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//Disable PatchGuard - the easy/lazy way.
//for Vista SP2 & Windows 7 (X64)
//
//by Fyyre (thank you Roxaz for helping me to test)
//http://fyyre.l2-fashion.de/
//http://twitter.com/Fyyre
last update: 19/03/2011
This txt file provides a general overview/outline for bypassing signature validation of critical system files (ntoskrnl, mainly) during
the Vista/Win 7 boot phase. It is documentation of the steps taken from start to finish, to reach the desired goal of removing
kernel patch protection "PatchGuard" without use of a driver. We will call this the 'lazy/easy' way to kill PatchGuard.
We cannot modify ntoskrnl without winload taking up issue...
winload.exe is the Windows loader for Vista & Windows 7. Along with this, he makes some verification of digital signatures and
checking to make sure the files have not been modified. If modification of ntoskrnl is detected, the result is winload *refusing*
to boot Windows and launching a WinPE looking "Recovery Mode".
//PART I { additional }: new way for patch of winload.exe
//
//Function ImgpValidateImageHash - signature we locate: 8B C3 49 8B 5B 20 49 8B 73 28 49 8B 7B 30 4D 8B -- you may play with this one to make him smaller. as for this
//patching, use of dUP2... size of not a concern. First bytes replaced with xor eax, eax (STATUS_SUCCESS) .. all validations successful.
PART I: disassembly and modification of winload.exe
Starting from OslpMain, after loading the System registry hives(registry)... occurs a call to OslInitializeCodeIntegrity:
.text:00000000004016C3 call OslpLoadSystemHive
.text:00000000004016C3
.text:00000000004016C8 cmp eax, ebx
.text:00000000004016CA mov edi, eax
.text:00000000004016CC jl loc_401A08
.text:00000000004016CC
.text:00000000004016D2 mov ecx, ebp
.text:00000000004016D4 call OslInitializeCodeIntegrity <<-- =(
.text:00000000004057E8 OslInitializeCodeIntegrity proc near
original code -->>
We will replace four bytes here:
48 8B C4 53
.text:00000000004057E8 mov rax, rsp
.text:00000000004057EB push rbx
.text:00000000004057EC push rbp
with: 0B0h, 01h, 0C3h, 090h ... which produce:
mov al, 1
ret
nop
Save as winload.exe as osloader.exe (or whatever..) & correct PE checksum (LordPE and/or CFF_Explorer will do).
Copy osloader.exe to \Windows\System32
PART II - new BCD entry:
bcdedit /copy {current} /d "PatchGuard Disabled"
"The entry was successfully copied to {01234567-89ab-cdef-00ff-fff000ffffff}" <<-- GUID of new entry. each is different!
bcdedit /timeout 10 <<-- number of seconds to show boot menu.
bcdedit /set {01234567-89ab-cdef-00ff-fff000ffffff} nointegritychecks 1 <<-- no validation of winload
bcdedit /set {01234567-89ab-cdef-00ff-fff000ffffff} recoveryenabled 0 <<-- optional... i dislike this feature, therefore disable.
bcdedit /set {01234567-89ab-cdef-00ff-fff000ffffff} path \Windows\system32\osloader.exe
bcdedit /set {01234567-89ab-cdef-00ff-fff000ffffff} kernel ntkrnlmp.exe (name of modified ntos... =))
Part III: Skip Initialization of PatchGuard - - (driver not required)
As for this .txt, and PatchGuard... we are concerned with one function KiInitializePatchGuard(*1) which is called by KiFilterFiberContext.
KiInitializePatchGuard is a very large function located in the INIT section of ntoskrnl, you can easily locate him via two calls from
KiFilterFiberContext, by examination xrefs to exported dword InitSafeBootMode, searching for db 20h dup(90h) + db 044h ... or 48 81 EC 58 0F 00 00 to name a few...
PatchGuard does not initialize if we boot into safe mode. So to disable we just patch one conditional jxx
KiInitializePatchGuard:
original code -->>
INIT:000000014055D359 sub rsp, 0F58h
INIT:000000014055D360 xor edi, edi
INIT:000000014055D362 cmp cs:InitSafeBootMode, edi
INIT:000000014055D368 jz short loc_14055D371
INIT:000000014055D368
INIT:000000014055D36A mov al, 1
INIT:000000014055D36C jmp loc_1405600D9
modified code -->>
INIT:000000014055D359 sub rsp, 0F58h
INIT:000000014055D360 xor edi, edi
INIT:000000014055D362 cmp cs:InitSafeBootMode, edi
INIT:000000014055D368 nop
INIT:000000014055D369 nop
INIT:000000014055D36A mov al, 1
INIT:000000014055D36C jmp loc_1405600D9 <<-- to end of KiInitializePatchGuard
and back to KiFilterFiberContext... and important detail:
The first jxx in KiInitializePatchGuard must not be taken & al == 1. When we return to KiFilterFiberContext, the jxx must be taken,
and EBX must not be xor'd ... (unless enjoy BSOD).
INIT:0000000140567110 loc_140567110:
INIT:0000000140567110 test al, al
INIT:0000000140567112 jnz short loc_140567116
INIT:0000000140567112
INIT:0000000140567114
INIT:0000000140567114 loc_140567114:
INIT:0000000140567114 xor ebx, ebx <<-- bad
INIT:0000000140567114
Anyways... nop the first jxx in KiInitializePatchGuard... save modified ntoskrnl.exe with a different name (i.e. ntkrnlmp.exe) ... fix checksum (PE header).
Then copy your modified kernel to \Windows\system32 -- with bcdedit -->>
bcdedit /set {guid-of-new-entry} kernel ntkrnlmp.exe
When you reboot the system, loading your modified kernel should be a success... He will load without PatchGuard initializing, which will allow you to once again play in kernel mode without receiving BSOD as result...
This could be worked into mbr bootkit code as well... this is beyond the scope of our intention.
-Fyyre
references:
*1: Bypassing PatchGuard on Windows x64, by Skywing 12/1/2005 |
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发表于 2011-12-12 14:25:55
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