2 * Copyright 2016 Andrei Pangin
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
21 typedef HMODULE (WINAPI *GetModuleHandle_t)(LPCTSTR lpModuleName);
22 typedef FARPROC (WINAPI *GetProcAddress_t)(HMODULE hModule, LPCSTR lpProcName);
23 typedef int (__stdcall *JVM_EnqueueOperation_t)(char* cmd, char* arg0, char* arg1, char* arg2, char* pipename);
26 GetModuleHandle_t GetModuleHandleA;
27 GetProcAddress_t GetProcAddress;
30 char pipeName[MAX_PATH];
31 char args[4][MAX_PATH];
35 #pragma check_stack(off)
37 // This code is executed in remote JVM process; be careful with memory it accesses
38 static DWORD WINAPI remote_thread_entry(LPVOID param) {
39 CallData* data = (CallData*)param;
41 HMODULE libJvm = data->GetModuleHandleA(data->strJvm);
46 JVM_EnqueueOperation_t JVM_EnqueueOperation = (JVM_EnqueueOperation_t)data->GetProcAddress(libJvm, data->strEnqueue + 1);
47 if (JVM_EnqueueOperation == NULL) {
48 // Try alternative name: _JVM_EnqueueOperation@20
49 data->strEnqueue[21] = '@';
50 data->strEnqueue[22] = '2';
51 data->strEnqueue[23] = '0';
52 data->strEnqueue[24] = 0;
54 JVM_EnqueueOperation = (JVM_EnqueueOperation_t)data->GetProcAddress(libJvm, data->strEnqueue);
55 if (JVM_EnqueueOperation == NULL) {
60 return (DWORD)JVM_EnqueueOperation(data->args[0], data->args[1], data->args[2], data->args[3], data->pipeName);
63 static VOID WINAPI remote_thread_entry_end() {
69 // Allocate executable memory in remote process
70 static LPTHREAD_START_ROUTINE allocate_code(HANDLE hProcess) {
71 SIZE_T codeSize = (SIZE_T)remote_thread_entry_end - (SIZE_T)remote_thread_entry;
72 LPVOID code = VirtualAllocEx(hProcess, NULL, codeSize, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
74 WriteProcessMemory(hProcess, code, remote_thread_entry, codeSize, NULL);
76 return (LPTHREAD_START_ROUTINE)code;
79 // Allocate memory for CallData in remote process
80 static LPVOID allocate_data(HANDLE hProcess, char* pipeName, int argc, char** argv) {
82 data.GetModuleHandleA = GetModuleHandleA;
83 data.GetProcAddress = GetProcAddress;
84 strcpy(data.strJvm, "jvm");
85 strcpy(data.strEnqueue, "_JVM_EnqueueOperation");
86 strcpy(data.pipeName, pipeName);
89 for (i = 0; i < 4; i++) {
90 strcpy(data.args[i], i < argc ? argv[i] : "");
93 LPVOID remoteData = VirtualAllocEx(hProcess, NULL, sizeof(CallData), MEM_COMMIT, PAGE_READWRITE);
94 if (remoteData != NULL) {
95 WriteProcessMemory(hProcess, remoteData, &data, sizeof(data), NULL);
100 static void print_error(const char* msg, DWORD code) {
101 printf("%s (error code = %d)\n", msg, code);
104 // If the process is owned by another user, request SeDebugPrivilege to open it.
105 // Debug privileges are typically granted to Administrators.
106 static int enable_debug_privileges() {
108 if (!OpenThreadToken(GetCurrentThread(), TOKEN_ADJUST_PRIVILEGES, FALSE, &hToken)) {
109 if (!ImpersonateSelf(SecurityImpersonation) ||
110 !OpenThreadToken(GetCurrentThread(), TOKEN_ADJUST_PRIVILEGES, FALSE, &hToken)) {
116 if (!LookupPrivilegeValue(NULL, SE_DEBUG_NAME, &luid)) {
121 tp.PrivilegeCount = 1;
122 tp.Privileges[0].Luid = luid;
123 tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
125 BOOL success = AdjustTokenPrivileges(hToken, FALSE, &tp, sizeof(tp), NULL, NULL);
127 return success ? 1 : 0;
130 // Fail if attaching 64-bit jattach to 32-bit JVM or vice versa
131 static int check_bitness(HANDLE hProcess) {
133 BOOL targetWow64 = FALSE;
134 if (IsWow64Process(hProcess, &targetWow64) && targetWow64) {
135 printf("Cannot attach 64-bit process to 32-bit JVM\n");
139 BOOL thisWow64 = FALSE;
140 BOOL targetWow64 = FALSE;
141 if (IsWow64Process(GetCurrentProcess(), &thisWow64) && IsWow64Process(hProcess, &targetWow64)) {
142 if (thisWow64 != targetWow64) {
143 printf("Cannot attach 32-bit process to 64-bit JVM\n");
151 // The idea of Dynamic Attach on Windows is to inject a thread into remote JVM
152 // that calls JVM_EnqueueOperation() function exported by HotSpot DLL
153 static int inject_thread(int pid, char* pipeName, int argc, char** argv) {
154 HANDLE hProcess = OpenProcess(PROCESS_ALL_ACCESS, FALSE, (DWORD)pid);
155 if (hProcess == NULL && GetLastError() == ERROR_ACCESS_DENIED) {
156 if (!enable_debug_privileges()) {
157 print_error("Not enough privileges", GetLastError());
160 hProcess = OpenProcess(PROCESS_ALL_ACCESS, FALSE, (DWORD)pid);
162 if (hProcess == NULL) {
163 print_error("Could not open process", GetLastError());
167 if (!check_bitness(hProcess)) {
168 CloseHandle(hProcess);
172 LPTHREAD_START_ROUTINE code = allocate_code(hProcess);
173 LPVOID data = code != NULL ? allocate_data(hProcess, pipeName, argc, argv) : NULL;
175 print_error("Could not allocate memory in target process", GetLastError());
176 CloseHandle(hProcess);
181 HANDLE hThread = CreateRemoteThread(hProcess, NULL, 0, code, data, 0, NULL);
182 if (hThread == NULL) {
183 print_error("Could not create remote thread", GetLastError());
186 printf("Connected to remote process\n");
187 WaitForSingleObject(hThread, INFINITE);
189 GetExitCodeThread(hThread, &exitCode);
191 print_error("Attach is not supported by the target process", exitCode);
194 CloseHandle(hThread);
197 VirtualFreeEx(hProcess, code, 0, MEM_RELEASE);
198 VirtualFreeEx(hProcess, data, 0, MEM_RELEASE);
199 CloseHandle(hProcess);
204 // JVM response is read from the pipe and mirrored to stdout
205 static int read_response(HANDLE hPipe) {
206 ConnectNamedPipe(hPipe, NULL);
210 if (!ReadFile(hPipe, buf, sizeof(buf) - 1, &bytesRead, NULL)) {
211 print_error("Error reading response", GetLastError());
215 // First line of response is the command result code
217 int result = atoi(buf);
220 fwrite(buf, 1, bytesRead, stdout);
221 } while (ReadFile(hPipe, buf, sizeof(buf), &bytesRead, NULL));
226 int main(int argc, char** argv) {
228 printf("jattach " JATTACH_VERSION " built on " __DATE__ "\n"
229 "Copyright 2021 Andrei Pangin\n"
231 "Usage: jattach <pid> <cmd> [args ...]\n"
234 " load threaddump dumpheap setflag properties\n"
235 " jcmd inspectheap datadump printflag agentProperties\n"
240 int pid = atoi(argv[1]);
242 char pipeName[MAX_PATH];
243 sprintf(pipeName, "\\\\.\\pipe\\javatool%d", GetTickCount());
244 HANDLE hPipe = CreateNamedPipe(pipeName, PIPE_ACCESS_INBOUND, PIPE_TYPE_BYTE | PIPE_READMODE_BYTE | PIPE_WAIT,
245 1, 4096, 8192, NMPWAIT_USE_DEFAULT_WAIT, NULL);
247 print_error("Could not create pipe", GetLastError());
251 if (!inject_thread(pid, pipeName, argc - 2, argv + 2)) {
256 printf("Response code = ");
259 int result = read_response(hPipe);