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Date: Tue, 9 Aug 2016 23:23:31 +0200
From: "Rafael J. Wysocki" <>
To: Jiri Kosina <>
Cc: "Rafael J. Wysocki" <>, Thomas Garnier <>, 
	"Rafael J. Wysocki" <>, Linux PM list <>, 
	"the arch/x86 maintainers" <>, Linux Kernel Mailing List <>, 
	Yinghai Lu <>, Thomas Gleixner <>, Ingo Molnar <>, 
	"H . Peter Anvin" <>, Kees Cook <>, Pavel Machek <>, 
	Kernel Hardening <>, Borislav Petkov <>
Subject: Re: [Resend][PATCH] x86/power/64: Always create temporary identity
 mapping correctly

On Tue, Aug 9, 2016 at 10:02 PM, Jiri Kosina <> 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.


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