mirror of
https://github.com/topjohnwu/Magisk.git
synced 2026-01-17 07:12:32 -08:00
484 lines
18 KiB
C++
484 lines
18 KiB
C++
#include <sys/mount.h>
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#include <dlfcn.h>
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#include <unwind.h>
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#include <lsplt.hpp>
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#include <base.hpp>
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#include <consts.hpp>
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#include "zygisk.hpp"
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#include "module.hpp"
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#include "jni_hooks.hpp"
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using namespace std;
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static void hook_unloader();
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static void unhook_functions();
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static void hook_jni_env();
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static void post_native_bridge_load();
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struct HookState {
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vector<tuple<dev_t, ino_t, const char *, void **>> plt_backup;
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map<string, vector<JNINativeMethod>, StringCmp> jni_backup;
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JNINativeInterface new_env{};
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const JNINativeInterface *old_env = nullptr;
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const NativeBridgeRuntimeCallbacks *runtime_callbacks = nullptr;
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};
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// Global contexts
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HookContext *g_ctx;
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static HookState *g_state;
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static bool should_unmap_zygisk = false;
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// -----------------------------------------------------------------
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#define DCL_HOOK_FUNC(ret, func, ...) \
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ret (*old_##func)(__VA_ARGS__); \
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ret new_##func(__VA_ARGS__)
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DCL_HOOK_FUNC(void, androidSetCreateThreadFunc, void *func) {
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ZLOGD("androidSetCreateThreadFunc\n");
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hook_jni_env();
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old_androidSetCreateThreadFunc(func);
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}
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// Skip actual fork and return cached result if applicable
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DCL_HOOK_FUNC(int, fork) {
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return (g_ctx && g_ctx->pid >= 0) ? g_ctx->pid : old_fork();
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}
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// Unmount stuffs in the process's private mount namespace
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DCL_HOOK_FUNC(int, unshare, int flags) {
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int res = old_unshare(flags);
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if (g_ctx && (flags & CLONE_NEWNS) != 0 && res == 0 &&
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// For some unknown reason, unmounting app_process in SysUI can break.
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// This is reproducible on the official AVD running API 26 and 27.
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// Simply avoid doing any unmounts for SysUI to avoid potential issues.
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(g_ctx->info_flags & PROCESS_IS_SYS_UI) == 0) {
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if (g_ctx->flags[DO_REVERT_UNMOUNT]) {
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revert_unmount();
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}
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// Restore errno back to 0
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errno = 0;
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}
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return res;
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}
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// This is the last moment before the secontext of the process changes
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DCL_HOOK_FUNC(int, selinux_android_setcontext,
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uid_t uid, bool isSystemServer, const char *seinfo, const char *pkgname) {
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// Pre-fetch logd before secontext transition
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zygisk_get_logd();
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return old_selinux_android_setcontext(uid, isSystemServer, seinfo, pkgname);
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}
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// Close file descriptors to prevent crashing
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DCL_HOOK_FUNC(void, android_log_close) {
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if (g_ctx == nullptr || !g_ctx->flags[SKIP_CLOSE_LOG_PIPE]) {
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// This happens during forks like nativeForkApp, nativeForkUsap,
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// nativeForkSystemServer, and nativeForkAndSpecialize.
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zygisk_close_logd();
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}
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old_android_log_close();
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}
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// We cannot directly call `dlclose` to unload ourselves, otherwise when `dlclose` returns,
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// it will return to our code which has been unmapped, causing segmentation fault.
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// Instead, we hook `pthread_attr_destroy` which will be called when VM daemon threads start.
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DCL_HOOK_FUNC(int, pthread_attr_destroy, void *target) {
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int res = old_pthread_attr_destroy((pthread_attr_t *)target);
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// Only perform unloading on the main thread
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if (gettid() != getpid())
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return res;
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ZLOGV("pthread_attr_destroy\n");
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if (should_unmap_zygisk) {
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unhook_functions();
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if (should_unmap_zygisk) {
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delete g_state;
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// Because both `pthread_attr_destroy` and `dlclose` have the same function signature,
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// we can use `musttail` to let the compiler reuse our stack frame and thus
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// `dlclose` will directly return to the caller of `pthread_attr_destroy`.
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[[clang::musttail]] return dlclose(self_handle);
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}
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}
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delete g_state;
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return res;
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}
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// it should be safe to assume all dlclose's in libnativebridge are for zygisk_loader
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DCL_HOOK_FUNC(int, dlclose, void *handle) {
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static bool kDone = false;
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if (!kDone) {
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ZLOGV("dlclose zygisk_loader\n");
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kDone = true;
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post_native_bridge_load();
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}
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[[clang::musttail]] return old_dlclose(handle);
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}
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#undef DCL_HOOK_FUNC
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// -----------------------------------------------------------------
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HookContext::HookContext(JNIEnv *env, void *args) :
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env(env), args{args}, process(nullptr), pid(-1), info_flags(0),
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hook_info_lock(PTHREAD_MUTEX_INITIALIZER) { g_ctx = this; }
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HookContext::~HookContext() {
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// This global pointer points to a variable on the stack.
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// Set this to nullptr to prevent leaking local variable.
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// This also disables most plt hooked functions.
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g_ctx = nullptr;
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if (!is_child())
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return;
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zygisk_close_logd();
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android_logging();
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should_unmap_zygisk = true;
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// Unhook JNI methods
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for (const auto &[clz, methods] : g_state->jni_backup) {
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if (!methods.empty() && env->RegisterNatives(
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env->FindClass(clz.data()), methods.data(),
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static_cast<int>(methods.size())) != 0) {
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ZLOGE("Failed to restore JNI hook of class [%s]\n", clz.data());
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should_unmap_zygisk = false;
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}
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}
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// Strip out all API function pointers
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for (auto &m : modules) {
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m.clearApi();
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}
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hook_unloader();
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}
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// -----------------------------------------------------------------
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inline void *unwind_get_region_start(_Unwind_Context *ctx) {
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auto fp = _Unwind_GetRegionStart(ctx);
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#if defined(__arm__)
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// On arm32, we need to check if the pc is in thumb mode,
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// if so, we need to set the lowest bit of fp to 1
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auto pc = _Unwind_GetGR(ctx, 15); // r15 is pc
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if (pc & 1) {
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// Thumb mode
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fp |= 1;
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}
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#endif
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return reinterpret_cast<void *>(fp);
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}
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// As we use NativeBridgeRuntimeCallbacks to reload native bridge and to hook jni functions,
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// we need to find it by the native bridge's unwind context.
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// For abis that use registers to pass arguments, i.e. arm32, arm64, x86_64, the registers are
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// caller-saved, and they are not preserved in the unwind context. However, they will be saved
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// into the callee-saved registers, so we will search the callee-saved registers for the second
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// argument, which is the pointer to NativeBridgeRuntimeCallbacks.
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// For x86, whose abi uses stack to pass arguments, we can directly get the pointer to
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// NativeBridgeRuntimeCallbacks from the stack.
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static const NativeBridgeRuntimeCallbacks* find_runtime_callbacks(struct _Unwind_Context *ctx) {
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// Find the writable memory region of libart.so, where the NativeBridgeRuntimeCallbacks is located.
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auto [start, end] = []()-> tuple<uintptr_t, uintptr_t> {
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for (const auto &map : lsplt::MapInfo::Scan()) {
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if (map.path.ends_with("/libart.so") && map.perms == (PROT_WRITE | PROT_READ)) {
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ZLOGV("libart.so: start=%p, end=%p\n",
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reinterpret_cast<void *>(map.start), reinterpret_cast<void *>(map.end));
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return {map.start, map.end};
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}
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}
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return {0, 0};
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}();
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#if defined(__aarch64__)
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// r19-r28 are callee-saved registers
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for (int i = 19; i <= 28; ++i) {
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auto val = static_cast<uintptr_t>(_Unwind_GetGR(ctx, i));
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ZLOGV("r%d = %p\n", i, reinterpret_cast<void *>(val));
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if (val >= start && val < end)
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return reinterpret_cast<const NativeBridgeRuntimeCallbacks*>(val);
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}
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#elif defined(__arm__)
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// r4-r10 are callee-saved registers
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for (int i = 4; i <= 10; ++i) {
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auto val = static_cast<uintptr_t>(_Unwind_GetGR(ctx, i));
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ZLOGV("r%d = %p\n", i, reinterpret_cast<void *>(val));
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if (val >= start && val < end)
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return reinterpret_cast<const NativeBridgeRuntimeCallbacks*>(val);
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}
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#elif defined(__i386__)
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// get ebp, which points to the bottom of the stack frame
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auto ebp = static_cast<uintptr_t>(_Unwind_GetGR(ctx, 5));
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// 1 pointer size above ebp is the old ebp
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// 2 pointer sizes above ebp is the return address
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// 3 pointer sizes above ebp is the 2nd arg
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auto val = *reinterpret_cast<uintptr_t *>(ebp + 3 * sizeof(void *));
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ZLOGV("ebp + 3 * ptr_size = %p\n", reinterpret_cast<void *>(val));
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if (val >= start && val < end)
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return reinterpret_cast<const NativeBridgeRuntimeCallbacks*>(val);
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#elif defined(__x86_64__)
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// r12-r15 and rbx are callee-saved registers, but the compiler is likely to use them reversely
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for (int i : {3, 15, 14, 13, 12}) {
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auto val = static_cast<uintptr_t>(_Unwind_GetGR(ctx, i));
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ZLOGV("r%d = %p\n", i, reinterpret_cast<void *>(val));
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if (val >= start && val < end)
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return reinterpret_cast<const NativeBridgeRuntimeCallbacks*>(val);
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}
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#else
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#error "Unsupported architecture"
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#endif
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return nullptr;
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}
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static void post_native_bridge_load() {
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// Unwind to find the address of android::LoadNativeBridge and NativeBridgeRuntimeCallbacks
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bool (*load_native_bridge)(const char *nb_library_filename,
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const NativeBridgeRuntimeCallbacks *runtime_cbs) = nullptr;
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_Unwind_Backtrace(+[](struct _Unwind_Context *ctx, void *arg) -> _Unwind_Reason_Code {
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void *fp = unwind_get_region_start(ctx);
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Dl_info info{};
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dladdr(fp, &info);
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ZLOGV("backtrace: %p %s\n", fp, info.dli_fname ? info.dli_fname : "???");
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if (info.dli_fname && std::string_view(info.dli_fname).ends_with("/libnativebridge.so")) {
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*reinterpret_cast<void **>(arg) = fp;
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g_state->runtime_callbacks = find_runtime_callbacks(ctx);
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ZLOGV("NativeBridgeRuntimeCallbacks: %p\n", g_state->runtime_callbacks);
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return _URC_END_OF_STACK;
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}
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return _URC_NO_REASON;
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}, &load_native_bridge);
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// Reload the real native bridge if necessary
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auto nb = get_prop(NBPROP);
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auto len = sizeof(ZYGISKLDR) - 1;
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if (nb.size() > len) {
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load_native_bridge(nb.data() + len, g_state->runtime_callbacks);
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}
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}
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static void hook_register(dev_t dev, ino_t inode, const char *symbol, void *new_func, void **old_func) {
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if (!lsplt::RegisterHook(dev, inode, symbol, new_func, old_func)) {
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ZLOGE("Failed to register plt_hook \"%s\"\n", symbol);
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return;
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}
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g_state->plt_backup.emplace_back(dev, inode, symbol, old_func);
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}
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static void hook_commit() {
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if (!lsplt::CommitHook())
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ZLOGE("plt_hook failed\n");
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}
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#define PLT_HOOK_REGISTER_SYM(DEV, INODE, SYM, NAME) \
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hook_register(DEV, INODE, SYM, \
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reinterpret_cast<void *>(new_##NAME), reinterpret_cast<void **>(&old_##NAME))
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#define PLT_HOOK_REGISTER(DEV, INODE, NAME) \
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PLT_HOOK_REGISTER_SYM(DEV, INODE, #NAME, NAME)
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void hook_functions() {
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default_new(g_state);
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ino_t android_runtime_inode = 0;
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dev_t android_runtime_dev = 0;
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ino_t native_bridge_inode = 0;
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dev_t native_bridge_dev = 0;
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for (auto &map : lsplt::MapInfo::Scan()) {
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if (map.path.ends_with("/libandroid_runtime.so")) {
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android_runtime_inode = map.inode;
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android_runtime_dev = map.dev;
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} else if (map.path.ends_with("/libnativebridge.so")) {
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native_bridge_inode = map.inode;
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native_bridge_dev = map.dev;
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}
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}
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PLT_HOOK_REGISTER(native_bridge_dev, native_bridge_inode, dlclose);
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PLT_HOOK_REGISTER(android_runtime_dev, android_runtime_inode, fork);
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PLT_HOOK_REGISTER(android_runtime_dev, android_runtime_inode, unshare);
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PLT_HOOK_REGISTER(android_runtime_dev, android_runtime_inode, androidSetCreateThreadFunc);
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PLT_HOOK_REGISTER(android_runtime_dev, android_runtime_inode, selinux_android_setcontext);
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PLT_HOOK_REGISTER_SYM(android_runtime_dev, android_runtime_inode, "__android_log_close", android_log_close);
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hook_commit();
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// Remove unhooked methods
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g_state->plt_backup.erase(
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std::remove_if(g_state->plt_backup.begin(), g_state->plt_backup.end(),
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[](auto &t) { return *std::get<3>(t) == nullptr;}),
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g_state->plt_backup.end());
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}
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static void hook_unloader() {
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ino_t art_inode = 0;
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dev_t art_dev = 0;
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for (auto &map : lsplt::MapInfo::Scan()) {
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if (map.path.ends_with("/libart.so")) {
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art_inode = map.inode;
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art_dev = map.dev;
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break;
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}
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}
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PLT_HOOK_REGISTER(art_dev, art_inode, pthread_attr_destroy);
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hook_commit();
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}
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static void unhook_functions() {
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// Unhook plt_hook
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for (const auto &[dev, inode, sym, old_func] : g_state->plt_backup) {
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if (!lsplt::RegisterHook(dev, inode, sym, *old_func, nullptr)) {
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ZLOGE("Failed to register plt_hook [%s]\n", sym);
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should_unmap_zygisk = false;
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}
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}
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if (!lsplt::CommitHook()) {
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ZLOGE("Failed to restore plt_hook\n");
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should_unmap_zygisk = false;
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}
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}
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// -----------------------------------------------------------------
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void hookJniNativeMethods(JNIEnv *env, const char *clz, JNINativeMethod *methods, int numMethods) {
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jclass clazz;
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if (!g_state || !g_state->runtime_callbacks || !env || !clz || !(clazz = env->FindClass(clz))) {
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for (auto i = 0; i < numMethods; ++i) {
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methods[i].fnPtr = nullptr;
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}
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return;
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}
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// Backup existing methods
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auto total = g_state->runtime_callbacks->getNativeMethodCount(env, clazz);
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vector<JNINativeMethod> old_methods(total);
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g_state->runtime_callbacks->getNativeMethods(env, clazz, old_methods.data(), total);
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// Replace the method
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for (auto i = 0; i < numMethods; ++i) {
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auto &method = methods[i];
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auto res = env->RegisterNatives(clazz, &method, 1);
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// It's normal that the method is not found
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if (res == JNI_ERR || env->ExceptionCheck()) {
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auto exception = env->ExceptionOccurred();
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if (exception) env->DeleteLocalRef(exception);
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env->ExceptionClear();
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method.fnPtr = nullptr;
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} else {
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// Find the old function pointer and return to caller
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for (const auto &old_method : old_methods) {
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if (strcmp(method.name, old_method.name) == 0 &&
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strcmp(method.signature, old_method.signature) == 0) {
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ZLOGD("replace %s#%s%s %p -> %p\n", clz,
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method.name, method.signature, old_method.fnPtr, method.fnPtr);
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method.fnPtr = old_method.fnPtr;
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}
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}
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}
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}
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}
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static string get_class_name(JNIEnv *env, jclass clazz) {
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static auto class_getName = env->GetMethodID(
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env->FindClass("java/lang/Class"), "getName", "()Ljava/lang/String;");
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auto nameRef = (jstring) env->CallObjectMethod(clazz, class_getName);
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const char *name = env->GetStringUTFChars(nameRef, nullptr);
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string className(name);
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env->ReleaseStringUTFChars(nameRef, name);
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std::replace(className.begin(), className.end(), '.', '/');
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return className;
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}
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static void replace_jni_methods(
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vector<JNINativeMethod> &methods, vector<JNINativeMethod> &backup,
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const JNINativeMethod *hook_methods, size_t hook_methods_size,
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void **orig_function) {
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for (auto &method : methods) {
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if (strcmp(method.name, hook_methods[0].name) == 0) {
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for (auto i = 0; i < hook_methods_size; ++i) {
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const auto &hook = hook_methods[i];
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if (strcmp(method.signature, hook.signature) == 0) {
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backup.push_back(method);
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*orig_function = method.fnPtr;
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method.fnPtr = hook.fnPtr;
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ZLOGI("replace %s\n", method.name);
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return;
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}
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}
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ZLOGE("unknown signature of %s%s\n", method.name, method.signature);
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}
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}
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}
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#define HOOK_JNI(method) \
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replace_jni_methods(newMethods, backup, method##_methods.data(), method##_methods.size(), &method##_orig)
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static jint env_RegisterNatives(
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JNIEnv *env, jclass clazz, const JNINativeMethod *methods, jint numMethods) {
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auto className = get_class_name(env, clazz);
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if (className == "com/android/internal/os/Zygote") {
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// Restore JNIEnv as we no longer need to replace anything
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env->functions = g_state->old_env;
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vector<JNINativeMethod> newMethods(methods, methods + numMethods);
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vector<JNINativeMethod> &backup = g_state->jni_backup[className];
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HOOK_JNI(nativeForkAndSpecialize);
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HOOK_JNI(nativeSpecializeAppProcess);
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HOOK_JNI(nativeForkSystemServer);
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return g_state->old_env->RegisterNatives(env, clazz, newMethods.data(), numMethods);
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} else {
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return g_state->old_env->RegisterNatives(env, clazz, methods, numMethods);
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}
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}
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static void hook_jni_env() {
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using method_sig = jint(*)(JavaVM **, jsize, jsize *);
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auto get_created_vms = reinterpret_cast<method_sig>(
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dlsym(RTLD_DEFAULT, "JNI_GetCreatedJavaVMs"));
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if (!get_created_vms) {
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|
for (auto &map: lsplt::MapInfo::Scan()) {
|
|
if (!map.path.ends_with("/libnativehelper.so")) continue;
|
|
void *h = dlopen(map.path.data(), RTLD_LAZY);
|
|
if (!h) {
|
|
ZLOGW("Cannot dlopen libnativehelper.so: %s\n", dlerror());
|
|
break;
|
|
}
|
|
get_created_vms = reinterpret_cast<method_sig>(dlsym(h, "JNI_GetCreatedJavaVMs"));
|
|
dlclose(h);
|
|
break;
|
|
}
|
|
if (!get_created_vms) {
|
|
ZLOGW("JNI_GetCreatedJavaVMs not found\n");
|
|
return;
|
|
}
|
|
}
|
|
|
|
JavaVM *vm = nullptr;
|
|
jsize num = 0;
|
|
jint res = get_created_vms(&vm, 1, &num);
|
|
if (res != JNI_OK || vm == nullptr) {
|
|
ZLOGW("JavaVM not found\n");
|
|
return;
|
|
}
|
|
JNIEnv *env = nullptr;
|
|
res = vm->GetEnv(reinterpret_cast<void **>(&env), JNI_VERSION_1_6);
|
|
if (res != JNI_OK || env == nullptr) {
|
|
ZLOGW("JNIEnv not found\n");
|
|
return;
|
|
}
|
|
|
|
// Replace the function table in JNIEnv to hook RegisterNatives
|
|
memcpy(&g_state->new_env, env->functions, sizeof(*env->functions));
|
|
g_state->new_env.RegisterNatives = &env_RegisterNatives;
|
|
g_state->old_env = env->functions;
|
|
env->functions = &g_state->new_env;
|
|
}
|