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[原创]VT虚拟化技术笔记（part 2）
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发表于: 2022-3-14 14:47
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本文讲解vmcs控制区中Guest state fields和Host state fields字段的填充方法，vm-control fields的相关填充方法将会在下一篇文章中讲解。
在intel白皮书的24.3章中，详细描述了VMCS控制区的字段。如上一篇文章所说，需要设置的vmcs字段为
vm-control fields
除这5个区域之外，vmcs还有一个区域是vm exit信息区域。这个区域是只读的，存储的是vmx指令失败后失败代码的编号。
在《处理器虚拟化技术》3.4章节中，展示了需要填充的字段以及其对应的ID。对于guest区域和host区域，需要填充的字段如下：
长度为16位的字段:
长度为64位的字段
长度为32位的字段
可以看到基本上都是进入guest区域之后的寄存器。其中对段寄存器的填充尤其麻烦，需要分别填充base、attribute、limit、selector。因此需要手动获取段寄存器并将其进行拆分然后进行相应的填充。根据保护模式的知识，段寄存器的结构大致如下
在填充时需要将其拆分并填充，此步骤较为繁琐。
填充guest和host区域时还有四个重要的字段需要获取。分别是进入guest区域之后的rip和rsp以及从guest返回到host区域之后的rip rsp。这里我们要使得进入guest区域之后系统仍然正常进行，还是从原来的地方往下跑。因此要通过函数获取需要返回的上一层函数的返回地址以及rsp。而对于返回host区域之后的host eip，由于从虚拟机中返回一定是发生了vmexit事件，需要对该事件进行处理，因此从虚拟机中返回之后的rip一定要设置为vmexit事件的处理函数。而rsp则需要重新开辟一块内存区域供vmexit事件处理函数使用。如果还是使用guest返回之前的堆栈，则会破坏堆栈中的内容，导致无法预知的结果。
接下来开始具体字段的填充讲解。
和设置vmon区域类似，首先也是申请内存区域然后填充IA32_VMX_BASIC。而在进行基本ID的填充之后，要通过vmclear初始化内存并通过vmptrld选择vmcs区域。这两步操作对应的是前一篇文章说的拔电源以及选中机器。在完成之后，便是最复杂的vmcs字段的填充。这里对于每一块vmcs字段，分别封装一个函数进行初始化。本篇文章讨论的是guest区域和host区域的初始化，分别对应的是 VmxInitGuest 和 VmxInitHost 函数。
对于guest相关的字段，需要传入的是guesteip和guestesp，以用来确定在进入guest虚拟机之后guest从哪里开始跑。其他的字段全部根据当前状态填入。首先需要填入的便是gdt表中各个段寄存器的base、limit、attribute、selector。在对其ID进行观察后可以发现，这些字段的id都是连在一起的，id的值相差2。而对于这些段寄存器，分离base、limit、attribute、selector的方法也非常类似。因此可以考虑将填写段寄存器的属性的方法封装成一个函数。这里将其封装成 fillGdtDataItem 函数。对于各个属性的分离，依照下图来进行。具体分离的细节不赘述，建议仔细读懂代码中切割bit的方法。
对于tr寄存器的gdt表项，并不能像其他寄存器一样进行填充。因为在64位下，tr寄存器的gdt表项是128位的。因此需要单独设置。64位下tr寄存器的gdt表项格式在intel白皮书的7.2.3章节中有解析。其结构如下
因此其需要用另外一套代码进行设置，具体代码如下。思路与其他gdt表项的设置思路相同，都是取出对应的位填入vmcs区域中。
int VmxInitVmOn()
{ PVMXCPUPCB pVcpu = VmxGetCurrentCPUPCB();
PHYSICAL_ADDRESS lowphys,heiPhy;
lowphys.QuadPart = 0;
heiPhy.QuadPart = -1;
pVcpu->VmxOnAddr = MmAllocateContiguousMemorySpecifyCache(PAGE_SIZE, lowphys, heiPhy, lowphys, MmCached);
if (!pVcpu->VmxOnAddr)
{
//申请内存失败
return -1;
}
memset(pVcpu->VmxOnAddr, 0, PAGE_SIZE);
pVcpu->VmxOnAddrPhys = MmGetPhysicalAddress(pVcpu->VmxOnAddr);
//填充ID
ULONG64 vmxBasic = __readmsr(IA32_VMX_BASIC);
*(PULONG)pVcpu->VmxOnAddr = (ULONG)vmxBasic;
//CR0,CR4
ULONG64 vcr00 = __readmsr(IA32_VMX_CR0_FIXED0);
ULONG64 vcr01 = __readmsr(IA32_VMX_CR0_FIXED1);
ULONG64 vcr04 = __readmsr(IA32_VMX_CR4_FIXED0);
ULONG64 vcr14 = __readmsr(IA32_VMX_CR4_FIXED1);
ULONG64 mcr4 = __readcr4();
ULONG64 mcr0 = __readcr0();
mcr4 |= vcr04;
mcr4 &= vcr14;
mcr0 |= vcr00;
mcr0 &= vcr01;
//
__writecr0(mcr0);
__writecr4(mcr4);
int error = __vmx_on(&pVcpu->VmxOnAddrPhys.QuadPart);
if (error)
{
//释放内存，重置CR4
mcr4 &= ~vcr04;
__writecr4(mcr4);
MmFreeContiguousMemorySpecifyCache(pVcpu->VmxOnAddr, PAGE_SIZE, MmCached);
pVcpu->VmxOnAddr = NULL;
pVcpu->VmxOnAddrPhys.QuadPart = 0;
}
return error;
}int VmxInitVmOn()
{ PVMXCPUPCB pVcpu = VmxGetCurrentCPUPCB();
PHYSICAL_ADDRESS lowphys,heiPhy;
lowphys.QuadPart = 0;
heiPhy.QuadPart = -1;
pVcpu->VmxOnAddr = MmAllocateContiguousMemorySpecifyCache(PAGE_SIZE, lowphys, heiPhy, lowphys, MmCached);
if (!pVcpu->VmxOnAddr)
{
//申请内存失败
return -1;
}
memset(pVcpu->VmxOnAddr, 0, PAGE_SIZE);
pVcpu->VmxOnAddrPhys = MmGetPhysicalAddress(pVcpu->VmxOnAddr);
//填充ID
ULONG64 vmxBasic = __readmsr(IA32_VMX_BASIC);
*(PULONG)pVcpu->VmxOnAddr = (ULONG)vmxBasic;
//CR0,CR4
ULONG64 vcr00 = __readmsr(IA32_VMX_CR0_FIXED0);
ULONG64 vcr01 = __readmsr(IA32_VMX_CR0_FIXED1);
ULONG64 vcr04 = __readmsr(IA32_VMX_CR4_FIXED0);
ULONG64 vcr14 = __readmsr(IA32_VMX_CR4_FIXED1);
ULONG64 mcr4 = __readcr4();
ULONG64 mcr0 = __readcr0();
mcr4 |= vcr04;
mcr4 &= vcr14;
mcr0 |= vcr00;
mcr0 &= vcr01;
//
__writecr0(mcr0);
__writecr4(mcr4);
int error = __vmx_on(&pVcpu->VmxOnAddrPhys.QuadPart);
if (error)
{
//释放内存，重置CR4
mcr4 &= ~vcr04;
__writecr4(mcr4);
MmFreeContiguousMemorySpecifyCache(pVcpu->VmxOnAddr, PAGE_SIZE, MmCached);
pVcpu->VmxOnAddr = NULL;
pVcpu->VmxOnAddrPhys.QuadPart = 0;
}
return error;
}PULONG64 retAddr = (PULONG64)_AddressOfReturnAddress();
ULONG64 guestEsp = retAddr + 1;
ULONG64 guestEip = *retAddr;
PULONG64 retAddr = (PULONG64)_AddressOfReturnAddress();
ULONG64 guestEsp = retAddr + 1;
ULONG64 guestEip = *retAddr;
int VmxInit(ULONG64 hostEip)
{ PVMXCPUPCB pVcpu = VmxGetCurrentCPUPCB();
pVcpu->cpuNumber = KeGetCurrentProcessorNumberEx(NULL);
PULONG64 retAddr = (PULONG64)_AddressOfReturnAddress();
ULONG64 guestEsp = retAddr + 1;
ULONG64 guestEip = *retAddr;
int error = VmxInitVmOn();
if (error)
{
DbgPrintEx(77, 0, "[db]:vmon 初始化失败 error = %d,cpunumber %d\r\n", error, pVcpu->cpuNumber);
return error;
}
error = VmxInitVmcs(guestEip, guestEsp, hostEip);
if (error)
{
DbgPrintEx(77, 0, "[db]:vmcs 初始化失败 error = %d,cpunumber %d\r\n", error, pVcpu->cpuNumber);
VmxDestory();
return error;
}
return 0;
}int VmxInit(ULONG64 hostEip)
{ PVMXCPUPCB pVcpu = VmxGetCurrentCPUPCB();
pVcpu->cpuNumber = KeGetCurrentProcessorNumberEx(NULL);
PULONG64 retAddr = (PULONG64)_AddressOfReturnAddress();
ULONG64 guestEsp = retAddr + 1;
ULONG64 guestEip = *retAddr;
int error = VmxInitVmOn();
if (error)
{
DbgPrintEx(77, 0, "[db]:vmon 初始化失败 error = %d,cpunumber %d\r\n", error, pVcpu->cpuNumber);
return error;
}
error = VmxInitVmcs(guestEip, guestEsp, hostEip);
if (error)
{
DbgPrintEx(77, 0, "[db]:vmcs 初始化失败 error = %d,cpunumber %d\r\n", error, pVcpu->cpuNumber);
VmxDestory();
return error;
}
return 0;
}int VmxInitVmcs(ULONG64 GuestEip,ULONG64 GuestEsp, ULONG64 hostEip)
{ PVMXCPUPCB pVcpu = VmxGetCurrentCPUPCB();
PHYSICAL_ADDRESS lowphys, heiPhy;
lowphys.QuadPart = 0;
heiPhy.QuadPart = -1;
pVcpu->VmxcsAddr = MmAllocateContiguousMemorySpecifyCache(PAGE_SIZE, lowphys, heiPhy, lowphys, MmCached);
if (!pVcpu->VmxcsAddr)
{
//申请内存失败
return -1;
}
memset(pVcpu->VmxcsAddr, 0, PAGE_SIZE);
pVcpu->VmxcsAddrPhys = MmGetPhysicalAddress(pVcpu->VmxcsAddr);
pVcpu->VmxHostStackTop = MmAllocateContiguousMemorySpecifyCache(PAGE_SIZE * 36, lowphys, heiPhy, lowphys, MmCached);
if (!pVcpu->VmxHostStackTop)
{
//申请内存失败
return -1;
}
memset(pVcpu->VmxHostStackTop, 0, PAGE_SIZE * 36);
pVcpu->VmxHostStackBase = (ULONG64)pVcpu->VmxHostStackTop + PAGE_SIZE * 36 - 0x200;
//填充ID
ULONG64 vmxBasic = __readmsr(IA32_VMX_BASIC);
*(PULONG)pVcpu->VmxcsAddr = (ULONG)vmxBasic;
//加载VMCS
__vmx_vmclear(&pVcpu->VmxcsAddrPhys.QuadPart);
__vmx_vmptrld(&pVcpu->VmxcsAddrPhys.QuadPart);
VmxInitGuest(GuestEip, GuestEsp);
VmxInitHost(hostEip);
}int VmxInitVmcs(ULONG64 GuestEip,ULONG64 GuestEsp, ULONG64 hostEip)
{ PVMXCPUPCB pVcpu = VmxGetCurrentCPUPCB();
PHYSICAL_ADDRESS lowphys, heiPhy;
lowphys.QuadPart = 0;
heiPhy.QuadPart = -1;
pVcpu->VmxcsAddr = MmAllocateContiguousMemorySpecifyCache(PAGE_SIZE, lowphys, heiPhy, lowphys, MmCached);
if (!pVcpu->VmxcsAddr)
{
//申请内存失败
return -1;
}
memset(pVcpu->VmxcsAddr, 0, PAGE_SIZE);
pVcpu->VmxcsAddrPhys = MmGetPhysicalAddress(pVcpu->VmxcsAddr);
pVcpu->VmxHostStackTop = MmAllocateContiguousMemorySpecifyCache(PAGE_SIZE * 36, lowphys, heiPhy, lowphys, MmCached);
if (!pVcpu->VmxHostStackTop)
{
//申请内存失败
return -1;
}
memset(pVcpu->VmxHostStackTop, 0, PAGE_SIZE * 36);
pVcpu->VmxHostStackBase = (ULONG64)pVcpu->VmxHostStackTop + PAGE_SIZE * 36 - 0x200;
//填充ID
ULONG64 vmxBasic = __readmsr(IA32_VMX_BASIC);
*(PULONG)pVcpu->VmxcsAddr = (ULONG)vmxBasic;
//加载VMCS
__vmx_vmclear(&pVcpu->VmxcsAddrPhys.QuadPart);
__vmx_vmptrld(&pVcpu->VmxcsAddrPhys.QuadPart);
VmxInitGuest(GuestEip, GuestEsp);
VmxInitHost(hostEip);
}void fillGdtDataItem(int index,short selector)
{ GdtTable gdtTable = {0};
AsmGetGdtTable(&gdtTable);
selector &= 0xFFF8;
ULONG limit = __segmentlimit(selector);
PULONG item = (PULONG)(gdtTable.Base + selector);
LARGE_INTEGER itemBase = {0};
itemBase.LowPart = (*item & 0xFFFF0000) >> 16;
item += 1;
itemBase.LowPart |= (*item & 0xFF000000) | ((*item & 0xFF) << 16);
//属性
ULONG attr = (*item & 0x00F0FF00) >> 8;
if (selector == 0)
{
attr |= 1 << 16;
}
__vmx_vmwrite(GUEST_ES_BASE + index * 2, itemBase.QuadPart);
__vmx_vmwrite(GUEST_ES_LIMIT + index * 2, limit);
__vmx_vmwrite(GUEST_ES_AR_BYTES + index * 2, attr);
__vmx_vmwrite(GUEST_ES_SELECTOR + index * 2, selector);
}void fillGdtDataItem(int index,short selector)
{ GdtTable gdtTable = {0};
AsmGetGdtTable(&gdtTable);
selector &= 0xFFF8;
ULONG limit = __segmentlimit(selector);
PULONG item = (PULONG)(gdtTable.Base + selector);
LARGE_INTEGER itemBase = {0};
itemBase.LowPart = (*item & 0xFFFF0000) >> 16;
item += 1;
itemBase.LowPart |= (*item & 0xFF000000) | ((*item & 0xFF) << 16);
//属性
ULONG attr = (*item & 0x00F0FF00) >> 8;
if (selector == 0)
{
attr |= 1 << 16;
}
__vmx_vmwrite(GUEST_ES_BASE + index * 2, itemBase.QuadPart);
__vmx_vmwrite(GUEST_ES_LIMIT + index * 2, limit);
__vmx_vmwrite(GUEST_ES_AR_BYTES + index * 2, attr);
__vmx_vmwrite(GUEST_ES_SELECTOR + index * 2, selector);
}GdtTable gdtTable = { 0 };
AsmGetGdtTable(&gdtTable);ULONG trSelector = AsmReadTR();
trSelector &= 0xFFF8;
ULONG trlimit = __segmentlimit(trSelector);
LARGE_INTEGER trBase = {0};
PULONG trItem = (PULONG)(gdtTable.Base + trSelector);
//读TR
trBase.LowPart = ((trItem[0] >> 16) & 0xFFFF) | ((trItem[1] & 0xFF) << 16) | ((trItem[1] & 0xFF000000));
trBase.HighPart = trItem[2];
//属性
ULONG attr = (trItem[1] & 0x00F0FF00) >> 8;
__vmx_vmwrite(GUEST_TR_BASE, trBase.QuadPart);__vmx_vmwrite(GUEST_TR_LIMIT, trlimit);__vmx_vmwrite(GUEST_TR_AR_BYTES, attr);__vmx_vmwrite(GUEST_TR_SELECTOR, trSelector);GdtTable gdtTable = { 0 };
AsmGetGdtTable(&gdtTable);ULONG trSelector = AsmReadTR();
trSelector &= 0xFFF8;
ULONG trlimit = __segmentlimit(trSelector);
LARGE_INTEGER trBase = {0};
PULONG trItem = (PULONG)(gdtTable.Base + trSelector);
//读TR
trBase.LowPart = ((trItem[0] >> 16) & 0xFFFF) | ((trItem[1] & 0xFF) << 16) | ((trItem[1] & 0xFF000000));
trBase.HighPart = trItem[2];
//属性
ULONG attr = (trItem[1] & 0x00F0FF00) >> 8;
__vmx_vmwrite(GUEST_TR_BASE, trBase.QuadPart);__vmx_vmwrite(GUEST_TR_LIMIT, trlimit);__vmx_vmwrite(GUEST_TR_AR_BYTES, attr);__vmx_vmwrite(GUEST_TR_SELECTOR, trSelector);__vmx_vmwrite(GUEST_CR0, __readcr0());__vmx_vmwrite(GUEST_CR4, __readcr4());__vmx_vmwrite(GUEST_CR3, __readcr3());__vmx_vmwrite(GUEST_DR7, __readdr(7));
__vmx_vmwrite(GUEST_RFLAGS, __readeflags());__vmx_vmwrite(GUEST_RSP, GuestEsp);__vmx_vmwrite(GUEST_RIP, GuestEip);__vmx_vmwrite(VMCS_LINK_POINTER, -1);
__vmx_vmwrite(GUEST_IA32_DEBUGCTL, __readmsr(IA32_MSR_DEBUGCTL));__vmx_vmwrite(GUEST_IA32_PAT, __readmsr(IA32_MSR_PAT));__vmx_vmwrite(GUEST_IA32_EFER, __readmsr(IA32_MSR_EFER));__vmx_vmwrite(GUEST_FS_BASE, __readmsr(IA32_FS_BASE));__vmx_vmwrite(GUEST_GS_BASE, __readmsr(IA32_GS_BASE));__vmx_vmwrite(GUEST_SYSENTER_CS, __readmsr(0x174));
__vmx_vmwrite(GUEST_SYSENTER_ESP, __readmsr(0x175));
__vmx_vmwrite(GUEST_SYSENTER_EIP, __readmsr(0x176));
//IDT GDT
GdtTable idtTable;__sidt(&idtTable);__vmx_vmwrite(GUEST_GDTR_BASE, gdtTable.Base);__vmx_vmwrite(GUEST_GDTR_LIMIT, gdtTable.limit);__vmx_vmwrite(GUEST_IDTR_LIMIT, idtTable.limit);__vmx_vmwrite(GUEST_IDTR_BASE, idtTable.Base);__vmx_vmwrite(GUEST_CR0, __readcr0());__vmx_vmwrite(GUEST_CR4, __readcr4());__vmx_vmwrite(GUEST_CR3, __readcr3());__vmx_vmwrite(GUEST_DR7, __readdr(7));
__vmx_vmwrite(GUEST_RFLAGS, __readeflags());__vmx_vmwrite(GUEST_RSP, GuestEsp);__vmx_vmwrite(GUEST_RIP, GuestEip);__vmx_vmwrite(VMCS_LINK_POINTER, -1);
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