How would you get the command line of a process? Some people have suggested that you use remote thread injection, call GetCommandLine(), then IPC the result back. This might work most of the time on Windows XP, but on Windows Vista it doesn’t work on system and service processes. This is because CreateRemoteThread only works on processes in the same session ID as the caller – in Windows Vista, services and other system processes run in session 0 while user programs run in higher sessions. The best and safest way is to read a structure present in every Windows process.
The Process Environment Block (PEB) is usually stored in the high regions of process memory, above 0x7ff00000. These regions also contain Thread Environment Blocks (TEBs). The PEB address is different for almost every process, so you can’t simply use a hardcoded constant. There’s only one way (in user mode) to get the PEB address:. Its (simplified) function definition is:
NtQueryInformationProcess( IN HANDLE ProcessHandle, IN PROCESS_INFORMATION_CLASS ProcessInformationClass, OUT PVOID ProcessInformation, IN ULONG ProcessInformationLength, OUT PULONG ReturnLength );
The ProcessInformationClass we want to use is the first one, ProcessBasicInformation (with a value of 0). The structure for this is named PROCESS_BASIC_INFORMATION:
typedef struct _PROCESS_BASIC_INFORMATION{ NTSTATUS ExitStatus; PVOID PebBaseAddress; /* contains the PEB address! */ ULONG_PTR AffinityMask; DWORD BasePriority; HANDLE UniqueProcessId; HANDLE InheritedFromUniqueProcessId;} PROCESS_BASIC_INFORMATION, *PPROCESS_BASIC_INFORMATION;
The problem with calling NtQueryInformationProcess is that you’ll have to find the address of it yourself. Here’s some code that finds the PEB address of any process:
typedef NTSTATUS (NTAPI *_NtQueryInformationProcess)( HANDLE ProcessHandle, DWORD ProcessInformationClass, /* can't be bothered defining the whole enum */ PVOID ProcessInformation, DWORD ProcessInformationLength, PDWORD ReturnLength );typedef struct _PROCESS_BASIC_INFORMATION{ ...} PROCESS_BASIC_INFORMATION, *PPROCESS_BASIC_INFORMATION;PVOID GetPebAddress(int pid){ _NtQueryInformationProcess NtQueryInformationProcess = (_NtQueryInformationProcess) GetProcAddress(GetModuleHandleA("ntdll.dll"), "NtQueryInformationProcess"); PROCESS_BASIC_INFORMATION pbi; HANDLE processHandle = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, pid); NtQueryInformationProcess(processHandle, 0, &pbi, sizeof(pbi), NULL); CloseHandle(processHandle); return pbi.PebBaseAddress;}
Once you get the address of the PEB, you’ll have to read its contents. This can easily be done using ReadProcessMemory. Inside the PEB, there’s a pointer to a second structure,RTL_USER_PROCESS_PARAMETERS. Here’s some stuff from the :
typedef struct _PEB{ /* +0x0 */ BOOLEAN InheritedAddressSpace; /* BOOLEANs are one byte each */ /* +0x1 */ BOOLEAN ReadImageFileExecOptions; /* +0x2 */ BOOLEAN BeingDebugged; /* +0x3 */ BOOLEAN Spare; /* +0x4 */ HANDLE Mutant; /* +0x8 */ PVOID ImageBaseAddress; /* +0xc */ PPEB_LDR_DATA LoaderData; /* +0x10 */ PRTL_USER_PROCESS_PARAMETERS ProcessParameters; ...
Those comments on the left hand side are offsets from the beginning of the PEB; if we want to get the address of ProcessParameters, we simply read 4 bytes from PEB address + 0x10. For example:
PVOID pebAddress = ...; /* get the PEB address */PVOID rtlUserProcParamsAddress;ReadProcessMemory(processHandle, /* open the process first... */ (PCHAR)pebAddress + 0x10, &rtlUserProcParamsAddress, /* we'll just read directly into our variable */ sizeof(PVOID), NULL );
So, now we have the address of ProcessParameters. Let’s look inside it:
typedef struct _RTL_USER_PROCESS_PARAMETERS{ ULONG MaximumLength; ULONG Length; ULONG Flags; ULONG DebugFlags; PVOID ConsoleHandle; ULONG ConsoleFlags; HANDLE StdInputHandle; HANDLE StdOutputHandle; HANDLE StdErrorHandle; /* +0x24 */ UNICODE_STRING CurrentDirectoryPath; HANDLE CurrentDirectoryHandle; /* +0x30 */ UNICODE_STRING DllPath; /* +0x38 */ UNICODE_STRING ImagePathName; /* +0x40 */ UNICODE_STRING CommandLine; ... /* more stuff you probably won't care about */ A UNICODE_STRING is simply a counted Unicode string:
typedef struct _UNICODE_STRING{ USHORT Length; USHORT MaximumLength; PWSTR Buffer;} UNICODE_STRING, *PUNICODE_STRING;
It’s pretty obvious what you have to do from here on. You have to read the desired UNICODE_STRING structure and then read the contents of Buffer (Length is in bytes, not characters). (Now that you’ve seen the definition of RTL_USER_PROCESS_PARAMETERS, you’ll probably want other strings as well!) A complete sample program is below. Note that the code does not work on x64 due to the hard-coded offsets; you may want to include the structure definitions for the PEB and process parameters and use FIELD_OFFSET to get the correct offsets.
#include#include typedef NTSTATUS (NTAPI *_NtQueryInformationProcess)( HANDLE ProcessHandle, DWORD ProcessInformationClass, PVOID ProcessInformation, DWORD ProcessInformationLength, PDWORD ReturnLength );typedef struct _UNICODE_STRING{ USHORT Length; USHORT MaximumLength; PWSTR Buffer;} UNICODE_STRING, *PUNICODE_STRING;typedef struct _PROCESS_BASIC_INFORMATION{ LONG ExitStatus; PVOID PebBaseAddress; ULONG_PTR AffinityMask; LONG BasePriority; ULONG_PTR UniqueProcessId; ULONG_PTR ParentProcessId;} PROCESS_BASIC_INFORMATION, *PPROCESS_BASIC_INFORMATION;PVOID GetPebAddress(HANDLE ProcessHandle){ _NtQueryInformationProcess NtQueryInformationProcess = (_NtQueryInformationProcess)GetProcAddress( GetModuleHandleA("ntdll.dll"), "NtQueryInformationProcess"); PROCESS_BASIC_INFORMATION pbi; NtQueryInformationProcess(ProcessHandle, 0, &pbi, sizeof(pbi), NULL); return pbi.PebBaseAddress;}int wmain(int argc, WCHAR *argv[]){ int pid; HANDLE processHandle; PVOID pebAddress; PVOID rtlUserProcParamsAddress; UNICODE_STRING commandLine; WCHAR *commandLineContents; if (argc < 2) { printf("Usage: getprocesscommandline [pid]\n"); return 1; } pid = _wtoi(argv[1]); if ((processHandle = OpenProcess( PROCESS_QUERY_INFORMATION | /* required for NtQueryInformationProcess */ PROCESS_VM_READ, /* required for ReadProcessMemory */ FALSE, pid)) == 0) { printf("Could not open process!\n"); return GetLastError(); } pebAddress = GetPebAddress(processHandle); /* get the address of ProcessParameters */ if (!ReadProcessMemory(processHandle, (PCHAR)pebAddress + 0x10, &rtlUserProcParamsAddress, sizeof(PVOID), NULL)) { printf("Could not read the address of ProcessParameters!\n"); return GetLastError(); } /* read the CommandLine UNICODE_STRING structure */ if (!ReadProcessMemory(processHandle, (PCHAR)rtlUserProcParamsAddress + 0x40, &commandLine, sizeof(commandLine), NULL)) { printf("Could not read CommandLine!\n"); return GetLastError(); } /* allocate memory to hold the command line */ commandLineContents = (WCHAR *)malloc(commandLine.Length); /* read the command line */ if (!ReadProcessMemory(processHandle, commandLine.Buffer, commandLineContents, commandLine.Length, NULL)) { printf("Could not read the command line string!\n"); return GetLastError(); } /* print it */ /* the length specifier is in characters, but commandLine.Length is in bytes */ /* a WCHAR is 2 bytes */ printf("%.*S\n", commandLine.Length / 2, commandLineContents); CloseHandle(processHandle); free(commandLineContents); return 0;}