char/lrng: add common generic hash support

The LRNG switchable DRNG support also allows the replacement of the hash
implementation used as conditioning component. The common generic hash
support code provides the required callbacks using the synchronous hash
implementations of the kernel crypto API.

All synchronous hash implementations supported by the kernel crypto API
can be used as part of the LRNG with this generic support.

The generic support is intended to be configured by separate switchable
DRNG backends.

CC: Torsten Duwe <duwe@lst.de>
CC: "Eric W. Biederman" <ebiederm@xmission.com>
CC: "Alexander E. Patrakov" <patrakov@gmail.com>
CC: "Ahmed S. Darwish" <darwish.07@gmail.com>
CC: "Theodore Y. Ts'o" <tytso@mit.edu>
CC: Willy Tarreau <w@1wt.eu>
CC: Matthew Garrett <mjg59@srcf.ucam.org>
CC: Vito Caputo <vcaputo@pengaru.com>
CC: Andreas Dilger <adilger.kernel@dilger.ca>
CC: Jan Kara <jack@suse.cz>
CC: Ray Strode <rstrode@redhat.com>
CC: William Jon McCann <mccann@jhu.edu>
CC: zhangjs <zachary@baishancloud.com>
CC: Andy Lutomirski <luto@kernel.org>
CC: Florian Weimer <fweimer@redhat.com>
CC: Lennart Poettering <mzxreary@0pointer.de>
CC: Nicolai Stange <nstange@suse.de>
CC: "Peter, Matthias" <matthias.peter@bsi.bund.de>
CC: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
CC: Neil Horman <nhorman@redhat.com>
Reviewed-by: Alexander Lobakin <alobakin@pm.me>
Tested-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: Stephan Mueller <smueller@chronox.de>

drivers/char/lrng/Kconfig

@@ -209,4 +209,12 @@ menuconfig LRNG_DRNG_SWITCH
 	  accessible via the external interfaces. With this configuration
 	  option other DRNGs can be selected and loaded at runtime.
 
+if LRNG_DRNG_SWITCH
+
+config LRNG_KCAPI_HASH
+	bool
+	select CRYPTO_HASH
+
+endif # LRNG_DRNG_SWITCH
+
 endif # LRNG

drivers/char/lrng/Makefile

@@ -11,3 +11,4 @@ obj-y				+= lrng_es_mgr.o lrng_aux.o \
 obj-$(CONFIG_NUMA)		+= lrng_numa.o
 obj-$(CONFIG_SYSCTL)		+= lrng_proc.o
 obj-$(CONFIG_LRNG_DRNG_SWITCH)	+= lrng_switch.o
+obj-$(CONFIG_LRNG_KCAPI_HASH)	+= lrng_kcapi_hash.o

drivers/char/lrng/lrng_kcapi_hash.c

@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * Backend for providing the hash primitive using the kernel crypto API.
+ *
+ * Copyright (C) 2021, Stephan Mueller <smueller@chronox.de>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <crypto/hash.h>
+
+#include "lrng_kcapi_hash.h"
+
+struct lrng_hash_info {
+	struct crypto_shash *tfm;
+};
+
+static inline void _lrng_kcapi_hash_free(struct lrng_hash_info *lrng_hash)
+{
+	struct crypto_shash *tfm = lrng_hash->tfm;
+
+	crypto_free_shash(tfm);
+	kfree(lrng_hash);
+}
+
+void *lrng_kcapi_hash_alloc(const char *name)
+{
+	struct lrng_hash_info *lrng_hash;
+	struct crypto_shash *tfm;
+	int ret;
+
+	if (!name) {
+		pr_err("Hash name missing\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	tfm = crypto_alloc_shash(name, 0, 0);
+	if (IS_ERR(tfm)) {
+		pr_err("could not allocate hash %s\n", name);
+		return ERR_CAST(tfm);
+	}
+
+	ret = sizeof(struct lrng_hash_info);
+	lrng_hash = kmalloc(ret, GFP_KERNEL);
+	if (!lrng_hash) {
+		crypto_free_shash(tfm);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	lrng_hash->tfm = tfm;
+
+	pr_info("Hash %s allocated\n", name);
+
+	return lrng_hash;
+}
+EXPORT_SYMBOL(lrng_kcapi_hash_alloc);
+
+u32 lrng_kcapi_hash_digestsize(void *hash)
+{
+	struct lrng_hash_info *lrng_hash = (struct lrng_hash_info *)hash;
+	struct crypto_shash *tfm = lrng_hash->tfm;
+
+	return crypto_shash_digestsize(tfm);
+}
+EXPORT_SYMBOL(lrng_kcapi_hash_digestsize);
+
+void lrng_kcapi_hash_dealloc(void *hash)
+{
+	struct lrng_hash_info *lrng_hash = (struct lrng_hash_info *)hash;
+
+	_lrng_kcapi_hash_free(lrng_hash);
+	pr_info("Hash deallocated\n");
+}
+EXPORT_SYMBOL(lrng_kcapi_hash_dealloc);
+
+int lrng_kcapi_hash_init(struct shash_desc *shash, void *hash)
+{
+	struct lrng_hash_info *lrng_hash = (struct lrng_hash_info *)hash;
+	struct crypto_shash *tfm = lrng_hash->tfm;
+
+	shash->tfm = tfm;
+	return crypto_shash_init(shash);
+}
+EXPORT_SYMBOL(lrng_kcapi_hash_init);
+
+int lrng_kcapi_hash_update(struct shash_desc *shash, const u8 *inbuf,
+			   u32 inbuflen)
+{
+	return crypto_shash_update(shash, inbuf, inbuflen);
+}
+EXPORT_SYMBOL(lrng_kcapi_hash_update);
+
+int lrng_kcapi_hash_final(struct shash_desc *shash, u8 *digest)
+{
+	return crypto_shash_final(shash, digest);
+}
+EXPORT_SYMBOL(lrng_kcapi_hash_final);
+
+void lrng_kcapi_hash_zero(struct shash_desc *shash)
+{
+	shash_desc_zero(shash);
+}
+EXPORT_SYMBOL(lrng_kcapi_hash_zero);

drivers/char/lrng/lrng_kcapi_hash.h

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
+/*
+ * Copyright (C) 2020 - 2021, Stephan Mueller <smueller@chronox.de>
+ */
+
+#ifndef _LRNG_KCAPI_HASH_H
+#define _LRNG_KCAPI_HASH_H
+
+#include <linux/module.h>
+
+void *lrng_kcapi_hash_alloc(const char *name);
+u32 lrng_kcapi_hash_digestsize(void *hash);
+void lrng_kcapi_hash_dealloc(void *hash);
+int lrng_kcapi_hash_init(struct shash_desc *shash, void *hash);
+int lrng_kcapi_hash_update(struct shash_desc *shash, const u8 *inbuf,
+			   u32 inbuflen);
+int lrng_kcapi_hash_final(struct shash_desc *shash, u8 *digest);
+void lrng_kcapi_hash_zero(struct shash_desc *shash);
+
+#endif /* _LRNG_KCAPI_HASH_H */