Re: [PATCH] crypto: mxs-dcp: handle zero-length skcipher requests

[Linmao Li <lilinmao@kylinos.cn>]

在 2026/8/31 23:01, Frank Li 写道:
> On Mon, Aug 31, 2026 at 08:42:20PM +0800, Linmao Li wrote:
>> [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>
>> 在 2026/8/29 3:25, Frank Li 写道:
>>> On Fri, Aug 28, 2026 at 05:32:09PM +0800, Linmao Li wrote:
>>>> [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>>>
>>>> Zero-length skcipher requests are valid no-ops, but MXS-DCP queues them.
>>> Any document show it? if return 0 when cryptelen, it is async, no
>>> call crypto_request_complete.
>>    Yes. CRYPTO_ALG_ASYNC means that the implementation may complete a
>>    request asynchronously, not that every request must do so.
>>
>>    A return value of 0 indicates synchronous completion.  Only
>>    -EINPROGRESS and -EBUSY cause crypto_wait_req() to wait for the
>>    completion callback.  The existing fallback path relies on the same
>>    semantics.
>>
>>    There is also a direct precedent in commit 8a4e047c6cc0
>>    ("crypto: marvell/cesa - Handle zero-length skcipher requests").
>>    Marvell CESA registers asynchronous skcipher algorithms but handles a
>>    zero-length request with:
>>
>>            if (!req->cryptlen)
>>                    return 0;
> Thanks, but still not answer my question,
>
> Any document show "Zero-length skcipher requests are valid no-ops", why
> not API direct return 0, instead of pass to every driver to check it.
>
> I suppose it should be checked before call driver's callback.
   You are right; I could not find an explicit Crypto API document defining
   the zero-length behavior, so the wording "valid no-ops" was too broad.

   With the current API, simply returning 0 in the core for every
   zero-length request would change XTS semantics, since the generic XTS
   implementation returns -EINVAL.  MXS-DCP only implements ECB and CBC
   here, whose generic implementations currently return 0.  Handling it in
   the driver therefore matches existing behavior; centralizing this would
   require algorithm-specific length information.

   I agree that the commit message should describe this as existing ECB/CBC
   behavior rather than a general skcipher API rule.

   Thanks,
   Linmao
>
> Frank
>
>>
>> Thanks,
>> Linmao
>>
>>> Frank
>>>
>>>> When such a request reaches the worker, last_out_len remains zero. The
>>>> CBC completion path then subtracts AES_BLOCK_SIZE from this unsigned
>>>> value when updating the IV, causing the offset to underflow. On
>>>> decryption, the resulting source address precedes aes_in_buf.
>>>>
>>>> Return success before enqueueing zero-length requests. This avoids the
>>>> invalid source access and leaves the IV unchanged for a no-op.
>>>>
>>>> Fixes: fadd7a6e616b ("crypto: mxs-dcp - Fix AES issues")
>>>> Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
>>>> ---
>>>>    drivers/crypto/mxs-dcp.c | 3 +++
>>>>    1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/crypto/mxs-dcp.c b/drivers/crypto/mxs-dcp.c
>>>> index 133ebc998236..60794b4d49fa 100644
>>>> --- a/drivers/crypto/mxs-dcp.c
>>>> +++ b/drivers/crypto/mxs-dcp.c
>>>> @@ -473,6 +473,9 @@ static int mxs_dcp_aes_enqueue(struct skcipher_request *req, int enc, int ecb)
>>>>           struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
>>>>           int ret;
>>>>
>>>> +       if (!req->cryptlen)
>>>> +               return 0;
>>>> +
>>>>           if (unlikely(actx->key_len != AES_KEYSIZE_128 && !actx->key_referenced))
>>>>                   return mxs_dcp_block_fallback(req, enc);
>>>>
>>>>
>>>> base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
>>>> --
>>>> 2.25.1
>>>>
>>>>