Re: KASLR causes intermittent boot failures on some systems

From: Jeff Moyer <jmoyer@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: Thomas Garnier <thgarnie@google.com>,
	Ingo Molnar <mingo@kernel.org>, Baoquan He <bhe@redhat.com>,
	Dan Williams <dan.j.williams@intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-nvdimm@ml01.01.org
Subject: Re: KASLR causes intermittent boot failures on some systems
Date: Mon, 10 Apr 2017 11:49:47 -0400	[thread overview]
Message-ID: <x49d1ck5kkk.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <CAGXu5jJ-Pny8_rrEBtO8W86zjw2Edk7a-My4EfRf7jePS4sQeg@mail.gmail.com> (Kees Cook's message of "Fri, 7 Apr 2017 14:25:35 -0700")

Kees Cook <keescook@chromium.org> writes:

> On Fri, Apr 7, 2017 at 7:41 AM, Jeff Moyer <jmoyer@redhat.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.

Cheers,
Jeff