On 8/14/2017 10:59 AM, Gilad Ben-Yossef wrote: > Hi, > > On Thu, Jun 29, 2017 at 1:19 PM, Horia Geantă <horia.geanta@xxxxxxx> wrote: >> On 6/28/2017 4:42 PM, Horia Geantă wrote: >>> On 6/28/2017 4:27 PM, David Gstir wrote: >>>> Certain cipher modes like CTS expect the IV (req->info) of >>>> ablkcipher_request (or equivalently req->iv of skcipher_request) to >>>> contain the last ciphertext block when the {en,de}crypt operation is done. >>>> This is currently not the case for the CAAM driver which in turn breaks >>>> e.g. cts(cbc(aes)) when the CAAM driver is enabled. >>>> >>>> This patch fixes the CAAM driver to properly set the IV after the >>>> {en,de}crypt operation of ablkcipher finishes. >>>> >>>> This issue was revealed by the changes in the SW CTS mode in commit >>>> 0605c41cc53ca ("crypto: cts - Convert to skcipher") >>>> >>>> Cc: <stable@xxxxxxxxxxxxxxx> # 4.8+ >>>> Signed-off-by: David Gstir <david@xxxxxxxxxxxxx> >>> Reviewed-by: Horia Geantă <horia.geanta@xxxxxxx> >>> >> Btw, instead of updating the IV in SW, CAAM engine could be programmed >> to do it - by saving the Context Register of the AES accelerator. >> >> Unfortunately this would require changes in quite a few places: shared >> descriptor, HW S/G generation logic, IV dma (un)mapping and maybe others. >> >> So it's better to have this fix now (which, considering size, is >> appropriate for -stable) and later, if needed, offload IV updating in HW. >> > > My apologies for reviving this thread from the dead, but doesn't the patch fail > for in-place decryption since we are copying from req->dst after > the operation is done, and therefore it no longer contains the ciphertext? > You are right, thanks! Will follow up with a fix. Though cts(cbc(aes)) in particular is working, see below. > I'm asking since I ran into a similar issue in the ccree driver and thought > to deploy a similar fix but could not convince myself why this works. > IIUC cts(cbc(aes)) in-place decryption (with cbc(aes) offloaded to CAAM engine) works since SW implementation of cts, when performing the ciphertext stealing phase in cts_cbc_decrypt() does not use req->iv, but a previously value, saved before staring decryption in crypto_cts_decrypt(): if (cbc_blocks <= 1) memcpy(space, req->iv, bsize); else scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize, bsize, 0); Horia