1 /* 2 * Copyright (C) 2016 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include <errno.h> 18 #include <fcntl.h> 19 #include <inttypes.h> 20 #include <pthread.h> 21 #include <sched.h> 22 #include <stddef.h> 23 #include <stdio.h> 24 #include <stdlib.h> 25 #include <string.h> 26 #include <unistd.h> 27 #include <sys/mman.h> 28 #include <sys/syscall.h> 29 #include <sys/types.h> 30 #include <sys/wait.h> 31 32 #include "android-base/macros.h" 33 34 #include "anon_vma_naming.h" 35 #include "log.h" 36 #include "PtracerThread.h" 37 38 class Stack { 39 public: 40 Stack(size_t size) : size_(size) { 41 int prot = PROT_READ | PROT_WRITE; 42 int flags = MAP_PRIVATE | MAP_ANONYMOUS; 43 page_size_ = sysconf(_SC_PAGE_SIZE); 44 size_ += page_size_*2; // guard pages 45 base_ = mmap(NULL, size_, prot, flags, -1, 0); 46 if (base_ == MAP_FAILED) { 47 base_ = NULL; 48 size_ = 0; 49 return; 50 } 51 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, base_, size_, "libmemunreachable stack"); 52 mprotect(base_, page_size_, PROT_NONE); 53 mprotect(top(), page_size_, PROT_NONE); 54 }; 55 ~Stack() { 56 munmap(base_, size_); 57 }; 58 void* top() { 59 return reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(base_) + size_ - page_size_); 60 }; 61 private: 62 DISALLOW_COPY_AND_ASSIGN(Stack); 63 64 void *base_; 65 size_t size_; 66 size_t page_size_; 67 }; 68 69 PtracerThread::PtracerThread(const std::function<int()>& func) : 70 child_pid_(0) { 71 stack_ = std::make_unique<Stack>(PTHREAD_STACK_MIN); 72 if (stack_->top() == nullptr) { 73 LOG_ALWAYS_FATAL("failed to mmap child stack: %s", strerror(errno)); 74 } 75 76 func_ = std::function<int()>{[&, func]() -> int { 77 // In the child thread, lock and unlock the mutex to wait for the parent 78 // to finish setting up for the child thread 79 std::unique_lock<std::mutex> lk(m_); 80 lk.unlock(); 81 _exit(func()); 82 }}; 83 } 84 85 PtracerThread::~PtracerThread() { 86 Kill(); 87 Join(); 88 ClearTracer(); 89 stack_ = nullptr; 90 } 91 92 bool PtracerThread::Start() { 93 std::unique_lock<std::mutex> lk(m_); 94 95 // Convert from void(*)(void*) to lambda with captures 96 auto proxy = [](void *arg) -> int { 97 prctl(PR_SET_NAME, "libmemunreachable ptrace thread"); 98 return (*reinterpret_cast<std::function<int()>*>(arg))(); 99 }; 100 101 child_pid_ = clone(proxy, stack_->top(), 102 CLONE_VM|CLONE_FS|CLONE_FILES/*|CLONE_UNTRACED*/, 103 reinterpret_cast<void*>(&func_)); 104 if (child_pid_ < 0) { 105 ALOGE("failed to clone child: %s", strerror(errno)); 106 return false; 107 } 108 109 SetTracer(child_pid_); 110 111 lk.unlock(); 112 113 return true; 114 } 115 116 int PtracerThread::Join() { 117 if (child_pid_ == -1) { 118 return -1; 119 } 120 int status; 121 int ret = TEMP_FAILURE_RETRY(waitpid(child_pid_, &status, __WALL)); 122 if (ret < 0) { 123 ALOGE("waitpid %d failed: %s", child_pid_, strerror(errno)); 124 return -1; 125 } 126 127 child_pid_ = -1; 128 129 if (WIFEXITED(status)) { 130 return WEXITSTATUS(status); 131 } else if (WIFSIGNALED(status)) { 132 return -WTERMSIG(status); 133 } else { 134 ALOGE("unexpected status %x", status); 135 return -1; 136 } 137 } 138 139 void PtracerThread::Kill() { 140 if (child_pid_ == -1) { 141 return; 142 } 143 144 syscall(SYS_tkill, child_pid_, SIGKILL); 145 } 146 147 void PtracerThread::SetTracer(pid_t tracer_pid) { 148 prctl(PR_SET_PTRACER, tracer_pid); 149 } 150 151 void PtracerThread::ClearTracer() { 152 prctl(PR_SET_PTRACER, 0); 153 } 154