[PATCH v3 0/4] Add SP800-108 KDF implementation to crypto API

[PATCH v3 0/4] Add SP800-108 KDF implementation to crypto API

[Stephan Müller]

Hi,

The key derviation functions are considered to be a cryptographic
operation. As cryptographic operations are provided via the kernel
crypto API, this patch set consolidates the SP800-108 KDF
implementation into the crypto API.

If this patch is accepted, another patch set will be published attempting
to move the HKDF implementation from the crypto file system code base
to the kernel crypto API.

The KDF implementation is provided as service functions. Yet, the
interface to the the provided KDF is modeled such, that additional
KDF implementation can use the same API style. The goal is to allow
the transformation from a service function into a crypto API template
eventually.

The KDF executes a power-on self test with test vectors from commonly
known sources.

Tbe SP800-108 KDF implementation is used to replace the implementation
in the keys subsystem. The implementation was verified using the
keyutils command line test code provided in
tests/keyctl/dh_compute/valid. All tests show that the expected values
are calculated with the new code.

Changes v3:

* port to kernel 5.16-rc1
* remove the HKDF patch to only leave the SP800-108 patch

Stephan Mueller (4):
  crypto: Add key derivation self-test support code
  crypto: add SP800-108 counter key derivation function
  security: DH - remove dead code for zero padding
  security: DH - use KDF implementation from crypto API

 crypto/Kconfig                         |   7 ++
 crypto/Makefile                        |   5 +
 crypto/kdf_sp800108.c                  | 149 +++++++++++++++++++++++++
 include/crypto/internal/kdf_selftest.h |  71 ++++++++++++
 include/crypto/kdf_sp800108.h          |  61 ++++++++++
 security/keys/Kconfig                  |   2 +-
 security/keys/dh.c                     | 118 +++-----------------
 7 files changed, 310 insertions(+), 103 deletions(-)
 create mode 100644 crypto/kdf_sp800108.c
 create mode 100644 include/crypto/internal/kdf_selftest.h
 create mode 100644 include/crypto/kdf_sp800108.h

-- 
2.33.1

[PATCH v3 1/4] crypto: Add key derivation self-test support code

[Stephan Müller]

As a preparation to add the key derivation implementations, the
self-test data structure definition and the common test code is made
available.

The test framework follows the testing applied by the NIST CAVP test
approach.

The structure of the test code follows the implementations found in
crypto/testmgr.c|h. In case the KDF implementations will be made
available via a kernel crypto API templates, the test code is intended
to be merged into testmgr.c|h.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 include/crypto/internal/kdf_selftest.h | 71 ++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 include/crypto/internal/kdf_selftest.h

diff --git a/include/crypto/internal/kdf_selftest.h b/include/crypto/internal/kdf_selftest.h
new file mode 100644
index 000000000000..4d03d2af57b7
--- /dev/null
+++ b/include/crypto/internal/kdf_selftest.h
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (C) 2021, Stephan Mueller <smueller@chronox.de>
+ */
+
+#ifndef _CRYPTO_KDF_SELFTEST_H
+#define _CRYPTO_KDF_SELFTEST_H
+
+#include <crypto/hash.h>
+#include <linux/uio.h>
+
+struct kdf_testvec {
+	unsigned char *key;
+	size_t keylen;
+	unsigned char *ikm;
+	size_t ikmlen;
+	struct kvec info;
+	unsigned char *expected;
+	size_t expectedlen;
+};
+
+static inline int
+kdf_test(const struct kdf_testvec *test, const char *name,
+	 int (*crypto_kdf_setkey)(struct crypto_shash *kmd,
+				  const u8 *key, size_t keylen,
+				  const u8 *ikm, size_t ikmlen),
+	 int (*crypto_kdf_generate)(struct crypto_shash *kmd,
+				    const struct kvec *info,
+				    unsigned int info_nvec,
+				    u8 *dst, unsigned int dlen))
+{
+	struct crypto_shash *kmd;
+	int ret;
+	u8 *buf = kzalloc(test->expectedlen, GFP_KERNEL);
+
+	if (!buf)
+		return -ENOMEM;
+
+	kmd = crypto_alloc_shash(name, 0, 0);
+	if (IS_ERR(kmd)) {
+		pr_err("alg: kdf: could not allocate hash handle for %s\n",
+		       name);
+		kfree(buf);
+		return -ENOMEM;
+	}
+
+	ret = crypto_kdf_setkey(kmd, test->key, test->keylen,
+				test->ikm, test->ikmlen);
+	if (ret) {
+		pr_err("alg: kdf: could not set key derivation key\n");
+		goto err;
+	}
+
+	ret = crypto_kdf_generate(kmd, &test->info, 1, buf, test->expectedlen);
+	if (ret) {
+		pr_err("alg: kdf: could not obtain key data\n");
+		goto err;
+	}
+
+	ret = memcmp(test->expected, buf, test->expectedlen);
+	if (ret)
+		ret = -EINVAL;
+
+err:
+	crypto_free_shash(kmd);
+	kfree(buf);
+	return ret;
+}
+
+#endif /* _CRYPTO_KDF_SELFTEST_H */
-- 
2.33.1

[PATCH v3 2/4] crypto: add SP800-108 counter key derivation function

[Stephan Müller]

SP800-108 defines three KDFs - this patch provides the counter KDF
implementation.

The KDF is implemented as a service function where the caller has to
maintain the hash / HMAC state. Apart from this hash/HMAC state, no
additional state is required to be maintained by either the caller or
the KDF implementation.

The key for the KDF is set with the crypto_kdf108_setkey function which
is intended to be invoked before the caller requests a key derivation
operation via crypto_kdf108_ctr_generate.

SP800-108 allows the use of either a HMAC or a hash as crypto primitive
for the KDF. When a HMAC primtive is intended to be used,
crypto_kdf108_setkey must be used to set the HMAC key. Otherwise, for a
hash crypto primitve crypto_kdf108_ctr_generate can be used immediately
after allocating the hash handle.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 crypto/Kconfig                |   7 ++
 crypto/Makefile               |   5 ++
 crypto/kdf_sp800108.c         | 149 ++++++++++++++++++++++++++++++++++
 include/crypto/kdf_sp800108.h |  61 ++++++++++++++
 4 files changed, 222 insertions(+)
 create mode 100644 crypto/kdf_sp800108.c
 create mode 100644 include/crypto/kdf_sp800108.h

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 285f82647d2b..09c393a57b58 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -1845,6 +1845,13 @@ config CRYPTO_JITTERENTROPY
 	  random numbers. This Jitterentropy RNG registers with
 	  the kernel crypto API and can be used by any caller.
 
+config CRYPTO_KDF800108_CTR
+	tristate "Counter KDF (SP800-108)"
+	select CRYPTO_HASH
+	help
+	  Enable the key derivation function in counter mode compliant to
+	  SP800-108.
+
 config CRYPTO_USER_API
 	tristate
 
diff --git a/crypto/Makefile b/crypto/Makefile
index 429c4d57458c..d76bff8d0ffd 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -200,3 +200,8 @@ obj-$(CONFIG_ASYMMETRIC_KEY_TYPE) += asymmetric_keys/
 obj-$(CONFIG_CRYPTO_HASH_INFO) += hash_info.o
 crypto_simd-y := simd.o
 obj-$(CONFIG_CRYPTO_SIMD) += crypto_simd.o
+
+#
+# Key derivation function
+#
+obj-$(CONFIG_CRYPTO_KDF800108_CTR) += kdf_sp800108.o
diff --git a/crypto/kdf_sp800108.c b/crypto/kdf_sp800108.c
new file mode 100644
index 000000000000..1b7516615c34
--- /dev/null
+++ b/crypto/kdf_sp800108.c
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * SP800-108 Key-derivation function
+ *
+ * Copyright (C) 2021, Stephan Mueller <smueller@chronox.de>
+ */
+
+#include <linux/module.h>
+#include <crypto/kdf_sp800108.h>
+#include <crypto/internal/kdf_selftest.h>
+
+/*
+ * SP800-108 CTR KDF implementation
+ */
+int crypto_kdf108_ctr_generate(struct crypto_shash *kmd,
+			       const struct kvec *info, unsigned int info_nvec,
+			       u8 *dst, unsigned int dlen)
+{
+	SHASH_DESC_ON_STACK(desc, kmd);
+	__be32 counter = cpu_to_be32(1);
+	const unsigned int h = crypto_shash_digestsize(kmd), dlen_orig = dlen;
+	unsigned int i;
+	int err = 0;
+	u8 *dst_orig = dst;
+
+	desc->tfm = kmd;
+
+	while (dlen) {
+		err = crypto_shash_init(desc);
+		if (err)
+			goto out;
+
+		err = crypto_shash_update(desc, (u8 *)&counter, sizeof(__be32));
+		if (err)
+			goto out;
+
+		for (i = 0; i < info_nvec; i++) {
+			err = crypto_shash_update(desc, info[i].iov_base,
+						  info[i].iov_len);
+			if (err)
+				goto out;
+		}
+
+		if (dlen < h) {
+			u8 tmpbuffer[HASH_MAX_DIGESTSIZE];
+
+			err = crypto_shash_final(desc, tmpbuffer);
+			if (err)
+				goto out;
+			memcpy(dst, tmpbuffer, dlen);
+			memzero_explicit(tmpbuffer, h);
+			goto out;
+		}
+
+		err = crypto_shash_final(desc, dst);
+		if (err)
+			goto out;
+
+		dlen -= h;
+		dst += h;
+		counter = cpu_to_be32(be32_to_cpu(counter) + 1);
+	}
+
+out:
+	if (err)
+		memzero_explicit(dst_orig, dlen_orig);
+	shash_desc_zero(desc);
+	return err;
+}
+EXPORT_SYMBOL(crypto_kdf108_ctr_generate);
+
+/*
+ * The seeding of the KDF
+ */
+int crypto_kdf108_setkey(struct crypto_shash *kmd,
+			 const u8 *key, size_t keylen,
+			 const u8 *ikm, size_t ikmlen)
+{
+	unsigned int ds = crypto_shash_digestsize(kmd);
+
+	/* SP800-108 does not support IKM */
+	if (ikm || ikmlen)
+		return -EINVAL;
+
+	/* Check according to SP800-108 section 7.2 */
+	if (ds > keylen)
+		return -EINVAL;
+
+	/*
+	 * We require that we operate on a MAC -- if we do not operate on a
+	 * MAC, this function returns an error.
+	 */
+	return crypto_shash_setkey(kmd, key, keylen);
+}
+EXPORT_SYMBOL(crypto_kdf108_setkey);
+
+/*
+ * Test vector obtained from
+ * http://csrc.nist.gov/groups/STM/cavp/documents/KBKDF800-108/CounterMode.zip
+ */
+static const struct kdf_testvec kdf_ctr_hmac_sha256_tv_template[] = {
+	{
+		.key = "\xdd\x1d\x91\xb7\xd9\x0b\x2b\xd3"
+		       "\x13\x85\x33\xce\x92\xb2\x72\xfb"
+		       "\xf8\xa3\x69\x31\x6a\xef\xe2\x42"
+		       "\xe6\x59\xcc\x0a\xe2\x38\xaf\xe0",
+		.keylen = 32,
+		.ikm = NULL,
+		.ikmlen = 0,
+		.info = {
+			.iov_base = "\x01\x32\x2b\x96\xb3\x0a\xcd\x19"
+				    "\x79\x79\x44\x4e\x46\x8e\x1c\x5c"
+				    "\x68\x59\xbf\x1b\x1c\xf9\x51\xb7"
+				    "\xe7\x25\x30\x3e\x23\x7e\x46\xb8"
+				    "\x64\xa1\x45\xfa\xb2\x5e\x51\x7b"
+				    "\x08\xf8\x68\x3d\x03\x15\xbb\x29"
+				    "\x11\xd8\x0a\x0e\x8a\xba\x17\xf3"
+				    "\xb4\x13\xfa\xac",
+			.iov_len  = 60
+		},
+		.expected	  = "\x10\x62\x13\x42\xbf\xb0\xfd\x40"
+				    "\x04\x6c\x0e\x29\xf2\xcf\xdb\xf0",
+		.expectedlen	  = 16
+	}
+};
+
+static int __init crypto_kdf108_init(void)
+{
+	int ret = kdf_test(&kdf_ctr_hmac_sha256_tv_template[0], "hmac(sha256)",
+			   crypto_kdf108_setkey, crypto_kdf108_ctr_generate);
+
+	if (ret)
+		pr_warn("alg: self-tests for CTR-KDF (hmac(sha256)) failed (rc=%d)\n",
+			ret);
+	else
+		pr_info("alg: self-tests for CTR-KDF (hmac(sha256)) passed\n");
+
+	return ret;
+}
+
+static void __exit crypto_kdf108_exit(void) { }
+
+module_init(crypto_kdf108_init);
+module_exit(crypto_kdf108_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
+MODULE_DESCRIPTION("Key Derivation Function conformant to SP800-108");
diff --git a/include/crypto/kdf_sp800108.h b/include/crypto/kdf_sp800108.h
new file mode 100644
index 000000000000..b7b20a778fb7
--- /dev/null
+++ b/include/crypto/kdf_sp800108.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (C) 2021, Stephan Mueller <smueller@chronox.de>
+ */
+
+#ifndef _CRYPTO_KDF108_H
+#define _CRYPTO_KDF108_H
+
+#include <crypto/hash.h>
+#include <linux/uio.h>
+
+/**
+ * Counter KDF generate operation according to SP800-108 section 5.1
+ * as well as SP800-56A section 5.8.1 (Single-step KDF).
+ *
+ * @kmd Keyed message digest whose key was set with crypto_kdf108_setkey or
+ *	unkeyed message digest
+ * @info optional context and application specific information - this may be
+ *	 NULL
+ * @info_vec number of optional context/application specific information entries
+ * @dst destination buffer that the caller already allocated
+ * @dlen length of the destination buffer - the KDF derives that amount of
+ *	 bytes.
+ *
+ * To comply with SP800-108, the caller must provide Label || 0x00 || Context
+ * in the info parameter.
+ *
+ * @return 0 on success, < 0 on error
+ */
+int crypto_kdf108_ctr_generate(struct crypto_shash *kmd,
+			       const struct kvec *info, unsigned int info_nvec,
+			       u8 *dst, unsigned int dlen);
+
+/**
+ * Counter KDF setkey operation
+ *
+ * @kmd Keyed message digest allocated by the caller. The key should not have
+ *	been set.
+ * @key Seed key to be used to initialize the keyed message digest context.
+ * @keylen This length of the key buffer.
+ * @ikm The SP800-108 KDF does not support IKM - this parameter must be NULL
+ * @ikmlen This parameter must be 0.
+ *
+ * According to SP800-108 section 7.2, the seed key must be at least as large as
+ * the message digest size of the used keyed message digest. This limitation
+ * is enforced by the implementation.
+ *
+ * SP800-108 allows the use of either a HMAC or a hash primitive. When
+ * the caller intends to use a hash primitive, the call to
+ * crypto_kdf108_setkey is not required and the key derivation operation can
+ * immediately performed using crypto_kdf108_ctr_generate after allocating
+ * a handle.
+ *
+ * @return 0 on success, < 0 on error
+ */
+int crypto_kdf108_setkey(struct crypto_shash *kmd,
+			 const u8 *key, size_t keylen,
+			 const u8 *ikm, size_t ikmlen);
+
+#endif /* _CRYPTO_KDF108_H */
-- 
2.33.1

[PATCH v3 3/4] security: DH - remove dead code for zero padding

[Stephan Müller]

Remove the specific code that adds a zero padding that was intended
to be invoked when the DH operation result was smaller than the
modulus. However, this cannot occur any more these days because the
function mpi_write_to_sgl is used in the code path that calculates the
shared secret in dh_compute_value. This MPI service function guarantees
that leading zeros are introduced as needed to ensure the resulting data
is exactly as long as the modulus. This implies that the specific code
to add zero padding is dead code which can be safely removed.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 security/keys/dh.c | 25 ++++---------------------
 1 file changed, 4 insertions(+), 21 deletions(-)

diff --git a/security/keys/dh.c b/security/keys/dh.c
index 1abfa70ed6e1..56e12dae4534 100644
--- a/security/keys/dh.c
+++ b/security/keys/dh.c
@@ -141,7 +141,7 @@ static void kdf_dealloc(struct kdf_sdesc *sdesc)
  * 'dlen' must be a multiple of the digest size.
  */
 static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
-		   u8 *dst, unsigned int dlen, unsigned int zlen)
+		   u8 *dst, unsigned int dlen)
 {
 	struct shash_desc *desc = &sdesc->shash;
 	unsigned int h = crypto_shash_digestsize(desc->tfm);
@@ -158,22 +158,6 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
 		if (err)
 			goto err;
 
-		if (zlen && h) {
-			u8 tmpbuffer[32];
-			size_t chunk = min_t(size_t, zlen, sizeof(tmpbuffer));
-			memset(tmpbuffer, 0, chunk);
-
-			do {
-				err = crypto_shash_update(desc, tmpbuffer,
-							  chunk);
-				if (err)
-					goto err;
-
-				zlen -= chunk;
-				chunk = min_t(size_t, zlen, sizeof(tmpbuffer));
-			} while (zlen);
-		}
-
 		if (src && slen) {
 			err = crypto_shash_update(desc, src, slen);
 			if (err)
@@ -198,7 +182,7 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
 
 static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
 				 char __user *buffer, size_t buflen,
-				 uint8_t *kbuf, size_t kbuflen, size_t lzero)
+				 uint8_t *kbuf, size_t kbuflen)
 {
 	uint8_t *outbuf = NULL;
 	int ret;
@@ -211,7 +195,7 @@ static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
 		goto err;
 	}
 
-	ret = kdf_ctr(sdesc, kbuf, kbuflen, outbuf, outbuf_len, lzero);
+	ret = kdf_ctr(sdesc, kbuf, kbuflen, outbuf, outbuf_len);
 	if (ret)
 		goto err;
 
@@ -384,8 +368,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
 		}
 
 		ret = keyctl_dh_compute_kdf(sdesc, buffer, buflen, outbuf,
-					    req->dst_len + kdfcopy->otherinfolen,
-					    outlen - req->dst_len);
+					    req->dst_len + kdfcopy->otherinfolen);
 	} else if (copy_to_user(buffer, outbuf, req->dst_len) == 0) {
 		ret = req->dst_len;
 	} else {
-- 
2.33.1

[PATCH v3 4/4] security: DH - use KDF implementation from crypto API

[Stephan Müller]

The kernel crypto API provides the SP800-108 counter KDF implementation.
Thus, the separate implementation provided as part of the keys subsystem
can be replaced with calls to the KDF offered by the kernel crypto API.

The keys subsystem uses the counter KDF with a hash primitive. Thus,
it only uses the call to crypto_kdf108_ctr_generate.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 security/keys/Kconfig |  2 +-
 security/keys/dh.c    | 97 +++++++------------------------------------
 2 files changed, 15 insertions(+), 84 deletions(-)

diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index 64b81abd087e..969122c7b92f 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -109,7 +109,7 @@ config KEY_DH_OPERATIONS
        bool "Diffie-Hellman operations on retained keys"
        depends on KEYS
        select CRYPTO
-       select CRYPTO_HASH
+       select CRYPTO_KDF800108_CTR
        select CRYPTO_DH
        help
 	 This option provides support for calculating Diffie-Hellman
diff --git a/security/keys/dh.c b/security/keys/dh.c
index 56e12dae4534..46fa442b81ec 100644
--- a/security/keys/dh.c
+++ b/security/keys/dh.c
@@ -11,6 +11,7 @@
 #include <crypto/hash.h>
 #include <crypto/kpp.h>
 #include <crypto/dh.h>
+#include <crypto/kdf_sp800108.h>
 #include <keys/user-type.h>
 #include "internal.h"
 
@@ -79,16 +80,9 @@ static void dh_crypto_done(struct crypto_async_request *req, int err)
 	complete(&compl->completion);
 }
 
-struct kdf_sdesc {
-	struct shash_desc shash;
-	char ctx[];
-};
-
-static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
+static int kdf_alloc(struct crypto_shash **hash, char *hashname)
 {
 	struct crypto_shash *tfm;
-	struct kdf_sdesc *sdesc;
-	int size;
 	int err;
 
 	/* allocate synchronous hash */
@@ -102,14 +96,7 @@ static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
 	if (crypto_shash_digestsize(tfm) == 0)
 		goto out_free_tfm;
 
-	err = -ENOMEM;
-	size = sizeof(struct shash_desc) + crypto_shash_descsize(tfm);
-	sdesc = kmalloc(size, GFP_KERNEL);
-	if (!sdesc)
-		goto out_free_tfm;
-	sdesc->shash.tfm = tfm;
-
-	*sdesc_ret = sdesc;
+	*hash = tfm;
 
 	return 0;
 
@@ -118,76 +105,20 @@ static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
 	return err;
 }
 
-static void kdf_dealloc(struct kdf_sdesc *sdesc)
-{
-	if (!sdesc)
-		return;
-
-	if (sdesc->shash.tfm)
-		crypto_free_shash(sdesc->shash.tfm);
-
-	kfree_sensitive(sdesc);
-}
-
-/*
- * Implementation of the KDF in counter mode according to SP800-108 section 5.1
- * as well as SP800-56A section 5.8.1 (Single-step KDF).
- *
- * SP800-56A:
- * The src pointer is defined as Z || other info where Z is the shared secret
- * from DH and other info is an arbitrary string (see SP800-56A section
- * 5.8.1.2).
- *
- * 'dlen' must be a multiple of the digest size.
- */
-static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
-		   u8 *dst, unsigned int dlen)
+static void kdf_dealloc(struct crypto_shash *hash)
 {
-	struct shash_desc *desc = &sdesc->shash;
-	unsigned int h = crypto_shash_digestsize(desc->tfm);
-	int err = 0;
-	u8 *dst_orig = dst;
-	__be32 counter = cpu_to_be32(1);
-
-	while (dlen) {
-		err = crypto_shash_init(desc);
-		if (err)
-			goto err;
-
-		err = crypto_shash_update(desc, (u8 *)&counter, sizeof(__be32));
-		if (err)
-			goto err;
-
-		if (src && slen) {
-			err = crypto_shash_update(desc, src, slen);
-			if (err)
-				goto err;
-		}
-
-		err = crypto_shash_final(desc, dst);
-		if (err)
-			goto err;
-
-		dlen -= h;
-		dst += h;
-		counter = cpu_to_be32(be32_to_cpu(counter) + 1);
-	}
-
-	return 0;
-
-err:
-	memzero_explicit(dst_orig, dlen);
-	return err;
+	if (hash)
+		crypto_free_shash(hash);
 }
 
-static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
+static int keyctl_dh_compute_kdf(struct crypto_shash *hash,
 				 char __user *buffer, size_t buflen,
 				 uint8_t *kbuf, size_t kbuflen)
 {
+	struct kvec kbuf_iov = { .iov_base = kbuf, .iov_len = kbuflen };
 	uint8_t *outbuf = NULL;
 	int ret;
-	size_t outbuf_len = roundup(buflen,
-				    crypto_shash_digestsize(sdesc->shash.tfm));
+	size_t outbuf_len = roundup(buflen, crypto_shash_digestsize(hash));
 
 	outbuf = kmalloc(outbuf_len, GFP_KERNEL);
 	if (!outbuf) {
@@ -195,7 +126,7 @@ static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
 		goto err;
 	}
 
-	ret = kdf_ctr(sdesc, kbuf, kbuflen, outbuf, outbuf_len);
+	ret = crypto_kdf108_ctr_generate(hash, &kbuf_iov, 1, outbuf, outbuf_len);
 	if (ret)
 		goto err;
 
@@ -224,7 +155,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
 	struct kpp_request *req;
 	uint8_t *secret;
 	uint8_t *outbuf;
-	struct kdf_sdesc *sdesc = NULL;
+	struct crypto_shash *hash = NULL;
 
 	if (!params || (!buffer && buflen)) {
 		ret = -EINVAL;
@@ -257,7 +188,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
 		}
 
 		/* allocate KDF from the kernel crypto API */
-		ret = kdf_alloc(&sdesc, hashname);
+		ret = kdf_alloc(&hash, hashname);
 		kfree(hashname);
 		if (ret)
 			goto out1;
@@ -367,7 +298,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
 			goto out6;
 		}
 
-		ret = keyctl_dh_compute_kdf(sdesc, buffer, buflen, outbuf,
+		ret = keyctl_dh_compute_kdf(hash, buffer, buflen, outbuf,
 					    req->dst_len + kdfcopy->otherinfolen);
 	} else if (copy_to_user(buffer, outbuf, req->dst_len) == 0) {
 		ret = req->dst_len;
@@ -386,7 +317,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
 out2:
 	dh_free_data(&dh_inputs);
 out1:
-	kdf_dealloc(sdesc);
+	kdf_dealloc(hash);
 	return ret;
 }
 
-- 
2.33.1

Re: [PATCH v3 2/4] crypto: add SP800-108 counter key derivation function

[Eric Biggers]

On Mon, Nov 15, 2021 at 09:43:13AM +0100, Stephan Müller wrote:
> SP800-108 defines three KDFs - this patch provides the counter KDF
> implementation.
> 
> The KDF is implemented as a service function where the caller has to
> maintain the hash / HMAC state. Apart from this hash/HMAC state, no
> additional state is required to be maintained by either the caller or
> the KDF implementation.
> 
> The key for the KDF is set with the crypto_kdf108_setkey function which
> is intended to be invoked before the caller requests a key derivation
> operation via crypto_kdf108_ctr_generate.
> 
> SP800-108 allows the use of either a HMAC or a hash as crypto primitive
> for the KDF. When a HMAC primtive is intended to be used,
> crypto_kdf108_setkey must be used to set the HMAC key. Otherwise, for a
> hash crypto primitve crypto_kdf108_ctr_generate can be used immediately
> after allocating the hash handle.
> 
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> ---
>  crypto/Kconfig                |   7 ++
>  crypto/Makefile               |   5 ++
>  crypto/kdf_sp800108.c         | 149 ++++++++++++++++++++++++++++++++++
>  include/crypto/kdf_sp800108.h |  61 ++++++++++++++
>  4 files changed, 222 insertions(+)
>  create mode 100644 crypto/kdf_sp800108.c
>  create mode 100644 include/crypto/kdf_sp800108.h
> 
> diff --git a/crypto/Kconfig b/crypto/Kconfig
> index 285f82647d2b..09c393a57b58 100644
> --- a/crypto/Kconfig
> +++ b/crypto/Kconfig
> @@ -1845,6 +1845,13 @@ config CRYPTO_JITTERENTROPY
>  	  random numbers. This Jitterentropy RNG registers with
>  	  the kernel crypto API and can be used by any caller.
>  
> +config CRYPTO_KDF800108_CTR
> +	tristate "Counter KDF (SP800-108)"
> +	select CRYPTO_HASH
> +	help
> +	  Enable the key derivation function in counter mode compliant to
> +	  SP800-108.

These are just some library functions, so they shouldn't be user-selectable.

> +/*
> + * The seeding of the KDF
> + */
> +int crypto_kdf108_setkey(struct crypto_shash *kmd,
> +			 const u8 *key, size_t keylen,
> +			 const u8 *ikm, size_t ikmlen)
> +{
> +	unsigned int ds = crypto_shash_digestsize(kmd);
> +
> +	/* SP800-108 does not support IKM */
> +	if (ikm || ikmlen)
> +		return -EINVAL;

Why have the ikm parameter if it's not supported?

> +	/*
> +	 * We require that we operate on a MAC -- if we do not operate on a
> +	 * MAC, this function returns an error.
> +	 */
> +	return crypto_shash_setkey(kmd, key, keylen);
> +}
> +EXPORT_SYMBOL(crypto_kdf108_setkey);

Well, crypto_shash_setkey() will succeed if the hash algorithm takes a "key".
That doesn't necessarily mean that it's a MAC.	It could be crc32 or xxhash64,
for example; those interpret the "key" as the initial value.

> +static int __init crypto_kdf108_init(void)
> +{
> +	int ret = kdf_test(&kdf_ctr_hmac_sha256_tv_template[0], "hmac(sha256)",
> +			   crypto_kdf108_setkey, crypto_kdf108_ctr_generate);
> +
> +	if (ret)
> +		pr_warn("alg: self-tests for CTR-KDF (hmac(sha256)) failed (rc=%d)\n",
> +			ret);

This should be a WARN() since it indicates a kernel bug.

- Eric

Re: [PATCH v3 3/4] security: DH - remove dead code for zero padding

[Mat Martineau]

[-- Attachment #1: Type: text/plain, Size: 3069 bytes --]

On Mon, 15 Nov 2021, Stephan Müller wrote:

> Remove the specific code that adds a zero padding that was intended
> to be invoked when the DH operation result was smaller than the
> modulus. However, this cannot occur any more these days because the
> function mpi_write_to_sgl is used in the code path that calculates the
> shared secret in dh_compute_value. This MPI service function guarantees
> that leading zeros are introduced as needed to ensure the resulting data
> is exactly as long as the modulus. This implies that the specific code
> to add zero padding is dead code which can be safely removed.
>
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> ---
> security/keys/dh.c | 25 ++++---------------------
> 1 file changed, 4 insertions(+), 21 deletions(-)

Hi Stephan -

Thanks for the cleanup!

Acked-by: Mat Martineau <mathew.j.martineau@linux.intel.com>



>
> diff --git a/security/keys/dh.c b/security/keys/dh.c
> index 1abfa70ed6e1..56e12dae4534 100644
> --- a/security/keys/dh.c
> +++ b/security/keys/dh.c
> @@ -141,7 +141,7 @@ static void kdf_dealloc(struct kdf_sdesc *sdesc)
>  * 'dlen' must be a multiple of the digest size.
>  */
> static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
> -		   u8 *dst, unsigned int dlen, unsigned int zlen)
> +		   u8 *dst, unsigned int dlen)
> {
> 	struct shash_desc *desc = &sdesc->shash;
> 	unsigned int h = crypto_shash_digestsize(desc->tfm);
> @@ -158,22 +158,6 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
> 		if (err)
> 			goto err;
>
> -		if (zlen && h) {
> -			u8 tmpbuffer[32];
> -			size_t chunk = min_t(size_t, zlen, sizeof(tmpbuffer));
> -			memset(tmpbuffer, 0, chunk);
> -
> -			do {
> -				err = crypto_shash_update(desc, tmpbuffer,
> -							  chunk);
> -				if (err)
> -					goto err;
> -
> -				zlen -= chunk;
> -				chunk = min_t(size_t, zlen, sizeof(tmpbuffer));
> -			} while (zlen);
> -		}
> -
> 		if (src && slen) {
> 			err = crypto_shash_update(desc, src, slen);
> 			if (err)
> @@ -198,7 +182,7 @@ static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
>
> static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
> 				 char __user *buffer, size_t buflen,
> -				 uint8_t *kbuf, size_t kbuflen, size_t lzero)
> +				 uint8_t *kbuf, size_t kbuflen)
> {
> 	uint8_t *outbuf = NULL;
> 	int ret;
> @@ -211,7 +195,7 @@ static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
> 		goto err;
> 	}
>
> -	ret = kdf_ctr(sdesc, kbuf, kbuflen, outbuf, outbuf_len, lzero);
> +	ret = kdf_ctr(sdesc, kbuf, kbuflen, outbuf, outbuf_len);
> 	if (ret)
> 		goto err;
>
> @@ -384,8 +368,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
> 		}
>
> 		ret = keyctl_dh_compute_kdf(sdesc, buffer, buflen, outbuf,
> -					    req->dst_len + kdfcopy->otherinfolen,
> -					    outlen - req->dst_len);
> +					    req->dst_len + kdfcopy->otherinfolen);
> 	} else if (copy_to_user(buffer, outbuf, req->dst_len) == 0) {
> 		ret = req->dst_len;
> 	} else {
> -- 
> 2.33.1
>
>
>
>
>

--
Mat Martineau
Intel

Re: [PATCH v3 4/4] security: DH - use KDF implementation from crypto API

[Mat Martineau]

[-- Attachment #1: Type: text/plain, Size: 6325 bytes --]

On Mon, 15 Nov 2021, Stephan Müller wrote:

> The kernel crypto API provides the SP800-108 counter KDF implementation.
> Thus, the separate implementation provided as part of the keys subsystem
> can be replaced with calls to the KDF offered by the kernel crypto API.
>
> The keys subsystem uses the counter KDF with a hash primitive. Thus,
> it only uses the call to crypto_kdf108_ctr_generate.
>
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> ---
> security/keys/Kconfig |  2 +-
> security/keys/dh.c    | 97 +++++++------------------------------------
> 2 files changed, 15 insertions(+), 84 deletions(-)
>
> diff --git a/security/keys/Kconfig b/security/keys/Kconfig
> index 64b81abd087e..969122c7b92f 100644
> --- a/security/keys/Kconfig
> +++ b/security/keys/Kconfig
> @@ -109,7 +109,7 @@ config KEY_DH_OPERATIONS
>        bool "Diffie-Hellman operations on retained keys"
>        depends on KEYS
>        select CRYPTO
> -       select CRYPTO_HASH
> +       select CRYPTO_KDF800108_CTR
>        select CRYPTO_DH
>        help
> 	 This option provides support for calculating Diffie-Hellman
> diff --git a/security/keys/dh.c b/security/keys/dh.c
> index 56e12dae4534..46fa442b81ec 100644
> --- a/security/keys/dh.c
> +++ b/security/keys/dh.c
> @@ -11,6 +11,7 @@
> #include <crypto/hash.h>
> #include <crypto/kpp.h>
> #include <crypto/dh.h>
> +#include <crypto/kdf_sp800108.h>
> #include <keys/user-type.h>
> #include "internal.h"
>
> @@ -79,16 +80,9 @@ static void dh_crypto_done(struct crypto_async_request *req, int err)
> 	complete(&compl->completion);
> }
>
> -struct kdf_sdesc {
> -	struct shash_desc shash;
> -	char ctx[];
> -};
> -
> -static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
> +static int kdf_alloc(struct crypto_shash **hash, char *hashname)
> {
> 	struct crypto_shash *tfm;
> -	struct kdf_sdesc *sdesc;
> -	int size;
> 	int err;
>
> 	/* allocate synchronous hash */
> @@ -102,14 +96,7 @@ static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
> 	if (crypto_shash_digestsize(tfm) == 0)
> 		goto out_free_tfm;

With the sdesc allocation failure path removed below, there's only one use 
of the 'err' variable and the out_free_tfm code path. I suggest furthering 
the cleanup by removing err and the goto path, and moving the 
crypto_free_shash() and return -EINVAL here (where the goto currently is).

-Mat


>
> -	err = -ENOMEM;
> -	size = sizeof(struct shash_desc) + crypto_shash_descsize(tfm);
> -	sdesc = kmalloc(size, GFP_KERNEL);
> -	if (!sdesc)
> -		goto out_free_tfm;
> -	sdesc->shash.tfm = tfm;
> -
> -	*sdesc_ret = sdesc;
> +	*hash = tfm;
>
> 	return 0;
>
> @@ -118,76 +105,20 @@ static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
> 	return err;
> }
>
> -static void kdf_dealloc(struct kdf_sdesc *sdesc)
> -{
> -	if (!sdesc)
> -		return;
> -
> -	if (sdesc->shash.tfm)
> -		crypto_free_shash(sdesc->shash.tfm);
> -
> -	kfree_sensitive(sdesc);
> -}
> -
> -/*
> - * Implementation of the KDF in counter mode according to SP800-108 section 5.1
> - * as well as SP800-56A section 5.8.1 (Single-step KDF).
> - *
> - * SP800-56A:
> - * The src pointer is defined as Z || other info where Z is the shared secret
> - * from DH and other info is an arbitrary string (see SP800-56A section
> - * 5.8.1.2).
> - *
> - * 'dlen' must be a multiple of the digest size.
> - */
> -static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
> -		   u8 *dst, unsigned int dlen)
> +static void kdf_dealloc(struct crypto_shash *hash)
> {
> -	struct shash_desc *desc = &sdesc->shash;
> -	unsigned int h = crypto_shash_digestsize(desc->tfm);
> -	int err = 0;
> -	u8 *dst_orig = dst;
> -	__be32 counter = cpu_to_be32(1);
> -
> -	while (dlen) {
> -		err = crypto_shash_init(desc);
> -		if (err)
> -			goto err;
> -
> -		err = crypto_shash_update(desc, (u8 *)&counter, sizeof(__be32));
> -		if (err)
> -			goto err;
> -
> -		if (src && slen) {
> -			err = crypto_shash_update(desc, src, slen);
> -			if (err)
> -				goto err;
> -		}
> -
> -		err = crypto_shash_final(desc, dst);
> -		if (err)
> -			goto err;
> -
> -		dlen -= h;
> -		dst += h;
> -		counter = cpu_to_be32(be32_to_cpu(counter) + 1);
> -	}
> -
> -	return 0;
> -
> -err:
> -	memzero_explicit(dst_orig, dlen);
> -	return err;
> +	if (hash)
> +		crypto_free_shash(hash);
> }
>
> -static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
> +static int keyctl_dh_compute_kdf(struct crypto_shash *hash,
> 				 char __user *buffer, size_t buflen,
> 				 uint8_t *kbuf, size_t kbuflen)
> {
> +	struct kvec kbuf_iov = { .iov_base = kbuf, .iov_len = kbuflen };
> 	uint8_t *outbuf = NULL;
> 	int ret;
> -	size_t outbuf_len = roundup(buflen,
> -				    crypto_shash_digestsize(sdesc->shash.tfm));
> +	size_t outbuf_len = roundup(buflen, crypto_shash_digestsize(hash));
>
> 	outbuf = kmalloc(outbuf_len, GFP_KERNEL);
> 	if (!outbuf) {
> @@ -195,7 +126,7 @@ static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
> 		goto err;
> 	}
>
> -	ret = kdf_ctr(sdesc, kbuf, kbuflen, outbuf, outbuf_len);
> +	ret = crypto_kdf108_ctr_generate(hash, &kbuf_iov, 1, outbuf, outbuf_len);
> 	if (ret)
> 		goto err;
>
> @@ -224,7 +155,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
> 	struct kpp_request *req;
> 	uint8_t *secret;
> 	uint8_t *outbuf;
> -	struct kdf_sdesc *sdesc = NULL;
> +	struct crypto_shash *hash = NULL;
>
> 	if (!params || (!buffer && buflen)) {
> 		ret = -EINVAL;
> @@ -257,7 +188,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
> 		}
>
> 		/* allocate KDF from the kernel crypto API */
> -		ret = kdf_alloc(&sdesc, hashname);
> +		ret = kdf_alloc(&hash, hashname);
> 		kfree(hashname);
> 		if (ret)
> 			goto out1;
> @@ -367,7 +298,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
> 			goto out6;
> 		}
>
> -		ret = keyctl_dh_compute_kdf(sdesc, buffer, buflen, outbuf,
> +		ret = keyctl_dh_compute_kdf(hash, buffer, buflen, outbuf,
> 					    req->dst_len + kdfcopy->otherinfolen);
> 	} else if (copy_to_user(buffer, outbuf, req->dst_len) == 0) {
> 		ret = req->dst_len;
> @@ -386,7 +317,7 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
> out2:
> 	dh_free_data(&dh_inputs);
> out1:
> -	kdf_dealloc(sdesc);
> +	kdf_dealloc(hash);
> 	return ret;
> }
>
> -- 
> 2.33.1
>
>
>
>
>

--
Mat Martineau
Intel

Re: [PATCH v3 2/4] crypto: add SP800-108 counter key derivation function

[Stephan Mueller]

Am Mittwoch, 17. November 2021, 20:11:03 CET schrieb Eric Biggers:

Hi Eric,

thanks for your comments.

> On Mon, Nov 15, 2021 at 09:43:13AM +0100, Stephan Müller wrote:
> > SP800-108 defines three KDFs - this patch provides the counter KDF
> > implementation.
> > 
> > The KDF is implemented as a service function where the caller has to
> > maintain the hash / HMAC state. Apart from this hash/HMAC state, no
> > additional state is required to be maintained by either the caller or
> > the KDF implementation.
> > 
> > The key for the KDF is set with the crypto_kdf108_setkey function which
> > is intended to be invoked before the caller requests a key derivation
> > operation via crypto_kdf108_ctr_generate.
> > 
> > SP800-108 allows the use of either a HMAC or a hash as crypto primitive
> > for the KDF. When a HMAC primtive is intended to be used,
> > crypto_kdf108_setkey must be used to set the HMAC key. Otherwise, for a
> > hash crypto primitve crypto_kdf108_ctr_generate can be used immediately
> > after allocating the hash handle.
> > 
> > Signed-off-by: Stephan Mueller <smueller@chronox.de>
> > ---
> > 
> >  crypto/Kconfig                |   7 ++
> >  crypto/Makefile               |   5 ++
> >  crypto/kdf_sp800108.c         | 149 ++++++++++++++++++++++++++++++++++
> >  include/crypto/kdf_sp800108.h |  61 ++++++++++++++
> >  4 files changed, 222 insertions(+)
> >  create mode 100644 crypto/kdf_sp800108.c
> >  create mode 100644 include/crypto/kdf_sp800108.h
> > 
> > diff --git a/crypto/Kconfig b/crypto/Kconfig
> > index 285f82647d2b..09c393a57b58 100644
> > --- a/crypto/Kconfig
> > +++ b/crypto/Kconfig
> > @@ -1845,6 +1845,13 @@ config CRYPTO_JITTERENTROPY
> > 
> >  	  random numbers. This Jitterentropy RNG registers with
> >  	  the kernel crypto API and can be used by any caller.
> > 
> > +config CRYPTO_KDF800108_CTR
> > +	tristate "Counter KDF (SP800-108)"
> > +	select CRYPTO_HASH
> > +	help
> > +	  Enable the key derivation function in counter mode compliant to
> > +	  SP800-108.
> 
> These are just some library functions, so they shouldn't be user-selectable.

Ok, I will remove the user-visible entry in the kernel configuration.

> > +/*
> > + * The seeding of the KDF
> > + */
> > +int crypto_kdf108_setkey(struct crypto_shash *kmd,
> > +			 const u8 *key, size_t keylen,
> > +			 const u8 *ikm, size_t ikmlen)
> > +{
> > +	unsigned int ds = crypto_shash_digestsize(kmd);
> > +
> > +	/* SP800-108 does not support IKM */
> > +	if (ikm || ikmlen)
> > +		return -EINVAL;
> 
> Why have the ikm parameter if it's not supported?

The original idea is that we have a common function declaration for SP800-108 
and HKDF. I am still thinking that in the long run, a KDF template support may 
make sense. In this case, a common function declaration would be needed for 
all KDF implementations.

Furthermore, the test code can be shared between the different KDFs when we 
allow the ikm/ikmlen parameter for this function.
> 
> > +	/*
> > +	 * We require that we operate on a MAC -- if we do not operate on a
> > +	 * MAC, this function returns an error.
> > +	 */
> > +	return crypto_shash_setkey(kmd, key, keylen);
> > +}
> > +EXPORT_SYMBOL(crypto_kdf108_setkey);
> 
> Well, crypto_shash_setkey() will succeed if the hash algorithm takes a
> "key". That doesn't necessarily mean that it's a MAC.	It could be crc32 or
> xxhash64, for example; those interpret the "key" as the initial value.

Agreed. But I am not sure a check in this regard would be needed considering 
that this KDF is only an internal service function.

I have updated the comment accordingly.
> 
> > +static int __init crypto_kdf108_init(void)
> > +{
> > +	int ret = kdf_test(&kdf_ctr_hmac_sha256_tv_template[0], 
"hmac(sha256)",
> > +			   crypto_kdf108_setkey, crypto_kdf108_ctr_generate);
> > +
> > +	if (ret)
> > +		pr_warn("alg: self-tests for CTR-KDF (hmac(sha256)) failed 
(rc=%d)\n",
> > +			ret);
> 
> This should be a WARN() since it indicates a kernel bug.

Changed. Considering that the test result behavior should be identical to 
testmgr.c, I have added also the panic() call in case of fips_enabled.

Thanks a lot for your review.
> 
> - Eric


Ciao
Stephan

Re: [PATCH v3 3/4] security: DH - remove dead code for zero padding

[Stephan Mueller]

Am Mittwoch, 17. November 2021, 22:28:46 CET schrieb Mat Martineau:

Hi Mat,

> On Mon, 15 Nov 2021, Stephan Müller wrote:
> > Remove the specific code that adds a zero padding that was intended
> > to be invoked when the DH operation result was smaller than the
> > modulus. However, this cannot occur any more these days because the
> > function mpi_write_to_sgl is used in the code path that calculates the
> > shared secret in dh_compute_value. This MPI service function guarantees
> > that leading zeros are introduced as needed to ensure the resulting data
> > is exactly as long as the modulus. This implies that the specific code
> > to add zero padding is dead code which can be safely removed.
> > 
> > Signed-off-by: Stephan Mueller <smueller@chronox.de>
> > ---
> > security/keys/dh.c | 25 ++++---------------------
> > 1 file changed, 4 insertions(+), 21 deletions(-)
> 
> Hi Stephan -
> 
> Thanks for the cleanup!

Thank you for the review.
> 
> Acked-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

I have added your signature to the patch.

Ciao
Stephan