Re: Fix hibernation in FIPS mode?

[Chris von Recklinghausen]

On 4/1/21 9:38 AM, Rafael J. Wysocki wrote:
> On Thu, Apr 1, 2021 at 10:47 AM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> > On Tue, 30 Mar 2021 at 21:56, Simo Sorce <simo@xxxxxxxxxx> wrote:
> > > On Tue, 2021-03-30 at 21:45 +0200, Ard Biesheuvel wrote:
> > > > On Tue, 30 Mar 2021 at 20:05, Simo Sorce <simo@xxxxxxxxxx> 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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx/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.

Does anyone have any other suggestions of algorithms to try?

Thanks,

Chris

> > > If the integrity check is used exclusively to verify there were no
> > > accidental changes and is not used as a security measure, by all means
> > > I agree that using crc32 is a better idea.
> > Looking at 62a03defeabd58f74e07ca030d6c21e069d4d88e which introduced
> > this, it is only a best effort check which is simply omitted if md5
> > happens to be unavailable, so there is definitely no need for crypto
> > here.
> Yes, it is about integrity checking only.  No, CRC32 is not equivalent
> to MD5 in that respect AFAICS.
>
> Thanks!