static int __maybe_unused xts_decrypt()

in crypto/aes-glue.c [560:631]

• 57 lines of code
• 10 McCabe index (conditional complexity)

static int __maybe_unused xts_decrypt(struct skcipher_request *req)
{
	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
	struct crypto_aes_xts_ctx *ctx = crypto_skcipher_ctx(tfm);
	int err, first, rounds = 6 + ctx->key1.key_length / 4;
	int tail = req->cryptlen % AES_BLOCK_SIZE;
	struct scatterlist sg_src[2], sg_dst[2];
	struct skcipher_request subreq;
	struct scatterlist *src, *dst;
	struct skcipher_walk walk;

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

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

	if (unlikely(tail > 0 && walk.nbytes < walk.total)) {
		int xts_blocks = DIV_ROUND_UP(req->cryptlen,
					      AES_BLOCK_SIZE) - 2;

		skcipher_walk_abort(&walk);

		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;
		err = skcipher_walk_virt(&walk, req, false);
	} else {
		tail = 0;
	}

	for (first = 1; walk.nbytes >= AES_BLOCK_SIZE; first = 0) {
		int nbytes = walk.nbytes;

		if (walk.nbytes < walk.total)
			nbytes &= ~(AES_BLOCK_SIZE - 1);

		kernel_neon_begin();
		aes_xts_decrypt(walk.dst.virt.addr, walk.src.virt.addr,
				ctx->key1.key_dec, rounds, nbytes,
				ctx->key2.key_enc, walk.iv, first);
		kernel_neon_end();
		err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
	}

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

	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, &subreq, false);
	if (err)
		return err;


	kernel_neon_begin();
	aes_xts_decrypt(walk.dst.virt.addr, walk.src.virt.addr,
			ctx->key1.key_dec, rounds, walk.nbytes,
			ctx->key2.key_enc, walk.iv, first);
	kernel_neon_end();

	return skcipher_walk_done(&walk, 0);
}