155 lines
3.8 KiB
C++
155 lines
3.8 KiB
C++
/*
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* Copyright (C) 2016 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <errno.h>
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#include <fcntl.h>
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#include <inttypes.h>
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#include <pthread.h>
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#include <sched.h>
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#include <stddef.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/mman.h>
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#include <sys/syscall.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <unistd.h>
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#include "android-base/macros.h"
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#include "PtracerThread.h"
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#include "anon_vma_naming.h"
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#include "log.h"
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namespace android {
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class Stack {
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public:
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explicit Stack(size_t size) : size_(size) {
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int prot = PROT_READ | PROT_WRITE;
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int flags = MAP_PRIVATE | MAP_ANONYMOUS;
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page_size_ = sysconf(_SC_PAGE_SIZE);
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size_ += page_size_ * 2; // guard pages
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base_ = mmap(NULL, size_, prot, flags, -1, 0);
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if (base_ == MAP_FAILED) {
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base_ = NULL;
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size_ = 0;
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return;
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}
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prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, base_, size_, "libmemunreachable stack");
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mprotect(base_, page_size_, PROT_NONE);
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mprotect(top(), page_size_, PROT_NONE);
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};
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~Stack() { munmap(base_, size_); };
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void* top() {
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return reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(base_) + size_ - page_size_);
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};
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private:
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DISALLOW_COPY_AND_ASSIGN(Stack);
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void* base_;
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size_t size_;
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size_t page_size_;
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};
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PtracerThread::PtracerThread(const std::function<int()>& func) : child_pid_(0) {
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stack_ = std::make_unique<Stack>(PTHREAD_STACK_MIN);
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if (stack_->top() == nullptr) {
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MEM_LOG_ALWAYS_FATAL("failed to mmap child stack: %s", strerror(errno));
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}
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func_ = std::function<int()>{[&, func]() -> int {
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// In the child thread, lock and unlock the mutex to wait for the parent
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// to finish setting up for the child thread
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std::unique_lock<std::mutex> lk(m_);
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lk.unlock();
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_exit(func());
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}};
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}
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PtracerThread::~PtracerThread() {
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Kill();
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Join();
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ClearTracer();
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stack_ = nullptr;
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}
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bool PtracerThread::Start() {
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std::unique_lock<std::mutex> lk(m_);
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// Convert from void(*)(void*) to lambda with captures
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auto proxy = [](void* arg) -> int {
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prctl(PR_SET_NAME, "libmemunreachable ptrace thread");
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return (*reinterpret_cast<std::function<int()>*>(arg))();
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};
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// See README.md for why we create the child process this way
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child_pid_ = clone(proxy, stack_->top(), CLONE_VM | CLONE_FS | CLONE_FILES /*|CLONE_UNTRACED*/,
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reinterpret_cast<void*>(&func_));
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if (child_pid_ < 0) {
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MEM_ALOGE("failed to clone child: %s", strerror(errno));
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return false;
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}
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SetTracer(child_pid_);
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lk.unlock();
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return true;
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}
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int PtracerThread::Join() {
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if (child_pid_ == -1) {
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return -1;
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}
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int status;
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int ret = TEMP_FAILURE_RETRY(waitpid(child_pid_, &status, __WALL));
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if (ret < 0) {
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MEM_ALOGE("waitpid %d failed: %s", child_pid_, strerror(errno));
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return -1;
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}
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child_pid_ = -1;
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if (WIFEXITED(status)) {
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return WEXITSTATUS(status);
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} else if (WIFSIGNALED(status)) {
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return -WTERMSIG(status);
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} else {
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MEM_ALOGE("unexpected status %x", status);
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return -1;
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}
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}
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void PtracerThread::Kill() {
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if (child_pid_ == -1) {
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return;
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}
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syscall(SYS_tkill, child_pid_, SIGKILL);
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}
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void PtracerThread::SetTracer(pid_t tracer_pid) {
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prctl(PR_SET_PTRACER, tracer_pid);
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}
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void PtracerThread::ClearTracer() {
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prctl(PR_SET_PTRACER, 0);
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}
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} // namespace android
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