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

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Date:   Sun, 28 Aug 2016 18:36:59 +0200
From:   Pavel Machek <pavel@....cz>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     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@....karlin.mff.cuni.cz,
        Chun-Yi <jlee@...e.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH][v8] PM / hibernate: Verify the consistent of e820 memory
 map by md5 value

On Mon 2016-08-29 00:35:40, 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.
> 
> Note:
> 1. Without this patch applied, it is possible that BIOS has
>    provided an inconsistent memory map, but the resume kernel is still
>    able to restore the image anyway(e.g.,  E820_RAM region is the subset
>    of the previous one), although the system might be unstable. So this
>    patch tries to treat any inconsistent e820 as illegal.
> 
> 2. Another case is, this patch replies on comparing the e820_saved, but
>    currently the e820_save might not be strictly the same across
>    hibernation, even if BIOS has provided consistent e820 map - In
>    theory mptable might modify the BIOS-provided e820_saved dynamically
>    in early_reserve_e820_mpc_new, which would allocate a buffer from
>    E820_RAM, and marks it from E820_RAM to E820_RESERVED). 
>    This is a potential and rare case we need to deal with in OS in
>    the future.
> 
> Suggested-by: Pavel Machek <pavel@....cz>
> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Lee, Chun-Yi <jlee@...e.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>

Acked-by: Pavel Machek <pavel@....cz>

You might want to verify that panic is actually visible on affected
platform. Thanks for your patience ;-).

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html