首先CR3是什么，CR3是一个寄存器，该寄存器内保存有页目录表物理地址(PDBR地址)，其实CR3内部存放的就是页目录表的内存基地址，运用CR3切换可实现对特定进程内存地址的强制读写操作，此类读写属于有痕读写，多数驱动保护都会将这个地址改为无效，此时CR3读写就失效了，当然如果能找到CR3的正确地址，此方式也是靠谱的一种读写机制。

在读写进程之前需要先找到进程的PEPROCESS结构，查找结构的方法也很简单，依次遍历进程并对比进程名称即可得到。

#include <ntifs.h>
#include <windef.h>
#include <intrin.h>

NTKERNELAPI NTSTATUS PsLookupProcessByProcessId(HANDLE ProcessId, PEPROCESS *Process);
NTKERNELAPI CHAR* PsGetProcessImageFileName(PEPROCESS Process);

// 定义全局EProcess结构
PEPROCESS Global_Peprocess = NULL;

// 根据进程名获得EPROCESS结构
NTSTATUS GetProcessObjectByName(char *name)
{
	NTSTATUS Status = STATUS_UNSUCCESSFUL;
	SIZE_T i;

	__try
	{
		for (i = 100; i<20000; i += 4)
		{
			NTSTATUS st;
			PEPROCESS ep;
			st = PsLookupProcessByProcessId((HANDLE)i, &ep);
			if (NT_SUCCESS(st))
			{
				char *pn = PsGetProcessImageFileName(ep);
				if (_stricmp(pn, name) == 0)
				{
					Global_Peprocess = ep;
				}
			}
		}
	}
	__except (EXCEPTION_EXECUTE_HANDLER)
	{
		return Status;
	}
	return Status;
}

VOID UnDriver(PDRIVER_OBJECT driver)
{
	DbgPrint(("Uninstall Driver Is OK \n"));
}

NTSTATUS DriverEntry(IN PDRIVER_OBJECT Driver, PUNICODE_STRING RegistryPath)
{
	DbgPrint("hello lyshark \n");

	NTSTATUS nt = GetProcessObjectByName("Tutorial-i386.exe");

	if (NT_SUCCESS(nt))
	{
		DbgPrint("[+] eprocess = %x \n", Global_Peprocess);
	}

	Driver->DriverUnload = UnDriver;
	return STATUS_SUCCESS;
}

以打开Tutorial-i386.exe为例，打开后即可返回他的Proces，当然也可以直接传入进程PID同样可以得到进程Process结构地址。

// 根据PID打开进程
PEPROCESS Peprocess = NULL;
DWORD PID = 6672;
NTSTATUS nt = PsLookupProcessByProcessId((HANDLE)PID, &Peprocess);

通过CR3读取内存实现代码如下，我们读取Tutorial-i386.exe里面的0x0009EDC8这段内存，读出长度是4字节，代码如下。

#include <ntifs.h>
#include <windef.h>
#include <intrin.h>

#define DIRECTORY_TABLE_BASE 0x028

#pragma  intrinsic(_disable)
#pragma  intrinsic(_enable)

NTKERNELAPI NTSTATUS PsLookupProcessByProcessId(HANDLE ProcessId, PEPROCESS *Process);
NTKERNELAPI CHAR* PsGetProcessImageFileName(PEPROCESS Process);

// 关闭写保护
KIRQL Open()
{
	KIRQL irql = KeRaiseIrqlToDpcLevel();
	UINT64 cr0 = __readcr0();
	cr0 &= 0xfffffffffffeffff;
	__writecr0(cr0);
	_disable();
	return irql;
}

// 开启写保护
void Close(KIRQL irql)
{
	UINT64 cr0 = __readcr0();
	cr0 |= 0x10000;
	_enable();
	__writecr0(cr0);
	KeLowerIrql(irql);
}

// 检查内存
ULONG64 CheckAddressVal(PVOID p)
{
	if (MmIsAddressValid(p) == FALSE)
		return 0;
	return *(PULONG64)p;
}

// CR3 寄存器读内存
BOOLEAN CR3_ReadProcessMemory(IN PEPROCESS Process, IN PVOID Address, IN UINT32 Length, OUT PVOID Buffer)
{
	ULONG64 pDTB = 0, OldCr3 = 0, vAddr = 0;
	pDTB = CheckAddressVal((UCHAR*)Process + DIRECTORY_TABLE_BASE);
	if (pDTB == 0)
	{
		return FALSE;
	}

	_disable();
	OldCr3 = __readcr3();
	__writecr3(pDTB);
	_enable();

	if (MmIsAddressValid(Address))
	{
		RtlCopyMemory(Buffer, Address, Length);
		DbgPrint("读入数据: %ld", *(PDWORD)Buffer);
		return TRUE;
	}

	_disable();
	__writecr3(OldCr3);
	_enable();
	return FALSE;
}

VOID UnDriver(PDRIVER_OBJECT driver)
{
	DbgPrint(("Uninstall Driver Is OK \n"));
}

NTSTATUS DriverEntry(IN PDRIVER_OBJECT Driver, PUNICODE_STRING RegistryPath)
{
	DbgPrint("hello lyshark \n");

	// 根据PID打开进程
	PEPROCESS Peprocess = NULL;
	DWORD PID = 6672;
	NTSTATUS nt = PsLookupProcessByProcessId((HANDLE)PID, &Peprocess);

	DWORD buffer = 0;

	BOOLEAN bl = CR3_ReadProcessMemory(Peprocess, (PVOID)0x0009EDC8, 4, &buffer);

	DbgPrint("readbuf = %x \n", buffer);
	DbgPrint("readbuf = %d \n", buffer);

	Driver->DriverUnload = UnDriver;
	return STATUS_SUCCESS;
}

读出后输出效果如下：

写出内存与读取基本一致，代码如下。

#include <ntifs.h>
#include <windef.h>
#include <intrin.h>

#define DIRECTORY_TABLE_BASE 0x028

#pragma  intrinsic(_disable)
#pragma  intrinsic(_enable)

NTKERNELAPI NTSTATUS PsLookupProcessByProcessId(HANDLE ProcessId, PEPROCESS *Process);
NTKERNELAPI CHAR* PsGetProcessImageFileName(PEPROCESS Process);

// 关闭写保护
KIRQL Open()
{
	KIRQL irql = KeRaiseIrqlToDpcLevel();
	UINT64 cr0 = __readcr0();
	cr0 &= 0xfffffffffffeffff;
	__writecr0(cr0);
	_disable();
	return irql;
}

// 开启写保护
void Close(KIRQL irql)
{
	UINT64 cr0 = __readcr0();
	cr0 |= 0x10000;
	_enable();
	__writecr0(cr0);
	KeLowerIrql(irql);
}

// 检查内存
ULONG64 CheckAddressVal(PVOID p)
{
	if (MmIsAddressValid(p) == FALSE)
		return 0;
	return *(PULONG64)p;
}

// CR3 寄存器写内存
BOOLEAN CR3_WriteProcessMemory(IN PEPROCESS Process, IN PVOID Address, IN UINT32 Length, IN PVOID Buffer)
{
	ULONG64 pDTB = 0, OldCr3 = 0, vAddr = 0;

	// 检查内存
	pDTB = CheckAddressVal((UCHAR*)Process + DIRECTORY_TABLE_BASE);
	if (pDTB == 0)
	{
		return FALSE;
	}

	_disable();

	// 读取CR3
	OldCr3 = __readcr3();

	// 写CR3
	__writecr3(pDTB);
	_enable();

	// 验证并拷贝内存
	if (MmIsAddressValid(Address))
	{
		RtlCopyMemory(Address, Buffer, Length);
		return TRUE;
	}
	_disable();

	// 恢复CR3
	__writecr3(OldCr3);
	_enable();
	return FALSE;
}

VOID UnDriver(PDRIVER_OBJECT driver)
{
	DbgPrint(("Uninstall Driver Is OK \n"));
}

NTSTATUS DriverEntry(IN PDRIVER_OBJECT Driver, PUNICODE_STRING RegistryPath)
{
	DbgPrint("hello lyshark \n");

	// 根据PID打开进程
	PEPROCESS Peprocess = NULL;
	DWORD PID = 6672;
	NTSTATUS nt = PsLookupProcessByProcessId((HANDLE)PID, &Peprocess);

	DWORD buffer = 999;

	BOOLEAN bl = CR3_WriteProcessMemory(Peprocess, (PVOID)0x0009EDC8, 4, &buffer);
	DbgPrint("写出状态: %d \n", bl);

	Driver->DriverUnload = UnDriver;
	return STATUS_SUCCESS;
}

写出后效果如下：