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

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Date:   Thu, 1 Apr 2021 09:54:21 -0400
From:   Chris von Recklinghausen <crecklin@...hat.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>
Cc:     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 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.

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!
>