64位操作系统Hook内核函数NtQuerySystemInformation遇到的坑

最近做个东西，修改某程序通过调用GetSystemInfo得到CPU内核数目的目的，起初想在进程内Hook GetSystemInfo 这个API来达到效果，但是这样HOOK还得向进程注入一个DLL，比较麻烦。后来得知GetSystemInfo 这个函数内部调用内核NtQuerySystemInformation来达到效果的。于是想直接Hook 内核NtQuerySystemInformation来达到效果。

 

HOOK的过程还算顺利，我是判断参数为SystemBasicInformation的时候就直接修改NtQuerySystemInformation返回的CPU数目来达到这个目的。

 

但是，实际测试发现，并不能达到修改CPU数目的效果。调试了两三个小时无果，最后在网上查发现问题所在。

In 32-bit Windows, the structure is filled exactly the same for all three information classes. The x64 builds treat SystemEmulationBasicInformation differently. This allows WOW64.DLL, executing 64-bit code in a 32-bit process, to get basic information that’s suited to the 32-bit caller.

于是修改HOOK函数条件为SystemEmulationBasicInformation 时总算解决了这个问题。

 

最终Hook函数代码如下：

NTSTATUS __fastcall FakeNtQuerySystemInformation(
	IN SYSTEM_INFORMATION_CLASS SystemInformationClass,
	OUT PVOID                   SystemInformation,
	IN ULONG                    SystemInformationLength,
	OUT PULONG                  ReturnLength
)
{
	if ((SystemBasicInformation == SystemInformationClass ||
		SystemEmulationBasicInformation == SystemInformationClass) && gGetProcessImageFileName != 0 && g_config_processor_count > 0) {
		PCHAR pImageName = gGetProcessImageFileName(PsGetCurrentProcess());
		if (NULL != pImageName)
		{
			CHAR buffer[100];
			strncpy(buffer, pImageName,100);
			int len = strlen(buffer);
			for (int i = 0; i < len && i < 100; i++)
				buffer[i] = (char)tolower((int)buffer[i]);

			if (strstr(buffer, "asktao") != NULL) {
				memset(SystemInformation, 0, SystemInformationLength);
				DbgPrint("[FakeCpuCount]FakeNtQuerySystemInformation pid: %s 
", pImageName);
				NTSTATUS status = NtQuerySystemInformation(SystemInformationClass,
					SystemInformation, SystemInformationLength, ReturnLength);
				if (SystemInformationClass == SystemEmulationBasicInformation) {
					if (NT_SUCCESS(status)) {
						(*(BYTE*)((ULONGLONG)SystemInformation + 0x38)) = (BYTE)g_config_processor_count;
					}
				}
				else
				{
					if (NT_SUCCESS(status)) {
						(*(BYTE*)((ULONGLONG)SystemInformation + 0x38)) = (BYTE)g_config_processor_count;
					}
				}
				return status;
			}
		}
	}
	return NtQuerySystemInformation(SystemInformationClass,
		SystemInformation, SystemInformationLength, ReturnLength);
}