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| author | Francis Rowe <info@gluglug.org.uk> | 2014-10-10 19:26:05 (EDT) |
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| committer | Francis Rowe <info@gluglug.org.uk> | 2014-10-10 19:26:05 (EDT) |
| commit | 8466ad2d70683856bcc07e8f305f66f55b1c701a (patch) | |
| tree | d63d774f0d1c8aa03e012067e7280860374c3619 /docs/howtos/dock.html | |
| parent | 52caa0b75ffb62511e4f73317243258bfa24d701 (diff) | |
| download | libreboot-8466ad2d70683856bcc07e8f305f66f55b1c701a.zip libreboot-8466ad2d70683856bcc07e8f305f66f55b1c701a.tar.gz libreboot-8466ad2d70683856bcc07e8f305f66f55b1c701a.tar.bz2 | |
Documentation: notes about DMA and the docking station (X60/T60)
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diff --git a/docs/howtos/dock.html b/docs/howtos/dock.html new file mode 100644 index 0000000..ef62e83 --- /dev/null +++ b/docs/howtos/dock.html @@ -0,0 +1,163 @@ +<!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> |