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：

至于进程将CR3改掉了读取不到该寄存器该如何处理，这里我找到了一段参考代码，可以实现寻找CR3地址这个功能。

#include <ntddk.h>
#include <ntstrsafe.h>
#include <windef.h>
#include <intrin.h>

#pragma pack(push, 1)

typedef struct _IDTR // IDT基址
{
	USHORT limit;    // 范围 占8位
	ULONG64 base;    // 基地址 占32位 _IDT_ENTRY类型指针
}IDTR, *PIDTR;

typedef union _IDT_ENTRY
{
	struct kidt
	{
		USHORT OffsetLow;
		USHORT Selector;
		USHORT IstIndex : 3;
		USHORT Reserved0 : 5;
		USHORT Type : 5;
		USHORT Dpl : 2;
		USHORT Present : 1;
		USHORT OffsetMiddle;
		ULONG OffsetHigh;
		ULONG Reserved1;
	}idt;
	UINT64 Alignment;
} IDT_ENTRY, *PIDT_ENTRY;

#pragma pack(pop)

// 输出调试内容
void DebugPrint(const char* fmt, ...)
{
	UNREFERENCED_PARAMETER(fmt);
	va_list ap;
	va_start(ap, fmt);
	vDbgPrintEx(DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, fmt, ap);
	va_end(ap);
	return;
}

// 获取IDT表地址
ULONG64 GetIdtAddr(ULONG64 pIdtBaseAddr, UCHAR pIndex)
{
	PIDT_ENTRY Pidt_info = (PIDT_ENTRY)(pIdtBaseAddr);
	Pidt_info += pIndex;
	ULONG64 vCurrentAddr = 0;
	ULONG64 vCurrentHighAddr = 0;
	vCurrentAddr = Pidt_info->idt.OffsetMiddle;
	vCurrentAddr = vCurrentAddr << 16;
	vCurrentAddr += Pidt_info->idt.OffsetLow;

	vCurrentHighAddr = Pidt_info->idt.OffsetHigh;
	vCurrentHighAddr = vCurrentHighAddr << 32;
	vCurrentAddr += vCurrentHighAddr;
	return vCurrentAddr;
}

VOID UnLoadDriver()
{

}

NTSTATUS DriverEntry(_In_ PDRIVER_OBJECT pPDriverObj, _In_ PUNICODE_STRING pRegistryPath)
{
	UNREFERENCED_PARAMETER(pRegistryPath);
	pPDriverObj->DriverUnload = (PDRIVER_UNLOAD)UnLoadDriver;

	/**
	TP版KiPageFault
	fffff880`09f54000 50              push    rax
	// 这里实际上是真实处理函数的地址 需要 & 0xFFFFFFFFFFF00000
	fffff880`09f54001 48b87830ce0980f8ffff mov rax,0FFFFF88009CE3078h
	fffff880`09f5400b 4883ec08        sub     rsp,8
	fffff880`09f5400f 48890424        mov     qword ptr [rsp],rax
	fffff880`09f54013 48311424        xor     qword ptr [rsp],rdx
	fffff880`09f54017 e810000000      call    fffff880`09f5402c
	fffff880`09f5401c 896eff          mov     dword ptr [rsi-1],ebp
	fffff880`09f5401f 230500000089    and     eax,dword ptr [fffff87f`92f54025]
	**/
	//得到TP KiPageFault地址
	// _IDTR vContent;
	// __sidt(&vContent);
	ULONG64 vTpKiPageFault = GetIdtAddr(vContent.base, 0xE);

	//得到TP 动态内存起始值
	ULONG64 vTpMemory = *(PULONG64)(vTpKiPageFault + 0x3) & 0xFFFFFFFFFFF00000;

	//得到TP KiPageFault真实处理函数
	ULONG64 vTpKiPageFaultFuncAddr = vTpMemory + 0x4CE7C;

	if (MmIsAddressValid((PVOID)vTpKiPageFaultFuncAddr))
	{//真实处理函数有效

		//得到TP数据对象基地址
		ULONG64 vTpDataObjectBase = *(PULONG)(vTpMemory + 0x1738B) + vTpMemory + 0x1738F;

		if (MmIsAddressValid((PVOID)vTpDataObjectBase))
		{//基地址有效

			//得到TP 用来保存真实CR3 保存当前所属进程ID 的对象
			ULONG64 vTpDataObject = *(PULONG64)vTpDataObjectBase;

			DebugPrint("数据对象:0x%016llx, 真实CR3:0x%016llx, 所属进程ID:%d\n", vTpDataObject, *(PULONG64)(vTpDataObject + 0x70), *(PULONG)(vTpDataObject + 0x18));
		}
		else
			DebugPrint("vTpDataObjectBase无法读取:0x%016llx\n", vTpDataObjectBase);
	}
	else
		DebugPrint("vTpKiPageFaultFuncAddr无法读取:0x%016llx\n", vTpKiPageFaultFuncAddr);

	return STATUS_SUCCESS;
}