[PATCH 1/4] crypto: add eboiv as a crypto API template

Gilad Ben-Yossef
2020-10-26T13:05:11Z

Encrypted byte-offset initialization vector (EBOIV) is an IV
generation method that is used in some cases by dm-crypt for
supporting the BitLocker volume encryption used by Windows 8
and onwards as a backwards compatible version in lieu of XTS
support. Support for eboiv was added to dm-crypt in 5.6.

This patch re-implements eboiv as a generic crypto API
template, thus allowing use of a alternative architecture
specific optimzied implementations (as well as saving a
memory allocation along the way).

Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
---
crypto/Kconfig | 21 ++++
crypto/Makefile | 1 +
crypto/eboiv.c | 295 ++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 317 insertions(+)
create mode 100644 crypto/eboiv.c

diff --git a/crypto/Kconfig b/crypto/Kconfig
index e85d8a059489..a29aac2b10d2 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -521,6 +521,27 @@ config CRYPTO_ESSIV
combined with ESSIV the only feasible mode for h/w accelerated
block encryption)

+config CRYPTO_EBOIV
+ tristate "EBOIV support for block encryption"
+ help
+ Encrypted byte-offset initialization vector (EBOIV) is an IV
+ generation method that is used in some cases by dm-crypt for
+ supporting the BitLocker volume encryption used by Windows 8
+ and onwards as a backwards compatible version in lieu of XTS
+ support.
+
+ It uses the block encryption key as the symmetric key for a
+ block encryption pass applied to the sector offset of the block.
+ Additional details can be found at
+ https://www.jedec.org/sites/default/files/docs/JESD223C.pdf
+
+ Note that the use of EBOIV is not recommended for new deployments,
+ and so this only needs to be enabled when interoperability with
+ existing encrypted volumes of filesystems is required, or when
+ building for a particular system that requires it (e.g., when
+ interop with BitLocker encrypted volumes of Windows systems
+ prior to Windows 10 is required)
+
comment "Hash modes"

config CRYPTO_CMAC
diff --git a/crypto/Makefile b/crypto/Makefile
index 4ca12b6044f7..bf47ee2ad5cf 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -166,6 +166,7 @@ obj-$(CONFIG_CRYPTO_ZSTD) += zstd.o
obj-$(CONFIG_CRYPTO_OFB) += ofb.o
obj-$(CONFIG_CRYPTO_ECC) += ecc.o
obj-$(CONFIG_CRYPTO_ESSIV) += essiv.o
+obj-$(CONFIG_CRYPTO_EBOIV) += eboiv.o
obj-$(CONFIG_CRYPTO_CURVE25519) += curve25519-generic.o

ecdh_generic-y += ecdh.o
diff --git a/crypto/eboiv.c b/crypto/eboiv.c
new file mode 100644
index 000000000000..467833e89139
--- /dev/null
+++ b/crypto/eboiv.c
@@ -0,0 +1,295 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * EBOIV skcipher template for block encryption
+ *
+ * This template encapsulates the Encrypted byte-offset IV generation algorithm
+ * used in Bitlocker in CBC mode by dm-crypt, which converts the initial vector
+ * for the skcipher used for block encryption, by encrypting it using the same
+ * skcipher key as encryption key. Usually, the input IV is a 64-bit sector
+ * offset (the byte offset of the start of the sector) in LE representation
+ * zero-padded to the size of the IV, but this * is not assumed by this driver.
+ *
+ * The typical use of this template is to instantiate the skcipher
+ * 'eboiv(cbc(aes))', which is the only instantiation used by
+ * dm-crypt for supporting BitLocker AES-CBC mode as specified in
+ * https://www.jedec.org/sites/default/files/docs/JESD223C.pdf
+ *
+ * Copyright (C) 2020 ARM Limited or its affiliates.
+ * Written by Gilad Ben-Yossef <gilad@benyossef.com>
+ *
+ * Heavily based on:
+ *
+ * ESSIV skcipher and aead template for block encryption
+ * Copyright (c) 2019 Linaro, Ltd. <ard.biesheuvel@linaro.org>
+ *
+ * and
+ *
+ * dm-crypt eboiv code
+ * by Milan Broz <gmazyland@gmail.com> and Ard Biesheuvel <ardb@kernel.org>
+ *
+ */
+
+#include <crypto/internal/skcipher.h>
+#include <crypto/scatterwalk.h>
+#include <linux/module.h>
+
+#include "internal.h"
+
+struct eboiv_instance_ctx {
+ struct crypto_skcipher_spawn skcipher_spawn;
+ char eboiv_cipher_name[CRYPTO_MAX_ALG_NAME];
+};
+
+struct eboiv_tfm_ctx {
+ struct crypto_skcipher *skcipher;
+};
+
+struct eboiv_req_ctx {
+ struct skcipher_request *req;
+ bool enc;
+ struct scatterlist src;
+ struct scatterlist dst;
+ u8 iv[MAX_CIPHER_BLOCKSIZE] __aligned(__alignof__(__le64));
+ struct skcipher_request subreq;
+};
+
+static int eboiv_skcipher_setkey(struct crypto_skcipher *tfm,
+ const u8 *key, unsigned int keylen)
+{
+ struct eboiv_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+
+ crypto_skcipher_clear_flags(tctx->skcipher, CRYPTO_TFM_REQ_MASK);
+ crypto_skcipher_set_flags(tctx->skcipher,
+ crypto_skcipher_get_flags(tfm) &
+ CRYPTO_TFM_REQ_MASK);
+ return crypto_skcipher_setkey(tctx->skcipher, key, keylen);
+}
+
+static void eboiv_skcipher_done(struct crypto_async_request *areq, int err)
+{
+ struct skcipher_request *req = areq->data;
+
+ if (err == -EINPROGRESS)
+ return;
+
+ skcipher_request_complete(req, err);
+}
+
+static int eboiv_skcipher_do_crypt(struct skcipher_request *req, bool enc)
+{
+ struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+ const struct eboiv_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+ struct eboiv_req_ctx *req_ctx = skcipher_request_ctx(req);
+ struct skcipher_request *subreq = &req_ctx->subreq;
+
+ skcipher_request_set_tfm(subreq, tctx->skcipher);
+ skcipher_request_set_crypt(subreq, req->src, req->dst, req->cryptlen, req_ctx->iv);
+ skcipher_request_set_callback(subreq, skcipher_request_flags(req), eboiv_skcipher_done,
+ req);
+
+ return enc ? crypto_skcipher_encrypt(subreq) :
+ crypto_skcipher_decrypt(subreq);
+}
+
+static void eboiv_skcipher_iv_done(struct crypto_async_request *areq, int err)
+{
+ struct eboiv_req_ctx *req_ctx = areq->data;
+ struct skcipher_request *req = req_ctx->req;
+ int ret;
+
+ if (!err) {
+
+ ret = eboiv_skcipher_do_crypt(req, req_ctx->enc);
+
+ if ((ret == -EINPROGRESS) || (ret == -EBUSY))
+ return;
+ }
+
+ skcipher_request_complete(req, err);
+}
+
+static int eboiv_skcipher_crypt(struct skcipher_request *req, bool enc)
+{
+ struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+ const struct eboiv_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+ struct eboiv_req_ctx *req_ctx = skcipher_request_ctx(req);
+ struct skcipher_request *subreq = &req_ctx->subreq;
+ size_t iv_size = crypto_skcipher_ivsize(tfm);
+ int ret;
+
+ /* The supplied IV is assumed to be in sector offset format (though
+ * we don't enforce it) - encrypt it.
+ */
+ sg_init_one(&req_ctx->src, page_address(ZERO_PAGE(0)), iv_size);
+ sg_init_one(&req_ctx->dst, req_ctx->iv, iv_size);
+ skcipher_request_set_tfm(subreq, tctx->skcipher);
+ skcipher_request_set_crypt(subreq, &req_ctx->src, &req_ctx->dst, iv_size, req->iv);
+
+ req_ctx->req = req;
+ req_ctx->enc = enc;
+
+ skcipher_request_set_callback(subreq, skcipher_request_flags(req), eboiv_skcipher_iv_done,
+ req_ctx);
+
+ ret = crypto_skcipher_encrypt(subreq);
+
+ if (ret)
+ return ret;
+
+ return eboiv_skcipher_do_crypt(req, enc);
+
+}
+
+static int eboiv_skcipher_encrypt(struct skcipher_request *req)
+{
+ return eboiv_skcipher_crypt(req, true);
+}
+
+static int eboiv_skcipher_decrypt(struct skcipher_request *req)
+{
+ return eboiv_skcipher_crypt(req, false);
+}
+
+static int eboiv_skcipher_init_tfm(struct crypto_skcipher *tfm)
+{
+ struct skcipher_instance *inst = skcipher_alg_instance(tfm);
+ struct eboiv_instance_ctx *ictx = skcipher_instance_ctx(inst);
+ struct eboiv_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+ struct crypto_skcipher *skcipher;
+
+ skcipher = crypto_spawn_skcipher(&ictx->skcipher_spawn);
+ if (IS_ERR(skcipher))
+ return PTR_ERR(skcipher);
+
+ crypto_skcipher_set_reqsize(tfm, sizeof(struct eboiv_req_ctx) +
+ crypto_skcipher_reqsize(skcipher));
+
+ tctx->skcipher = skcipher;
+ return 0;
+}
+
+static void eboiv_skcipher_exit_tfm(struct crypto_skcipher *tfm)
+{
+ struct eboiv_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+
+ crypto_free_skcipher(tctx->skcipher);
+}
+
+static void eboiv_skcipher_free_instance(struct skcipher_instance *inst)
+{
+ struct eboiv_instance_ctx *ictx = skcipher_instance_ctx(inst);
+
+ crypto_drop_skcipher(&ictx->skcipher_spawn);
+ kfree(inst);
+}
+
+static int eboiv_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+ struct crypto_attr_type *algt;
+ const char *inner_cipher_name;
+ struct skcipher_instance *skcipher_inst = NULL;
+ struct crypto_instance *inst;
+ struct crypto_alg *base, *block_base;
+ struct eboiv_instance_ctx *ictx;
+ struct skcipher_alg *skcipher_alg = NULL;
+ int ivsize;
+ u32 mask;
+ int err;
+
+ algt = crypto_get_attr_type(tb);
+ if (IS_ERR(algt))
+ return PTR_ERR(algt);
+
+ inner_cipher_name = crypto_attr_alg_name(tb[1]);
+ if (IS_ERR(inner_cipher_name))
+ return PTR_ERR(inner_cipher_name);
+
+ mask = crypto_algt_inherited_mask(algt);
+
+ skcipher_inst = kzalloc(sizeof(*skcipher_inst) + sizeof(*ictx), GFP_KERNEL);
+ if (!skcipher_inst)
+ return -ENOMEM;
+
+ inst = skcipher_crypto_instance(skcipher_inst);
+ base = &skcipher_inst->alg.base;
+ ictx = crypto_instance_ctx(inst);
+
+ /* Symmetric cipher, e.g., "cbc(aes)" */
+ err = crypto_grab_skcipher(&ictx->skcipher_spawn, inst, inner_cipher_name, 0, mask);
+ if (err)
+ goto out_free_inst;
+
+ skcipher_alg = crypto_spawn_skcipher_alg(&ictx->skcipher_spawn);
+ block_base = &skcipher_alg->base;
+ ivsize = crypto_skcipher_alg_ivsize(skcipher_alg);
+
+ if (ivsize != block_base->cra_blocksize)
+ goto out_drop_skcipher;
+
+ /* Instance fields */
+
+ err = -ENAMETOOLONG;
+ if (snprintf(base->cra_name, CRYPTO_MAX_ALG_NAME, "eboiv(%s)",
+ block_base->cra_name) >= CRYPTO_MAX_ALG_NAME)
+ goto out_drop_skcipher;
+
+ if (snprintf(base->cra_driver_name, CRYPTO_MAX_ALG_NAME,
+ "eboiv(%s)", block_base->cra_driver_name) >= CRYPTO_MAX_ALG_NAME)
+ goto out_drop_skcipher;
+
+ base->cra_blocksize = block_base->cra_blocksize;
+ base->cra_ctxsize = sizeof(struct eboiv_tfm_ctx);
+ base->cra_alignmask = block_base->cra_alignmask;
+ base->cra_priority = block_base->cra_priority;
+
+ skcipher_inst->alg.setkey = eboiv_skcipher_setkey;
+ skcipher_inst->alg.encrypt = eboiv_skcipher_encrypt;
+ skcipher_inst->alg.decrypt = eboiv_skcipher_decrypt;
+ skcipher_inst->alg.init = eboiv_skcipher_init_tfm;
+ skcipher_inst->alg.exit = eboiv_skcipher_exit_tfm;
+
+ skcipher_inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(skcipher_alg);
+ skcipher_inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(skcipher_alg);
+ skcipher_inst->alg.ivsize = ivsize;
+ skcipher_inst->alg.chunksize = crypto_skcipher_alg_chunksize(skcipher_alg);
+ skcipher_inst->alg.walksize = crypto_skcipher_alg_walksize(skcipher_alg);
+
+ skcipher_inst->free = eboiv_skcipher_free_instance;
+
+ err = skcipher_register_instance(tmpl, skcipher_inst);
+
+ if (err)
+ goto out_drop_skcipher;
+
+ return 0;
+
+out_drop_skcipher:
+ crypto_drop_skcipher(&ictx->skcipher_spawn);
+out_free_inst:
+ kfree(skcipher_inst);
+ return err;
+}
+
+/* eboiv(cipher_name) */
+static struct crypto_template eboiv_tmpl = {
+ .name = "eboiv",
+ .create = eboiv_create,
+ .module = THIS_MODULE,
+};
+
+static int __init eboiv_module_init(void)
+{
+ return crypto_register_template(&eboiv_tmpl);
+}
+
+static void __exit eboiv_module_exit(void)
+{
+ crypto_unregister_template(&eboiv_tmpl);
+}
+
+subsys_initcall(eboiv_module_init);
+module_exit(eboiv_module_exit);
+
+MODULE_DESCRIPTION("EBOIV (BitLocker) skcipher wrapper for block encryption");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS_CRYPTO("eboiv");
--
2.28.0