Re: [RFC V4 PATCH 00/15] Signature verification of hibernate snapshot

[joeyli <jlee@suse.com>]

於 四，2013-09-26 於 10:19 +0800，joeyli 提到：
> 於 三，2013-09-25 於 17:25 -0400，Alan Stern 提到：
> > On Wed, 25 Sep 2013, David Howells wrote:
> > 
> > > I have pushed some keyrings patches that will likely affect this to:
> > > 
> > > 	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=keys-devel
> > > 
> > > I intend to ask James to pull these into his next branch.  If he's happy to do
> > > so, I can look at pulling at least your asymmetric keys patch on top of them.
> > 
> > This suggests a point that I raised at the Linux Plumbers conference:
> > 
> > Why are asymmetric keys used for verifying the hibernation image?  It
> > seems that a symmetric key would work just as well.  And it would be a
> > lot quicker to generate, because it wouldn't need any high-precision
> > integer computations.
> > 
> > Alan Stern
> > 
> > 
> 
> Per my understood, it's like add salt to snapshot when generate
> signature, then remove the salt when store the snapshot to swap. (or
> pass snapshot to userland).
> 
> Let me explain the symmetric key solution base on my understand:
> 
>  + EFI stub kernel generate a hash value from a random seed, then store
> it to EFi boot varaible. It should protected by UEFI secure boot
> environment.
> 
>  + When hibernate launched:
>     - Kernel create the snapshot image of memory. It's included the
> random hash value(salt) that generated in EFI stub stage.
>     - Then kernel hash the snapshot image, put the hash to snapshot
> header, just like current asymmetric keys solution.
>     - Kernel erase the salt in snapshot image before it go to swap or
> pass to userspace tool.
> 
>  + When hibernate resume:
>     - Kernel or userspace tool load the snapshot(without salt) from swap
> to temporary memory space.
>     - Kernel fill the salt back to snapshot image in memory, hash it.
>     - Kernel compare the hash with the hash that put in snapshot header.
>     - Verification done! The follow-up action as current solution.
> 
> Please current me if I missed anything.
> 
> 
> Thanks a lot!
> Joey Lee
> 

For the symmetric key solution, I will try HMAC (Hash Message
Authentication Code). It's already used in networking, hope the
performance is not too bad to a big image.


Thanks
Joey Lee