Re: 32-bit x86 system reboots automatically on resume from hibernate (ASLR issue?)

[Evgenii Shatokhin <eugene.shatokhin@yandex.ru>]

On 21.03.2017 23:40, Kees Cook wrote:
> On Tue, Mar 21, 2017 at 6:54 AM, Evgenii Shatokhin
> <eugene.shatokhin@yandex.ru> wrote:
>> Hi,
>>
>> One of my x86 machines with a 32-bit Linux system (ROSA Linux in this case)
>> automatically reboots when it tries to resume from hibernate. This happens
>> shortly after "Image loading progress 100%" message is shown on the screen.
>>
>> No traces of the error are in the system log after reboot though.
>>
>> The problem is present at least in the mainline kernels 4.8 - 4.10. With
>> earlier versions (I tried 4.4, 4.5, etc.), the system resumes OK.
>>
>> The bisection pointed to the following commit as the first "bad" one:
>>
>> commit 65fe935dd2387a4faf15314c73f5e6d31ef0217e
>> Author: Kees Cook <keescook@chromium.org>
>> Date:   Mon Jun 13 15:10:02 2016 -0700
>>
>>      x86/KASLR, x86/power: Remove x86 hibernation restrictions
>
> Hrm, perhaps the 32-bit hibernation code still isn't KASLR-safe. If
> you boot with nokaslr on the kernel command line, does the problem go
> away?

Yes. The problem does not show up when I boot the system with 'nokaslr'.

>
>> Hardware: https://linux-hardware.org/index.php?probe=e6a06c64c7
>> Config used to build the kernel at rev. 65fe935:
>> http://pastebin.com/AxEA6ahb
>>
>> If I understand it correctly, this commit just enabled ASLR by default
>> regardless of whether hibernation support was present or not. Before this
>> commit, ASLR was disabled on that system because hibernation was supported.
>>
>> To check if ASLR is really involved here, I rebuilt the kernel with
>> CONFIG_RANDOMIZE_BASE unset - now the system resumes OK from hibernation, no
>> auto reboots, no other visible problems so far.
>>
>> The problem does not show up in a 64-bit Linux system installed on the same
>> machine. Only the 32-bit system is affected.
>
> (Why would you want to run 32-bit kernels on a 64-bit system?)

Mostly for testing and debugging.

While most of ROSA Linux users are OK with the 64-bit version of the 
distro, some still need its 32-bit variant. They reported (unrelated) 
problems with hibernate. I was debugging these and stumbled upon this 
problem as well.

Regards,
Evgenii

>
> -Kees
>