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Fix race condition and remote hwbp removal (#44) #45

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Fix race condition and remote hwbp removal (#44) #45

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82 changes: 59 additions & 23 deletions TitanHide/hooks.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -602,45 +602,81 @@ static NTSTATUS NTAPI HookNtGetContextThread(
return ret;
}

static NTSTATUS NTAPI HookNtSetContextThread(
static NTSTATUS NTAPI SetContextThreadWithoutDebugRegisters(
IN HANDLE ThreadHandle,
IN PCONTEXT Context)
{
ULONG pid = (ULONG)(ULONG_PTR)PsGetCurrentProcessId();
KPROCESSOR_MODE PreviousMode = ExGetPreviousMode();
bool IsHidden = PreviousMode != KernelMode && Hider::IsHidden(pid, HideNtSetContextThread);
ULONG OriginalContextFlags = 0;
if(IsHidden)
CONTEXT contextCopy;
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Sorry for the delay, but I now remember why I didn't implement this. It's undocumented, but the sizeof(CONTEXT) isn't actually the maximum size a user might pass to Get/SetThreadContext. See https://github.com/x64dbg/TitanEngine/blob/x64dbg/TitanEngine/TitanEngine.Debugger.Context.cpp#L987, but I'm unfortunately not sure how to deal with this...

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@dauthleikr dauthleikr Mar 9, 2020 •
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Hm, I have two possible solutions in mind. I took a look at what InitializeContext does, and it calls a function called RtlGetExtendedContextLength2 to get the length for its ContextFlags.

Solution 1: Figure out the maximum size and go with that
Solution 2: The same functions also exists in the kernel, add it to the other undocumented functions and use it.

I can do one of those when I have some spare time, right now the bad fix works for me.

PCONTEXT contextPtr;
bool copyContextSuccess;

__try
{
//http://lifeinhex.com/dont-touch-this-writing-good-drivers-is-really-hard
//http://lifeinhex.com/when-software-is-good-enough
Log("[TITANHIDE] NtSetContextThread by %d\r\n", pid);
__try
{
ProbeForWrite(&Context->ContextFlags, sizeof(ULONG), 1);
OriginalContextFlags = Context->ContextFlags;
Context->ContextFlags = OriginalContextFlags & ~0x10; //CONTEXT_DEBUG_REGISTERS ^ CONTEXT_AMD64/CONTEXT_i386
}
__except(EXCEPTION_EXECUTE_HANDLER)
{
IsHidden = false;
}
// Copy the context, then strip flags: https://github.com/mrexodia/TitanHide/issues/44
ProbeForRead(Context, sizeof(CONTEXT), 1);
contextCopy = *Context;
contextPtr = &contextCopy;

OriginalContextFlags = contextPtr->ContextFlags;
contextPtr->ContextFlags = OriginalContextFlags & ~0x10; //CONTEXT_DEBUG_REGISTERS ^ CONTEXT_AMD64/CONTEXT_i386
copyContextSuccess = true;
}
NTSTATUS ret = Undocumented::NtSetContextThread(ThreadHandle, Context);
if(IsHidden)
__except (EXCEPTION_EXECUTE_HANDLER)
{
contextPtr = Context;
copyContextSuccess = false;
}

NTSTATUS ret = Undocumented::NtSetContextThread(ThreadHandle, contextPtr);
if (copyContextSuccess)
{
// Copy the result context back
contextPtr->ContextFlags = OriginalContextFlags;
__try
{
ProbeForWrite(&Context->ContextFlags, sizeof(ULONG), 1);
Context->ContextFlags = OriginalContextFlags;
ProbeForWrite(Context, sizeof(CONTEXT), 1);
*Context = *contextPtr;
}
__except(EXCEPTION_EXECUTE_HANDLER)
__except (EXCEPTION_EXECUTE_HANDLER)
{
}
}
return ret;
}

static NTSTATUS NTAPI HookNtSetContextThread(
IN HANDLE ThreadHandle,
IN PCONTEXT Context)
{
ULONG callerPid = (ULONG)(ULONG_PTR)PsGetCurrentProcessId();;
KPROCESSOR_MODE PreviousMode = ExGetPreviousMode();
bool StripDebugRegisterFlags;

if (PreviousMode == KernelMode)
{
StripDebugRegisterFlags = false;
}
else
{
ULONG targetPid = Misc::GetProcessIDFromThreadHandle(ThreadHandle);

// To prevent other processes from erasing breakpoints, they need to be "hidden" too
StripDebugRegisterFlags = Hider::IsHidden(targetPid, HideNtSetContextThread) &&
Hider::IsHidden(callerPid, HideNtSetContextThread);
}

if (StripDebugRegisterFlags)
{
//http://lifeinhex.com/dont-touch-this-writing-good-drivers-is-really-hard
//http://lifeinhex.com/when-software-is-good-enough
Log("[TITANHIDE] NtSetContextThread on %d\r\n", callerPid);
return SetContextThreadWithoutDebugRegisters(ThreadHandle, Context);
}

return Undocumented::NtSetContextThread(ThreadHandle, Context);
}

static NTSTATUS NTAPI HookNtSystemDebugControl(
IN SYSDBG_COMMAND Command,
IN PVOID InputBuffer,
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