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/*
* Copyright (C) 2016 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <pthread.h>
#include <sched.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include "android-base/macros.h"
#include "PtracerThread.h"
#include "log.h"
namespace android {
class Stack {
public:
explicit Stack(size_t size) : size_(size) {
int prot = PROT_READ | PROT_WRITE;
int flags = MAP_PRIVATE | MAP_ANONYMOUS;
page_size_ = sysconf(_SC_PAGE_SIZE);
size_ += page_size_ * 2; // guard pages
base_ = mmap(NULL, size_, prot, flags, -1, 0);
if (base_ == MAP_FAILED) {
base_ = NULL;
size_ = 0;
return;
}
prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, base_, size_, "libmemunreachable stack");
mprotect(base_, page_size_, PROT_NONE);
mprotect(top(), page_size_, PROT_NONE);
};
~Stack() { munmap(base_, size_); };
void* top() {
return reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(base_) + size_ - page_size_);
};
private:
DISALLOW_COPY_AND_ASSIGN(Stack);
void* base_;
size_t size_;
size_t page_size_;
};
PtracerThread::PtracerThread(const std::function<int()>& func) : child_pid_(0) {
stack_ = std::make_unique<Stack>(128*PAGE_SIZE);
if (stack_->top() == nullptr) {
MEM_LOG_ALWAYS_FATAL("failed to mmap child stack: %s", strerror(errno));
}
func_ = std::function<int()>{[&, func]() -> int {
// In the child thread, lock and unlock the mutex to wait for the parent
// to finish setting up for the child thread
std::unique_lock<std::mutex> lk(m_);
lk.unlock();
_exit(func());
}};
}
PtracerThread::~PtracerThread() {
Kill();
Join();
ClearTracer();
stack_ = nullptr;
}
bool PtracerThread::Start() {
std::unique_lock<std::mutex> lk(m_);
// Convert from void(*)(void*) to lambda with captures
auto proxy = [](void* arg) -> int {
prctl(PR_SET_NAME, "libmemunreachable ptrace thread");
return (*reinterpret_cast<std::function<int()>*>(arg))();
};
// See README.md for why we create the child process this way
child_pid_ = clone(proxy, stack_->top(), CLONE_VM | CLONE_FS | CLONE_FILES /*|CLONE_UNTRACED*/,
reinterpret_cast<void*>(&func_));
if (child_pid_ < 0) {
MEM_ALOGE("failed to clone child: %s", strerror(errno));
return false;
}
SetTracer(child_pid_);
lk.unlock();
return true;
}
int PtracerThread::Join() {
if (child_pid_ == -1) {
return -1;
}
int status;
int ret = TEMP_FAILURE_RETRY(waitpid(child_pid_, &status, __WALL));
if (ret < 0) {
MEM_ALOGE("waitpid %d failed: %s", child_pid_, strerror(errno));
return -1;
}
child_pid_ = -1;
if (WIFEXITED(status)) {
return WEXITSTATUS(status);
} else if (WIFSIGNALED(status)) {
return -WTERMSIG(status);
} else {
MEM_ALOGE("unexpected status %x", status);
return -1;
}
}
void PtracerThread::Kill() {
if (child_pid_ == -1) {
return;
}
syscall(SYS_tkill, child_pid_, SIGKILL);
}
void PtracerThread::SetTracer(pid_t tracer_pid) {
prctl(PR_SET_PTRACER, tracer_pid);
}
void PtracerThread::ClearTracer() {
prctl(PR_SET_PTRACER, 0);
}
} // namespace android
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