linux-kernel - Re: [PATCH 17/18] Hibernate: introduced SNAPSHOT_SIG

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Date:	Tue, 27 Aug 2013 20:54:57 +0800
From:	joeyli <jlee@...e.com>
To:	Pavel Machek <pavel@....cz>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-crypto@...r.kernel.org,
	opensuse-kernel@...nsuse.org, David Howells <dhowells@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Len Brown <len.brown@...el.com>,
	Josh Boyer <jwboyer@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Matt Fleming <matt.fleming@...el.com>,
	James Bottomley <james.bottomley@...senpartnership.com>,
	Greg KH <gregkh@...uxfoundation.org>, JKosina@...e.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Gary Lin <GLin@...e.com>, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 17/18] Hibernate: introduced SNAPSHOT_SIG_HASH config
 for select hash algorithm

於 二，2013-08-27 於 13:30 +0200，Pavel Machek 提到：
> On Tue 2013-08-27 18:22:17, joeyli wrote:
> > 於 日，2013-08-25 於 18:43 +0200，Pavel Machek 提到：
> > > On Thu 2013-08-22 19:01:56, Lee, Chun-Yi wrote:
> > > > This patch introduced SNAPSHOT_SIG_HASH config for user to select which
> > > > hash algorithm will be used during signature generation of snapshot.
> > > > 
> > > > v2:
> > > > Add define check of oCONFIG_SNAPSHOT_VERIFICATION in snapshot.c before
> > > > declare pkey_hash().
> > > > 
> > > > Reviewed-by: Jiri Kosina <jkosina@...e.cz>
> > > > Signed-off-by: Lee, Chun-Yi <jlee@...e.com>
> > > > ---
> > > >  kernel/power/Kconfig    |   46 ++++++++++++++++++++++++++++++++++++++++++++++
> > > >  kernel/power/snapshot.c |   27 ++++++++++++++++++++++-----
> > > >  2 files changed, 68 insertions(+), 5 deletions(-)
> > > > 
> > > > diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
> > > > index b592d88..79b34fa 100644
> > > > --- a/kernel/power/Kconfig
> > > > +++ b/kernel/power/Kconfig
> > > > @@ -78,6 +78,52 @@ config SNAPSHOT_VERIFICATION
> > > >  	  dependent on UEFI environment. EFI bootloader should generate the
> > > >  	  key-pair.
> > > >  
> > > > +choice
> > > > +	prompt "Which hash algorithm should snapshot be signed with?"
> > > > +        depends on SNAPSHOT_VERIFICATION
> > > > +        help
> > > > +          This determines which sort of hashing algorithm will be used during
> > > > +          signature generation of snapshot. This algorithm _must_ be built into
> > > > +	  the kernel directly so that signature verification can take place.
> > > > +	  It is not possible to load a signed snapshot containing the algorithm
> > > > +	  to check the signature on that module.
> > > 
> > > Like if 1000 ifdefs you already added to the code are not enough, you
> > > make some new ones?
> > > 									Pavel
> > > 
> > 
> > This SNAPSHOT_SIG_HASH kernel config is to select which SHA algorithms
> > used for generate digest of snapshot. The configuration will captured by
> > a const char* in code:
> > 
> > +static const char *snapshot_hash = CONFIG_SNAPSHOT_SIG_HASH;
> > +
> > +static int pkey_hash(void)
> > 
> > So, there doesn't have any ifdef block derived from this new config.
> 
> I'd say select one hash function, and use it. There's no need to make
> it configurable.
> 									Pavel

There have better performance when SHA algorithm output shorter hash
result. On the other hand, longer hash result provide better security.

And, on 64-bits system, the SHA512 has better performance then SHA256.

Due to user have different use case and different hardware, why not give
them this option to make decision?


Thanks a lot!
Joey LEe

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