crypto: remove HKDF library

Remove crypto/hkdf.c, since it's no longer used.  Originally it had two
users, but now both of them just inline the needed HMAC computations
using the HMAC library APIs.  That ends up being better, since it
eliminates all the complexity and performance issues associated with the
crypto_shash abstraction and multi-step HMAC input formatting.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>

crypto/Kconfig

@@ -141,12 +141,6 @@ config CRYPTO_ACOMP
 	select CRYPTO_ALGAPI
 	select CRYPTO_ACOMP2
 
-config CRYPTO_HKDF
-	tristate
-	select CRYPTO_SHA256 if CRYPTO_SELFTESTS
-	select CRYPTO_SHA512 if CRYPTO_SELFTESTS
-	select CRYPTO_HASH2
-
 config CRYPTO_MANAGER
 	tristate
 	default CRYPTO_ALGAPI if CRYPTO_SELFTESTS

crypto/Makefile

@@ -36,7 +36,6 @@ obj-$(CONFIG_CRYPTO_HASH2) += crypto_hash.o
 obj-$(CONFIG_CRYPTO_AKCIPHER2) += akcipher.o
 obj-$(CONFIG_CRYPTO_SIG2) += sig.o
 obj-$(CONFIG_CRYPTO_KPP2) += kpp.o
-obj-$(CONFIG_CRYPTO_HKDF) += hkdf.o
 
 dh_generic-y := dh.o
 dh_generic-y += dh_helper.o

include/crypto/hkdf.h

@@ -1,20 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * HKDF: HMAC-based Key Derivation Function (HKDF), RFC 5869
- *
- * Extracted from fs/crypto/hkdf.c, which has
- * Copyright 2019 Google LLC
- */
-
-#ifndef _CRYPTO_HKDF_H
-#define _CRYPTO_HKDF_H
-
-#include <crypto/hash.h>
-
-int hkdf_extract(struct crypto_shash *hmac_tfm, const u8 *ikm,
-		 unsigned int ikmlen, const u8 *salt, unsigned int saltlen,
-		 u8 *prk);
-int hkdf_expand(struct crypto_shash *hmac_tfm,
-		const u8 *info, unsigned int infolen,
-		u8 *okm, unsigned int okmlen);
-#endif