Re: [PATCH v9 4/4] crypto: Add Allwinner Security System crypto accelerator

[Corentin LABBE]

Le 17/05/2015 10:45, Boris Brezillon a écrit :
> Hi Corentin,
> 
> I started to review this new version, and I still think there's
> something wrong with the way your processing crypto requests.
> From my POV this is not asynchronous at all (see my comments inline),
> but maybe Herbert can confirm that.
> I haven't reviewed the hash part yet, but I guess it has the same
> problem.

For resuming your conversation with Herbert, I have removed all CRYPTO_ALG_ASYNC flags.

> 
> Best Regards,
> 
> Boris
> 
> On Thu, 14 May 2015 14:59:01 +0200
> LABBE Corentin <clabbe.montjoie@xxxxxxxxx> wrote:
> 
>> Add support for the Security System included in Allwinner SoC A20.
>> The Security System is a hardware cryptographic accelerator that support:
>> - MD5 and SHA1 hash algorithms
>> - AES block cipher in CBC/ECB mode with 128/196/256bits keys.
>> - DES and 3DES block cipher in CBC/ECB mode
>>
>> Signed-off-by: LABBE Corentin <clabbe.montjoie@xxxxxxxxx>
>> ---
> 
> [...]
> 
>> +
>> +int sun4i_ss_aes_poll(struct ablkcipher_request *areq, u32 mode)
>> +{
>> +	u32 spaces;
>> +	struct crypto_ablkcipher *tfm = crypto_ablkcipher_reqtfm(areq);
>> +	struct sun4i_tfm_ctx *op = crypto_ablkcipher_ctx(tfm);
>> +	struct sun4i_ss_ctx *ss = op->ss;
>> +	unsigned int ivsize = crypto_ablkcipher_ivsize(tfm);
>> +	/* when activating SS, the default FIFO space is 32 */
>> +	u32 rx_cnt = 32;
>> +	u32 tx_cnt = 0;
>> +	u32 v;
>> +	int i, sgnum, err = 0;
>> +	unsigned int ileft = areq->nbytes;
>> +	unsigned int oleft = areq->nbytes;
>> +	unsigned int todo, miter_flag;
>> +	unsigned long flags;
>> +	struct sg_mapping_iter mi, mo;
>> +	unsigned int oi, oo; /* offset for in and out */
>> +
>> +	if (areq->nbytes == 0)
>> +		return 0;
>> +
>> +	if (areq->info == NULL) {
>> +		dev_err(ss->dev, "ERROR: Empty IV\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	if (areq->src == NULL || areq->dst == NULL) {
>> +		dev_err(ss->dev, "ERROR: Some SGs are NULL\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	spin_lock_irqsave(&ss->slock, flags);
> 
> Do you really need to take this lock so early ?
> BTW, what is this lock protecting ?

As I have written in the header, the spinlock protect the usage of the device.
In this case, I need to lock just before writing the key in the device.

> 
> IMHO, taking a spinlock and disabling irqs for the whole time you're
> executing a crypto request is not a good idea (it will prevent all
> other irqs from running, and potentially introduce latencies in other
> parts of the kernel).

Since crypto operation could be called by software interrupt, I need to disable them.
(Confirmed by http://www.makelinux.net/ldd3/chp-5-sect-5 5.5.3)

> 
> What you can do though is declare the following fields in your crypto
> engine struct (sun4i_ss_ctx):
> - a crypto request queue (struct crypto_queue [1])
> - a crypto_async_request variable storing the request being processed
> - a lock protecting the queue and the current request variable
> 
> This way you'll only have to take the lock when queuing or dequeuing a
> request.
> 
> Another comment, your implementation does not seem to be asynchronous at
> all: you're blocking the caller until its crypto request is complete.
> 
> 
>> +
>> +	for (i = 0; i < op->keylen; i += 4)
>> +		writel(*(op->key + i / 4), ss->base + SS_KEY0 + i);
>> +
>> +	if (areq->info != NULL) {
>> +		for (i = 0; i < 4 && i < ivsize / 4; i++) {
>> +			v = *(u32 *)(areq->info + i * 4);
>> +			writel(v, ss->base + SS_IV0 + i * 4);
>> +		}
>> +	}
>> +	writel(mode, ss->base + SS_CTL);
>> +
>> +	sgnum = sg_nents(areq->src);
>> +	if (sgnum == 1)
>> +		miter_flag = SG_MITER_FROM_SG | SG_MITER_ATOMIC;
>> +	else
>> +		miter_flag = SG_MITER_FROM_SG;
> 
> 
> Why is the ATOMIC flag depending on the number of sg elements.
> IMO it should only depends on the context you're currently in, and in
> your specific case, you're always in atomic context since you've taken
> a spinlock (and disabled irqs) a few lines above.
> 
> Note that with the approach I previously proposed, you can even get rid
> of this ATMIC flag (or always set it depending on the context you're in
> when dequeuing the crypto requests).
> 

For sg_miter, the ATOMIC flag control the usage of kmap vs kmap_atomic.
Since kmap_atomic must not be held too long, I use them only for short crypto operation.
But I need to rebench for be sure that using kmap_atomic give faster result.
If I keep that, I will add a comment explaining that.

> 
>> +	sg_miter_start(&mi, areq->src, sgnum, miter_flag);
>> +	sgnum = sg_nents(areq->dst);
>> +	if (sgnum == 1)
>> +		miter_flag = SG_MITER_TO_SG | SG_MITER_ATOMIC;
>> +	else
>> +		miter_flag = SG_MITER_TO_SG;
> 
> Ditto
> 
>> +	sg_miter_start(&mo, areq->dst, sgnum, miter_flag);
>> +	sg_miter_next(&mi);
>> +	sg_miter_next(&mo);
>> +	if (mi.addr == NULL || mo.addr == NULL) {
>> +		err = -EINVAL;
>> +		goto release_ss;
>> +	}
>> +
>> +	ileft = areq->nbytes / 4;
>> +	oleft = areq->nbytes / 4;
>> +	oi = 0;
>> +	oo = 0;
>> +	do {
>> +		todo = min3(rx_cnt, ileft, (mi.length - oi) / 4);
>> +		if (todo > 0) {
>> +			ileft -= todo;
>> +			writesl(ss->base + SS_RXFIFO, mi.addr + oi, todo);
> 
> Is there anything guaranteeing that your pointer is aligned on a 4 byte
> boundary ? If that's not the case, I guess you should copy it in a
> temporary variable before using writesl.

The cra_alignmask is my guarantee.

> 
>> +			oi += todo * 4;
>> +		}
>> +		if (oi == mi.length) {
>> +			sg_miter_next(&mi);
>> +			oi = 0;
>> +		}
>> +
>> +		ispaces = readl_relaxed(ss->base + SS_FCSR);
> 
> Is there a good reason for using the _relaxed version of readl/writel
> (the same comment applies a few lines below) ?

No, it is clearly a remaining of the times where all my read/write was with _relaxed.

> 
>> +		rx_cnt = SS_RXFIFO_SPACES(spaces);
>> +		tx_cnt = SS_TXFIFO_SPACES(spaces);
>> +
>> +		todo = min3(tx_cnt, oleft, (mo.length - oo) / 4);
>> +		if (todo > 0) {
>> +			oleft -= todo;
>> +			readsl(ss->base + SS_TXFIFO, mo.addr + oo, todo);
>> +			oo += todo * 4;
>> +		}
>> +		if (oo == mo.length) {
>> +			sg_miter_next(&mo);
>> +			oo = 0;
>> +		}
>> +	} while (mo.length > 0);
>> +
>> +release_ss:
>> +	sg_miter_stop(&mi);
>> +	sg_miter_stop(&mo);
>> +	writel_relaxed(0, ss->base + SS_CTL);
> 
> Ditto.
> 
>> +	spin_unlock_irqrestore(&ss->slock, flags);
>> +	return err;
>> +}
>> +
>> +/* Pure CPU driven way of doing DES/3DES with SS */
>> +int sun4i_ss_des_poll(struct ablkcipher_request *areq, u32 mode)
>> +{
>> +	struct crypto_ablkcipher *tfm = crypto_ablkcipher_reqtfm(areq);
>> +	struct sun4i_tfm_ctx *op = crypto_ablkcipher_ctx(tfm);
>> +	struct sun4i_ss_ctx *ss = op->ss;
>> +	int i, err = 0;
>> +	int no_chunk = 1;
>> +	struct scatterlist *in_sg = areq->src;
>> +	struct scatterlist *out_sg = areq->dst;
>> +	u8 kkey[256 / 8];
>> +
>> +	if (areq->nbytes == 0)
>> +		return 0;
>> +
>> +	if (areq->info == NULL) {
>> +		dev_err(ss->dev, "ERROR: Empty IV\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	if (areq->src == NULL || areq->dst == NULL) {
>> +		dev_err(ss->dev, "ERROR: Some SGs are NULL\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	/*
>> +	 * if we have only SGs with size multiple of 4,
>> +	 * we can use the SS AES function
>> +	 */
>> +	while (in_sg != NULL && no_chunk == 1) {
>> +		if ((in_sg->length % 4) != 0)
>> +			no_chunk = 0;
>> +		in_sg = sg_next(in_sg);
>> +	}
>> +	while (out_sg != NULL && no_chunk == 1) {
>> +		if ((out_sg->length % 4) != 0)
>> +			no_chunk = 0;
>> +		out_sg = sg_next(out_sg);
>> +	}
>> +
>> +	if (no_chunk == 1)
>> +		return sun4i_ss_aes_poll(areq, mode);
>> +
>> +	/*
>> +	 * if some SG are not multiple of 4bytes use a fallback
>> +	 * it is much easy and clean
>> +	 */
> 
> Hm, is this really the best solution. I mean, you can easily pack
> values from non aligned sg buffers so that you have only a 4 byte
> aligned buffers.
> Moreover, by doing this you'll end up with a single
> sun4i_ss_ablkcipher_poll function.
> 
> BTW, I wonder if there's anything preventing an AES crypto request to be
> forged the same way DES/3DES requests are (sg entries not aligned on 4
> bytes boundary).

There are two different problem: chunking and alignment.
The correct alignment is handled by the crypto API with the alignmask, so the driver do not need to care about it.
The chunking is the fact that I can have a SG with a size that is non multiple of 4.
For DES/3DES I handle this problem by using a fallback since DES/3DES was not my priority. (but yes I will handle it in the future)
For AES I have assumed that it cannot happen since no test in tcrypt check for it.
Since all SG I get was always a multiple of 16 (AES BLOCK SIZE) it was a sort of confirmation.

Herbert ? does am I right or a chunking test is missing for cbc(aes) in testmgr.h

> 
>> +	ablkcipher_request_set_tfm(areq, op->fallback);
>> +	for (i = 0; i < op->keylen; i++)
>> +		*(u32 *)(kkey + i * 4) = op->key[i];
>> +
>> +	err = crypto_ablkcipher_setkey(op->fallback, kkey, op->keylen);
>> +	if (err != 0) {
>> +		dev_err(ss->dev, "Cannot set key on fallback\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	if ((mode & SS_DECRYPTION) == SS_DECRYPTION)
>> +		err = crypto_ablkcipher_decrypt(areq);
>> +	else
>> +		err = crypto_ablkcipher_encrypt(areq);
>> +	ablkcipher_request_set_tfm(areq, tfm);
>> +	return err;
>> +}
> 
> [1]http://lxr.free-electrons.com/source/include/crypto/algapi.h#L68
> 

Thanks for your review.

LABBE Corentin

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