hamgammon
/
nonlibreboot-x201


			
				
					
						
						
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	<title>GM45 chipsets: remove the ME (manageability engine)</title>
</head>

<body>

	<div class="section">
		
		<h1 id="pagetop">GM45 chipsets: remove the ME (manageability engine)</h1>
			<p>
				This sections relates to disabling and removing the ME (Intel <b>M</b>anagement <b>E</b>ngine) on
				GM45. This was originally done on the ThinkPad X200, and later adapted for the ThinkPad R400/T400/T500. It can
				in principle be done on any GM45 or GS45 machine.
			</p>
			<p>
				The ME is a blob that typically must be left inside the flash chip (in the ME region, as outlined
				by the default descriptor). On GM45, it is possible to remove it without any ill effects. All
				other parts of coreboot on GM45 machines (provided GMA MHD4500 / Intel graphics) can be blob-free,
				so removing the ME was the last obstacle to
				make GM45 a feasible target in libreboot (the machines can also work without the microcode blobs). 
			</p>
			<p>
				The ME is removed and disabled in libreboot by modifying the descriptor. More info about
				this can be found in the ich9deblob/ich9gen source code in resources/utilities/ich9deblob/
				in libreboot, or more generally on this page.
			</p>
			<p>
				More information about the ME can be found at
				<a href="http://www.coreboot.org/Intel_Management_Engine">http://www.coreboot.org/Intel_Management_Engine</a>
				and <a href="http://me.bios.io/Main_Page">http://me.bios.io/Main_Page</a>.
			</p>
			<p>
				Another project recently found:
				<a href="http://io.smashthestack.org/me/">http://io.smashthestack.org/me/</a>
			</p>
			<p>
				<a href="index.html">Back to previous index</a>.
			</p>
			
	</div>

	<div class="section">

		<h1 id="ich9gen">ICH9 gen utility</h1>
		
			<p>
				It is no longer necessary to use <a href="#ich9deblob">ich9deblob</a> to generate
				a deblobbed descriptor+gbe image for GM45 targets. ich9gen is a small utility within
				ich9deblob that can generate them from scratch, without a factory.bin dump.
			</p>
			
			<p>
				ich9gen executables can be found under ./ich9deblob/ statically compiled in
				libreboot_util. If you are using src or git, build ich9gen from source with:<br/>
				$ <b>./build module ich9deblob</b><br/>
				The executable will appear under resources/utilities/ich9deblob/
			</p>
				
			<p>
				Run:<br/>
				$ <b>./ich9gen</b>
			</p>
			
			<p>
				Running ich9gen this way (without any arguments) generates
				a default descriptor+gbe image with a generic MAC address.
				You probably don't want to use the generic one; the ROM images
				in libreboot contain a descriptor+gbe image by default (already
				inserted) just to prevent or mitigate the risk of bricking
				your laptop, but with the generic MAC address (the libreboot
				project does not know what your real MAC address is).
			</p>
			
			<p>
				You can find out your MAC address from <b>ip addr</b> or <b>ifconfig</b> in GNU/Linux. 
				Alternatively, if you are running libreboot already (with the correct MAC address in your
				ROM), dump it (flashrom -r) and read the first 6 bytes from position 0x1000 (or 0x2000) in a hex editor
				(or, rename it to factory.rom and run it in ich9deblob: in the newly created mkgbe.c
				will be the individual bytes of your MAC address). If you are currently running the stock firmware
				and haven't installed libreboot yet, you can also run that through ich9deblob to get the mac address.
			</p>
			
			<p>
				An even simpler way to get the MAC address would be to read what's on the little sticker on
				the bottom/base of the laptop.
			</p>
			
			<p>
				On GM45 laptops that use flash descriptors, the MAC address
				or the onboard ethernet chipset is flashed (inside the ROM image).
				You should generate a descriptor+gbe image with your own MAC address
				inside (with the Gbe checksum updated to match). Run:<br/>
				$ <b>./ich9gen --macaddress XX:XX:XX:XX:XX:XX</b><br/>
				(replace the XX chars with the hexadecimal chars in the MAC address that you want)
			</p>
			
			<p>
				Two new files will be created:
			</p>
				<ul>
					<li><b>ich9fdgbe_4m.bin</b>: this is for GM45 laptops with the 4MB flash chip.</li>
					<li><b>ich9fdgbe_8m.bin</b>: this is for GM45 laptops with the 8MB flash chip.</li>
				</ul>
			
			<p>
				Assuming that your libreboot image is named <b>libreboot.rom</b>, copy
				the file to where <b>libreboot.rom</b> is located
				and then insert the descriptor+gbe file into the ROM image. For 8MiB flash chips:<br/>
				$ <b>dd if=ich9fdgbe_8m.bin of=libreboot.rom bs=1 count=12k conv=notrunc</b><br/>
				For 4MiB flash chips:<br/>
				$ <b>dd if=ich9fdgbe_4m.bin of=libreboot.rom bs=1 count=12k conv=notrunc</b>
			</p>
			
			<p>
				Your libreboot.rom image is now ready to be flashed on the machine. Refer back to 
				<a href="../install/index.html#flashrom">../install/index.html#flashrom</a>
				for how to flash it.
			</p>
			
			<h2>
				Write-protecting the flash chip
			</h2>
				<p>
					Look in <i>resources/utilities/ich9deblob/src/descriptor/descriptor.c</i>
					for the following lines in the <i>descriptorHostRegionsUnlocked</i> function:
				</p>
<pre>
   descriptorStruct.masterAccessSection.flMstr1.fdRegionWriteAccess = 0x1;
   descriptorStruct.masterAccessSection.flMstr1.biosRegionWriteAccess = 0x1;
   descriptorStruct.masterAccessSection.flMstr1.meRegionWriteAccess = 0x1;
   descriptorStruct.masterAccessSection.flMstr1.gbeRegionWriteAccess = 0x1;
   descriptorStruct.masterAccessSection.flMstr1.pdRegionWriteAccess = 0x1;
</pre>

				<p>
					Change them all to 0x0, then re-compile ich9gen. After you have done that,
					follow the notes in <a href="#ich9gen">#ich9gen</a> to generate a new
					descriptor+gbe image and insert that into your ROM image, then flash it.
					The next time you boot, the flash chip will be read-only in software
					(hardware re-flashing will still work, which you will need for re-flashing
					the chip after write-protecting it, to clear the write protection or
					to flash yet another ROM image with write protection set in the descriptor).
				</p>
				<p>
					For external flashing guides, refer to <a href="../install/index.html">../install/index.html</a>.
				</p>
			
	</div>

	<div class="section">

		<h1 id="ich9deblob">ICH9 deblob utility</h1>
		
			<p>
				<b>This is no longer strictly necessary. Libreboot ROM images for GM45 machines now
				contain the 12KiB descriptor+gbe generated from ich9gen, by default.</b>
			</p>
			
			<p>
				This was the tool originally used to disable the ME on X200 (later adapted for other machines that use the
				GM45 chipset). <a href="#ich9gen">ich9gen</a> now supersedes it;
				ich9gen is better because it does not rely on dumping the factory.rom image (whereas, ich9deblob does).
			</p>
		
			<p>
				This is what you will use to generate the deblobbed descriptor+gbe regions for your libreboot ROM image.
			</p>
			<p>
				If you are working with libreboot_src (or git), you can find the source under resources/utilities/ich9deblob/
				and will already be compiled if you ran <b>./build module all</b> or <b>./build module ich9deblob</b> from the main directory (./), 
				otherwise you can build it like so:<br/>
				$ <b>./build module ich9deblob</b><br/>
				An executable file named <b>ich9deblob</b> will now appear under resources/utilities/ich9deblob/
			</p>
			<p>
				If you are working with libreboot_util release archive, you can find the utility included, statically compiled
				(for i686 and x86_64 on GNU/Linux) under ./ich9deblob/.
			</p>
			
			<p>
				Place the factory.rom from your machine 
				(can be obtained using the external flashing guides for GM45 targets linked <a href="../install/index.html">../install/index.html</a>) in
				the directory where you have your ich9deblob executable, then run the tool:<br/>
				$ <b>./ich9deblob</b>
			</p>
			<p>
				A 12kiB file named <b>deblobbed_descriptor.bin</b> will now appear. <b>Keep this and the factory.rom stored in a safe location!</b>
				The first 4KiB contains the descriptor data region for your machine, and the next 8KiB contains the gbe region (config data for your
				gigabit NIC). These 2 regions could actually be separate files, but they are joined into 1 file in this case.
			</p>
			
			<p>
				Assuming that your libreboot image is named <b>libreboot.rom</b>, copy
				the <b>deblobbed_descriptor.bin</b> file to where <b>libreboot.rom</b> is located
				and then run:<br/>
				$ <b>dd if=deblobbed_descriptor.bin of=libreboot.rom bs=1 count=12k conv=notrunc</b>
			</p>
			
			<p>
				The utility will also generate 4 additional files:
			</p>
				<ul>
					<li>mkdescriptor.c</li>
					<li>mkdescriptor.h</li>
					<li>mkgbe.c</li>
					<li>mkgbe.h</li>
				</ul>
			<p>
				These are C source files that can re-generate the very same Gbe and Descriptor structs
				(from ich9deblob/ich9gen). To use these, place them in src/ich9gen/ in ich9deblob, then re-build. 
				The newly built <b>ich9gen</b> executable will be able to re-create the very same 12KiB file from scratch,
				based on the C structs, this time <b>without</b> the need for a factory.rom dump!
			</p>
			
			<p>
				You should now have a <b>libreboot.rom</b> image containing the correct 4K descriptor and 8K gbe regions, which
				will then be safe to flash. Refer back to <a href="../install/index.html#flashrom">../install/index.html#flashrom</a>
				for how to flash it.
			</p>
			
	</div>
	
	<div class="section">

		<h1 id="demefactory">demefactory utility</h1>

			<p>
				This takes a factory.rom dump and disables the ME/TPM, but leaves the region intact.
				It also sets all regions read-write.
			</p>
			
			<p>
				The ME interferes with flash read/write in flashrom, and the default descriptor
				locks some regions. The idea is that doing this will remove all of those restrictions.
			</p>
			
			<p>
				Simply run (with factory.rom in the same directory):<br/>
				$ <b>./demefactory</b>
			</p>
			
			<p>
				It will generate a 4KiB descriptor file (only the descriptor, no GbE). Insert that into
				a factory.rom image (NOTE: do this on a copy of it. Keep the original factory.rom stored
				safely somewhere):<br/>
				$ <b>dd if=demefactory_4kdescriptor.bin of=factory_nome.rom bs=1 count=4k conv=notrunc</b>
			</p>
			
			<p>
				TODO: test this.<br/>
				TODO: lenovobios (GM45 thinkpads) still write-protects parts of the flash. Modify the assembly code
				inside.
				Note: the factory.rom (BIOS region) from lenovobios is in a compressed format, which you have to extract.
				bios_extract upstream won't work, but the following was said in #coreboot on freenode IRC:
			</p>
<pre>
&lt;roxfan&gt; fchmmr: try bios_extract with ffv patch <a href="http://patchwork.coreboot.org/patch/3444/">http://patchwork.coreboot.org/patch/3444/</a>
&lt;roxfan&gt; or <a href="https://github.com/coreboot/bios_extract/blob/master/phoenix_extract.py">https://github.com/coreboot/bios_extract/blob/master/phoenix_extract.py</a>
&lt;roxfan&gt; what are you looking for specifically, btw?

0x74: 0x9fff03e0 PR0: Warning: 0x003e0000-0x01ffffff is read-only.
0x84: 0x81ff81f8 PR4: Warning: 0x001f8000-0x001fffff is locked.
</pre>

			<p>
				Use-case: a factory.rom image modified in this way would theoretically have no
				flash protections whatsoever, making it easy to quickly switch between factory/libreboot
				in software, without ever having to disassemble and re-flash externally unless you brick
				the device.
			</p>
			
			<p>
				demefactory is part of the ich9deblob src, found at <i>resources/utilities/ich9deblob/</i>
			</p>

	</div>
		
	<div class="section">
		
		<p>
			The sections below are adapted from (mostly) IRC logs related to early development getting the ME removed on GM45.
			They are useful for background information. This could not have been done without sgsit's help.
		</p>
		
		<div class="subsection">
			
			<h2 id="early_notes">Early notes</h2>
		
				<ul>
					<li>
						<a href="http://www.intel.co.uk/content/dam/doc/datasheet/io-controller-hub-10-family-datasheet.pdf">http://www.intel.co.uk/content/dam/doc/datasheet/io-controller-hub-10-family-datasheet.pdf</a>
						page 230 mentions about descriptor and non-descriptor mode (which wipes out gbe and ME/AMT).
					</li>
					<li>
						<s><b>See reference to HDA_SDO (disable descriptor security)</b></s> 
						strap connected GPIO33 pin is it on ICH9-M (X200). HDA_SDO applies to later chipsets (series 6 or higher).
						Disabling descriptor security also disables the ethernet according to sgsit. sgsit's method
						involves use of 'soft straps' (see IRC logs below) instead of disabling the descriptor.
					</li>
					<li>
						<b>and the location of GPIO33 on the x200s: (was an external link. Putting it here instead)</b>
						<a href="images/x200/gpio33_location.jpg">images/x200/gpio33_location.jpg</a>
						- it's above the number 7 on TP37 (which is above the big intel chip at the bottom)
					</li>
					<li>
						The ME datasheet may not be for the mobile chipsets but it doesn't vary that much. 
						This one gives some detail and covers QM67 which is what the X201 uses: 
						<a href="http://www.intel.co.uk/content/dam/www/public/us/en/documents/datasheets/6-chipset-c200-chipset-datasheet.pdf">http://www.intel.co.uk/content/dam/www/public/us/en/documents/datasheets/6-chipset-c200-chipset-datasheet.pdf</a>
					</li>
				</ul>
		
		</div>
		
	</div>
		
	<div class="section">

		<div class="subsection">

			<h2 id="flashchips">Flash chips</h2>
			
				<ul>
					<li>
						Schematics for X200 laptop: <a href="http://pdf.datasheetarchive.com/indexerfiles/Datasheets-USER/DSAUPLD00006075.pdf">http://pdf.datasheetarchive.com/indexerfiles/Datasheets-USER/DSAUPLD00006075.pdf</a>
						<b><s>- Page 20 and page 9 refer to SDA_HDO or SDA_HDOUT</s></b> only on series 6 or higher chipsets. ICH9-M (X200) does it with a strap connected to GPIO33 pin (see IRC notes below)<br/>
						- According to page 29, the X200 can have any of the following flash chips:
						<ul>
							<li>ATMEL AT26DF321-SU 72.26321.A01 - this is a 32Mb (4MiB) chip</li>
							<li>MXIC (Macronix?) MX25L3205DM2I-12G 72.25325.A01 - another 32Mb (4MiB) chip</li>
							<li>MXIC (Macronix?) MX25L6405DMI-12G 41R0820AA - this is a 64Mb (8MiB) chip</li>
							<li>Winbond W25X64VSFIG 41R0820BA - another 64Mb (8MiB) chip</li>
						</ul>
						sgsit says that the X200s with the 64Mb flash chips are (probably) the ones with AMT (alongside the ME), whereas
						the 32Mb chips contain only the ME.
					</li>
					<li>
						Schematics for X200s laptop: <a href="http://pdf.datasheetarchive.com/indexerfiles/Datasheets-USER/DSAUPLD00006104.pdf">http://pdf.datasheetarchive.com/indexerfiles/Datasheets-USER/DSAUPLD00006104.pdf</a>.
					</li>
				</ul>
		
		</div>
		
	</div>
		
	<div class="section">
		
		<h2 id="early_development_notes">Early development notes</h2>
				
<pre>
<i>
Start (hex)	End (hex)	Length (hex)	Area Name
-----------	---------	------------	---------
00000000	003FFFFF	00400000	Flash Image

00000000	00000FFF	00001000	Descriptor Region
00000004	0000000F	0000000C		Descriptor Map
00000010	0000001B	0000000C		Component Section
00000040	0000004F	00000010		Region Section
00000060	0000006B	0000000C		Master Access Section
00000060	00000063	00000004			CPU/BIOS
00000064	00000067	00000004			Manageability Engine (ME)
00000068	0000006B	00000004			GbE LAN
00000100	00000103	00000004		ICH Strap 0
00000104	00000107	00000004		ICH Strap 1
00000200	00000203	00000004		MCH Strap 0
00000EFC	00000EFF	00000004		Descriptor Map 2
00000ED0	00000EF7	00000028		ME VSCC Table
00000ED0	00000ED7	00000008			Flash device 1
00000ED8	00000EDF	00000008			Flash device 2
00000EE0	00000EE7	00000008			Flash device 3
00000EE8	00000EEF	00000008			Flash device 4
00000EF0	00000EF7	00000008			Flash device 5
00000F00	00000FFF	00000100		OEM Section
00001000	001F5FFF	001F5000	ME Region
001F6000	001F7FFF	00002000	GbE Region
001F8000	001FFFFF	00008000	PDR Region
00200000	003FFFFF	00200000	BIOS Region

Start (hex)	End (hex)	Length (hex)	Area Name
-----------	---------	------------	---------
00000000	003FFFFF	00400000	Flash Image

00000000	00000FFF	00001000	Descriptor Region
00000004	0000000F	0000000C		Descriptor Map
00000010	0000001B	0000000C		Component Section
00000040	0000004F	00000010		Region Section
00000060	0000006B	0000000C		Master Access Section
00000060	00000063	00000004			CPU/BIOS
00000064	00000067	00000004			Manageability Engine (ME)
00000068	0000006B	00000004			GbE LAN
00000100	00000103	00000004		ICH Strap 0
00000104	00000107	00000004		ICH Strap 1
00000200	00000203	00000004		MCH Strap 0
00000ED0	00000EF7	00000028		ME VSCC Table
00000ED0	00000ED7	00000008			Flash device 1
00000ED8	00000EDF	00000008			Flash device 2
00000EE0	00000EE7	00000008			Flash device 3
00000EE8	00000EEF	00000008			Flash device 4
00000EF0	00000EF7	00000008			Flash device 5
00000EFC	00000EFF	00000004		Descriptor Map 2
00000F00	00000FFF	00000100		OEM Section
00001000	00002FFF	00002000	GbE Region
00003000	00202FFF	00200000	BIOS Region

Build Settings
--------------
Flash Erase Size = 0x1000

</i>
</pre>

			<p>
				It's a utility called 'Flash Image Tool' for ME 4.x that was used for this. You drag a complete
				image into in and the utility decomposes the various components, allowing you to set soft straps.
			</p>
			<p>
				This tool is proprietary, for Windows only, but was used to deblob the X200. End justified means, and
				the utility is no longer needed since the ich9deblob utility (documented on this page) can now be
				used to create deblobbed descriptors.
			</p>

	</div>

	<div class="section">
		
		<h2 id="gbe_region">
			GBE (gigabit ethernet) region in SPI flash
		</h2>

			<p>
				Of the 8K, about 95% is 0xFF. 
				The data is the gbe region is fully documented in this public datasheet:
				<a href="http://www.intel.co.uk/content/dam/doc/application-note/i-o-controller-hub-9m-82567lf-lm-v-nvm-map-appl-note.pdf">http://www.intel.co.uk/content/dam/doc/application-note/i-o-controller-hub-9m-82567lf-lm-v-nvm-map-appl-note.pdf</a>
			</p>

			<p>
				The only actual content found was:
			</p>

<pre>
<i>
00  1F  1F  1F  1F  1F  00  08  FF  FF  83  10  FF  FF  FF  FF  
08  10  FF  FF  C3  10  EE  20  AA  17  F5  10  86  80  00  00  
01  0D  00  00  00  00  05  06  20  30  00  0A  00  00  8B  8D  
02  06  40  2B  43  00  00  00  F5  10  AD  BA  F5  10  BF  10  
AD  BA  CB  10  AD  BA  AD  BA  00  00  00  00  00  00  00  00  
00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  
00  01  00  40  28  12  07  40  FF  FF  FF  FF  FF  FF  FF  FF  
FF  FF  FF  FF  FF  FF  FF  FF  FF  FF  FF  FF  FF  FF  D9  F0  
20  60  1F  00  02  00  13  00  00  80  1D  00  FF  00  16  00  
DD  CC  18  00  11  20  17  00  DD  DD  18  00  12  20  17  00  
00  80  1D  00  00  00  1F  
</i>
</pre>

		<p>
			The first part is the MAC address set to all 0x1F. It's repeated haly way through
			the 8K area, and the rest is all 0xFF. This is all documented in the datasheet.
		</p>
		
		<p>
			The GBe region starts at 0x20A000 bytes from the *end* of a factory image and is 0x2000 bytes long.
			In libreboot (deblobbed) the descriptor is set to put gbe directly after the initial 4K flash descriptor. 
			So the first 4K of the ROM is the descriptor, and then the next 8K is the gbe region.
		</p>

		<div class="subsection">
			
			<h3 id="gbe_region_changemacaddress">GBE region: change MAC address</h3>

				<p>
					According to the datasheet, it's supposed to add up to 0xBABA but can actually be others on the X200.
					<a href="https://communities.intel.com/community/wired/blog/2010/10/14/how-to-basic-eeprom-checksums">https://communities.intel.com/community/wired/blog/2010/10/14/how-to-basic-eeprom-checksums</a>
				</p>
				<p>
					<i>&quot;One of those engineers loves classic rock music, so he selected 0xBABA&quot;</i>
				</p>
				<p>In honour of the song <i>Baba O'Reilly</i> by <i>The Who</i> apparently. We're not making this stuff up...</p>

				<p>
					0x3ABA, 0x34BA, 0x40BA and more have been observed in the main Gbe regions on the X200 factory.rom dumps.
					The checksums of the backup regions match BABA, however. 
				</p>
				
				<p>
					By default, the X200 (as shipped by Lenovo) actually has an invalid main gbe checksum. The backup gbe region is correct,
					and is what these machines default to. Basically, you should do what you need on the *backup* gbe region, and
					then correct the main one by copying from the backup.
				</p>
				
				<p>
					Look at resources/utilities/ich9deblob/ich9deblob.c.
				</p>
					<ul>
						<li>Add the first 0x3F 16bit numbers (unsigned) of the GBe descriptor together (this includes the checksum value)
						and that has to add up to 0xBABA. In other words, the checksum is 0xBABA minus the total of the first
						0x3E 16bit numbers (unsigned), ignoring any overflow.</li>
					</ul>
					
		</div>
		
	</div>

	<div class="section">
		
		<h2 id="flash_descriptor_region">Flash descriptor region</h2>
			
			<p>
				<a href="http://www.intel.co.uk/content/dam/doc/datasheet/io-controller-hub-9-datasheet.pdf">http://www.intel.co.uk/content/dam/doc/datasheet/io-controller-hub-9-datasheet.pdf</a>
				from page 850 onwards. This explains everything that is in the flash descriptor, which can be used to understand what libreboot
				is doing about modifying it.
			</p>
				
			<p>
				How to deblob:
			</p>
				<ul>
					<li>patch the number of regions present in the descriptor from 5 - 3</li>
					<li>originally descriptor + bios + me + gbe + platform</li>
					<li>modified = descriptor + bios + gbe</li>
					<li>the next stage is to patch the part of the descriptor which defines the start and end point of each section</li>
					<li>then cut out the gbe region and insert it just after the region</li>
					<li>all this can be substantiated with public docs (ICH9 datasheet)</li>
					<li>the final part is flipping 2 bits. Halting the ME via 1 MCH soft strap and 1 ICH soft strap</li>
					<li>the part of the descriptor described there gives the base address and length of each region (bits 12:24 of each address)</li>
					<li>to disable a region, you set the base address to 0xFFF and the length to 0</li>
					<li>and you change the number of regions from 4 (zero based) to 2</li>
				</ul>
				
			<p>
				There's an interesting parameter called 'ME Alternate disable', which allows the ME to only handle hardware errata in the southbridge,
				but disables any other functionality. This is similar to the 'ignition' in the 5 series and higher but using the standard firmware
				instead of a small 128K version. Useless for libreboot, though.
			</p>
				
			<p>
				To deblob GM45, you chop out the platform and ME regions and correct the addresses in flReg1-4.
				Then you set meDisable to 1 in ICHSTRAP0 and MCHSTRAP0.
			</p>
				
			<p>How to patch the descriptor from the factory.rom dump</p>
				<ul>
					<li>map the first 4k into the struct (minus the gbe region)</li>
					<li>set NR in FLMAP0 to 2 (from 4)</li>
					<li>adjust BASE and LIMIT in flReg1,2,3,4 to reflect the new location of each region (or remove them in the case of Platform and ME)</li>
					<li>set meDisable to 1/true in ICHSTRAP0 and MCHSTRAP0</li>
					<li>extract the 8k GBe region and append that to the end of the 4k descriptor</li>
					<li>output the 12k concatenated chunk</li>
					<li>Then it can be dd'd into the first 12K part of a coreboot image.</li>
					<li>the GBe region always starts 0x20A000 bytes from the end of the ROM</li>
				</ul>
					
			<p>
				This means that libreboot's descriptor region will simply define the following regions:
			</p>
				<ul>
					<li>descriptor (4K)</li>
					<li>gbe (8K)</li>
					<li>bios (rest of flash chip. CBFS also set to occupy this whole size)</li>
				</ul>

			<p>
				The data in the descriptor region is little endian, and it represents bits 24:12 of the address
				(bits 12-24, written this way since bit 24 is nearer to left than bit 12 in the binary representation).
			</p>
			<p>
				So, <i>x &lt;&lt; 12 = address</i>
			</p>
			<p>
				If it's in descriptor mode, then the first 4 bytes will be 5A A5 F0 0F.
			</p>
				
	</div>
		
		
	<div class="section">
		
		<h2 id="platform_data_region">platform data partition in boot flash (factory.rom / lenovo bios)</h2>
			
			<p>
				Basically useless for libreboot, since it appears to be a blob.
				Removing it didn't cause any issues in libreboot.
			</p>
			<p>
				This is a 32K region from the factory image. It could be data
				(non-functional) that the original Lenovo BIOS used, but we don't know.
			</p>
		
			<p>
				It has only a 448 byte fragment different from 0x00 or 0xFF.
			</p>
		
	</div>

	<div class="section">

		<p>
			Copyright &copy; 2014, 2015 Francis Rowe &lt;info@gluglug.org.uk&gt;<br/>
			This document is released under the Creative Commons Attribution-ShareAlike 4.0 International Public License and all future versions.
			A copy of the license can be found at <a href="../cc-by-sa-4.txt">../cc-by-sa-4.txt</a>.
		</p>

		<p>
			This document is distributed in the hope that it will be useful,
			but WITHOUT ANY WARRANTY; without even the implied warranty of
			MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See <a href="../cc-by-sa-4.txt">../cc-by-sa-4.txt</a> for more information.
		</p>
		
	</div>

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