[PATCH v9 9/9] certs: Add support for using elliptic curve keys for signing modules

[Stefan Berger]

From: Stefan Berger <stefanb@xxxxxxxxxxxxx>

This patch adds support for using elliptic curve keys for signing
modules. It uses a NIST P384 (secp384r1) key if the user chooses an
elliptic curve key and will have ECDSA support built into the kernel.

Note: A developer choosing an ECDSA key for signing modules has to
manually delete the signing key (rm certs/signing_key.*) when falling
back to building an older version of a kernel that only supports RSA
keys since otherwise ECDSA-signed modules will not be usable when that
older kernel runs and the ECDSA key was still used for signing modules.

Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>

---

v8->v9:
 - Automatically select CONFIG_ECDSA for built-in ECDSA support
 - Added help documentation

This patch builds on top Nayna's series for 'kernel build support for
loading the kernel module signing key'.
- https://lkml.org/lkml/2021/2/18/856
---
 certs/Kconfig                         | 22 ++++++++++++++++++++++
 certs/Makefile                        | 14 ++++++++++++++
 crypto/asymmetric_keys/pkcs7_parser.c |  4 ++++
 3 files changed, 40 insertions(+)

diff --git a/certs/Kconfig b/certs/Kconfig
index 48675ad319db..919db43ce80b 100644
--- a/certs/Kconfig
+++ b/certs/Kconfig
@@ -15,6 +15,28 @@ config MODULE_SIG_KEY
          then the kernel will automatically generate the private key and
          certificate as described in Documentation/admin-guide/module-signing.rst
 
+choice
+	prompt "Type of module signing key to be generated"
+	default MODULE_SIG_KEY_TYPE_RSA
+	help
+	 The type of module signing key type to generated. This option
+	 does not apply if a #PKCS11 URI is used.
+
+config MODULE_SIG_KEY_TYPE_RSA
+	bool "RSA"
+	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
+	help
+	 Use an RSA key for module signing.
+
+config MODULE_SIG_KEY_TYPE_ECDSA
+	bool "ECDSA"
+	select CRYPTO_ECDSA
+	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
+	help
+	 Use an elliptic curve key (NIST P384) for module signing.
+
+endchoice
+
 config SYSTEM_TRUSTED_KEYRING
 	bool "Provide system-wide ring of trusted keys"
 	depends on KEYS
diff --git a/certs/Makefile b/certs/Makefile
index 3fe6b73786fa..c487d7021c54 100644
--- a/certs/Makefile
+++ b/certs/Makefile
@@ -69,6 +69,18 @@ else
 SIGNER = -signkey $(obj)/signing_key.key
 endif # CONFIG_IMA_APPRAISE_MODSIG
 
+X509TEXT=$(shell openssl x509 -in $(CONFIG_MODULE_SIG_KEY) -text)
+
+# Support user changing key type
+ifdef CONFIG_MODULE_SIG_KEY_TYPE_ECDSA
+keytype_openssl = -newkey ec -pkeyopt ec_paramgen_curve:secp384r1
+$(if $(findstring ecdsa-with-,$(X509TEXT)),,$(shell rm -f $(CONFIG_MODULE_SIG_KEY)))
+endif
+
+ifdef CONFIG_MODULE_SIG_KEY_TYPE_RSA
+$(if $(findstring rsaEncryption,$(X509TEXT)),,$(shell rm -f $(CONFIG_MODULE_SIG_KEY)))
+endif
+
 $(obj)/signing_key.pem: $(obj)/x509.genkey
 	@$(kecho) "###"
 	@$(kecho) "### Now generating an X.509 key pair to be used for signing modules."
@@ -86,12 +98,14 @@ ifeq ($(CONFIG_IMA_APPRAISE_MODSIG),y)
 		-batch -x509 -config $(obj)/x509.genkey \
 		-outform PEM -out $(CA_KEY) \
 		-keyout $(CA_KEY) -extensions ca_ext \
+		$(keytype_openssl) \
 		$($(quiet)redirect_openssl)
 endif # CONFIG_IMA_APPRAISE_MODSIG
 	$(Q)openssl req -new -nodes -utf8 \
 		-batch -config $(obj)/x509.genkey \
 		-outform PEM -out $(obj)/signing_key.csr \
 		-keyout $(obj)/signing_key.key -extensions myexts \
+		$(keytype_openssl) \
 		$($(quiet)redirect_openssl)
 	$(Q)openssl x509 -req -days 36500 -in $(obj)/signing_key.csr \
 		-outform PEM -out $(obj)/signing_key.crt $(SIGNER) \
diff --git a/crypto/asymmetric_keys/pkcs7_parser.c b/crypto/asymmetric_keys/pkcs7_parser.c
index 967329e0a07b..2546ec6a0505 100644
--- a/crypto/asymmetric_keys/pkcs7_parser.c
+++ b/crypto/asymmetric_keys/pkcs7_parser.c
@@ -269,6 +269,10 @@ int pkcs7_sig_note_pkey_algo(void *context, size_t hdrlen,
 		ctx->sinfo->sig->pkey_algo = "rsa";
 		ctx->sinfo->sig->encoding = "pkcs1";
 		break;
+	case OID_id_ecdsa_with_sha256:
+		ctx->sinfo->sig->pkey_algo = "ecdsa";
+		ctx->sinfo->sig->encoding = "x962";
+		break;
 	default:
 		printk("Unsupported pkey algo: %u\n", ctx->last_oid);
 		return -ENOPKG;
-- 
2.29.2