linux-kernel - Re: [PATCH] hibernation: on 32-bit x86, disabled in favor of KASLR

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Date:   Thu, 23 Mar 2017 16:30:06 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Evgenii Shatokhin <eugene.shatokhin@...dex.ru>
Cc:     Kees Cook <keescook@...omium.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] hibernation: on 32-bit x86, disabled in favor of KASLR

On Thu, Mar 23, 2017 at 2:23 PM, Evgenii Shatokhin
<eugene.shatokhin@...dex.ru> wrote:
> On 23.03.2017 03:27, Kees Cook wrote:
>>
>> This is a modified revert of commit 65fe935dd238 ("x86/KASLR, x86/power:
>> Remove x86 hibernation restrictions"), since it appears that 32-bit
>> hibernation still can't support KASLR. 64-bit is fine. Since people have
>> been running with KASLR by default on 32-bit since v4.8, this disables
>> hibernation (with a warning). Booting with "nokaslr" will disable KASLR
>> and enable hibernation.
>>
>> Reported-by: Evgenii Shatokhin <eugene.shatokhin@...dex.ru>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> Cc: stable@...r.kernel.org # v4.8+
>
>
> The patch does not work as intended on my system, unfortunately.
>
> I tried the mainline kernel v4.11-rc3 and added this patch. With "nokaslr"
> in the kernel command line, the system fails to hibernate. It complains this
> way in the log:
>
> <...>
> kernel: PM: writing image.
> kernel: PM: Cannot find swap device, try swapon -a.
> kernel: PM: Cannot get swap writer
> kernel: PM: Basic memory bitmaps freed
> kernel: Restarting tasks ... done.
> systemd[1]: Time has been changed
> systemd[3948]: Time has been changed
> systemd[14825]: Time has been changed
> systemd[1]: systemd-hibernate.service: main process exited, code=exited,
> status=1/FAILURE
> systemd[1]: Failed to start Hibernate.
> <...>
>
> The swap device (swap file, actually) is available, however:
> -------------
> # swapon -s
> Filename  Type  Size    Used  Priority
> /swap     file  6297596 0     -1
> -------------
>
> I built the same kernel without this patch then, added "nokaslr" in the
> kernel command line again, and the system hibernates and resumes fine.

With the patch applied and "nokaslr" in the kernel command line, what
shows up when you do

$ cat /sys/power/state

?

Thanks,
Rafael