linux-kernel - Re: [PATCH][v8] PM / hibernate: Verify the consistent of e820 memory map by md5 value

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Date:   Mon, 29 Aug 2016 09:15:00 +0200
From:   Pavel Machek <pavel@....cz>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Chen Yu <yu.c.chen@...el.com>, linux-pm@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Lee@...gul.tnic,
        Chun-Yi <jlee@...e.com>
Subject: Re: [PATCH][v8] PM / hibernate: Verify the consistent of e820 memory
 map by md5 value

On Mon 2016-08-29 06:59:42, Borislav Petkov wrote:
> On Mon, Aug 29, 2016 at 12:35:40AM +0800, Chen Yu wrote:
> > On some platforms, there is occasional panic triggered when trying to
> > resume from hibernation, a typical panic looks like:
> > 
> > "BUG: unable to handle kernel paging request at ffff880085894000
> > IP: [<ffffffff810c5dc2>] load_image_lzo+0x8c2/0xe70"
> > 
> > This is because e820 map has been changed by BIOS across
> > hibernation, and one of the page frames from first kernel
> > is right located in second kernel's unmapped region, so panic
> > comes out when accessing unmapped kernel address.
> > 
> > In order to expose this issue earlier, the md5 hash of e820 map
> > is passed from suspend kernel to resume kernel, and the system will
> > trigger panic once it finds the md5 value of previous kernel is not
> > the same as current resume kernel.
> 
> ... so basically now even the cases where it managed to resume would
> panic because the digests differ, even if the original panic condition
> doesn't trigger the bug, i.e. your Note 1 below.

Note where?

You can't guarantee that e820 mismatch results in kernel panic, it
could also be endless loop or data corruption. 

> The more important question IMHO would be, can we resume our system
> successfully *even* if BIOS fiddled with the e820 map?

Sounds about as easy as hot unplugging arbitrary memory address. IOW
"not easy".

									Pavel

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