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

[Evgenii Shatokhin]

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'.

> > 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