From 8466ad2d70683856bcc07e8f305f66f55b1c701a Mon Sep 17 00:00:00 2001
From: Francis Rowe <info@gluglug.org.uk>
Date: Fri, 10 Oct 2014 19:26:05 -0400
Subject: Documentation: notes about DMA and the docking station (X60/T60)
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+<!DOCTYPE html>
+<html>
+<head>
+ <meta charset="utf-8">
+ <meta name="viewport" content="width=device-width, initial-scale=1">
+
+ <style type="text/css">
+ body {
+ background:#fff;
+ color:#000;
+ font-family:sans-serif;
+ font-size:1em;
+ }
+ div.important {
+ background-color:#ccc;
+ }
+ </style>
+
+ <title>Notes about DMA and the docking station (X60/T60)</title>
+</head>
+
+<body>
+ <header>
+ <h1>Notes about DMA and the docking station (X60/T60)</h1>
+ <aside>Or <a href="../index.html">back to main index</a></aside>
+ </header>
+
+<pre>
+
+Use case:
+---------
+Usually when people do full disk encryption, it's not really full disk,
+instead they still have a /boot in clear.
+
+So an evil maid attack can still be done, in two passes:
+1) Clone the hdd, Infect the initramfs or the kernel.
+2) Wait for the user to enter its password, recover the password,
+luksOpen the hdd image.
+
+I wanted a real full-disk encryption so I've put grub in flash and I
+have the following: The HDD has a LUKS rootfs(containing /boot) on an
+lvm partition, so no partition is in clear.
+
+So when the computer boots it executes coreboot, then grub as a payload.
+Grub then opens the LUKS partition and loads the kernel and initramfs
+from there.
+
+To prevent hardware level tempering(like reflashing), I used nail
+polish with a lot of gilder, that acts like a seal. Then a high
+resolution picture of it is taken, to be able to tell the difference.
+
+The problem:
+------------
+But then comes the docking port issue: Some LPC pins are exported
+there, such as the CLKRUN and LDRQ#.
+
+LDRQ# is "Encoded DMA/Bus Master Request": "Only needed by
+peripherals that need DMA or bus mastering. Requires an
+individual signal per peripheral. Peripherals may not share
+an LDRQ# signal."
+
+So now DMA access is possible trough the dock connector.
+So I want to be able to turn that off.
+
+If I got it right, the X60 has 2 superio, one is in the dock, and the
+other one is in the laptop, so we have:
+ ________________
+ _________________ | |
+| | | Dock connector:|
+|Dock: NSC pc87982|<--LPC--->D_LPC_DREQ0 |
+|_________________| |_______^________|
+ |
+ |
+ |
+ |
+ ___________________|____
+ | v |
+ | SuperIO: DLDRQ# |
+ | NSC pc87382 LDRQ# |
+ |___________________^____|
+ |
+ |
+ |
+ |
+ ___________________|___
+ | v |
+ | Southbridge: LDRQ0 |
+ | ICH7 |
+ |_______________________|
+
+
+The code:
+---------
+Now if I look at the existing code, there is some superio drivers, like
+pc87382 in src/superio/nsc, the code is very small.
+The only interesting part is the pnp_info pnp_dev_info struct.
+
+Now if I look inside src/mainboard/lenovo/x60 there is some more
+complete dock driver:
+
+Inside dock.c I see some dock_connect and dock_disconnect functions.
+
+Such functions are called during the initialisation (romstage.c) and
+from the x60's SMI handler (smihandler.c).
+
+Questions:
+----------
+1) Would the following be sufficent to prevent DMA access from the
+outside:
+> int dock_connect(void)
+> {
+> int timeout = 1000;
+> + int val;
+> +
+> + if (get_option(&val, "dock") != CB_SUCCESS)
+> + val = 1;
+> + if (val == 0)
+> + return 0;
+> [...]
+> }
+>
+> void dock_disconnect(void) {
+> + if (dock_present())
+> + return;
+> [...]
+> }
+2) Would an nvram option be ok for that? Should a Kconfig option be
+added too?
+
+> config DOCK_AUTODETECT
+> bool "Autodetect"
+> help
+> The dock is autodetected. If unsure select this option.
+>
+> config DOCK_DISABLED
+> bool "Disabled"
+> help
+> The dock is always disabled.
+>
+> config DOCK_NVRAM_ENABLE
+> bool "Nvram"
+> help
+> The dock autodetection is tried only if it is also enabled
+> trough nvram.
+
+</pre>
+
+<hr/>
+
+ <p>
+ Copyright © 2014 Francis Rowe <info@gluglug.org.uk><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="../license.txt">../license.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="../license.txt">../license.txt</a> for more information.
+ </p>
+
+</body>
+</html>
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