linux-kernel - Re: Fix hibernation in FIPS mode?

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Date:   Thu, 1 Apr 2021 15:56:34 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     crecklin@...hat.com
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Simo Sorce <simo@...hat.com>, Dexuan Cui <decui@...rosoft.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Fix hibernation in FIPS mode?

On Thu, 1 Apr 2021 at 15:54, Chris von Recklinghausen
<crecklin@...hat.com> wrote:
>
> On 4/1/21 9:38 AM, Rafael J. Wysocki wrote:
> > On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <ardb@...nel.org> wrote:
> >> On Tue, 30 Mar 2021 at 21:56, Simo Sorce <simo@...hat.com> wrote:
> >>> On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> >>>> On Tue, 30 Mar 2021 at 20:05, Simo Sorce <simo@...hat.com> wrote:
> >>>>> On Tue, 2021-03-30 at 16:46 +0200, Rafael J. Wysocki wrote:
> >>>>>> On Tue, Mar 30, 2021 at 12:14 AM Dexuan Cui <decui@...rosoft.com> wrote:
> >>>>>>> Hi,
> >>>>>>> MD5 was marked incompliant with FIPS in 2009:
> >>>>>>> a3bef3a31a19 ("crypto: testmgr - Skip algs not flagged fips_allowed in fips mode")
> >>>>>>> a1915d51e8e7 ("crypto: testmgr - Mark algs allowed in fips mode")
> >>>>>>>
> >>>>>>> But hibernation_e820_save() is still using MD5, and fails in FIPS mode
> >>>>>>> due to the 2018 patch:
> >>>>>>> 749fa17093ff ("PM / hibernate: Check the success of generating md5 digest before hibernation")
> >>>>>>>
> >>>>>>> As a result, hibernation doesn't work when FIPS is on.
> >>>>>>>
> >>>>>>> Do you think if hibernation_e820_save() should be changed to use a
> >>>>>>> FIPS-compliant algorithm like SHA-1?
> >>>>>> I would say yes, it should.
> >>>>>>
> >>>>>>> PS, currently it looks like FIPS mode is broken in the mainline:
> >>>>>>> https://www.mail-archive.com/linux-crypto@vger.kernel.org/msg49414.html
> >>>>> FYI, SHA-1 is not a good choice, it is only permitted in HMAC
> >>>>> constructions and only for specified uses. If you need to change
> >>>>> algorithm you should go straight to SHA-2 or SHA-3 based hashes.
> >>>>>
> >>>> What is the reason for using a [broken] cryptographic hash here? if
> >>>> this is just an integrity check, better use CRC32
> > Not really.
> >
> > CRC32 is not really sufficient for integrity checking here AFAICS.  It
> > might be made a fallback option if MD5 is not available, but making it
> > the default would be somewhat over the top IMO.
>
>
> Would ghash be a better choice? It produces the same size digest as md5.
>

No, ghash is a MAC not a hash. It should only ever be used with GCM
and nowhere else.

> Does anyone have any other suggestions of algorithms to try?
>

Just use crc32