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SubjectRe: [PATCH v2 2/2] certs: Add support for using elliptic curve keys for signing modules
+++ Stefan Berger [08/04/21 11:24 -0400]:
>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>
>
>---
>v2:
> - check for ECDSA key by id-ecPublicKey from output line
> 'Public Key Algorithm: id-ecPublicKey'.
>---
> certs/Kconfig | 25 +++++++++++++++++++++++++
> certs/Makefile | 9 +++++++++
> crypto/asymmetric_keys/pkcs7_parser.c | 4 ++++
> 3 files changed, 38 insertions(+)
>
>diff --git a/certs/Kconfig b/certs/Kconfig
>index 48675ad319db..6f8337874ae0 100644
>--- a/certs/Kconfig
>+++ b/certs/Kconfig
>@@ -15,6 +15,31 @@ 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
>+ 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.
>+
>+ 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 f64bc89ccbf1..c2fabc288550 100644
>--- a/certs/Makefile
>+++ b/certs/Makefile
>@@ -62,7 +62,15 @@ 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) "###"
>@@ -77,6 +85,7 @@ $(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..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;

Hi Stefan,

Does CONFIG_MODULE_SIG_KEY_TYPE_ECDSA have a dependency on MODULE_SIG_SHA256?
By default, MODULE_SIG_SHA1 is selected when CONFIG_MODULE_SIG is enabled.
I was doing some quick testing and found that when I enabled
MODULE_SIG_KEY_TYPE_ECDSA I get a "Unsupported pkey algo: 5" error on
module load, which goes away after fixing my config and selecting
MODULE_SIG_SHA256.

Thanks,

Jessica

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