linux-kernel - Re: [RFC] swap image signature check upon resume

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Date:	Fri, 7 Dec 2007 21:19:09 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	bbpetkov@...oo.de
Cc:	Pavel Machek <pavel@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] swap image signature check upon resume

On Friday, 7 of December 2007, Borislav Petkov wrote:
> On Thu, Dec 06, 2007 at 10:46:48PM +0100, Rafael J. Wysocki wrote:
> > On Thursday, 6 of December 2007, Borislav Petkov wrote:
> > > Hi Pavel,
> > > hi Rafael,
> > > 
> > > after a quick search i couldn't find anything dealing with the topic in the
> > > subject line so here we go:
> > > 
> > > One sometimes can mix up (and by one i mean me) the
> > > kernel images one boots after having suspended the machine previously. There can
> > > be at least two reasons for that:
> > > 
> > > 1. too many kernels in grub and having forgotten with which i suspended.
> > > 2. compile and install a new kernel and forget about it, suspend in the evening
> > > and then boot with the new kernel;
> > > 
> > > in both cases you end up staring at fsck since they filesystems haven't been unmounted,
> > > of course. Or at least see the warning message of some journal recovery whisk away.
> > > 
> > > In order to alleviate that, one could probably go, imho, and write in the swsusp_header
> > > the kernel version which suspended the machine (UTS_RELEASE) alongside
> > > SWSUSP_SIG and check that against the kernel version of the image just booting.
> > > If they match then all is well, if not, one could
> > > 
> > > a) issue a BIG FAT WARNING and reboot telling the user to select the proper
> > > image
> > > b) ask the user what to do:
> > > 	- proceed as if "noresume" has been entered on the kernel command line
> > > 	- reboot after issuing the kernel version which suspended the machine
> > > 	-
> > > c)...
> > > 
> > > In case you guys think something like that might be of use i can come up with a
> > > patch in the next coupla days...
> > 
> > Well, there's a patchset in the current mainline that allows you to use
> > arbitrary (sufficiently new) kernel to load the image and then restore the
> > image kernel.  So, you can hibernate 2.6.24-rc3 and use 2.6.24-rc2 to restore
> > it, for example.
> > 
> > I'm going to do that for i386 too.
> right, this is d307c4a8e826c44f9633bd3f7e60d0491e7d885a (Hibernation: Arbitrary
> boot kernel support - generic code), i should've seen that. What's the status of
> those bits, from a quick scan it seems they need some rewiring (Kconfig, e.g.
> CONFIG_ARCH_HIBERNATION_HEADER etc..) and arch-specific save and restore
> functions?

No, this code is fully functional. :-)

The arch save and restore functions are in arch/x86/kernel/suspend_64.c .

As I said, i386 is not yet supported.

Greetings,
Rafael
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