linux-kernel - Re: KASLR causes intermittent boot failures on some systems

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Date:   Mon, 10 Apr 2017 12:03:55 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jeff Moyer <jmoyer@...hat.com>
Cc:     Thomas Garnier <thgarnie@...gle.com>,
        Ingo Molnar <mingo@...nel.org>, Baoquan He <bhe@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-nvdimm@...ts.01.org
Subject: Re: KASLR causes intermittent boot failures on some systems

On Mon, Apr 10, 2017 at 11:22 AM, Jeff Moyer <jmoyer@...hat.com> wrote:
> Kees Cook <keescook@...omium.org> writes:
>
>> On Mon, Apr 10, 2017 at 8:49 AM, Jeff Moyer <jmoyer@...hat.com> wrote:
>>> Kees Cook <keescook@...omium.org> writes:
>>>
>>>> On Fri, Apr 7, 2017 at 7:41 AM, Jeff Moyer <jmoyer@...hat.com> wrote:
>>>>> Hi,
>>>>>
>>>>> commit 021182e52fe01 ("x86/mm: Enable KASLR for physical mapping memory
>>>>> regions") causes some of my systems with persistent memory (whether real
>>>>> or emulated) to fail to boot with a couple of different crash
>>>>> signatures.  The first signature is a NMI watchdog lockup of all but 1
>>>>> cpu, which causes much difficulty in extracting useful information from
>>>>> the console.  The second variant is an invalid paging request, listed
>>>>> below.
>>>>
>>>> Just to rule out some of the stuff in the boot path, does booting with
>>>> "nokaslr" solve this? (i.e. I want to figure out if this is from some
>>>> of the rearrangements done that are exposed under that commit, or if
>>>> it is genuinely the randomization that is killing the systems...)
>>>
>>> Adding "nokaslr" to the boot line does indeed make the problem go away.
>>
>> Are you booting with a memmap= flag?
>
> From my first email:
>
> [ 0.000000] Command line: BOOT_IMAGE=/vmlinuz-4.11.0-rc5+
> root=/dev/mapper/rhel_intel--lizardhead--04-root ro memmap=192G!1024G
> crashkernel=auto rd.lvm.lv=rhel_intel-lizardhead-04/root
> rd.lvm.lv=rhel_intel-lizardhead-04/swap console=ttyS0,115200n81
> LANG=en_US.UTF-8
>
> Did you not receive the attachments?

I see it now, thanks!

The memmap parsing was added in -rc1 (f28442497b5ca), so I'd expect
that to be handled. Hmmm.

-Kees

-- 
Kees Cook
Pixel Security