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

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Message-ID: <20160829045942.GA6163@nazgul.tnic>
Date:   Mon, 29 Aug 2016 06:59:42 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        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, 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.

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

We'd still warn the hell out of it and even make that the md5 digest
comparison a default-enabled thing without even having a config option
to disable it but can we try harder not to panic and deal with this next
BIOS f*ckup more intelligently than throwing our hands in the air and
giving up?

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--