linux-kernel - Re: [PATCH v11 10/10] certs: Add support for using elliptic curve keys for signing modules

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Date:   Wed, 10 Mar 2021 19:31:14 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        davem@...emloft.net, herbert@...dor.apana.org.au,
        dhowells@...hat.com, zohar@...ux.ibm.com,
        linux-kernel@...r.kernel.org, patrick@...terwijk.org,
        linux-integrity@...r.kernel.org,
        Stefan Berger <stefanb@...ux.ibm.com>
Subject: Re: [PATCH v11 10/10] certs: Add support for using elliptic curve
 keys for signing modules

On Fri, Mar 05, 2021 at 03:59:56PM -0500, Stefan Berger wrote:
> From: Stefan Berger <stefanb@...ux.ibm.com>
> 
> 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 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@...ux.ibm.com>
> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>

Acked-by: Jarkko Sakkinen <jarkko@...nel.org>

/Jarkko

> ---
> 
> 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
> 
>