nvme: add nvme_auth_derive_tls_psk()

Add a function to derive the TLS PSK as specified TP8018.

Signed-off-by: Hannes Reinecke <[e-mail]>
Reviewed-by: Sagi Grimberg <[e-mail]>
Signed-off-by: Keith Busch <[e-mail]>

drivers/nvme/common/Kconfig

···
 	select CRYPTO_SHA512
 	select CRYPTO_DH
 	select CRYPTO_DH_RFC7919_GROUPS
+	select CRYPTO_HKDF

drivers/nvme/common/auth.c

···
 #include <linux/nvme.h>
 #include <linux/nvme-auth.h>
 
+#define HKDF_MAX_HASHLEN 64
+
 static u32 nvme_dhchap_seqnum;
 static DEFINE_MUTEX(nvme_dhchap_mutex);
 
···
 	return ret;
 }
 EXPORT_SYMBOL_GPL(nvme_auth_generate_digest);
+
+/**
+ * nvme_auth_derive_tls_psk - Derive TLS PSK
+ * @hmac_id: Hash function identifier
+ * @psk: generated input PSK
+ * @psk_len: size of @psk
+ * @psk_digest: TLS PSK digest
+ * @ret_psk: Pointer to the resulting TLS PSK
+ *
+ * Derive a TLS PSK as specified in TP8018 Section 3.6.1.3:
+ *   TLS PSK and PSK identity Derivation
+ *
+ * The TLS PSK shall be derived as follows from an input PSK
+ * (i.e., either a retained PSK or a generated PSK) and a PSK
+ * identity using the HKDF-Extract and HKDF-Expand-Label operations
+ * (refer to RFC 5869 and RFC 8446) where the hash function is the
+ * one specified by the hash specifier of the PSK identity:
+ * 1. PRK = HKDF-Extract(0, Input PSK); and
+ * 2. TLS PSK = HKDF-Expand-Label(PRK, "nvme-tls-psk", PskIdentityContext, L),
+ * where PskIdentityContext is the hash identifier indicated in
+ * the PSK identity concatenated to a space character and to the
+ * Base64 PSK digest (i.e., "<hash> <PSK digest>") and L is the
+ * output size in bytes of the hash function (i.e., 32 for SHA-256
+ * and 48 for SHA-384).
+ *
+ * Returns 0 on success with a valid psk pointer in @ret_psk or a negative
+ * error number otherwise.
+ */
+int nvme_auth_derive_tls_psk(int hmac_id, u8 *psk, size_t psk_len,
+		u8 *psk_digest, u8 **ret_psk)
+{
+	struct crypto_shash *hmac_tfm;
+	const char *hmac_name;
+	const char *psk_prefix = "tls13 nvme-tls-psk";
+	static const char default_salt[HKDF_MAX_HASHLEN];
+	size_t info_len, prk_len;
+	char *info;
+	unsigned char *prk, *tls_key;
+	int ret;
+
+	hmac_name = nvme_auth_hmac_name(hmac_id);
+	if (!hmac_name) {
+		pr_warn("%s: invalid hash algorithm %d\n",
+			__func__, hmac_id);
+		return -EINVAL;
+	}
+	if (hmac_id == NVME_AUTH_HASH_SHA512) {
+		pr_warn("%s: unsupported hash algorithm %s\n",
+			__func__, hmac_name);
+		return -EINVAL;
+	}
+
+	hmac_tfm = crypto_alloc_shash(hmac_name, 0, 0);
+	if (IS_ERR(hmac_tfm))
+		return PTR_ERR(hmac_tfm);
+
+	prk_len = crypto_shash_digestsize(hmac_tfm);
+	prk = kzalloc(prk_len, GFP_KERNEL);
+	if (!prk) {
+		ret = -ENOMEM;
+		goto out_free_shash;
+	}
+
+	if (WARN_ON(prk_len > HKDF_MAX_HASHLEN)) {
+		ret = -EINVAL;
+		goto out_free_prk;
+	}
+	ret = hkdf_extract(hmac_tfm, psk, psk_len,
+			   default_salt, prk_len, prk);
+	if (ret)
+		goto out_free_prk;
+
+	ret = crypto_shash_setkey(hmac_tfm, prk, prk_len);
+	if (ret)
+		goto out_free_prk;
+
+	/*
+	 * 2 addtional bytes for the length field from HDKF-Expand-Label,
+	 * 2 addtional bytes for the HMAC ID, and one byte for the space
+	 * separator.
+	 */
+	info_len = strlen(psk_digest) + strlen(psk_prefix) + 5;
+	info = kzalloc(info_len + 1, GFP_KERNEL);
+	if (!info) {
+		ret = -ENOMEM;
+		goto out_free_prk;
+	}
+
+	put_unaligned_be16(psk_len, info);
+	memcpy(info + 2, psk_prefix, strlen(psk_prefix));
+	sprintf(info + 2 + strlen(psk_prefix), "%02d %s", hmac_id, psk_digest);
+
+	tls_key = kzalloc(psk_len, GFP_KERNEL);
+	if (!tls_key) {
+		ret = -ENOMEM;
+		goto out_free_info;
+	}
+	ret = hkdf_expand(hmac_tfm, info, info_len, tls_key, psk_len);
+	if (ret) {
+		kfree(tls_key);
+		goto out_free_info;
+	}
+	*ret_psk = tls_key;
+
+out_free_info:
+	kfree(info);
+out_free_prk:
+	kfree(prk);
+out_free_shash:
+	crypto_free_shash(hmac_tfm);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(nvme_auth_derive_tls_psk);
 
 MODULE_DESCRIPTION("NVMe Authentication framework");
 MODULE_LICENSE("GPL v2");

include/linux/nvme-auth.h

···
 			   u8 **ret_psk, size_t *ret_len);
 int nvme_auth_generate_digest(u8 hmac_id, u8 *psk, size_t psk_len,
 		char *subsysnqn, char *hostnqn, u8 **ret_digest);
+int nvme_auth_derive_tls_psk(int hmac_id, u8 *psk, size_t psk_len,
+		u8 *psk_digest, u8 **ret_psk);
 
 #endif /* _NVME_AUTH_H */