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
