Re: [PATCH 06/12] RISC-V: crypto: add accelerated AES-CBC/CTR/ECB/XTS implementations

[Jerry Shih]

On Nov 2, 2023, at 13:16, Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> On Thu, Oct 26, 2023 at 02:36:38AM +0800, Jerry Shih wrote:
>> +config CRYPTO_AES_BLOCK_RISCV64
>> +	default y if RISCV_ISA_V
>> +	tristate "Ciphers: AES, modes: ECB/CBC/CTR/XTS"
>> +	depends on 64BIT && RISCV_ISA_V
>> +	select CRYPTO_AES_RISCV64
>> +	select CRYPTO_SKCIPHER
>> +	help
>> +	  Length-preserving ciphers: AES cipher algorithms (FIPS-197)
>> +	  with block cipher modes:
>> +	  - ECB (Electronic Codebook) mode (NIST SP 800-38A)
>> +	  - CBC (Cipher Block Chaining) mode (NIST SP 800-38A)
>> +	  - CTR (Counter) mode (NIST SP 800-38A)
>> +	  - XTS (XOR Encrypt XOR Tweakable Block Cipher with Ciphertext
>> +	    Stealing) mode (NIST SP 800-38E and IEEE 1619)
>> +
>> +	  Architecture: riscv64 using:
>> +	  - Zvbb vector extension (XTS)
>> +	  - Zvkb vector crypto extension (CTR/XTS)
>> +	  - Zvkg vector crypto extension (XTS)
>> +	  - Zvkned vector crypto extension
> 
> Maybe list Zvkned first since it's the most important one in this context.

Fixed.


>> +#define AES_BLOCK_VALID_SIZE_MASK (~(AES_BLOCK_SIZE - 1))
>> +#define AES_BLOCK_REMAINING_SIZE_MASK (AES_BLOCK_SIZE - 1)
> 
> I think it would be easier to read if these values were just used directly.

Fixed.

>> +static int ecb_encrypt(struct skcipher_request *req)
>> +{
>> +	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
>> +	const struct riscv64_aes_ctx *ctx = crypto_skcipher_ctx(tfm);
>> +	struct skcipher_walk walk;
>> +	unsigned int nbytes;
>> +	int err;
>> +
>> +	/* If we have error here, the `nbytes` will be zero. */
>> +	err = skcipher_walk_virt(&walk, req, false);
>> +	while ((nbytes = walk.nbytes)) {
>> +		kernel_vector_begin();
>> +		rv64i_zvkned_ecb_encrypt(walk.src.virt.addr, walk.dst.virt.addr,
>> +					 nbytes & AES_BLOCK_VALID_SIZE_MASK,
>> +					 &ctx->key);
>> +		kernel_vector_end();
>> +		err = skcipher_walk_done(
>> +			&walk, nbytes & AES_BLOCK_REMAINING_SIZE_MASK);
>> +	}
>> +
>> +	return err;
>> +}
> 
> There's no fallback for !crypto_simd_usable() here.  I really like it this way.
> However, for it to work (for skciphers and aeads), RISC-V needs to allow the
> vector registers to be used in softirq context.  Is that already the case?

I turn to use simd skcipher interface. More details will be in the v2 patch set.

>> +/* ctr */
>> +static int ctr_encrypt(struct skcipher_request *req)
>> +{
>> +	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
>> +	const struct riscv64_aes_ctx *ctx = crypto_skcipher_ctx(tfm);
>> +	struct skcipher_walk walk;
>> +	unsigned int ctr32;
>> +	unsigned int nbytes;
>> +	unsigned int blocks;
>> +	unsigned int current_blocks;
>> +	unsigned int current_length;
>> +	int err;
>> +
>> +	/* the ctr iv uses big endian */
>> +	ctr32 = get_unaligned_be32(req->iv + 12);
>> +	err = skcipher_walk_virt(&walk, req, false);
>> +	while ((nbytes = walk.nbytes)) {
>> +		if (nbytes != walk.total) {
>> +			nbytes &= AES_BLOCK_VALID_SIZE_MASK;
>> +			blocks = nbytes / AES_BLOCK_SIZE;
>> +		} else {
>> +			/* This is the last walk. We should handle the tail data. */
>> +			blocks = (nbytes + (AES_BLOCK_SIZE - 1)) /
>> +				 AES_BLOCK_SIZE;
> 
> '(nbytes + (AES_BLOCK_SIZE - 1)) / AES_BLOCK_SIZE' can be replaced with
> 'DIV_ROUND_UP(nbytes, AES_BLOCK_SIZE)'

Fixed.

>> +static int xts_crypt(struct skcipher_request *req, aes_xts_func func)
>> +{
>> +	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
>> +	const struct riscv64_aes_xts_ctx *ctx = crypto_skcipher_ctx(tfm);
>> +	struct skcipher_request sub_req;
>> +	struct scatterlist sg_src[2], sg_dst[2];
>> +	struct scatterlist *src, *dst;
>> +	struct skcipher_walk walk;
>> +	unsigned int walk_size = crypto_skcipher_walksize(tfm);
>> +	unsigned int tail_bytes;
>> +	unsigned int head_bytes;
>> +	unsigned int nbytes;
>> +	unsigned int update_iv = 1;
>> +	int err;
>> +
>> +	/* xts input size should be bigger than AES_BLOCK_SIZE */
>> +	if (req->cryptlen < AES_BLOCK_SIZE)
>> +		return -EINVAL;
>> +
>> +	/*
>> +	 * The tail size should be small than walk_size. Thus, we could make sure the
>> +	 * walk size for tail elements could be bigger than AES_BLOCK_SIZE.
>> +	 */
>> +	if (req->cryptlen <= walk_size) {
>> +		tail_bytes = req->cryptlen;
>> +		head_bytes = 0;
>> +	} else {
>> +		if (req->cryptlen & AES_BLOCK_REMAINING_SIZE_MASK) {
>> +			tail_bytes = req->cryptlen &
>> +				     AES_BLOCK_REMAINING_SIZE_MASK;
>> +			tail_bytes = walk_size + tail_bytes - AES_BLOCK_SIZE;
>> +			head_bytes = req->cryptlen - tail_bytes;
>> +		} else {
>> +			tail_bytes = 0;
>> +			head_bytes = req->cryptlen;
>> +		}
>> +	}
>> +
>> +	riscv64_aes_encrypt_zvkned(&ctx->ctx2, req->iv, req->iv);
>> +
>> +	if (head_bytes && tail_bytes) {
>> +		skcipher_request_set_tfm(&sub_req, tfm);
>> +		skcipher_request_set_callback(
>> +			&sub_req, skcipher_request_flags(req), NULL, NULL);
>> +		skcipher_request_set_crypt(&sub_req, req->src, req->dst,
>> +					   head_bytes, req->iv);
>> +		req = &sub_req;
>> +	}
>> +
>> +	if (head_bytes) {
>> +		err = skcipher_walk_virt(&walk, req, false);
>> +		while ((nbytes = walk.nbytes)) {
>> +			if (nbytes == walk.total)
>> +				update_iv = (tail_bytes > 0);
>> +
>> +			nbytes &= AES_BLOCK_VALID_SIZE_MASK;
>> +			kernel_vector_begin();
>> +			func(walk.src.virt.addr, walk.dst.virt.addr, nbytes,
>> +			     &ctx->ctx1.key, req->iv, update_iv);
>> +			kernel_vector_end();
>> +
>> +			err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
>> +		}
>> +		if (err || !tail_bytes)
>> +			return err;
>> +
>> +		dst = src = scatterwalk_next(sg_src, &walk.in);
>> +		if (req->dst != req->src)
>> +			dst = scatterwalk_next(sg_dst, &walk.out);
>> +		skcipher_request_set_crypt(req, src, dst, tail_bytes, req->iv);
>> +	}
>> +
>> +	/* tail */
>> +	err = skcipher_walk_virt(&walk, req, false);
>> +	if (err)
>> +		return err;
>> +	if (walk.nbytes != tail_bytes)
>> +		return -EINVAL;
>> +	kernel_vector_begin();
>> +	func(walk.src.virt.addr, walk.dst.virt.addr, walk.nbytes,
>> +	     &ctx->ctx1.key, req->iv, 0);
>> +	kernel_vector_end();
>> +
>> +	return skcipher_walk_done(&walk, 0);
>> +}
> 
> This function looks a bit weird.  I see it's also the only caller of the
> scatterwalk_next() function that you're adding.  I haven't looked at this super
> closely, but I expect that there's a cleaner way of handling the "tail" than
> this -- maybe use scatterwalk_map_and_copy() to copy from/to a stack buffer?
> 
> - Eric

I put more comments in v2 patch set. Hope it will be more clear.
Even though we use `scatterwalk_map_and_copy()`, it still use
`scatterwalk_ffwd()` inside. The `scatterwalk_next()` is used
for just `moving the next scatterlist` from from the previous
walk instead of iterating from the head.

-Jerry