我们讨论了INTEL的 VT-X的情况,对于AMD的SVM,我们还没有做过多讨论,本篇文章就会继续讨论SVM的情况.
网上关于AMD的资料几乎为0,我希望这篇文章给你带来启发
1.准备工作
首先我们要确保SVM是否是支持的:
这是万事开头
之后分配VCPU结构区域跟上篇文章一样,我这边直接拿了上次的文章的代码,
唯一不同的是,vcpu区域多了这些
relative_hvm相当于一个全局变量,这部分我是参考zero-tang的noir虚拟机,我会在文末放参考资料
guest_vmcb和host_state是重要的信息,分别代表:
用户的VMCB区域(intel是叫做VMCS),主机的状态(AMD用一个msr叫做VM_HSAVE_PA来放主机状态的)
他们大小都是一个page_size
顺便一提vmcb的结构是这样的:
由_vmcb_control_area和_vmcb_state_save_area结构控制,结构如下:
typedef struct _vmcb_control_area
{
UINT16 InterceptCrRead; // +0x000
UINT16 InterceptCrWrite; // +0x002
UINT16 InterceptDrRead; // +0x004
UINT16 InterceptDrWrite; // +0x006
UINT32 InterceptException; // +0x008
UINT32 InterceptMisc1; // +0x00c
UINT32 InterceptMisc2; // +0x010
UINT8 Reserved1[0x03c - 0x014]; // +0x014
UINT16 PauseFilterThreshold; // +0x03c
UINT16 PauseFilterCount; // +0x03e
UINT64 IopmBasePa; // +0x040
UINT64 MsrpmBasePa; // +0x048
UINT64 TscOffset; // +0x050
UINT32 GuestAsid; // +0x058
UINT32 TlbControl; // +0x05c
UINT64 VIntr; // +0x060
UINT64 InterruptShadow; // +0x068
UINT64 ExitCode; // +0x070
UINT64 ExitInfo1; // +0x078
UINT64 ExitInfo2; // +0x080
UINT64 ExitIntInfo; // +0x088
UINT64 NpEnable; // +0x090
UINT64 AvicApicBar; // +0x098
UINT64 GuestPaOfGhcb; // +0x0a0
UINT64 EventInj; // +0x0a8
UINT64 NCr3; // +0x0b0
UINT64 LbrVirtualizationEnable; // +0x0b8
UINT64 VmcbClean; // +0x0c0
UINT64 NRip; // +0x0c8
UINT8 NumOfBytesFetched; // +0x0d0
UINT8 GuestInstructionBytes[15]; // +0x0d1
UINT64 AvicApicBackingPagePointer; // +0x0e0
UINT64 Reserved2; // +0x0e8
UINT64 AvicLogicalTablePointer; // +0x0f0
UINT64 AvicPhysicalTablePointer; // +0x0f8
UINT64 Reserved3; // +0x100
UINT64 VmcbSaveStatePointer; // +0x108
UINT8 Reserved4[0x400 - 0x110]; // +0x110
};
static_assert(sizeof(_vmcb_control_area) == 0x400, "size check");
typedef struct _vmcb_state_save_area
{
UINT16 EsSelector; // +0x000
UINT16 EsAttrib; // +0x002
UINT32 EsLimit; // +0x004
UINT64 EsBase; // +0x008
UINT16 CsSelector; // +0x010
UINT16 CsAttrib; // +0x012
UINT32 CsLimit; // +0x014
UINT64 CsBase; // +0x018
UINT16 SsSelector; // +0x020
UINT16 SsAttrib; // +0x022
UINT32 SsLimit; // +0x024
UINT64 SsBase; // +0x028
UINT16 DsSelector; // +0x030
UINT16 DsAttrib; // +0x032
UINT32 DsLimit; // +0x034
UINT64 DsBase; // +0x038
UINT16 FsSelector; // +0x040
UINT16 FsAttrib; // +0x042
UINT32 FsLimit; // +0x044
UINT64 FsBase; // +0x048
UINT16 GsSelector; // +0x050
UINT16 GsAttrib; // +0x052
UINT32 GsLimit; // +0x054
UINT64 GsBase; // +0x058
UINT16 GdtrSelector; // +0x060
UINT16 GdtrAttrib; // +0x062
UINT32 GdtrLimit; // +0x064
UINT64 GdtrBase; // +0x068
UINT16 LdtrSelector; // +0x070
UINT16 LdtrAttrib; // +0x072
UINT32 LdtrLimit; // +0x074
UINT64 LdtrBase; // +0x078
UINT16 IdtrSelector; // +0x080
UINT16 IdtrAttrib; // +0x082
UINT32 IdtrLimit; // +0x084
UINT64 IdtrBase; // +0x088
UINT16 TrSelector; // +0x090
UINT16 TrAttrib; // +0x092
UINT32 TrLimit; // +0x094
UINT64 TrBase; // +0x098
UINT8 Reserved1[0x0cb - 0x0a0]; // +0x0a0
UINT8 Cpl; // +0x0cb
UINT32 Reserved2; // +0x0cc
UINT64 Efer; // +0x0d0
UINT8 Reserved3[0x148 - 0x0d8]; // +0x0d8
UINT64 Cr4; // +0x148
UINT64 Cr3; // +0x150
UINT64 Cr0; // +0x158
UINT64 Dr7; // +0x160
UINT64 Dr6; // +0x168
UINT64 Rflags; // +0x170
UINT64 Rip; // +0x178
UINT8 Reserved4[0x1d8 - 0x180]; // +0x180
UINT64 Rsp; // +0x1d8
UINT8 Reserved5[0x1f8 - 0x1e0]; // +0x1e0
UINT64 Rax; // +0x1f8
UINT64 Star; // +0x200
UINT64 LStar; // +0x208
UINT64 CStar; // +0x210
UINT64 SfMask; // +0x218
UINT64 KernelGsBase; // +0x220
UINT64 SysenterCs; // +0x228
UINT64 SysenterEsp; // +0x230
UINT64 SysenterEip; // +0x238
UINT64 Cr2; // +0x240
UINT8 Reserved6[0x268 - 0x248]; // +0x248
UINT64 GPat; // +0x268
UINT64 DbgCtl; // +0x270
UINT64 BrFrom; // +0x278
UINT64 BrTo; // +0x280
UINT64 LastExcepFrom; // +0x288
UINT64 LastExcepTo; // +0x290
};
static_assert(sizeof(_vmcb_state_save_area) == 0x298, "size check");
这个结构很关键.不要随便乱动
2. 初始化SVM
我们一样用我们的DPC Callback让我们每个核心处理器都同步执行这些代码
init_logical_processor的逻辑非常简单
首先你必须要给msr的amd64_efer(0xC0000080)增加一个amd64_efer_svme_bit(0x1000)
其次你要操作你要拦截的msr的列表,不设置的话我们没办法拦截到特定的msr的中断:
跟AMD白皮书里面写的一样
----
Secure Virtual Machine Enable (SVME) Bit
Bit 12, read/write. Enables the SVM extensions. (...) The
effect of turning off EFER.SVME while a guest is running is
undefined; therefore, the VMM should always prevent guests
from writing EFER.
----
Each MSR is controlled by two bits in the MSRPM. The LSB of
the two bits controls read access to the MSR and the MSB
controls write access. A value of 1 indicates that the
operation is intercepted. This function locates an offset for
IA32_MSR_EFER and sets the MSB bit. For details of logic, see
"MSR Intercepts".
这就是为啥之前用g_relative_hvm的原因,这些全局变量放一个结构里面就行
第三步,设置guest_vmcb
Amd CPU的SVM不同于Intel VT-X 他的进入vm的方式是vmrun guest_vmcb
而不是intel VT-X的 _write_vmcs(这一点AMD NO)
所以我们要设置一下这个重要参数
基本上 就是一些寄存器信息
vcpu->guest_vmcb->state_save.CsSelector = state_p.cs.selector; vcpu->guest_vmcb->state_save.CsAttrib = svm_attrib(state_p.cs.attrib); vcpu->guest_vmcb->state_save.CsLimit = state_p.cs.limit; vcpu->guest_vmcb->state_save.CsBase = state_p.cs.base; vcpu->guest_vmcb->state_save.DsSelector = state_p.cs.selector; vcpu->guest_vmcb->state_save.DsAttrib = svm_attrib(state_p.ds.attrib); vcpu->guest_vmcb->state_save.DsLimit = state_p.ds.limit; vcpu->guest_vmcb->state_save.DsBase = state_p.ds.base; vcpu->guest_vmcb->state_save.EsSelector = state_p.es.selector; vcpu->guest_vmcb->state_save.EsAttrib = svm_attrib(state_p.es.attrib); vcpu->guest_vmcb->state_save.EsLimit = state_p.es.limit; vcpu->guest_vmcb->state_save.EsBase = state_p.es.base; vcpu->guest_vmcb->state_save.FsSelector = state_p.fs.selector; vcpu->guest_vmcb->state_save.FsAttrib = svm_attrib(state_p.fs.attrib); vcpu->guest_vmcb->state_save.FsLimit = state_p.fs.limit; vcpu->guest_vmcb->state_save.FsBase = state_p.fs.base; vcpu->guest_vmcb->state_save.GsSelector = state_p.gs.selector; vcpu->guest_vmcb->state_save.GsAttrib = svm_attrib(state_p.gs.attrib); vcpu->guest_vmcb->state_save.GsLimit = state_p.gs.limit; vcpu->guest_vmcb->state_save.GsBase = state_p.gs.base; vcpu->guest_vmcb->state_save.SsSelector = state_p.ss.selector; vcpu->guest_vmcb->state_save.SsAttrib = svm_attrib(state_p.ss.attrib); vcpu->guest_vmcb->state_save.SsLimit = state_p.ss.limit; vcpu->guest_vmcb->state_save.SsBase = state_p.ss.base; vcpu->guest_vmcb->state_save.TrSelector = state_p.tr.selector; vcpu->guest_vmcb->state_save.TrAttrib = svm_attrib(state_p.tr.attrib); vcpu->guest_vmcb->state_save.TrLimit = state_p.tr.limit; vcpu->guest_vmcb->state_save.TrBase = state_p.tr.base; //gdtr vcpu->guest_vmcb->state_save.GdtrBase = state_p.gdtr.base; vcpu->guest_vmcb->state_save.GdtrLimit = state_p.gdtr.limit; //idtr vcpu->guest_vmcb->state_save.IdtrLimit = state_p.idtr.limit; vcpu->guest_vmcb->state_save.IdtrBase = state_p.idtr.base; //ldtr vcpu->guest_vmcb->state_save.LdtrSelector = state_p.ldtr.selector; vcpu->guest_vmcb->state_save.LdtrAttrib = svm_attrib(state_p.ldtr.attrib); vcpu->guest_vmcb->state_save.LdtrLimit = state_p.ldtr.limit; vcpu->guest_vmcb->state_save.LdtrBase = state_p.ldtr.base; //cr vcpu->guest_vmcb->state_save.Cr0 = state_p.cr0; vcpu->guest_vmcb->state_save.Cr2 = state_p.cr2; vcpu->guest_vmcb->state_save.Cr3 = state_p.cr3; vcpu->guest_vmcb->state_save.Cr4 = state_p.cr4; // Save Debug Registers vcpu->guest_vmcb->state_save.Dr6 = state_p.dr6; vcpu->guest_vmcb->state_save.Dr7 = state_p.dr7; vcpu->guest_vmcb->state_save.Rflags = 2; vcpu->guest_vmcb->state_save.Rsp = vcpu->context_frame.Rsp; vcpu->guest_vmcb->state_save.Rip = vcpu->context_frame.Rip; vcpu->guest_vmcb->state_save.GPat = state_p.pat; vcpu->guest_vmcb->state_save.Efer = state_p.efer; vcpu->guest_vmcb->state_save.Star = state_p.star; vcpu->guest_vmcb->state_save.CStar = state_p.cstar; vcpu->guest_vmcb->state_save.SfMask = state_p.sfmask; vcpu->guest_vmcb->state_save.GsBase = state_p.gsswap;
然后是关键的IopmBasePa、MsrpmBasePa,这两个要指向我们的relative_hvm所设置的东西(作用拦截msr中断)
vcpu->guest_vmcb->control.IopmBasePa = vcpu->relative_hvm->iopm.physical_address; vcpu->guest_vmcb->control.MsrpmBasePa = vcpu->relative_hvm->msr_bitmap.physical_address;
最后是GuestAsid,这个东西全称”Specify guest’s address space ID” 我们要做到是顶级top level虚拟机,所以设置1就行
具体可以看amd的白皮书的”CPUID Fn8000_000A_EBX SVM Revision and Feature Identification” 这一章介绍
最后最后一步,设置我们要处理的vmexit事件:
结构如下:
typedef union _svm_instruction_intercept1
{
struct
{
unsigned __int32 intercept_intr : 1;
unsigned __int32 intercept_nmi : 1;
unsigned __int32 intercept_smi : 1;
unsigned __int32 intercept_init : 1;
unsigned __int32 intercept_vint : 1;
unsigned __int32 intercept_cr0_tsmp : 1;
unsigned __int32 intercept_sidt : 1;
unsigned __int32 intercept_sgdt : 1;
unsigned __int32 intercept_sldt : 1;
unsigned __int32 intercept_str : 1;
unsigned __int32 intercept_lidt : 1;
unsigned __int32 intercept_lgdt : 1;
unsigned __int32 intercept_lldt : 1;
unsigned __int32 intercept_ltr : 1;
unsigned __int32 intercept_rdtsc : 1;
unsigned __int32 intercept_rdpmc : 1;
unsigned __int32 intercept_pushf : 1;
unsigned __int32 intercept_popf : 1;
unsigned __int32 intercept_cpuid : 1;
unsigned __int32 intercept_rsm : 1;
unsigned __int32 intercept_iret : 1;
unsigned __int32 intercept_int : 1;
unsigned __int32 intercept_invd : 1;
unsigned __int32 intercept_pause : 1;
unsigned __int32 intercept_hlt : 1;
unsigned __int32 intercept_invlpg : 1;
unsigned __int32 intercept_invlpga : 1;
unsigned __int32 intercept_io : 1;
unsigned __int32 intercept_msr : 1;
unsigned __int32 intercept_task_switch : 1;
unsigned __int32 intercept_ferr_freeze : 1;
unsigned __int32 intercept_shutdown : 1;
};
unsigned __int32 value;
}svm_instruction_intercept1, * svm_instruction_intercept1_p;
typedef union _nvc_svm_instruction_intercept2
{
struct
{
unsigned __int16 intercept_vmrun : 1;
unsigned __int16 intercept_vmmcall : 1;
unsigned __int16 intercept_vmload : 1;
unsigned __int16 intercept_vmsave : 1;
unsigned __int16 intercept_stgi : 1;
unsigned __int16 intercept_clgi : 1;
unsigned __int16 intercept_skinit : 1;
unsigned __int16 intercept_rdtscp : 1;
unsigned __int16 intercept_icebp : 1;
unsigned __int16 intercept_wbinvd : 1;
unsigned __int16 intercept_monitor : 1;
unsigned __int16 intercept_mwait : 1;
unsigned __int16 intercept_mwait_c : 1;
unsigned __int16 intercept_xsetbv : 1;
unsigned __int16 reserved1 : 1;
unsigned __int16 intercept_post_efer_write : 1;
};
unsigned __int16 value;
}svm_instruction_intercept2, * svm_instruction_intercept2_p;
设置guest_vmcb的control字段来控制我们接受什么vmexit事件:
void svm::svm_setup_control_area(_vcpu_t* vcpu)
{
svm_instruction_intercept1 intercept_misc_1;
svm_instruction_intercept2 intercept_misc_2;
intercept_misc_1.value = 0;
intercept_misc_1.intercept_msr = 1; //中断msr
intercept_misc_1.intercept_rdtsc = 1;// 中断rdtsc
intercept_misc_2.value = 0;
intercept_misc_2.intercept_vmrun = 1; //中断vmrun
intercept_misc_2.intercept_vmmcall = 1;//中断vmcall
intercept_misc_2.intercept_rdtscp = 1;//中断rdtscp
vcpu->guest_vmcb->control.InterceptMisc1 = intercept_misc_1.value;
vcpu->guest_vmcb->control.InterceptMisc2 = intercept_misc_2.value;
}
保存我们的guest_vmcb
__svm_vmsave(vcpu->guest_vmcb_physical_address);
指定host机状态存放位置(通过amd64_hsave_pa这个msr来控制区域(AMD挺迷惑的,为什么要用一个寄存器来存放host状态而不是intel的VMCS)):
__svm_vmsave(vcpu->host_state_physical_address); __writemsr(amd64_hsave_pa, vcpu->host_state_physical_address);
3. 进入SVM
一切就绪后,在vm stack上开辟一个空间,用来给我们的vmexit_handler函数传值:
_svm_initial_stack_p stack = (_svm_initial_stack_p)((uintptr_t)vcpu->stack + _stack_size - sizeof(_svm_initial_stack)); stack->guest_vmcb_pa = svm::svm_set_vmcb(vcpu); stack->vcpu = vcpu; stack->proc_id = processor_number; launch_svm(stack); __debugbreak(); return false;
还记得汇编中X64传参吗?
从左到右四个参数传递是RCX，RDX，R8，R9, 其余在RSP里面传参
返回信息寄存器是RAX
知道这些,我们就可以写launch_svm了:
这里有个坑是360的一个cc大佬提醒的我加上看了看zero tang的代码才想到
就是svm的要切CR3,因为默认的驱动启动是挂靠在进程里面的,访问线性地址会炸,必须要切换成系统的CR3才行.之前被这个坑搞了好久,现在才搞定
INTEL VTX的没这个问题,因为intel的VTX是在vmcs区域里面就指定了host cr3
核心思想就是,vmrun guest_vmcb后,就已经到guest机里面了,这个时候就要等待vmrun执行结束,vmrun结束后就是host机区域,就可以操作我们的vmexit_handler,在进vmexit_handler之前,要用vmsave保存一次vmcb的情况
这边给的参数1是栈,参数2是当前cpu的number 我们试试
good 成功进入vmexit_handler
4. 后记
没什么难的,所谓的难只不过是自己内心害怕自己搞不定罢了,,不过技术是给人用的还害怕搞不定???
参考资料:
https://github.com/tandasat/SimpleSvm<-国际友人tandasat的simpleSVM,他的虚拟机有问题没办法在vmexit_handler中断
https://github.com/Zero-Tang/NoirVisor<- Zero-Tang 很完备的虚拟机例子,本篇文章一些结构和代码是抄他的.不过抄的位置都已经标出
来源：freebuf.com 2021-04-11 15:15:08 by: huoji120
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