[PATCH v8 0/2] Add support for ECDSA-signed kernel modules

[PATCH v8 0/2] Add support for ECDSA-signed kernel modules

[Stefan Berger]

From: Stefan Berger <stefanb@linux.ibm.com>

This series adds support for ECDSA-signed kernel modules. It also
attempts to address a kbuild issue where a developer created an ECDSA
key for signing kernel modules and then builds an older version of the
kernel, when bisecting the kernel for example, that does not support
ECDSA keys.

The first patch addresses the kbuild issue of needing to delete that
ECDSA key if it is in certs/signing_key.pem and trigger the creation
of an RSA key. However, for this to work this patch would have to be
backported to previous versions of the kernel but would also only work
for the developer if he/she used a stable version of the kernel to which
this patch was applied. So whether this patch actually achieves the
wanted effect is not always guaranteed.

The 2nd patch adds the support for the ECSDA-signed kernel modules.

  Stefan

v8:
  - Removed R-b tags and reordered Cc tags

v7:
  - Changed Kconfig reference to kernel version from 5.11 to 5.13
  - Redirecting stderr of openssl to NULL device to address kernel robot
    detected issue
  - Replaced $(CONFIG_MODULE_SIG_KEY) with "certs/signing_key.pem" following
    Linus's suggestion

v6:
  - Patch 2/4 is fixing V4's 1/2 and 4/4 is fixing V4's 2/2. Both fixup
    patches to be squashed.

v5:
  - do not touch the key files if openssl is not installed; likely
    addresses an issue pointed out by kernel test robot

v4:
  - extending 'depends on' with MODULES to (IMA_APPRAISE_MODSIG && MODULES)
  
v3:
  - added missing OIDs for ECDSA signed hashes to pkcs7_sig_note_pkey_algo
  - added recommendation to use string hash to Kconfig help text

v2:
  - Adjustment to ECDSA key detector string in 2/2
  - Rephrased cover letter and patch descriptions with Mimi


Stefan Berger (2):
  certs: Trigger creation of RSA module signing key if it's not an RSA
    key
  certs: Add support for using elliptic curve keys for signing modules

 certs/Kconfig                         | 26 ++++++++++++++++++++++++++
 certs/Makefile                        | 21 +++++++++++++++++++++
 crypto/asymmetric_keys/pkcs7_parser.c |  8 ++++++++
 3 files changed, 55 insertions(+)

-- 
2.31.1

[PATCH v8 1/2] certs: Trigger creation of RSA module signing key if it's not an RSA key

[Stefan Berger]

From: Stefan Berger <stefanb@linux.ibm.com>

Address a kbuild issue where a developer created an ECDSA key for signing
kernel modules and then builds an older version of the kernel, when bi-
secting the kernel for example, that does not support ECDSA keys.

If openssl is installed, trigger the creation of an RSA module signing
key if it is not an RSA key.

Fixes: cfc411e7fff3 ("Move certificate handling to its own directory")
Cc: David Howells <dhowells@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 certs/Makefile | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/certs/Makefile b/certs/Makefile
index 359239a0ee9e..f9344e52ecda 100644
--- a/certs/Makefile
+++ b/certs/Makefile
@@ -57,11 +57,19 @@ endif
 redirect_openssl	= 2>&1
 quiet_redirect_openssl	= 2>&1
 silent_redirect_openssl = 2>/dev/null
+openssl_available       = $(shell openssl help 2>/dev/null && echo yes)
 
 # We do it this way rather than having a boolean option for enabling an
 # external private key, because 'make randconfig' might enable such a
 # boolean option and we unfortunately can't make it depend on !RANDCONFIG.
 ifeq ($(CONFIG_MODULE_SIG_KEY),"certs/signing_key.pem")
+
+ifeq ($(openssl_available),yes)
+X509TEXT=$(shell openssl x509 -in "certs/signing_key.pem" -text 2>/dev/null)
+
+$(if $(findstring rsaEncryption,$(X509TEXT)),,$(shell rm -f "certs/signing_key.pem"))
+endif
+
 $(obj)/signing_key.pem: $(obj)/x509.genkey
 	@$(kecho) "###"
 	@$(kecho) "### Now generating an X.509 key pair to be used for signing modules."
-- 
2.31.1

[PATCH v8 2/2] certs: Add support for using elliptic curve keys for signing modules

[Stefan Berger]

From: Stefan Berger <stefanb@linux.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 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.

Cc: David Howells <dhowells@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 certs/Kconfig                         | 26 ++++++++++++++++++++++++++
 certs/Makefile                        | 13 +++++++++++++
 crypto/asymmetric_keys/pkcs7_parser.c |  8 ++++++++
 3 files changed, 47 insertions(+)

diff --git a/certs/Kconfig b/certs/Kconfig
index f4e61116f94e..7d38d65e2128 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 5.13 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 f9344e52ecda..279433783b10 100644
--- a/certs/Makefile
+++ b/certs/Makefile
@@ -66,9 +66,21 @@ ifeq ($(CONFIG_MODULE_SIG_KEY),"certs/signing_key.pem")
 
 ifeq ($(openssl_available),yes)
 X509TEXT=$(shell openssl x509 -in "certs/signing_key.pem" -text 2>/dev/null)
+endif
 
+# Support user changing key type
+ifdef CONFIG_MODULE_SIG_KEY_TYPE_ECDSA
+keytype_openssl = -newkey ec -pkeyopt ec_paramgen_curve:secp384r1
+ifeq ($(openssl_available),yes)
+$(if $(findstring id-ecPublicKey,$(X509TEXT)),,$(shell rm -f "certs/signing_key.pem"))
+endif
+endif # CONFIG_MODULE_SIG_KEY_TYPE_ECDSA
+
+ifdef CONFIG_MODULE_SIG_KEY_TYPE_RSA
+ifeq ($(openssl_available),yes)
 $(if $(findstring rsaEncryption,$(X509TEXT)),,$(shell rm -f "certs/signing_key.pem"))
 endif
+endif # CONFIG_MODULE_SIG_KEY_TYPE_RSA
 
 $(obj)/signing_key.pem: $(obj)/x509.genkey
 	@$(kecho) "###"
@@ -83,6 +95,7 @@ $(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;
-- 
2.31.1

Re: [PATCH v8 1/2] certs: Trigger creation of RSA module signing key if it's not an RSA key

[Linus Torvalds]

On Tue, Jun 29, 2021 at 2:34 PM Stefan Berger
<stefanb@linux.vnet.ibm.com> wrote:
>
> Address a kbuild issue where a developer created an ECDSA key for signing
> kernel modules and then builds an older version of the kernel, when bi-
> secting the kernel for example, that does not support ECDSA keys.

Thanks, these two don't confuse me any more.

                Linus

Re: [PATCH v8 1/2] certs: Trigger creation of RSA module signing key if it's not an RSA key

[Jarkko Sakkinen]

On Wed, Jun 30, 2021 at 12:17:38PM -0700, Linus Torvalds wrote:
> On Tue, Jun 29, 2021 at 2:34 PM Stefan Berger
> <stefanb@linux.vnet.ibm.com> wrote:
> >
> > Address a kbuild issue where a developer created an ECDSA key for signing
> > kernel modules and then builds an older version of the kernel, when bi-
> > secting the kernel for example, that does not support ECDSA keys.
> 
> Thanks, these two don't confuse me any more.
> 
>                 Linus

I'll (re-)test the changes, and make a PR after rc1 out.

/Jarkko

Re: [PATCH v8 0/2] Add support for ECDSA-signed kernel modules

[Jarkko Sakkinen]

On Tue, Jun 29, 2021 at 05:34:19PM -0400, Stefan Berger wrote:
> From: Stefan Berger <stefanb@linux.ibm.com>
> 
> This series adds support for ECDSA-signed kernel modules. It also
> attempts to address a kbuild issue where a developer created an ECDSA
> key for signing kernel modules and then builds an older version of the
> kernel, when bisecting the kernel for example, that does not support
> ECDSA keys.
> 
> The first patch addresses the kbuild issue of needing to delete that
> ECDSA key if it is in certs/signing_key.pem and trigger the creation
> of an RSA key. However, for this to work this patch would have to be
> backported to previous versions of the kernel but would also only work
> for the developer if he/she used a stable version of the kernel to which
> this patch was applied. So whether this patch actually achieves the
> wanted effect is not always guaranteed.
> 
> The 2nd patch adds the support for the ECSDA-signed kernel modules.
> 
>   Stefan
> 
> v8:
>   - Removed R-b tags and reordered Cc tags
> 
> v7:
>   - Changed Kconfig reference to kernel version from 5.11 to 5.13
>   - Redirecting stderr of openssl to NULL device to address kernel robot
>     detected issue
>   - Replaced $(CONFIG_MODULE_SIG_KEY) with "certs/signing_key.pem" following
>     Linus's suggestion
> 
> v6:
>   - Patch 2/4 is fixing V4's 1/2 and 4/4 is fixing V4's 2/2. Both fixup
>     patches to be squashed.
> 
> v5:
>   - do not touch the key files if openssl is not installed; likely
>     addresses an issue pointed out by kernel test robot
> 
> v4:
>   - extending 'depends on' with MODULES to (IMA_APPRAISE_MODSIG && MODULES)
>   
> v3:
>   - added missing OIDs for ECDSA signed hashes to pkcs7_sig_note_pkey_algo
>   - added recommendation to use string hash to Kconfig help text
> 
> v2:
>   - Adjustment to ECDSA key detector string in 2/2
>   - Rephrased cover letter and patch descriptions with Mimi
> 
> 
> Stefan Berger (2):
>   certs: Trigger creation of RSA module signing key if it's not an RSA
>     key
>   certs: Add support for using elliptic curve keys for signing modules
> 
>  certs/Kconfig                         | 26 ++++++++++++++++++++++++++
>  certs/Makefile                        | 21 +++++++++++++++++++++
>  crypto/asymmetric_keys/pkcs7_parser.c |  8 ++++++++
>  3 files changed, 55 insertions(+)
> 
> -- 
> 2.31.1
> 
> 

LGTM

For both:

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

/Jarkko