[PATCH v5 2/2] certs: Add support for using elliptic curve keys for signing modules

Stefan Berger
2021-06-01T10:53:25Z

Add 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 should still
delete the signing key (rm certs/signing_key.*) when building an older
version of a kernel that only supports RSA keys. Unless kbuild automati-
cally detects and generates a new kernel module key, ECDSA-signed kernel
modules will fail signature verification.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Mimi Zohar <zohar@linux.ibm.com>
---
certs/Kconfig | 26 ++++++++++++++++++++++++++
certs/Makefile | 9 +++++++++
crypto/asymmetric_keys/pkcs7_parser.c | 8 ++++++++
3 files changed, 43 insertions(+)

diff --git a/certs/Kconfig b/certs/Kconfig
index f4e61116f94e..916cbb1af928 100644
--- a/certs/Kconfig
+++ b/certs/Kconfig
@@ -15,6 +15,32 @@ 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 generate. 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 && MODULES)
+ 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 && MODULES)
+ help
+ Use an elliptic curve key (NIST P384) for module signing. Consider
+ using a strong hash like sha256 or sha384 for hashing modules.
+
+ Note: Remove all ECDSA signing keys, e.g. certs/signing_key.pem,
+ when falling back to building Linux 5.11 and older kernels.
+
+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 e6f97c64aa99..3a790d07e951 100644
--- a/certs/Makefile
+++ b/certs/Makefile
@@ -65,7 +65,15 @@ ifeq ($(CONFIG_MODULE_SIG_KEY),"certs/signing_key.pem")

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 $(findstring id-ecPublicKey,$(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) "###"
@@ -80,6 +88,7 @@ $(obj)/signing_key.pem: $(obj)/x509.genkey
-batch -x509 -config $(obj)/x509.genkey \
-outform PEM -out $(obj)/signing_key.pem \
-keyout $(obj)/signing_key.pem \
+ $(keytype_openssl) \
$($(quiet)redirect_openssl)
@$(kecho) "###"
@$(kecho) "### Key pair generated."
diff --git a/crypto/asymmetric_keys/pkcs7_parser.c b/crypto/asymmetric_keys/pkcs7_parser.c
index 967329e0a07b..6592279d839a 100644
--- a/crypto/asymmetric_keys/pkcs7_parser.c
+++ b/crypto/asymmetric_keys/pkcs7_parser.c
@@ -269,6 +269,14 @@ 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_sha1:
+ case OID_id_ecdsa_with_sha224:
+ case OID_id_ecdsa_with_sha256:
+ case OID_id_ecdsa_with_sha384:
+ case OID_id_ecdsa_with_sha512:
+ 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