 此函数为了在老版本到*.img中引导R。OTA模式下init的第1阶段不会更新boot.img，所以在此第二阶段挂载system_ext。
void MountMissingSystemPartitions() {
    //  略
}

// 入口
// system/core/init/selinux.cpp约673行
int SetupSelinux(char** argv) {
    SetStdioToDevNull(argv); // 将标准输入输出标准错误重定向到/dev/null
    InitKernelLogging(argv); // 初始化内核Log系统，重定向到/dev/kmsg

    if (REBOOT_BOOTLOADER_ON_PANIC) {
        InstallRebootSignalHandlers(); // 当init挂掉时重启bootloader
    }

    boot_clock::time_point start_time = boot_clock::now(); // 启动计时

    // 本文件约606行。
    MountMissingSystemPartitions(); // 挂载boot.img的更新

    // Set up SELinux, loading the SELinux policy.
    SelinuxSetupKernelLogging();  // 注册回调，用来设置需要写入kmsg的selinux日志
    SelinuxInitialize();          // 加载SELinux规则配置文件

    // We're in the kernel domain and want to transition to the init domain.  
    // File systems that store SELabels in their xattrs, such as ext4 do not need an explicit restorecon here,
    // but other file systems do. In particular, this is needed for ramdisks such as the recovery image for A/B devices.
    // 从这里，开始从内核域转换到init域。已有SE标签的扩展文件系统(如ext4)不需显式转换；但其它文件系统须要，尤其是虚拟磁盘，如双机A/B恢复镜像。
    if (selinux_android_restorecon("/system/bin/init", 0) == -1) {
        PLOG(FATAL) << "restorecon failed of /system/bin/init failed";
    }

    // 设置环境变量kEnvSelinuxStartedAt当前时间
    setenv(kEnvSelinuxStartedAt, std::to_string(start_time.time_since_epoch().count()).c_str(), 1);

    const char* path = "/system/bin/init";
    const char* args[] = {path, "second_stage", nullptr};
    execv(path, const_cast<char**>(args)); //【重点】通过execv重新给该进程装载并携带参数 “/system/bin/init second_stage” 进入第2阶段second_stage

    // execv() only returns if an error happened, in which case we panic and never return from this function.
    PLOG(FATAL) << "execv(\"" << path << "\") failed";

    return 1;
}

}  // namespace init
}  // namespace android

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

#include "selinux.h"

#include <android/api-level.h>

#include <fcntl.h>

#include <linux/audit.h>

#include <linux/netlink.h>

#include <stdlib.h>

#include <sys/wait.h>

#include <unistd.h>

#include <android-base/chrono_utils.h>

#include <android-base/file.h>

#include <android-base/logging.h>

#include <android-base/parseint.h>

#include <android-base/strings.h>

#include <android-base/unique_fd.h>

#include <fs_avb/fs_avb.h>

#include <fs_mgr.h>

#include <libgsi/libgsi.h>

#include <libsnapshot/snapshot.h>

#include <selinux/android.h>

#include "block_dev_initializer.h"

#include "debug_ramdisk.h"

#include "reboot_utils.h"

#include "util.h"

using namespace std::string_literals;

using android::base::ParseInt;

using android::base::Timer;

using android::base::unique_fd;

using android::fs_mgr::AvbHandle;

using android::snapshot::SnapshotManager;

namespace android {

namespace init {

namespace {

enum EnforcingStatus { SELINUX_PERMISSIVE, SELINUX_ENFORCING };

EnforcingStatus StatusFromCmdline() {

// 略

}

bool IsEnforcing() {

// 略

}

bool ForkExecveAndWaitForCompletion(const char* filename, char* const argv[]) {

// 略

}

bool ReadFirstLine(const char* file, std::string* line) {

// 略

}

bool FindPrecompiledSplitPolicy(std::string* file) {

// 略

}

bool GetVendorMappingVersion(std::string* plat_vers) {

// 略

}

constexpr const char plat_policy_cil_file[] = "/system/etc/selinux/plat_sepolicy.cil";

bool IsSplitPolicyDevice() {

// 略

}

bool LoadSplitPolicy() {

// 略

}

bool LoadMonolithicPolicy() {

// 略

}

bool LoadPolicy() {

// 略

}

void SelinuxInitialize() {

// 略

}

constexpr size_t kKlogMessageSize = 1024;

void SelinuxAvcLog(char* buf, size_t buf_len) {

// 略

}

} // namespace

void SelinuxRestoreContext() {

// 略

}

int SelinuxKlogCallback(int type, const char* fmt, ...) {

// 略

}

void SelinuxSetupKernelLogging() {

// 略

}

int SelinuxGetVendorAndroidVersion() {

// 略

}

// This is for R(指Android 11，api 30) system.img/system_ext.img to work on old vendor.img as system_ext.img is introduced in R.

// We mount system_ext in second stage init because the first-stage init in boot.img won't be updated in the system-only OTA scenario.

// 此函数为了在老版本到*.img中引导R。OTA模式下init的第1阶段不会更新boot.img，所以在此第二阶段挂载system_ext。

void MountMissingSystemPartitions() {

// 略

}

// 入口

// system/core/init/selinux.cpp约673行

int SetupSelinux(char** argv) {

SetStdioToDevNull(argv); // 将标准输入输出标准错误重定向到/dev/null

InitKernelLogging(argv); // 初始化内核Log系统，重定向到/dev/kmsg

if (REBOOT_BOOTLOADER_ON_PANIC) {

InstallRebootSignalHandlers(); // 当init挂掉时重启bootloader

}

boot_clock::time_point start_time = boot_clock::now(); // 启动计时

// 本文件约606行。

MountMissingSystemPartitions(); // 挂载boot.img的更新

// Set up SELinux, loading the SELinux policy.

SelinuxSetupKernelLogging(); // 注册回调，用来设置需要写入kmsg的selinux日志

SelinuxInitialize(); // 加载SELinux规则配置文件

// We're in the kernel domain and want to transition to the init domain.

// File systems that store SELabels in their xattrs, such as ext4 do not need an explicit restorecon here,

// but other file systems do. In particular, this is needed for ramdisks such as the recovery image for A/B devices.

// 从这里，开始从内核域转换到init域。已有SE标签的扩展文件系统(如ext4)不需显式转换；但其它文件系统须要，尤其是虚拟磁盘，如双机A/B恢复镜像。

if (selinux_android_restorecon("/system/bin/init", 0) == -1) {

PLOG(FATAL) << "restorecon failed of /system/bin/init failed";

}

// 设置环境变量kEnvSelinuxStartedAt当前时间

setenv(kEnvSelinuxStartedAt, std::to_string(start_time.time_since_epoch().count()).c_str(), 1);

const char* path = "/system/bin/init";

const char* args[] = {path, "second_stage", nullptr};

execv(path, const_cast<char**>(args)); //【重点】通过execv重新给该进程装载并携带参数 “/system/bin/init second_stage” 进入第2阶段second_stage

// execv() only returns if an error happened, in which case we panic and never return from this function.

PLOG(FATAL) << "execv(\"" << path << "\") failed";

return 1;

}

} // namespace init

} // namespace android

- end

声明

本文由 cuiweiyou 原创，转载请注明出处：http://www.gaohaiyan.com/4030.html

承接App定制、企业web站点、办公系统软件设计开发，外包项目，毕设

aosp

aosp启动流程5-init.rc内容执行顺序
aosp02-编译android源码
aosp启动流程4-init.rc简介
aosp04-查看LineageOS支持的手机设备