Magisk/native/jni/init/init.hpp

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#include <utils.hpp>
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#include "raw_data.hpp"
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struct cmdline {
bool skip_initramfs;
bool force_normal_boot;
bool rootwait;
char slot[3];
char dt_dir[64];
char fstab_suffix[32];
char hardware[32];
char hardware_plat[32];
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};
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struct fstab_entry {
std::string dev;
std::string mnt_point;
std::string type;
std::string mnt_flags;
std::string fsmgr_flags;
fstab_entry() = default;
fstab_entry(const fstab_entry &) = delete;
fstab_entry(fstab_entry &&) = default;
void to_file(FILE *fp);
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};
#define INIT_SOCKET "MAGISKINIT"
#define DEFAULT_DT_DIR "/proc/device-tree/firmware/android"
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extern std::vector<std::string> mount_list;
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bool unxz(int fd, const uint8_t *buf, size_t size);
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void load_kernel_info(cmdline *cmd);
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bool check_two_stage();
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void setup_klog();
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/***************
Logical Resizable Android Partitions support The way how logical partition, or "Logical Resizable Android Partitions" as they say in AOSP source code, is setup makes it impossible to early mount the partitions from the shared super partition with just a few lines of code; in fact, AOSP has a whole "fs_mgr" folder which consist of multiple complex libraries, with 15K lines of code just to deal with the device mapper shenanigans. In order to keep the already overly complicated MagiskInit more managable, I chose NOT to go the route of including fs_mgr directly into MagiskInit. Luckily, starting from Android Q, Google decided to split init startup into 3 stages, with the first stage doing _only_ early mount. This is great news, because we can simply let the stock init do its own thing for us, and we intercept the bootup sequence. So the workflow can be visualized roughly below: Magisk First Stage --> First Stage Mount --> Magisk Second Stage --+ (MagiskInit) (Original Init) (MagiskInit) + + + ...Rest of the boot... <-- Second Stage <-- Selinux Setup <--+ (__________________ Original Init ____________________) The catch here is that after doing all the first stage mounting, /init will pivot /system as root directory (/), leaving us impossible to regain control after we hand it over. So the solution here is to patch fstab in /first_stage_ramdisk on-the-fly to redirect /system to /system_root, making the original init do all the hard work for us and mount required early mount partitions, but skips the step of switching root directory. It will also conveniently hand over execution back to MagiskInit, which we will reuse the routine for patching root directory in normal system-as-root situations.
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* Base classes
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***************/
Logical Resizable Android Partitions support The way how logical partition, or "Logical Resizable Android Partitions" as they say in AOSP source code, is setup makes it impossible to early mount the partitions from the shared super partition with just a few lines of code; in fact, AOSP has a whole "fs_mgr" folder which consist of multiple complex libraries, with 15K lines of code just to deal with the device mapper shenanigans. In order to keep the already overly complicated MagiskInit more managable, I chose NOT to go the route of including fs_mgr directly into MagiskInit. Luckily, starting from Android Q, Google decided to split init startup into 3 stages, with the first stage doing _only_ early mount. This is great news, because we can simply let the stock init do its own thing for us, and we intercept the bootup sequence. So the workflow can be visualized roughly below: Magisk First Stage --> First Stage Mount --> Magisk Second Stage --+ (MagiskInit) (Original Init) (MagiskInit) + + + ...Rest of the boot... <-- Second Stage <-- Selinux Setup <--+ (__________________ Original Init ____________________) The catch here is that after doing all the first stage mounting, /init will pivot /system as root directory (/), leaving us impossible to regain control after we hand it over. So the solution here is to patch fstab in /first_stage_ramdisk on-the-fly to redirect /system to /system_root, making the original init do all the hard work for us and mount required early mount partitions, but skips the step of switching root directory. It will also conveniently hand over execution back to MagiskInit, which we will reuse the routine for patching root directory in normal system-as-root situations.
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class BaseInit {
protected:
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cmdline *cmd = nullptr;
char **argv = nullptr;
Logical Resizable Android Partitions support The way how logical partition, or "Logical Resizable Android Partitions" as they say in AOSP source code, is setup makes it impossible to early mount the partitions from the shared super partition with just a few lines of code; in fact, AOSP has a whole "fs_mgr" folder which consist of multiple complex libraries, with 15K lines of code just to deal with the device mapper shenanigans. In order to keep the already overly complicated MagiskInit more managable, I chose NOT to go the route of including fs_mgr directly into MagiskInit. Luckily, starting from Android Q, Google decided to split init startup into 3 stages, with the first stage doing _only_ early mount. This is great news, because we can simply let the stock init do its own thing for us, and we intercept the bootup sequence. So the workflow can be visualized roughly below: Magisk First Stage --> First Stage Mount --> Magisk Second Stage --+ (MagiskInit) (Original Init) (MagiskInit) + + + ...Rest of the boot... <-- Second Stage <-- Selinux Setup <--+ (__________________ Original Init ____________________) The catch here is that after doing all the first stage mounting, /init will pivot /system as root directory (/), leaving us impossible to regain control after we hand it over. So the solution here is to patch fstab in /first_stage_ramdisk on-the-fly to redirect /system to /system_root, making the original init do all the hard work for us and mount required early mount partitions, but skips the step of switching root directory. It will also conveniently hand over execution back to MagiskInit, which we will reuse the routine for patching root directory in normal system-as-root situations.
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[[noreturn]] void exec_init();
void read_dt_fstab(std::vector<fstab_entry> &fstab);
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public:
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BaseInit(char *argv[], cmdline *cmd) : cmd(cmd), argv(argv) {}
virtual ~BaseInit() = default;
virtual void start() = 0;
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};
class MagiskInit : public BaseInit {
protected:
mmap_data self;
mmap_data config;
std::string custom_rules_dir;
void mount_with_dt();
bool patch_sepolicy(const char *file);
void setup_tmp(const char *path);
void mount_rules_dir(const char *dev_base, const char *mnt_base);
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public:
MagiskInit(char *argv[], cmdline *cmd) : BaseInit(argv, cmd) {}
};
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class SARBase : virtual public MagiskInit {
protected:
std::vector<raw_file> overlays;
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void backup_files();
void patch_rootdir();
void mount_system_root();
public:
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SARBase() = default;
};
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/***************
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* 2 Stage Init
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***************/
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Introduce new boot flow to handle SAR 2SI The existing method for handling legacy SAR is: 1. Mount /sbin tmpfs overlay 2. Dump all patched/new files into /sbin 3. Magic mount root dir and re-exec patched stock init With Android 11 removing the /sbin folder, it is quite obvious that things completely break down right in step 1. To overcome this issue, we have to find a way to swap out the init binary AFTER we re-exec stock init. This is where 2SI comes to rescue! 2SI normal boot procedure is: 1st stage -> Load sepolicy -> 2nd stage -> boot continue... 2SI Magisk boot procedure is: MagiskInit 1st stage -> Stock 1st stage -> MagiskInit 2nd Stage -> -> Stock init load sepolicy -> Stock 2nd stage -> boot continue... As you can see, the trick is to make stock 1st stage init re-exec back into MagiskInit so we can do our setup. This is possible by manipulating some ramdisk files on initramfs based 2SI devices (old ass non SAR devices AND super modern devices like Pixel 3/4), but not possible on device that are stuck using legacy SAR (device that are not that modern but not too old, like Pixel 1/2. Fucking Google logic!!) This commit introduces a new way to intercept stock init re-exec flow: ptrace init with forked tracer, monitor PTRACE_EVENT_EXEC, then swap out the init file with bind mounts right before execv returns! Going through this flow however will lose some necessary backup files, so some bookkeeping has to be done by making the tracer hold these files in memory and act as a daemon. 2nd stage MagiskInit will ack the daemon to release these files at the correct time. It just works™ ¯\_(ツ)_/¯
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class FirstStageInit : public BaseInit {
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private:
void prepare();
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public:
FirstStageInit(char *argv[], cmdline *cmd) : BaseInit(argv, cmd) {
LOGD("%s\n", __FUNCTION__);
};
void start() override {
prepare();
exec_init();
}
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};
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/*************
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* Legacy SAR
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*************/
Logical Resizable Android Partitions support The way how logical partition, or "Logical Resizable Android Partitions" as they say in AOSP source code, is setup makes it impossible to early mount the partitions from the shared super partition with just a few lines of code; in fact, AOSP has a whole "fs_mgr" folder which consist of multiple complex libraries, with 15K lines of code just to deal with the device mapper shenanigans. In order to keep the already overly complicated MagiskInit more managable, I chose NOT to go the route of including fs_mgr directly into MagiskInit. Luckily, starting from Android Q, Google decided to split init startup into 3 stages, with the first stage doing _only_ early mount. This is great news, because we can simply let the stock init do its own thing for us, and we intercept the bootup sequence. So the workflow can be visualized roughly below: Magisk First Stage --> First Stage Mount --> Magisk Second Stage --+ (MagiskInit) (Original Init) (MagiskInit) + + + ...Rest of the boot... <-- Second Stage <-- Selinux Setup <--+ (__________________ Original Init ____________________) The catch here is that after doing all the first stage mounting, /init will pivot /system as root directory (/), leaving us impossible to regain control after we hand it over. So the solution here is to patch fstab in /first_stage_ramdisk on-the-fly to redirect /system to /system_root, making the original init do all the hard work for us and mount required early mount partitions, but skips the step of switching root directory. It will also conveniently hand over execution back to MagiskInit, which we will reuse the routine for patching root directory in normal system-as-root situations.
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class SARInit : public SARBase {
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private:
bool is_two_stage;
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void early_mount();
void first_stage_prep();
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public:
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SARInit(char *argv[], cmdline *cmd) : MagiskInit(argv, cmd), is_two_stage(false) {
LOGD("%s\n", __FUNCTION__);
};
void start() override {
early_mount();
if (is_two_stage)
first_stage_prep();
else
patch_rootdir();
exec_init();
}
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};
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/************
Logical Resizable Android Partitions support The way how logical partition, or "Logical Resizable Android Partitions" as they say in AOSP source code, is setup makes it impossible to early mount the partitions from the shared super partition with just a few lines of code; in fact, AOSP has a whole "fs_mgr" folder which consist of multiple complex libraries, with 15K lines of code just to deal with the device mapper shenanigans. In order to keep the already overly complicated MagiskInit more managable, I chose NOT to go the route of including fs_mgr directly into MagiskInit. Luckily, starting from Android Q, Google decided to split init startup into 3 stages, with the first stage doing _only_ early mount. This is great news, because we can simply let the stock init do its own thing for us, and we intercept the bootup sequence. So the workflow can be visualized roughly below: Magisk First Stage --> First Stage Mount --> Magisk Second Stage --+ (MagiskInit) (Original Init) (MagiskInit) + + + ...Rest of the boot... <-- Second Stage <-- Selinux Setup <--+ (__________________ Original Init ____________________) The catch here is that after doing all the first stage mounting, /init will pivot /system as root directory (/), leaving us impossible to regain control after we hand it over. So the solution here is to patch fstab in /first_stage_ramdisk on-the-fly to redirect /system to /system_root, making the original init do all the hard work for us and mount required early mount partitions, but skips the step of switching root directory. It will also conveniently hand over execution back to MagiskInit, which we will reuse the routine for patching root directory in normal system-as-root situations.
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* Initramfs
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************/
Logical Resizable Android Partitions support The way how logical partition, or "Logical Resizable Android Partitions" as they say in AOSP source code, is setup makes it impossible to early mount the partitions from the shared super partition with just a few lines of code; in fact, AOSP has a whole "fs_mgr" folder which consist of multiple complex libraries, with 15K lines of code just to deal with the device mapper shenanigans. In order to keep the already overly complicated MagiskInit more managable, I chose NOT to go the route of including fs_mgr directly into MagiskInit. Luckily, starting from Android Q, Google decided to split init startup into 3 stages, with the first stage doing _only_ early mount. This is great news, because we can simply let the stock init do its own thing for us, and we intercept the bootup sequence. So the workflow can be visualized roughly below: Magisk First Stage --> First Stage Mount --> Magisk Second Stage --+ (MagiskInit) (Original Init) (MagiskInit) + + + ...Rest of the boot... <-- Second Stage <-- Selinux Setup <--+ (__________________ Original Init ____________________) The catch here is that after doing all the first stage mounting, /init will pivot /system as root directory (/), leaving us impossible to regain control after we hand it over. So the solution here is to patch fstab in /first_stage_ramdisk on-the-fly to redirect /system to /system_root, making the original init do all the hard work for us and mount required early mount partitions, but skips the step of switching root directory. It will also conveniently hand over execution back to MagiskInit, which we will reuse the routine for patching root directory in normal system-as-root situations.
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class RootFSBase : virtual public MagiskInit {
protected:
void patch_rootfs();
public:
RootFSBase() = default;
void start() = 0;
};
class RootFSInit : public RootFSBase {
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private:
void early_mount();
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public:
RootFSInit(char *argv[], cmdline *cmd) : MagiskInit(argv, cmd) {
LOGD("%s\n", __FUNCTION__);
}
void start() override {
early_mount();
patch_rootfs();
exec_init();
}
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};
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class SecondStageInit : public RootFSBase, public SARBase {
private:
bool prepare();
public:
SecondStageInit(char *argv[]) : MagiskInit(argv, nullptr) {
LOGD("%s\n", __FUNCTION__);
};
void start() override {
if (prepare()) patch_rootfs();
else patch_rootdir();
exec_init();
}
};
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class MagiskProxy : public MagiskInit {
public:
explicit MagiskProxy(char *argv[]) : MagiskInit(argv, nullptr) {
LOGD("%s\n", __FUNCTION__);
}
void start() override;
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};