XEX

File Format Speculation

XEX is the executable file format used by the Xbox 360 operating system. It seems to be a crypto and packing container for PPC PE executable files, comparable to UPX or TEEE Burneye. It's likely the 360 knows how to grab the section it needs into memory and decrypt/decompress on demand, instead of traditional all at once extraction.

Cryptography

The executable code seems to be crypted, though, there exists some uncrypted XEX files in the wild.

The following program dumps what is supposed to be a hash table. Actually it has been reported to work with the first official "Backward Compatibility" .XEX File from Microsoft. It takes the XEX file as argument.

// default.xex table dumper
 // only works with the default.xex from the xbox360 emulator update package.
 // - th0mas, th0mas.sixbit.org [at] gmail.com
 
 #include <stdio.h>
 #include <string.h>
 
 #define TABLE_START 0x288
 
 struct table {
    unsigned int unknown[6];
 };
 
 unsigned int ByteSwap (unsigned int nInt)
 {
    union u {unsigned int vi; unsigned char c[sizeof(unsigned int)];};
    union v {unsigned int ni; unsigned char d[sizeof(unsigned int)];};
    union u un;
    union v vn;
    un.vi = nInt;
    vn.d[0]=un.c[3];
    vn.d[1]=un.c[2];
    vn.d[2]=un.c[1];
    vn.d[3]=un.c[0];
    return (vn.ni);
 }
 
 void printTable(struct table *t)
 {
    int i;
    for (i = 0; i < 6; i  ) {
       int j = ByteSwap(t->unknown[i]);
       printf("0x%08x ", j);
    }
    printf("\n");
 }
 
 int main(int argc, char **argv)
 {
    FILE *fp = fopen(argv[1], "rb");
    struct table tmp;
    int numEntries = 0;
    int i;
 
    fseek(fp, TABLE_START, SEEK_SET);
    fread(&numEntries, sizeof(unsigned int), 1, fp);
    numEntries = ByteSwap(numEntries);
    for (i = 0; i < numEntries; i  ) {
         fread(&tmp, sizeof(struct table), 1, fp);
         printTable(&tmp);
    }
 }
 
 

Structure of the XEX File

A XEX file is composed of the following:

• A 24 bytes XEX Header
• Variable-length program/section headers
• Program/Section content

XEX Header

Total length: 24 bytes.

Byte ordering: Big Endian.

Offset	Length	Type	Information
0x0	0x4	ascii string	"XEX2" magic
0x4	0x4	module flags (see below)	Flags
0x8	0x4	unsigned int	PE data offset
0xC	0x4	unsigned int	Reserved
0x10	0x4	unsigned int	Security Info Offset
0x14	0x4	unsigned int	Optional Header Count

The Flags field is a bitfield, as shown below:

bit 0 - Title Module
bit 1 - Exports To Title
bit 2 - System Debugger
bit 3 - DLL Module
bit 4 - Module Patch
bit 5 - Patch Full
bit 6 - Patch Delta
bit 7 - User Mode

Optional Headers

Following the XEX header is a list of the optional headers within the file. Use the Optional Header Count field to determine how many there are.

Each Optional Header is composed of the following:

Offset	Length	Type	Information
0x0	0x4	unsigned int	Header ID (see below)
0x4	0x8	unsigned int	Header Data / Offset to data (see below)

To handle the data you would first check to see what its size is, to do this you need to AND the Header ID by 0xFF.

If ID & 0xFF == 0x01 then the Header Data field is used to store the headers data, otherwise it's used to store the data's offset.
if ID & 0xFF == 0xFF then the Header's data will contain its size
if ID & 0xFF == (Anything else) the value of this is the size of the entry in number of DWORDS (times by 4 to get real size)

Header IDs

Value	Description
0x2FF	Resource Info
0x3FF	Base File Format
0x405	Base Reference
0x5FF	Delta Patch Descriptor
0x80FF	Bounding Path
0x8105	Device ID
0x10001	Original Base Address
0x10100	Entry Point
0x10201	Image Base Address
0x103FF	Import Libraries
0x18002	Checksum Timestamp
0x18102	Enabled For Callcap
0x18200	Enabled For Fastcap
0x183FF	Original PE Name
0x200FF	Static Libraries
0x20104	TLS Info
0x20200	Default Stack Size
0x20301	Default Filesystem Cache Size
0x20401	Default Heap Size
0x28002	Page Heap Size and Flags
0x30000	System Flags
0x40006	Execution ID
0x401FF	Service ID List
0x40201	Title Workspace Size
0x40310	Game Ratings
0x40404	LAN Key
0x405FF	Xbox 360 Logo
0x406FF	Multidisc Media IDs
0x407FF	Alternate Title IDs
0x40801	Additional Title Memory
0xE10402	Exports by Name

Program / Section content

The program holds a PE file which is crypted/packed, usually starting at offset 0x2000 (described in the XEX header). It's possible to have this PE uncrypted/unpacked on debug XEX files. Section contents are encrypted with CBC AES, with the key changing for each file. It's probably derived from the RSA(?) block at the beginning and a "secret" public key in the box. Contents are compressed with microsoft's proprietary LDIC compression (hello, xbox1!).

Miscellaneous

Strings found in some XEX Files

These appear to be important strings found in the update file

• Directories?
  • XAdu
  • $UPDATES
  • MEDIA

• \Device\CdRom0\default.xex

• installupdate.exe

• The xboxkrnl is updated using the updates.

• xam.xex

• xboxkrnl.exe

• Library includes:
  • XUIRNDR
  • XAUD
  • XGRAPHC
  • XRTLLIB
  • XAPILIB
  • LIBCMT
  • XBOXKRNL
  • D3D9
  • XUIRUN
  • XUIRNDR

Availability of XEX files

There are currently at least four XEX files freely available on the net:

• Original Xbox Game Support November 2005 update found on http://www.xbox.com/en-US/games/backwardscompatibility.htm.

• Original Xbox Game Support December 2005 update found on http://www.xbox.com/en-US/games/backwardscompatibility.htm.

• Windows XP Media Center Edition Update Rollup 2 from http://www.xbox.com/en-US/pcsetup/alldownloads.htm. Use cabextract to extract the executable file, then do the same on mcrdinstaller/ehd.cab inside the archive. This cabinet file contains XboxMcx.xex.

• XBOX 360 HD DVD Update found on http://www.xbox.com/en-us/hardware/x/xbox360hddvdplayer/download.htm#disc

Programs

• xextools -- A library and tools for manipulating xex files (xexread replacement).
• xexdump -- Dumps information about xex files (perl)
• xexdump -- Dumps information about xex files (windows)

Executable Format

XEX files are the default executable format.

File-offset	Description
0		"XEX2"
0x4		(module flags?)
0x10		File header offset
0x14		Definition count (see below)
0x18		Definition[]

Definition	Description
0x2FF		Module Sections
0x3FF		
0x5FF		Delta patch descriptor
0x4004		
0x4104		
0x42FF		
0x80FF		Binding path(s)
0x8105		
0x10001		Load Address
0x10100		Entry Point
0x10201		Base Address
0x103FF		Import Libraries
0x18002		Checksum[4], Filetime[4]
0x18102		(something debug related)
0x183FF		PE Name

0x200FF		Static Libraries
		UINT32 Total size
		entries[total size / 0x10]
0x20104		TLS
		UINT32 Number of Slots
		UINT32 Raw Data Address
		UINT32 Data Size
		UINT32 Raw Data Size
0x20200		Get Stack Size
0x20301		Cache Element Count
0x30000
0x40006		MediaID[4], Version[4], Baseversion[4], TitleID[4]
0x40310		Game Ratings
		UINT8 ESRB
		UINT8 PEGI
		UINT8 PEGI-FI
		UINT8 PEGI-PT
		UINT8 PEGI_BBFC
		UINT8 CERO
		UINT8 USK
		UINT8 OFLCAU
		UINT8 OFLCNZ
		UINT8 KMRB
		UINT8 BRASIL
		UINT8 FPB

0x40404		Lan Key (16 Bytes)
0x406FF		Multidisc, accepted Media IDs
0x40801			

FileHeaderOffset	Description
0			HeaderSize[4]
0x4			Image Size[4]
0x8			RSA Signature
0x10C			(resulting Image size?)[4]
0x110			LoadAddress
0x140			MediaID[16]
0x150			(AES key seed?)[16]
0x164			(Input to SHA)[0x14]
0x178			Region[4]
0x17C			SHA Hash[0x14]
0x180			ImageDataCount[4]
0x184...0x184+(IDC*24)	ImageData0[8], ImageData1[8], ImageData2[8]