static int __xts_crypt()

in crypto/aes-neonbs-glue.c [271:374]

• 83 lines of code
• 17 McCabe index (conditional complexity)

static int __xts_crypt(struct skcipher_request *req, bool encrypt,
		       void (*fn)(u8 out[], u8 const in[], u8 const rk[],
				  int rounds, int blocks, u8 iv[]))
{
	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
	struct aesbs_xts_ctx *ctx = crypto_skcipher_ctx(tfm);
	int tail = req->cryptlen % (8 * AES_BLOCK_SIZE);
	struct scatterlist sg_src[2], sg_dst[2];
	struct skcipher_request subreq;
	struct scatterlist *src, *dst;
	struct skcipher_walk walk;
	int nbytes, err;
	int first = 1;
	u8 *out, *in;

	if (req->cryptlen < AES_BLOCK_SIZE)
		return -EINVAL;

	/* ensure that the cts tail is covered by a single step */
	if (unlikely(tail > 0 && tail < AES_BLOCK_SIZE)) {
		int xts_blocks = DIV_ROUND_UP(req->cryptlen,
					      AES_BLOCK_SIZE) - 2;

		skcipher_request_set_tfm(&subreq, tfm);
		skcipher_request_set_callback(&subreq,
					      skcipher_request_flags(req),
					      NULL, NULL);
		skcipher_request_set_crypt(&subreq, req->src, req->dst,
					   xts_blocks * AES_BLOCK_SIZE,
					   req->iv);
		req = &subreq;
	} else {
		tail = 0;
	}

	err = skcipher_walk_virt(&walk, req, false);
	if (err)
		return err;

	while (walk.nbytes >= AES_BLOCK_SIZE) {
		unsigned int blocks = walk.nbytes / AES_BLOCK_SIZE;

		if (walk.nbytes < walk.total || walk.nbytes % AES_BLOCK_SIZE)
			blocks = round_down(blocks,
					    walk.stride / AES_BLOCK_SIZE);

		out = walk.dst.virt.addr;
		in = walk.src.virt.addr;
		nbytes = walk.nbytes;

		kernel_neon_begin();
		if (likely(blocks > 6)) { /* plain NEON is faster otherwise */
			if (first)
				neon_aes_ecb_encrypt(walk.iv, walk.iv,
						     ctx->twkey,
						     ctx->key.rounds, 1);
			first = 0;

			fn(out, in, ctx->key.rk, ctx->key.rounds, blocks,
			   walk.iv);

			out += blocks * AES_BLOCK_SIZE;
			in += blocks * AES_BLOCK_SIZE;
			nbytes -= blocks * AES_BLOCK_SIZE;
		}

		if (walk.nbytes == walk.total && nbytes > 0)
			goto xts_tail;

		kernel_neon_end();
		err = skcipher_walk_done(&walk, nbytes);
	}

	if (err || likely(!tail))
		return err;

	/* handle ciphertext stealing */
	dst = src = scatterwalk_ffwd(sg_src, req->src, req->cryptlen);
	if (req->dst != req->src)
		dst = scatterwalk_ffwd(sg_dst, req->dst, req->cryptlen);

	skcipher_request_set_crypt(req, src, dst, AES_BLOCK_SIZE + tail,
				   req->iv);

	err = skcipher_walk_virt(&walk, req, false);
	if (err)
		return err;

	out = walk.dst.virt.addr;
	in = walk.src.virt.addr;
	nbytes = walk.nbytes;

	kernel_neon_begin();
xts_tail:
	if (encrypt)
		neon_aes_xts_encrypt(out, in, ctx->cts.key_enc, ctx->key.rounds,
				     nbytes, ctx->twkey, walk.iv, first ?: 2);
	else
		neon_aes_xts_decrypt(out, in, ctx->cts.key_dec, ctx->key.rounds,
				     nbytes, ctx->twkey, walk.iv, first ?: 2);
	kernel_neon_end();

	return skcipher_walk_done(&walk, 0);
}