Re: [PATCH] crypto: ccp

* Re: [PATCH] crypto: ccp - Assign DMA commands to the channel's CCP
       [not found] <20170310180341.21062.82465.stgit@taos>
@ 2017-03-13 19:35 ` Gary R Hook
  2017-03-14  7:17   ` Stephan Müller
  0 siblings, 1 reply; 6+ messages in thread
From: Gary R Hook @ 2017-03-13 19:35 UTC (permalink / raw)
  To: linux-crypto; +Cc: Stephan Müller

On 03/03/2017 7:15 AM, Stephan Mueller wrote:

> Am Donnerstag, 2. März 2017, 22:26:54 CET schrieb Gary R Hook:
>
> Hi Gary,

Thanks for your comments, Stephan.

>
> > A version 5 device provides the primitive commands
> > required for AES GCM. This patch adds support for
> > en/decryption.
> >
> > Signed-off-by: Gary R Hook <gary.hook@amd.com>
> > ---
> >  drivers/crypto/ccp/Makefile                |    1
> >  drivers/crypto/ccp/ccp-crypto-aes-galois.c |  257
> > ++++++++++++++++++++++++++++ drivers/crypto/ccp/ccp-crypto-main.c       |
> > 12 +
> >  drivers/crypto/ccp/ccp-crypto.h            |   14 ++
> >  drivers/crypto/ccp/ccp-dev-v5.c            |    2
> >  drivers/crypto/ccp/ccp-dev.h               |    1
> >  drivers/crypto/ccp/ccp-ops.c               |  252
> > +++++++++++++++++++++++++++ include/linux/ccp.h                        |
> > 9 +
> >  8 files changed, 548 insertions(+)
> >  create mode 100644 drivers/crypto/ccp/ccp-crypto-aes-galois.c
> >
> > diff --git a/drivers/crypto/ccp/ccp-crypto-aes-galois.c
> > b/drivers/crypto/ccp/ccp-crypto-aes-galois.c new file mode 100644
> > index 0000000..8bc18c9
> > --- /dev/null
> > +++ b/drivers/crypto/ccp/ccp-crypto-aes-galois.c
> > @@ -0,0 +1,257 @@
> > +/*
> > + * AMD Cryptographic Coprocessor (CCP) AES GCM crypto API support
> > + *
> > + * Copyright (C) 2016 Advanced Micro Devices, Inc.
> > + *
> > + * Author: Gary R Hook <gary.hook@amd.com>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <linux/sched.h>
> > +#include <linux/delay.h>
> > +#include <linux/scatterlist.h>
> > +#include <linux/crypto.h>
> > +#include <crypto/internal/aead.h>
> > +#include <crypto/algapi.h>
> > +#include <crypto/aes.h>
> > +#include <crypto/ctr.h>
> > +#include <crypto/scatterwalk.h>
> > +#include <linux/delay.h>
> > +
> > +#include "ccp-crypto.h"
> > +
> > +#define    AES_GCM_IVSIZE  12
> > +
> > +static int ccp_aes_gcm_complete(struct crypto_async_request *async_req, int
> > ret) +{
> > +   return ret;
> > +}
> > +
> > +static int ccp_aes_gcm_setkey(struct crypto_aead *tfm, const u8 *key,
> > +                         unsigned int key_len)
> > +{
> > +   struct ccp_ctx *ctx = crypto_aead_ctx(tfm);
> > +
> > +   switch (key_len) {
> > +   case AES_KEYSIZE_128:
> > +           ctx->u.aes.type = CCP_AES_TYPE_128;
> > +           break;
> > +   case AES_KEYSIZE_192:
> > +           ctx->u.aes.type = CCP_AES_TYPE_192;
> > +           break;
> > +   case AES_KEYSIZE_256:
> > +           ctx->u.aes.type = CCP_AES_TYPE_256;
> > +           break;
> > +   default:
> > +           crypto_aead_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
> > +           return -EINVAL;
> > +   }
> > +
> > +   ctx->u.aes.mode = CCP_AES_MODE_GCM;
> > +   ctx->u.aes.key_len = key_len;
> > +
> > +   memcpy(ctx->u.aes.key, key, key_len);
> > +   sg_init_one(&ctx->u.aes.key_sg, ctx->u.aes.key, key_len);
> > +
> > +   return 0;
> > +}
> > +
> > +static int ccp_aes_gcm_setauthsize(struct crypto_aead *tfm,
> > +                              unsigned int authsize)
> > +{
> > +   return 0;
> > +}
> > +
> > +static int ccp_aes_gcm_crypt(struct aead_request *req, bool encrypt)
> > +{
> > +   struct crypto_aead *tfm = crypto_aead_reqtfm(req);
> > +   struct ccp_ctx *ctx = crypto_aead_ctx(tfm);
> > +   struct ccp_aes_req_ctx *rctx = aead_request_ctx(req);
> > +   struct scatterlist *iv_sg = NULL;
> > +   unsigned int iv_len = 0;
> > +   int i;
> > +   int ret = 0;
> > +
> > +   if (!ctx->u.aes.key_len)
> > +           return -EINVAL;
> > +
> > +   if (ctx->u.aes.mode != CCP_AES_MODE_GCM)
> > +           return -EINVAL;
> > +
> > +   if (!req->iv)
> > +           return -EINVAL;
> > +
> > +   /*
> > +    * 5 parts:
> > +    *   plaintext/ciphertext input
> > +    *   AAD
> > +    *   key
> > +    *   IV
> > +    *   Destination+tag buffer
> > +    */
> > +
> > +   /* According to the way AES GCM has been implemented here,
> > +    * per RFC 4106 it seems, the provided IV is fixed at 12 bytes,
>
> When you have that restriction, should the cipher be called rfc4106(gcm(aes))?
>
> But then, the key is 4 bytes longer than a normal AES key as it contains the
> leading 32 bits of the IV.

I had my wires crossed due to an incomplete understanding of an AEAD cipher
in general, and GCM in particular. I'm hopeful that someone can help me
understand:

For the AES GCM encryption tests in testmgr.h, where there is an IV, 
they're all
12 bytes in length. As I understand AES GCM the IV can be anywhere from 
1 to 2^64
bits in length; the value of 96 makes for convenience and efficiency. 
But it's
neither a requirement nor restriction.

There are no tests (in testmgr.h) that use an IV length other than  0 or 96.
My comment about RFC4106 has to do with requiring an IV 0f 96 bits + a 
word that
is incremented for each block (making every nonce unique, per the 
requirement).
But let's ignore that, please.

It looks as if:

What seems to be missing is the ability to register a (GCM) transform 
that can
handle an IV of arbitrary (allowable) length. I have to specify the 
length (ivsize)
when I register an algorithm, and everything I see in the existing code 
appears
to expect a GCM ivsize to be 96 bits, period (or zero). This is what I 
meant when
I referenced RFC4106: I perceive restrictions not in my code, but n the 
way GCM seems
to be supported in the crypto AEAD framework. A complete GCM 
implementation would not
seem to have a restriction to a specific IV length (rather, a range of 
allowed
values).

Is my reading of the GCM description in error? Do we need/want the ability
to have a flexible IV length for GCM? What am I not understanding?

For reference, I'm working from the NIST doc:
http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf

>
> > +    * occupies the beginning of the IV array. Write a 32-bit
> > +    * integer after that (bytes 13-16) with a value of "1".
> > +    */
> > +   memcpy(rctx->iv, req->iv, AES_GCM_IVSIZE);
> > +   for (i = 0; i < 3; i++)
> > +           rctx->iv[i + AES_GCM_IVSIZE] = 0;
> > +   rctx->iv[AES_BLOCK_SIZE - 1] = 1;
> > +
> > +   /* Set up a scatterlist for the IV */
> > +   iv_sg = &rctx->iv_sg;
> > +   iv_len = AES_BLOCK_SIZE;
> > +   sg_init_one(iv_sg, rctx->iv, iv_len);
> > +
> > +   /* The AAD + plaintext are concatenated in the src buffer */
> > +   memset(&rctx->cmd, 0, sizeof(rctx->cmd));
> > +   INIT_LIST_HEAD(&rctx->cmd.entry);
> > +   rctx->cmd.engine = CCP_ENGINE_AES;
> > +   rctx->cmd.u.aes.type = ctx->u.aes.type;
> > +   rctx->cmd.u.aes.mode = ctx->u.aes.mode;
> > +   rctx->cmd.u.aes.action =
> > +           (encrypt) ? CCP_AES_ACTION_ENCRYPT : CCP_AES_ACTION_DECRYPT;
>
> Instead of this condition, why not changing the encrypt/decrypt function to
> directly provide the enc/dec variables?

Our existing code that uses this construct doesn't do that, but I
have no problem with the idea. Done.

> > +   rctx->cmd.u.aes.key = &ctx->u.aes.key_sg;
> > +   rctx->cmd.u.aes.key_len = ctx->u.aes.key_len;
> > +   rctx->cmd.u.aes.iv = iv_sg;
> > +   rctx->cmd.u.aes.iv_len = iv_len;
> > +   rctx->cmd.u.aes.src = req->src;
> > +   rctx->cmd.u.aes.src_len = req->cryptlen;
> > +   rctx->cmd.u.aes.aad_len = req->assoclen;
>
> Just to be on the safe side: is the implementation good when cryptlen or
> assoclen is 0?

The engine has been designed to handle those two conditions. I've been
watching the discussions around these issues.

The first encryption test in testmgr.h has no input data nor IV. This
implementation passes that test.

The second encryption test in testmgr.h has input data but no IV, and this
implementation passes.

Is that an acceptable validation, or do we need more?

Thanks,
Gary

-- 
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