[PATCH v6 0/4] Check codeSigning extended key usage extension

[PATCH v6 0/4] Check codeSigning extended key usage extension

[Lee, Chun-Yi]

NIAP PP_OS certification requests that the OS shall validate the
CodeSigning extended key usage extension field for integrity
verifiction of exectable code:

    https://www.niap-ccevs.org/MMO/PP/-442-/
        FIA_X509_EXT.1.1

This patchset adds the logic for parsing the codeSigning EKU extension
field in X.509. And checking the CodeSigning EKU when verifying
signature of kernel module or kexec PE binary in PKCS#7.

v6:
- Add more length checking when parsing extKeyUsage and EKU's OID blob.
- Add 'usage' parameter to the comment of pkcs7_validate_trust function.

v5:
Fixed the wording in module-signing.rst.

v4:
Fixed the wording in patch description.

v3:
- Add codeSigning EKU to x509.genkey key generation config.
- Add openssl command option example for generating CodeSign EKU to
  module-signing.rst document. 

v2:
Changed the help wording in the Kconfig.

Lee, Chun-Yi (4):
  X.509: Add CodeSigning extended key usage parsing
  PKCS#7: Check codeSigning EKU for kernel module and kexec pe
    verification
  modsign: Add codeSigning EKU when generating X.509 key generation
    config
  Documentation/admin-guide/module-signing.rst: add openssl command
    option example for CodeSign EKU

 Documentation/admin-guide/module-signing.rst |  6 +++++
 certs/Makefile                               |  1 +
 certs/system_keyring.c                       |  2 +-
 crypto/asymmetric_keys/Kconfig               |  9 +++++++
 crypto/asymmetric_keys/pkcs7_trust.c         | 37 +++++++++++++++++++++++++---
 crypto/asymmetric_keys/x509_cert_parser.c    | 24 ++++++++++++++++++
 include/crypto/pkcs7.h                       |  3 ++-
 include/crypto/public_key.h                  |  1 +
 include/linux/oid_registry.h                 |  5 ++++
 9 files changed, 83 insertions(+), 5 deletions(-)

-- 
2.16.4

[PATCH v6,1/4] X.509: Add CodeSigning extended key usage parsing

[Lee, Chun-Yi]

This patch adds the logic for parsing the CodeSign extended key usage
extension in X.509. The parsing result will be set to the eku flag
which is carried by public key. It can be used in the PKCS#7
verification.

Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
---
 crypto/asymmetric_keys/x509_cert_parser.c | 25 +++++++++++++++++++++++++
 include/crypto/public_key.h               |  1 +
 include/linux/oid_registry.h              |  5 +++++
 3 files changed, 31 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 6d003096b5bc..996db9419474 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -542,6 +542,8 @@ int x509_process_extension(void *context, size_t hdrlen,
 	struct x509_parse_context *ctx = context;
 	struct asymmetric_key_id *kid;
 	const unsigned char *v = value;
+	int i = 0;
+	enum OID oid;
 
 	pr_debug("Extension: %u\n", ctx->last_oid);
 
@@ -571,6 +573,29 @@ int x509_process_extension(void *context, size_t hdrlen,
 		return 0;
 	}
 
+	if (ctx->last_oid == OID_extKeyUsage) {
+		if (vlen < 2 ||
+		    v[0] != ((ASN1_UNIV << 6) | ASN1_CONS_BIT | ASN1_SEQ) ||
+		    v[1] != vlen - 2)
+			return -EBADMSG;
+		i += 2;
+
+		while (i < vlen) {
+			/* A 10 bytes EKU OID Octet blob =
+			 * ASN1_OID + size byte + 8 bytes OID */
+			if ((i + 10) > vlen || v[i] != ASN1_OID || v[i + 1] != 8)
+				return -EBADMSG;
+
+			oid = look_up_OID(v + i + 2, v[i + 1]);
+			if (oid == OID_codeSigning) {
+				ctx->cert->pub->eku |= EKU_codeSigning;
+			}
+			i += 10;
+		}
+		pr_debug("extKeyUsage: %d\n", ctx->cert->pub->eku);
+		return 0;
+	}
+
 	return 0;
 }
 
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 47accec68cb0..1ccaebe2a28b 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -28,6 +28,7 @@ struct public_key {
 	bool key_is_private;
 	const char *id_type;
 	const char *pkey_algo;
+	unsigned int eku : 9;      /* Extended Key Usage (9-bit) */
 };
 
 extern void public_key_free(struct public_key *key);
diff --git a/include/linux/oid_registry.h b/include/linux/oid_registry.h
index 461b7aa587ba..8c8935f0eb73 100644
--- a/include/linux/oid_registry.h
+++ b/include/linux/oid_registry.h
@@ -125,9 +125,14 @@ enum OID {
 	OID_TPMImportableKey,		/* 2.23.133.10.1.4 */
 	OID_TPMSealedData,		/* 2.23.133.10.1.5 */
 
+	/* Extended key purpose OIDs [RFC 5280] */
+	OID_codeSigning,		/* 1.3.6.1.5.5.7.3.3 */
+
 	OID__NR
 };
 
+#define EKU_codeSigning	(1 << 2)
+
 extern enum OID look_up_OID(const void *data, size_t datasize);
 extern int parse_OID(const void *data, size_t datasize, enum OID *oid);
 extern int sprint_oid(const void *, size_t, char *, size_t);
-- 
2.16.4

[PATCH v6,2/4] PKCS#7: Check codeSigning EKU for kernel module and kexec pe verification

[Lee, Chun-Yi]

This patch adds the logic for checking the CodeSigning extended
key usage when verifying signature of kernel module or
kexec PE binary in PKCS#7.

Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
---
 certs/system_keyring.c               |  2 +-
 crypto/asymmetric_keys/Kconfig       |  9 +++++++++
 crypto/asymmetric_keys/pkcs7_trust.c | 38 +++++++++++++++++++++++++++++++++---
 include/crypto/pkcs7.h               |  3 ++-
 4 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index 0c9a4795e847..302ca0555e75 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -206,7 +206,7 @@ int verify_pkcs7_message_sig(const void *data, size_t len,
 			goto error;
 		}
 	}
-	ret = pkcs7_validate_trust(pkcs7, trusted_keys);
+	ret = pkcs7_validate_trust(pkcs7, trusted_keys, usage);
 	if (ret < 0) {
 		if (ret == -ENOKEY)
 			pr_devel("PKCS#7 signature not signed with a trusted key\n");
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index 1f1f004dc757..1754812df989 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -96,4 +96,13 @@ config SIGNED_PE_FILE_VERIFICATION
 	  This option provides support for verifying the signature(s) on a
 	  signed PE binary.
 
+config CHECK_CODESIGN_EKU
+	bool "Check codeSigning extended key usage"
+	depends on PKCS7_MESSAGE_PARSER=y
+	depends on SYSTEM_DATA_VERIFICATION
+	help
+	  This option provides support for checking the codeSigning extended
+	  key usage when verifying the signature in PKCS#7. It affects kernel
+	  module verification and kexec PE binary verification.
+
 endif # ASYMMETRIC_KEY_TYPE
diff --git a/crypto/asymmetric_keys/pkcs7_trust.c b/crypto/asymmetric_keys/pkcs7_trust.c
index b531df2013c4..7c27bf81aca9 100644
--- a/crypto/asymmetric_keys/pkcs7_trust.c
+++ b/crypto/asymmetric_keys/pkcs7_trust.c
@@ -16,12 +16,36 @@
 #include <crypto/public_key.h>
 #include "pkcs7_parser.h"
 
+#ifdef CONFIG_CHECK_CODESIGN_EKU
+static bool check_codesign_eku(struct key *key,
+			     enum key_being_used_for usage)
+{
+	struct public_key *public_key = key->payload.data[asym_crypto];
+
+	switch (usage) {
+	case VERIFYING_MODULE_SIGNATURE:
+	case VERIFYING_KEXEC_PE_SIGNATURE:
+		return !!(public_key->eku & EKU_codeSigning);
+	default:
+		break;
+	}
+	return true;
+}
+#else
+static bool check_codesign_eku(struct key *key,
+			     enum key_being_used_for usage)
+{
+	return true;
+}
+#endif
+
 /*
  * Check the trust on one PKCS#7 SignedInfo block.
  */
 static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
 				    struct pkcs7_signed_info *sinfo,
-				    struct key *trust_keyring)
+				    struct key *trust_keyring,
+				    enum key_being_used_for usage)
 {
 	struct public_key_signature *sig = sinfo->sig;
 	struct x509_certificate *x509, *last = NULL, *p;
@@ -112,6 +136,12 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
 	return -ENOKEY;
 
 matched:
+	if (!check_codesign_eku(key, usage)) {
+		pr_warn("sinfo %u: The signer %x key is not CodeSigning\n",
+			sinfo->index, key_serial(key));
+		key_put(key);
+		return -ENOKEY;
+	}
 	ret = verify_signature(key, sig);
 	key_put(key);
 	if (ret < 0) {
@@ -135,6 +165,7 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
  * pkcs7_validate_trust - Validate PKCS#7 trust chain
  * @pkcs7: The PKCS#7 certificate to validate
  * @trust_keyring: Signing certificates to use as starting points
+ * @usage: The use to which the key is being put.
  *
  * Validate that the certificate chain inside the PKCS#7 message intersects
  * keys we already know and trust.
@@ -156,7 +187,8 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
  * May also return -ENOMEM.
  */
 int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
-			 struct key *trust_keyring)
+			 struct key *trust_keyring,
+			 enum key_being_used_for usage)
 {
 	struct pkcs7_signed_info *sinfo;
 	struct x509_certificate *p;
@@ -167,7 +199,7 @@ int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
 		p->seen = false;
 
 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
-		ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
+		ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring, usage);
 		switch (ret) {
 		case -ENOKEY:
 			continue;
diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
index 38ec7f5f9041..b3b48240ba73 100644
--- a/include/crypto/pkcs7.h
+++ b/include/crypto/pkcs7.h
@@ -30,7 +30,8 @@ extern int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
  * pkcs7_trust.c
  */
 extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
-				struct key *trust_keyring);
+				struct key *trust_keyring,
+				enum key_being_used_for usage);
 
 /*
  * pkcs7_verify.c
-- 
2.16.4

[PATCH v6,3/4] modsign: Add codeSigning EKU when generating X.509 key generation config

[Lee, Chun-Yi]

Add codeSigning EKU to the X.509 key generation config for the build time
autogenerated kernel key.

Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
---
 certs/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/certs/Makefile b/certs/Makefile
index b6db52ebf0be..d9515d68778f 100644
--- a/certs/Makefile
+++ b/certs/Makefile
@@ -89,6 +89,7 @@ $(obj)/x509.genkey:
 	@echo >>$@ "keyUsage=digitalSignature"
 	@echo >>$@ "subjectKeyIdentifier=hash"
 	@echo >>$@ "authorityKeyIdentifier=keyid"
+	@echo >>$@ "extendedKeyUsage=codeSigning"
 endif # CONFIG_MODULE_SIG_KEY
 
 $(eval $(call config_filename,MODULE_SIG_KEY))
-- 
2.16.4

[PATCH v6,4/4] Documentation/admin-guide/module-signing.rst: add openssl command option example for CodeSign EKU

[Lee, Chun-Yi]

Add an openssl command option example for generating CodeSign extended
key usage in X.509 when CONFIG_CHECK_CODESIGN_EKU is enabled.

Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
---
 Documentation/admin-guide/module-signing.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/admin-guide/module-signing.rst b/Documentation/admin-guide/module-signing.rst
index 7d7c7c8a545c..ca3b8f19466c 100644
--- a/Documentation/admin-guide/module-signing.rst
+++ b/Documentation/admin-guide/module-signing.rst
@@ -170,6 +170,12 @@ generate the public/private key files::
 	   -config x509.genkey -outform PEM -out kernel_key.pem \
 	   -keyout kernel_key.pem
 
+When ``CONFIG_CHECK_CODESIGN_EKU`` option is enabled, the following openssl
+command option should be added where for generating CodeSign extended key usage
+in X.509::
+
+        -addext "extendedKeyUsage=codeSigning"
+
 The full pathname for the resulting kernel_key.pem file can then be specified
 in the ``CONFIG_MODULE_SIG_KEY`` option, and the certificate and key therein will
 be used instead of an autogenerated keypair.
-- 
2.16.4

Re: [PATCH v6,2/4] PKCS#7: Check codeSigning EKU for kernel module and kexec pe verification

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 3375 bytes --]

Hi Chun-Yi",

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on next-20210429]
[cannot apply to cryptodev/master crypto/master v5.12]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Lee-Chun-Yi/Check-codeSigning-extended-key-usage-extension/20210429-153115
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git d72cd4ad4174cfd2257c426ad51e4f53bcfde9c9
config: powerpc64-randconfig-m031-20210429 (attached as .config)
compiler: powerpc-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/63e6809a57ca114d297694a24283256990aa10df
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Lee-Chun-Yi/Check-codeSigning-extended-key-usage-extension/20210429-153115
        git checkout 63e6809a57ca114d297694a24283256990aa10df
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross W=1 ARCH=powerpc64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   certs/blacklist.c: In function 'is_key_on_revocation_list':
>> certs/blacklist.c:188:8: error: too few arguments to function 'pkcs7_validate_trust'
     188 |  ret = pkcs7_validate_trust(pkcs7, blacklist_keyring);
         |        ^~~~~~~~~~~~~~~~~~~~
   In file included from certs/blacklist.h:3,
                    from certs/blacklist.c:19:
   include/crypto/pkcs7.h:32:12: note: declared here
      32 | extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
         |            ^~~~~~~~~~~~~~~~~~~~


vim +/pkcs7_validate_trust +188 certs/blacklist.c

56c5812623f953 Eric Snowberg 2021-01-22  179  
56c5812623f953 Eric Snowberg 2021-01-22  180  /**
56c5812623f953 Eric Snowberg 2021-01-22  181   * is_key_on_revocation_list - Determine if the key for a PKCS#7 message is revoked
56c5812623f953 Eric Snowberg 2021-01-22  182   * @pkcs7: The PKCS#7 message to check
56c5812623f953 Eric Snowberg 2021-01-22  183   */
56c5812623f953 Eric Snowberg 2021-01-22  184  int is_key_on_revocation_list(struct pkcs7_message *pkcs7)
56c5812623f953 Eric Snowberg 2021-01-22  185  {
56c5812623f953 Eric Snowberg 2021-01-22  186  	int ret;
56c5812623f953 Eric Snowberg 2021-01-22  187  
56c5812623f953 Eric Snowberg 2021-01-22 @188  	ret = pkcs7_validate_trust(pkcs7, blacklist_keyring);
56c5812623f953 Eric Snowberg 2021-01-22  189  
56c5812623f953 Eric Snowberg 2021-01-22  190  	if (ret == 0)
56c5812623f953 Eric Snowberg 2021-01-22  191  		return -EKEYREJECTED;
56c5812623f953 Eric Snowberg 2021-01-22  192  
56c5812623f953 Eric Snowberg 2021-01-22  193  	return -ENOKEY;
56c5812623f953 Eric Snowberg 2021-01-22  194  }
56c5812623f953 Eric Snowberg 2021-01-22  195  #endif
56c5812623f953 Eric Snowberg 2021-01-22  196  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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