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

[Kees Cook]

On Wed, Mar 22, 2017 at 5:50 AM, Evgenii Shatokhin
<eugene.shatokhin@xxxxxxxxx> wrote:
> On 21.03.2017 23:40, Kees Cook wrote:
>>
>> On Tue, Mar 21, 2017 at 6:54 AM, Evgenii Shatokhin
>> <eugene.shatokhin@xxxxxxxxx> 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@xxxxxxxxxxxx>
>>> 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'.

Okay, it looks like we need to either partially revert that commit
(i.e. make the by-default-prefer-hibernation logic only happen on
32-bit x86), swap the logic (i.e. by-default-prefer-KASLR on 32-bit),
or make KASLR be blocked by hibernation in Kconfig (as it was a long
time ago).

Rafael, do you have a preference here?

-Kees

-- 
Kees Cook
Pixel Security