Check codeSigning extended key usage extension

PATCH In review Lee, Chun-Yi 3 participants 7 messages Nov 25, 2020 – Nov 26, 2020

Subsystems (5)

Documentation Crypto API Keys/keyrings Asymmetric keys +1 more subsystems

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Lee, Chun-Yi

author

2020-11-25 07:27 UTC #0 lore raw

cover Check codeSigning extended key usage extension

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.

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(-)

Signature · 1 line

2.16.4

Lee, Chun-Yi

author

2020-11-25 07:27 UTC #1 lore raw

PATCH v2 1/4 X.509: Add CodeSigning extended key usage parsing

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" <[email protected]>

---
 crypto/asymmetric_keys/x509_cert_parser.c | 24 ++++++++++++++++++++++++
 include/crypto/public_key.h               |  1 +
 include/linux/oid_registry.h              |  5 +++++
 3 files changed, 30 insertions(+)

crypto/asymmetric_keys/x509_cert_parser.c +24 -0

index 52c9b455fc7d..65721313b265 100644
@@ -497,6 +497,8 @@ 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);

@@ -526,6 +528,28 @@ int x509_process_extension(void *context, size_t hdrlen,
 		return 0;
 	}
 
+	if (ctx->last_oid == OID_extKeyUsage) {
+		if (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 (v[i] != ASN1_OID || v[i + 1] != 8 || (i + 10) > vlen)
+				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;
 }

include/crypto/public_key.h +1 -0

index 948c5203ca9c..07a1b28460a2 100644
@@ -29,6 +29,7 @@ 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);

include/linux/oid_registry.h +5 -0

index 4462ed2c18cd..e20e8eb53b21 100644
@@ -113,9 +113,14 @@ enum OID {
 	OID_SM2_with_SM3,		/* 1.2.156.10197.1.501 */
 	OID_sm3WithRSAEncryption,	/* 1.2.156.10197.1.504 */
 
+	/* 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 sprint_oid(const void *, size_t, char *, size_t);
 extern int sprint_OID(enum OID, char *, size_t);

Signature · 1 line

2.16.4

Lee, Chun-Yi

author

2020-11-25 07:27 UTC #2 lore raw

PATCH v2 2/4 PKCS#7: Check codeSigning EKU for kernel module and kexec pe verification

In reply to 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" <[email protected]>

---
 certs/system_keyring.c               |  2 +-
 crypto/asymmetric_keys/Kconfig       |  9 +++++++++
 crypto/asymmetric_keys/pkcs7_trust.c | 37 +++++++++++++++++++++++++++++++++---
 include/crypto/pkcs7.h               |  3 ++-
 4 files changed, 46 insertions(+), 5 deletions(-)

certs/system_keyring.c +1 -1

index 798291177186..4104f5465d8a 100644
@@ -242,7 +242,7 @@ 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");

crypto/asymmetric_keys/Kconfig +9 -0

index 1f1f004dc757..1754812df989 100644
@@ -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

crypto/asymmetric_keys/pkcs7_trust.c +34 -3

index 61af3c4d82cc..1d2318ff63db 100644
@@ -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) {

@@ -156,7 +186,8 @@ 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 +198,7 @@ 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;

include/crypto/pkcs7.h +2 -1

index 38ec7f5f9041..b3b48240ba73 100644
@@ -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

Signature · 1 line

2.16.4

Lee, Chun-Yi

author

2020-11-25 07:27 UTC #3 lore raw

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

In reply to 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" <[email protected]>

---
 certs/Makefile | 1 +
 1 file changed, 1 insertion(+)

certs/Makefile +1 -0

index f4c25b67aad9..1ef4d6ca43b7 100644
@@ -88,6 +88,7 @@ $(obj)/x509.genkey:
 	@echo >>$@ "keyUsage=digitalSignature"
 	@echo >>$@ "subjectKeyIdentifier=hash"
 	@echo >>$@ "authorityKeyIdentifier=keyid"
+	@echo >>$@ "extendedKeyUsage=codeSigning"
 endif # CONFIG_MODULE_SIG_KEY
 
 $(eval $(call config_filename,MODULE_SIG_KEY))

Signature · 1 line

2.16.4

Lee, Chun-Yi

author

2020-11-25 07:28 UTC #4 lore raw

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

In reply to Lee, Chun-Yi

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

Signed-off-by "Lee, Chun-Yi" <[email protected]>

---
 Documentation/admin-guide/module-signing.rst | 6 ++++++
 1 file changed, 6 insertions(+)

Documentation/admin-guide/module-signing.rst +6 -0

index f8b584179cff..bc184124d646 100644
@@ -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 be enabled, the following openssl
+command option should be added 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.

Signature · 1 line

2.16.4

Randy Dunlap

reviewer

2020-11-25 17:26 UTC #5 lore raw

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

Hi--

Quoted 2 lines · Chun-Yi

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

is enabled.

Quoted 11 lines

Signed-off-by "Lee, Chun-Yi" <[email protected]>
---
 Documentation/admin-guide/module-signing.rst | 6 ++++++
 1 file changed, 6 insertions(+)
Documentation/admin-guide/module-signing.rst +0 -0
index f8b584179cff..bc184124d646 100644

Documentation/admin-guide/module-signing.rst generate the public/private key files:: · line 173

Quoted 4 lines

Documentation/admin-guide/module-signing.rst +1 -0

@@ -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 be enabled, the following openssl

is enabled,

Quoted 9 lines

Documentation/admin-guide/module-signing.rst +5 -0

+command option should be added 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.

Signature · 1 line

~Randy

joeyli

2020-11-26 06:59 UTC #6 lore raw

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

Hi Randy,

Thanks for your review! I will update it in next version.

Joey Lee

Quoted 39 lines · Randy Dunlap

Hi--
Quoted 2 lines · Chun-Yi
Add an openssl command option example for generating CodeSign extended key usage in X.509 when CONFIG_CHECK_CODESIGN_EKU be enabled.
is enabled.
Quoted 11 lines
Signed-off-by "Lee, Chun-Yi" <[email protected]>
---
 Documentation/admin-guide/module-signing.rst | 6 ++++++
 1 file changed, 6 insertions(+)
Documentation/admin-guide/module-signing.rst +0 -0
index f8b584179cff..bc184124d646 100644
Documentation/admin-guide/module-signing.rst generate the public/private key files:: · line 173
Quoted 4 lines
Documentation/admin-guide/module-signing.rst +1 -0
@@ -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 be enabled, the following openssl
is enabled,
Quoted 9 lines
Documentation/admin-guide/module-signing.rst +5 -0
+command option should be added 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.
Signature · 1 line
~Randy