Received-SPF: pass (google.com: best guess record for domain of linux-crypto-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Sun, 11 Aug 2019 13:34:06 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Milan Broz <gmazyland@gmail.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Pascal Van Leeuwen <pvanleeuwen@verimatrix.com>,
        "dm-devel@redhat.com" <dm-devel@redhat.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Horia Geanta <horia.geanta@nxp.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>
Subject: Re: [dm-devel] xts fuzz testing and lack of ciphertext stealing
 support
Message-ID: <20190811203406.GA17421@sol.localdomain>
Mail-Followup-To: Milan Broz <gmazyland@gmail.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Pascal Van Leeuwen <pvanleeuwen@verimatrix.com>,
        "dm-devel@redhat.com" <dm-devel@redhat.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Horia Geanta <horia.geanta@nxp.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>
References: <VI1PR0402MB34856F03FCE57AB62FC2257998D40@VI1PR0402MB3485.eurprd04.prod.outlook.com>
 <MN2PR20MB2973127E4C159A8F5CFDD0C9CAD70@MN2PR20MB2973.namprd20.prod.outlook.com>
 <VI1PR0402MB3485689B4B65C879BC1D137398D70@VI1PR0402MB3485.eurprd04.prod.outlook.com>
 <20190809024821.GA7186@gondor.apana.org.au>
 <CAKv+Gu9hk=PGpsAWWOU61VrA3mVQd10LudA1qg0LbiX7DG9RjA@mail.gmail.com>
 <VI1PR0402MB3485F94AECC495F133F6B3D798D60@VI1PR0402MB3485.eurprd04.prod.outlook.com>
 <CAKv+Gu-_WObNm+ySXDWjhqe2YPzajX83MofuF-WKPSdLg5t4Ew@mail.gmail.com>
 <MN2PR20MB297361CA3C29C236D6D8F6F4CAD60@MN2PR20MB2973.namprd20.prod.outlook.com>
 <CAKv+Gu-xWxZ58tzyYoH_jDKfJoM+KzOWWpzCeHEmOXQ39Bv15g@mail.gmail.com>
 <d6d0b155-476b-d495-3418-4b171003cdd7@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <d6d0b155-476b-d495-3418-4b171003cdd7@gmail.com>
User-Agent: Mutt/1.12.1 (2019-06-15)
Sender: linux-crypto-owner@vger.kernel.org
Precedence: bulk

On Sun, Aug 11, 2019 at 01:12:56PM +0200, Milan Broz wrote:
> On 10/08/2019 06:39, Ard Biesheuvel wrote:
> > Truncated IVs are a huge issue, since we already expose the correct
> > API via AF_ALG (without any restrictions on how many of the IV bits
> > are populated), and apparently, if your AF_ALG request for xts(aes)
> > happens to be fulfilled by the CAAM driver and your implementation
> > uses more than 64 bits for the IV, the top bits get truncated silently
> > and your data might get eaten.
> 
> Actually, I think we have already serious problem with in in kernel (no AF_ALG needed).
> 
> I do not have the hardware, but please could you check that dm-crypt big-endian IV
> (plain64be) produces the same output on CAAM?
> 
> It is 64bit IV, but big-endian and we use size of cipher block (16bytes) here,
> so the first 8 bytes are zero in this case.
> 
> I would expect data corruption in comparison to generic implementation,
> if it supports only the first 64bit...
> 
> Try this:
> 
> # create small null device of 8 sectors,  we use zeroes as fixed ciphertext
> dmsetup create zero --table "0 8 zero"
> 
> # create crypt device on top of it (with some key), using plain64be IV
> dmsetup create crypt --table "0 8 crypt aes-xts-plain64be e8cfa3dbfe373b536be43c5637387786c01be00ba5f730aacb039e86f3eb72f3 0 /dev/mapper/zero 0"
> 
> # and compare it with and without your driver, this is what I get here:
> # sha256sum /dev/mapper/crypt 
> 532f71198d0d84d823b8e410738c6f43bc3e149d844dd6d37fa5b36d150501e1  /dev/mapper/crypt
> # dmsetup remove crypt
> 
> You can try little-endian version (plain64), this should always work even with CAAM
> dmsetup create crypt --table "0 8 crypt aes-xts-plain64 e8cfa3dbfe373b536be43c5637387786c01be00ba5f730aacb039e86f3eb72f3 0 /dev/mapper/zero 0"
> 
> # sha256sum /dev/mapper/crypt 
> f17abd27dedee4e539758eabdb6c15fa619464b509cf55f16433e6a25da42857  /dev/mapper/crypt
> # dmsetup remove crypt
> 
> # dmsetup remove zero
> 
> 
> If you get different plaintext in the first case, your driver is actually creating
> data corruption in this configuration and it should be fixed!
> (Only the first sector must be the same, because it has IV == 0.)
> 
> Milan
> 
> p.s.
> If you ask why we have this IV, it was added per request to allow map some chipset-based
> encrypted drives directly. I guess it is used for some data forensic things.
> 

Also, if the CAAM driver is really truncating the IV for "xts(aes)", it should
already be failing the extra crypto self-tests, since the fuzz testing in
test_skcipher_vs_generic_impl() uses random IVs.

- Eric