最近在看HyperDbg这个项目,看到了一种基于VT的syscall挂钩方法,记录一下。EFER(Extended Feature Enable Register)是MSR寄存器的一种,相关功能可以在intel白皮书卷3A,第2.2.1节中找到。
EFER寄存器的SCE位用来控制对SYSCALL/SYSRET的支持。
在卷2B,第4.3节可以找到SYSCALL指令的操作
可以看出当EFER寄存器的SCE位为0时会产生#UD异常,如果我们手动将SCE清零,那么就会导致#UD异常,再通过设置VT中对#UD异常的响应事件就可以拦截SYSCALL。
用代码模拟SYSCALL:
看下SYSRET的操作,可以看出也是SCE位置0时抛出#UD异常
用代码模拟:
手动清除SCE位并设置拦截:
对#UD事件的响应:
IF (CS.L ≠
1
)
or
(IA32_EFER.LMA ≠
1
)
or
(IA32_EFER.SCE ≠
1
)
(
*
Not
in
64
-
Bit Mode
or
SYSCALL
/
SYSRET
not
enabled
in
IA32_EFER
*
)
THEN
FI;
RCX ← RIP; (
*
Will contain address of
next
instruction
*
)
RIP ← IA32_LSTAR;
R11 ← RFLAGS;
RFLAGS ← RFLAGS AND NOT(IA32_FMASK);
CS.Selector ← IA32_STAR[
47
:
32
] AND FFFCH (
*
Operating system provides CS; RPL forced to
0
*
)
(
*
Set
rest of CS to a fixed value
*
)
CS.Base ←
0
; (
*
Flat segment
*
)
CS.Limit ← FFFFFH; (
*
With
4
-
KByte granularity, implies a
4
-
GByte limit
*
)
CS.
Type
←
11
; (
*
Execute
/
read code, accessed
*
)
CS.S ←
1
;
CS.DPL ←
0
;
CS.P ←
1
;
CS.L ←
1
; (
*
Entry
is
to
64
-
bit mode
*
)
CS.D ←
0
; (
*
Required
if
CS.L
=
1
*
)
CS.G ←
1
; (
*
4
-
KByte granularity
*
)
CPL ←
0
;
SS.Selector ← IA32_STAR[
47
:
32
]
+
8
; (
*
SS just above CS
*
)
(
*
Set
rest of SS to a fixed value
*
)
SS.Base ←
0
; (
*
Flat segment
*
)
SS.Limit ← FFFFFH; (
*
With
4
-
KByte granularity, implies a
4
-
GByte limit
*
)
SS.
Type
←
3
; (
*
Read
/
write data, accessed
*
)
SS.S ←
1
;
SS.DPL ←
0
;
SS.P ←
1
;
SS.B ←
1
; (
*
32
-
bit stack segment
*
)
SS.G ←
1
; (
*
4
-
KByte granularity
*
)
IF (CS.L ≠
1
)
or
(IA32_EFER.LMA ≠
1
)
or
(IA32_EFER.SCE ≠
1
)
(
*
Not
in
64
-
Bit Mode
or
SYSCALL
/
SYSRET
not
enabled
in
IA32_EFER
*
)
THEN
FI;
RCX ← RIP; (
*
Will contain address of
next
instruction
*
)
RIP ← IA32_LSTAR;
R11 ← RFLAGS;
RFLAGS ← RFLAGS AND NOT(IA32_FMASK);
CS.Selector ← IA32_STAR[
47
:
32
] AND FFFCH (
*
Operating system provides CS; RPL forced to
0
*
)
(
*
Set
rest of CS to a fixed value
*
)
CS.Base ←
0
; (
*
Flat segment
*
)
CS.Limit ← FFFFFH; (
*
With
4
-
KByte granularity, implies a
4
-
GByte limit
*
)
CS.
Type
←
11
; (
*
Execute
/
read code, accessed
*
)
CS.S ←
1
;
CS.DPL ←
0
;
CS.P ←
1
;
CS.L ←
1
; (
*
Entry
is
to
64
-
bit mode
*
)
CS.D ←
0
; (
*
Required
if
CS.L
=
1
*
)
CS.G ←
1
; (
*
4
-
KByte granularity
*
)
CPL ←
0
;
SS.Selector ← IA32_STAR[
47
:
32
]
+
8
; (
*
SS just above CS
*
)
(
*
Set
rest of SS to a fixed value
*
)
SS.Base ←
0
; (
*
Flat segment
*
)
SS.Limit ← FFFFFH; (
*
With
4
-
KByte granularity, implies a
4
-
GByte limit
*
)
SS.
Type
←
3
; (
*
Read
/
write data, accessed
*
)
SS.S ←
1
;
SS.DPL ←
0
;
SS.P ←
1
;
SS.B ←
1
; (
*
32
-
bit stack segment
*
)
SS.G ←
1
; (
*
4
-
KByte granularity
*
)
_Use_decl_annotations_
BOOLEAN
SyscallHookEmulateSYSCALL(PGUEST_REGS Regs)
{
VMX_SEGMENT_SELECTOR Cs, Ss;
UINT32 InstructionLength;
UINT64 MsrValue;
UINT64 GuestRip;
UINT64 GuestRflags;
/
/
/
/
Reading guest's RIP
/
/
__vmx_vmread(VMCS_GUEST_RIP, &GuestRip);
/
/
/
/
Reading instruction length
/
/
__vmx_vmread(VMCS_VMEXIT_INSTRUCTION_LENGTH, &InstructionLength);
/
/
/
/
Reading guest's Rflags
/
/
__vmx_vmread(VMCS_GUEST_RFLAGS, &GuestRflags);
/
/
/
/
Save the address of the instruction following SYSCALL into RCX
and
then
/
/
load RIP
from
IA32_LSTAR.
/
/
MsrValue
=
__readmsr(IA32_LSTAR);
Regs
-
>rcx
=
GuestRip
+
InstructionLength;
GuestRip
=
MsrValue;
__vmx_vmwrite(VMCS_GUEST_RIP, GuestRip);
/
/
/
/
Save RFLAGS into R11
and
then mask RFLAGS using IA32_FMASK
/
/
MsrValue
=
__readmsr(IA32_FMASK);
Regs
-
>r11
=
GuestRflags;
GuestRflags &
=
~(MsrValue | X86_FLAGS_RF);
__vmx_vmwrite(VMCS_GUEST_RFLAGS, GuestRflags);
/
/
/
/
Load the CS
and
SS selectors with values derived
from
bits
47
:
32
of IA32_STAR
/
/
MsrValue
=
__readmsr(IA32_STAR);
Cs.Selector
=
(UINT16)((MsrValue >>
32
) & ~
3
);
/
/
STAR[
47
:
32
] & ~RPL3
Cs.Base
=
0
;
/
/
flat segment
Cs.Limit
=
(UINT32)~
0
;
/
/
4GB
limit
Cs.Attributes.AsUInt
=
0xA09B
;
/
/
L
+
DB
+
P
+
S
+
DPL0
+
Code
SetGuestCs(&Cs);
Ss.Selector
=
(UINT16)(((MsrValue >>
32
) & ~
3
)
+
8
);
/
/
STAR[
47
:
32
]
+
8
Ss.Base
=
0
;
/
/
flat segment
Ss.Limit
=
(UINT32)~
0
;
/
/
4GB
limit
Ss.Attributes.AsUInt
=
0xC093
;
/
/
G
+
DB
+
P
+
S
+
DPL0
+
Data
SetGuestSs(&Ss);
return
TRUE;
}
_Use_decl_annotations_
BOOLEAN
SyscallHookEmulateSYSCALL(PGUEST_REGS Regs)
{
VMX_SEGMENT_SELECTOR Cs, Ss;
UINT32 InstructionLength;
UINT64 MsrValue;
UINT64 GuestRip;
UINT64 GuestRflags;
/
/
/
/
Reading guest's RIP
/
/
__vmx_vmread(VMCS_GUEST_RIP, &GuestRip);
/
/
/
/
Reading instruction length
/
/
__vmx_vmread(VMCS_VMEXIT_INSTRUCTION_LENGTH, &InstructionLength);
/
/
/
/
Reading guest's Rflags
/
/
__vmx_vmread(VMCS_GUEST_RFLAGS, &GuestRflags);
/
/
/
/
Save the address of the instruction following SYSCALL into RCX
and
then
/
/
load RIP
from
IA32_LSTAR.
/
/
MsrValue
=
__readmsr(IA32_LSTAR);
Regs
-
>rcx
=
GuestRip
+
InstructionLength;
GuestRip
=
MsrValue;
__vmx_vmwrite(VMCS_GUEST_RIP, GuestRip);
/
/
/
/
Save RFLAGS into R11
and
then mask RFLAGS using IA32_FMASK
/
/
MsrValue
=
__readmsr(IA32_FMASK);
Regs
-
>r11
=
GuestRflags;
GuestRflags &
=
~(MsrValue | X86_FLAGS_RF);
__vmx_vmwrite(VMCS_GUEST_RFLAGS, GuestRflags);
/
/
/
/
Load the CS
and
SS selectors with values derived
from
bits
47
:
32
of IA32_STAR
/
/
MsrValue
=
__readmsr(IA32_STAR);
Cs.Selector
=
(UINT16)((MsrValue >>
32
) & ~
3
);
/
/
STAR[
47
:
32
] & ~RPL3
Cs.Base
=
0
;
/
/
flat segment
Cs.Limit
=
(UINT32)~
0
;
/
/
4GB
limit
Cs.Attributes.AsUInt
=
0xA09B
;
/
/
L
+
DB
+
P
+
S
+
DPL0
+
Code
SetGuestCs(&Cs);
Ss.Selector
=
(UINT16)(((MsrValue >>
32
) & ~
3
)
+
8
);
/
/
STAR[
47
:
32
]
+
8
Ss.Base
=
0
;
/
/
flat segment
Ss.Limit
=
(UINT32)~
0
;
/
/
4GB
limit
Ss.Attributes.AsUInt
=
0xC093
;
/
/
G
+
DB
+
P
+
S
+
DPL0
+
Data
SetGuestSs(&Ss);
return
TRUE;
}
IF (CS.L ≠
1
)
or
(IA32_EFER.LMA ≠
1
)
or
(IA32_EFER.SCE ≠
1
)
(
*
Not
in
64
-
Bit Mode
or
SYSCALL
/
SYSRET
not
enabled
in
IA32_EFER
*
)
THEN
IF (CPL ≠
0
) OR (RCX
is
not
canonical) THEN
IF (operand size
is
64
-
bit)
THEN (
*
Return to
64
-
Bit Mode
*
)
RIP ← RCX;
ELSE (
*
Return to Compatibility Mode
*
)
RIP ← ECX;
FI;
RFLAGS ← (R11 &
3C7FD7H
) |
2
; (
*
Clear RF, VM, reserved bits;
set
bit
2
*
)
IF (operand size
is
64
-
bit)
THEN CS.Selector ← IA32_STAR[
63
:
48
]
+
16
;
ELSE CS.Selector ← IA32_STAR[
63
:
48
];
FI;
CS.Selector ← CS.Selector OR
3
; (
*
RPL forced to
3
*
)
(
*
Set
rest of CS to a fixed value
*
)
CS.Base ←
0
; (
*
Flat segment
*
)
CS.Limit ← FFFFFH; (
*
With
4
-
KByte granularity, implies a
4
-
GByte limit
*
)
CS.
Type
←
11
; (
*
Execute
/
read code, accessed
*
)
CS.S ←
1
;
CS.DPL ←
3
;
CS.P ←
1
;
IF (operand size
is
64
-
bit)
THEN (
*
Return to
64
-
Bit Mode
*
)
CS.L ←
1
; (
*
64
-
bit code segment
*
)
CS.D ←
0
; (
*
Required
if
CS.L
=
1
*
)
ELSE (
*
Return to Compatibility Mode
*
)
CS.L ←
0
; (
*
Compatibility mode
*
)
CS.D ←
1
; (
*
32
-
bit code segment
*
)
FI;
CS.G ←
1
; (
*
4
-
KByte granularity
*
)
CPL ←
3
;
SS.Selector ← (IA32_STAR[
63
:
48
]
+
8
) OR
3
; (
*
RPL forced to
3
*
)
(
*
Set
rest of SS to a fixed value
*
)
SS.Base ←
0
; (
*
Flat segment
*
)
SS.Limit ← FFFFFH; (
*
With
4
-
KByte granularity, implies a
4
-
GByte limit
*
)
SS.
Type
←
3
; (
*
Read
/
write data, accessed
*
)
SS.S ←
1
;
SS.DPL ←
3
;
SS.P ←
1
;
SS.B ←
1
; (
*
32
-
bit stack segment
*
)
SS.G ←
1
; (
*
4
-
KByte granularity
*
)
IF (CS.L ≠
1
)
or
(IA32_EFER.LMA ≠
1
)
or
(IA32_EFER.SCE ≠
1
)
(
*
Not
in
64
-
Bit Mode
or
SYSCALL
/
SYSRET
not
enabled
in
IA32_EFER
*
)
THEN
IF (CPL ≠
0
) OR (RCX
is
not
canonical) THEN
IF (operand size
is
64
-
bit)
THEN (
*
Return to
64
-
Bit Mode
*
)
RIP ← RCX;
ELSE (
*
Return to Compatibility Mode
*
)
RIP ← ECX;
FI;
RFLAGS ← (R11 &
3C7FD7H
) |
2
; (
*
Clear RF, VM, reserved bits;
set
bit
2
*
)
IF (operand size
is
64
-
bit)
THEN CS.Selector ← IA32_STAR[
63
:
48
]
+
16
;
ELSE CS.Selector ← IA32_STAR[
63
:
48
];
FI;
CS.Selector ← CS.Selector OR
3
; (
*
RPL forced to
3
*
)
(
*
Set
rest of CS to a fixed value
*
)
CS.Base ←
0
; (
*
Flat segment
*
)
CS.Limit ← FFFFFH; (
*
With
4
-
KByte granularity, implies a
4
-
GByte limit
*
)
CS.
Type
←
11
; (
*
Execute
/
read code, accessed
*
)
CS.S ←
1
;
CS.DPL ←
3
;
CS.P ←
1
;
IF (operand size
is
64
-
bit)
THEN (
*
Return to
64
-
Bit Mode
*
)
CS.L ←
1
; (
*
64
-
bit code segment
*
)
CS.D ←
0
; (
*
Required
if
CS.L
=
1
*
)
ELSE (
*
Return to Compatibility Mode
*
)
CS.L ←
0
; (
*
Compatibility mode
*
)
CS.D ←
1
; (
*
32
-
bit code segment
*
)
FI;
CS.G ←
1
; (
*
4
-
KByte granularity
*
)
CPL ←
3
;
SS.Selector ← (IA32_STAR[
63
:
48
]
+
8
) OR
3
; (
*
RPL forced to
3
*
)
(
*
Set
rest of SS to a fixed value
*
)
SS.Base ←
0
; (
*
Flat segment
*
)
SS.Limit ← FFFFFH; (
*
With
4
-
KByte granularity, implies a
4
-
GByte limit
*
)
SS.
Type
←
3
; (
*
Read
/
write data, accessed
*
)
SS.S ←
1
;
SS.DPL ←
3
;
SS.P ←
1
;
SS.B ←
1
; (
*
32
-
bit stack segment
*
)
SS.G ←
1
; (
*
4
-
KByte granularity
*
)
_Use_decl_annotations_
BOOLEAN
SyscallHookEmulateSYSRET(PGUEST_REGS Regs)
{
VMX_SEGMENT_SELECTOR Cs, Ss;
UINT64 MsrValue;
UINT64 GuestRip;
UINT64 GuestRflags;
/
/
/
/
Load RIP
from
RCX
/
/
GuestRip
=
Regs
-
>rcx;
__vmx_vmwrite(VMCS_GUEST_RIP, GuestRip);
/
/
/
/
Load RFLAGS
from
R11. Clear RF, VM, reserved bits
/
/
GuestRflags
=
(Regs
-
>r11 & ~(X86_FLAGS_RF | X86_FLAGS_VM | X86_FLAGS_RESERVED_BITS)) | X86_FLAGS_FIXED;
__vmx_vmwrite(VMCS_GUEST_RFLAGS, GuestRflags);
/
/
/
/
SYSRET loads the CS
and
SS selectors with values derived
from
bits
63
:
48
of IA32_STAR
/
/
MsrValue
=
__readmsr(IA32_STAR);
Cs.Selector
=
(UINT16)(((MsrValue >>
48
)
+
16
) |
3
);
/
/
(STAR[
63
:
48
]
+
16
) |
3
(
*
RPL forced to
3
*
)
Cs.Base
=
0
;
/
/
Flat segment
Cs.Limit
=
(UINT32)~
0
;
/
/
4GB
limit
Cs.Attributes.AsUInt
=
0xA0FB
;
/
/
L
+
DB
+
P
+
S
+
DPL3
+
Code
SetGuestCs(&Cs);
Ss.Selector
=
(UINT16)(((MsrValue >>
48
)
+
8
) |
3
);
/
/
(STAR[
63
:
48
]
+
8
) |
3
(
*
RPL forced to
3
*
)
Ss.Base
=
0
;
/
/
Flat segment
Ss.Limit
=
(UINT32)~
0
;
/
/
4GB
limit
Ss.Attributes.AsUInt
=
0xC0F3
;
/
/
G
+
DB
+
P
+
S
+
DPL3
+
Data
SetGuestSs(&Ss);
return
TRUE;
}
_Use_decl_annotations_
BOOLEAN
SyscallHookEmulateSYSRET(PGUEST_REGS Regs)
{
VMX_SEGMENT_SELECTOR Cs, Ss;
UINT64 MsrValue;
UINT64 GuestRip;
UINT64 GuestRflags;
/
/
/
/
Load RIP
from
RCX
/
/
GuestRip
=
Regs
-
>rcx;
__vmx_vmwrite(VMCS_GUEST_RIP, GuestRip);
/
/
/
/
Load RFLAGS
from
R11. Clear RF, VM, reserved bits
/
/
GuestRflags
=
(Regs
-
>r11 & ~(X86_FLAGS_RF | X86_FLAGS_VM | X86_FLAGS_RESERVED_BITS)) | X86_FLAGS_FIXED;
__vmx_vmwrite(VMCS_GUEST_RFLAGS, GuestRflags);
/
/
/
/
SYSRET loads the CS
and
SS selectors with values derived
from
bits
63
:
48
of IA32_STAR
/
/
MsrValue
=
__readmsr(IA32_STAR);
Cs.Selector
=
(UINT16)(((MsrValue >>
48
)
+
16
) |
3
);
/
/
(STAR[
63
:
48
]
+
16
) |
3
(
*
RPL forced to
3
*
)
Cs.Base
=
0
;
/
/
Flat segment
Cs.Limit
=
(UINT32)~
0
;
/
/
4GB
limit
Cs.Attributes.AsUInt
=
0xA0FB
;
/
/
L
+
DB
+
P
+
S
+
DPL3
+
Code
SetGuestCs(&Cs);
Ss.Selector
=
(UINT16)(((MsrValue >>
48
)
+
8
) |
3
);
/
/
(STAR[
63
:
48
]
+
8
) |
3
(
*
RPL forced to
3
*
)
Ss.Base
=
0
;
/
/
Flat segment
Ss.Limit
=
(UINT32)~
0
;
/
/
4GB
limit
Ss.Attributes.AsUInt
=
0xC0F3
;
/
/
G
+
DB
+
P
+
S
+
DPL3
+
Data
SetGuestSs(&Ss);
return
TRUE;
}
VOID
SyscallHookConfigureEFER(BOOLEAN EnableEFERSyscallHook)
{
IA32_EFER_REGISTER MsrValue;
IA32_VMX_BASIC_REGISTER VmxBasicMsr
=
{
0
};
UINT32 VmEntryControls
=
0
;
UINT32 VmExitControls
=
0
;
/
/
/
/
Reading IA32_VMX_BASIC_MSR
/
/
VmxBasicMsr.AsUInt
=
__readmsr(IA32_VMX_BASIC);
/
/
/
/
Read previous VM
-
Entry
and
VM
-
Exit controls
/
/
__vmx_vmread(VMCS_CTRL_VMENTRY_CONTROLS, &VmEntryControls);
__vmx_vmread(VMCS_CTRL_PRIMARY_VMEXIT_CONTROLS, &VmExitControls);
MsrValue.AsUInt
=
__readmsr(IA32_EFER);
if
(EnableEFERSyscallHook)
{
MsrValue.SyscallEnable
=
FALSE;
/
/
/
/
Set
VM
-
Entry controls to load EFER
/
/
__vmx_vmwrite(VMCS_CTRL_VMENTRY_CONTROLS, HvAdjustControls(VmEntryControls | VM_ENTRY_LOAD_IA32_EFER, VmxBasicMsr.VmxControls ? IA32_VMX_TRUE_ENTRY_CTLS : IA32_VMX_ENTRY_CTLS));
/
/
/
/
Set
VM
-
Exit controls to save EFER
/
/
__vmx_vmwrite(VMCS_CTRL_PRIMARY_VMEXIT_CONTROLS, HvAdjustControls(VmExitControls | VM_EXIT_SAVE_IA32_EFER, VmxBasicMsr.VmxControls ? IA32_VMX_TRUE_EXIT_CTLS : IA32_VMX_EXIT_CTLS));
/
/
/
/
Set
the GUEST EFER to use this value as the EFER
/
/
__vmx_vmwrite(VMCS_GUEST_EFER, MsrValue.AsUInt);
/
/
/
/
also, we have to
set
exception bitmap to cause vm
-
exit on
/
/
HvSetExceptionBitmap(EXCEPTION_VECTOR_UNDEFINED_OPCODE);
}
else
{
MsrValue.SyscallEnable
=
TRUE;
/
/
/
/
Set
VM
-
Entry controls to load EFER
/
/
__vmx_vmwrite(VMCS_CTRL_VMENTRY_CONTROLS, HvAdjustControls(VmEntryControls & ~VM_ENTRY_LOAD_IA32_EFER, VmxBasicMsr.VmxControls ? IA32_VMX_TRUE_ENTRY_CTLS : IA32_VMX_ENTRY_CTLS));
/
/
/
/
Set
VM
-
Exit controls to save EFER
/
/
__vmx_vmwrite(VMCS_CTRL_PRIMARY_VMEXIT_CONTROLS, HvAdjustControls(VmExitControls & ~VM_EXIT_SAVE_IA32_EFER, VmxBasicMsr.VmxControls ? IA32_VMX_TRUE_EXIT_CTLS : IA32_VMX_EXIT_CTLS));
/
/
/
/
Set
the GUEST EFER to use this value as the EFER
/
/
__vmx_vmwrite(VMCS_GUEST_EFER, MsrValue.AsUInt);
/
/
/
/
Because we're
not
save
or
load EFER on vm
-
exits so
/
/
we have to
set
it manually
/
/
__writemsr(IA32_EFER, MsrValue.AsUInt);
/
/
/
/
unset the exception to
not
cause vm
-
exit on
/
/
ProtectedHvRemoveUndefinedInstructionForDisablingSyscallSysretCommands();
}
}
VOID
SyscallHookConfigureEFER(BOOLEAN EnableEFERSyscallHook)
{
IA32_EFER_REGISTER MsrValue;
IA32_VMX_BASIC_REGISTER VmxBasicMsr
=
{
0
};
UINT32 VmEntryControls
=
0
;
UINT32 VmExitControls
=
0
;
/
/
/
/
Reading IA32_VMX_BASIC_MSR
/
/
VmxBasicMsr.AsUInt
=
__readmsr(IA32_VMX_BASIC);
/
/
/
/
Read previous VM
-
Entry
and
VM
-
Exit controls
/
/
__vmx_vmread(VMCS_CTRL_VMENTRY_CONTROLS, &VmEntryControls);
__vmx_vmread(VMCS_CTRL_PRIMARY_VMEXIT_CONTROLS, &VmExitControls);
MsrValue.AsUInt
=
__readmsr(IA32_EFER);
if
(EnableEFERSyscallHook)
{
MsrValue.SyscallEnable
=
FALSE;
[招生]科锐逆向工程师培训(2024年11月15日实地,远程教学同时开班, 第51期)
最后于 2022-11-4 22:19
被N1ptune编辑
,原因: 修改格式