x64 SEH & Explorer Suite Update

Yesterday I took a bit of time and updated the Explorer Suite. One important new feauture is the addition of the Exception Directory. I’m no longer working on the old CFF Explorer. However, I thought this feature was too important for people to wait for the new CFF Explorer. Here’s a screenshot of the Exception Directory UI:

CFF Exception Directory

If you have no idea how the x64 Structured Exception Handling works, you can briefly read this article on osronline or my article about Vista x64. There’s also a pretty in depth quantity of information in a series of posts on Ken Johnson’s blog. However, don’t hope to find too much information on the web about the real physical layout of the Exception Directory. The MSDN information is incomplete if not wrong and even the SDK doesn’t help. This post isn’t a complete guide to x64 exceptions, I just want to explain how to analyze them inside the CFF Explorer.

In the screenshot above you can see two arrays of tables. The first one is an array of RUNTIME_FUNCTION structures. The last column isn’t part of this structure though: it shows the five high bits of the first byte of the UNWIND_INFO structure refrenced by the UnwindData member of RUNTIME_FUNCTION. This is the declaration of UNWIND_INFO:

[cc lang=”cpp”]typedef struct _UNWIND_INFO {
UBYTE Version : 3;
UBYTE Flags : 5;
UBYTE SizeOfProlog;
UBYTE CountOfCodes;
UBYTE FrameRegister : 4;
UBYTE FrameOffset : 4;
UNWIND_CODE UnwindCode[1];
/* UNWIND_CODE MoreUnwindCode[((CountOfCodes + 1) & ~1) – 1];
* union {
* OPTIONAL ULONG ExceptionHandler;
* OPTIONAL ULONG FunctionEntry;
* };
* OPTIONAL ULONG ExceptionData[]; */
} UNWIND_INFO, *PUNWIND_INFO;[/cc]

The flags represent the type of handlers. An exception flag represents __try/__except blocks, while the termination flag represents __try/__finally blocks.

The second is an array of scope records. An UNWIND_INFO can contain more than one scope records. Let’s consider this little code sample:

[cc lang=”cpp”]__try
{
__try
{
// code
}
__finally
{
// code
}

__try
{
// code
}
__finally
{
// code
}
}
__except (EXCEPTION_EXECUTE_HANDLER)
{
// code
}[/cc]

As you can see from the screenshot, it results in 3 scope records. The HandlerAddress in a scope record structure can be an RVA to a C_exception_handler function. Or it can be a simple value like EXCEPTION_EXECUTE_HANDLER (which is 1). The last scope record represents the __except statement. Don’t confuse the exception handler (or filter) with its code.

The JumpTarget member, if not 0, is an RVA to the exception code. It’s possible to see if a particular address has an entry inside the Exception Directory by right clicking on the first table and then clicking ‘Is Address Handled’ in the pop-up menu. Nevertheless, remember that exception handlers can be added at runtime with APIs like RtlAddFunctionTable and RtlInstallFunctionTableCallback.

I fixed some minor bugs in the CFF Explorer and one major bug in the Task Explorer. I noticed this bug years ago but never took time to fix it. It showed only when trying to dump the region of an x86 process using the 64 bit version of the Task Explorer. However, x64 is becoming very used and so the bug is now fixed. Also, I thought it would be a good idea on 64-bit platforms to install a 32-bit version of the Task Explorer and a 64-bit one. Thus, the installer now behaves accordingly.

Qt Internals & Reversing

Today I took a break from the larger article I’m currently writing. To relax, I wrote a smaller article about the Qt framework. I hope you enjoy.

Qt Internals & Reversing

Half of the text of this article comes from my larger paper “Dynamic C++ Proposal”. I decided that it was useful to take the part about Qt internals, put it into another article and extend it by adding a reversing part. Because of its nature, this is not the usual kind of article I write. In fact, I wrote the reversing part in less than a day. So, this is a very easy one. However, I think it is useful for people who need to reverse a Qt application and certainly wouldn’t consider reading my other paper about Dynamic C++, which doesn’t sound like a paper about Qt and, in fact, isn’t a paper about Qt: the paragraph about Qt is only one among many others. Moreover, I haven’t seen serious articles about this subject.

The first thing which needs to be considered when reversing Qt applications is what Qt brought to the C++ language. Events (inside the Qt framework) are just virtual functions, so nothing new there. This is not a C++ reversing guide. What is new in Qt are signals and slots, which rely on the dynamism of the Qt framework.

So, first thing I’m going to show how this dynamism works. The second part focus on reversing and, at that point, I will show how to obtain all the metadata one needs when disassembling a “Q_OBJECT” class.

Microsoft’s Rich Signature (undocumented)

In the last days I’ve been quite sick, so I decided that as long as I had to stay in bed I might at least use the time to do something useful (or quite so). What happened is that someone asked what the Rich Signature was. It might seems strange but in all these years I didn’t even notice it, I just overlooked it as part of the dos stub (incredible but true). Unable to answer, I noticed together with this person that the subject was completely undocumented. It might not even be much important, but you might find it an interesting reading after all.

http://ntcore.com/Files/richsign.htm

Since information about this topic is non-existent, the reader might not know what I’m talking about:

00000070 6D 6F 64 65 2E 0D 0D 0A 24 00 00 00 00 00 00 00 mode….$…….
00000080 E7 B3 9D E7 A3 D2 F3 B4 A3 D2 F3 B4 A3 D2 F3 B4 糝ç£Òó´£Òó´£Òó´
00000090 60 DD AC B4 A8 D2 F3 B4 60 DD AE B4 BE D2 F3 B4 ݬ´¨Òó´Ý®´¾Òó´
000000A0 A3 D2 F2 B4 F8 D0 F3 B4 84 14 8E B4 BA D2 F3 B4 £Òò´øÐó´„Ž´ºÒó´
000000B0 84 14 9E B4 3A D2 F3 B4 84 14 9D B4 3F D2 F3 B4 „ž´:Ò󴄝´?Òó´
000000C0 84 14 81 B4 B3 D2 F3 B4 84 14 8F B4 A2 D2 F3 B4 „´³Ò󴄏´¢Òó´
000000D0 84 14 8B B4 A2 D2 F3 B4 52 69 63 68 A3 D2 F3 B4 „‹´¢Òó´Rich£Òó´
000000E0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 …………….
000000F0 00 00 00 00 00 00 00 00 50 45 00 00 4C 01 04 00 ……..PE..L.

The data between the dos stub and the PE Header. It ends with the word Rich. It is produced by microsoft VC++ compilers only and it is encrypted.