linux-kernel - Re: PROBLEM: [Launchpad #1396889] [Lenovo ThinkPad T400] kexec reboot fails

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Date:	Mon, 1 Dec 2014 14:59:38 -0800
From:	Kees Cook <keescook@...omium.org>
To:	MegaBrutal <megabrutal@...il.com>
Cc:	Linux kernel <linux-kernel@...r.kernel.org>,
	Baoquan He <bhe@...hat.com>, "x86@...nel.org" <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: PROBLEM: [Launchpad #1396889] [Lenovo ThinkPad T400] kexec reboot fails

On Mon, Dec 1, 2014 at 2:45 PM, MegaBrutal <megabrutal@...il.com> wrote:
> 2014-12-01 7:32 GMT+01:00 MegaBrutal <megabrutal@...il.com>:
>> [X.] Other notes, patches, fixes, workarounds:
>> Downstream report (Ubuntu Launchpad):
>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1396889
>>
>> With kernel bisection, I've found, the first bad commit is
>> 8ab3820fd5b2896d66da7bb2a906bc382e63e7bc x86, kaslr: Return location
>> from decompress_kernel
>> which introduces KASLR.
>> http://lkml.kernel.org/r/1381450698-28710-3-git-send-email-keescook@chromium.org
>>
>> The problem only presents itself when CONFIG_RANDOMIZE_BASE=y.
>>
>> For workaround, there is a "nokaslr" kernel parameter to disable the
>> feature, even if the kernel was compiled with CONFIG_RANDOMIZE_BASE.
>
> Need to add: as I tested today, unfortunately the "nokaslr" kernel
> option doesn't work around the bug. If a kernel was compiled with
> CONFIG_RANDOMIZE_BASE, it won't properly kexec on my ThinkPad T400,
> even if the "nokaslr" kernel option is provided!
>
> This could actually help to find the bug, as whatever bad happens must
> happen before the kernel checks for the presence of the "nokaslr"
> kernel parameter.

I suspect you're encountering a subset of the same problems as
described in this thread:
https://lkml.org/lkml/2014/9/30/90

If you can test those patches, that may help demonstrate their utility.

Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security
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