linux-kernel - Re: [Resend][PATCH] x86/power/64: Always create temporary identity mapping correctly

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Date:	Tue, 9 Aug 2016 23:23:31 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Jiri Kosina <jikos@...nel.org>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Thomas Garnier <thgarnie@...gle.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>, Pavel Machek <pavel@....cz>,
	Kernel Hardening <kernel-hardening@...ts.openwall.com>,
	Borislav Petkov <bpetkov@...e.de>
Subject: Re: [Resend][PATCH] x86/power/64: Always create temporary identity
 mapping correctly

On Tue, Aug 9, 2016 at 10:02 PM, Jiri Kosina <jikos@...nel.org> wrote:
> On Tue, 9 Aug 2016, Rafael J. Wysocki wrote:
>
>> I have a murky suspicion, but it is really weird.  Namely, what if
>> restore_jump_address in set_up_temporary_text_mapping() happens to be
>> covered by the restore kernel's identity mapping?  Then, the image
>> kernel's entry point may get overwritten by something else in
>> core_restore_code().
>
> So this made me to actually test a scenario where I'd suspend a kernel
> that's known-broken (i.e. contains 021182e52fe), and then have it resumed
> by a kernel that has 021182e52fe reverted. It resumed successfully.
>
> Just a datapoint.

That indicates the problem is somewhere in the restore kernel and no
surprises there.

I am able to reproduce the original problem (a triple fault on resume
with CONFIG_RANDOMIZE_MEMORY set) without the $subject patch, but the
patch fixes it for me.

Question is why it is not sufficient for you and Boris and the above
theory is about the only one I can come up with ATM.

I'm going to compare the configs etc, but I guess I just end up
writing a patch to test that theory unless someone has any other idea
in the meantime.

Thanks,
Rafael