[RFC PATCH 0/2] Check codeSigning extended key usage extension

[RFC PATCH 0/2] 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.

Lee, Chun-Yi (2):
  X.509: Add CodeSigning extended key usage parsing
  PKCS#7: Check codeSigning EKU for kernel module and kexec pe
    verification

 certs/system_keyring.c                    |  2 +-
 crypto/asymmetric_keys/Kconfig            | 10 +++++++++
 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 +++++
 7 files changed, 77 insertions(+), 5 deletions(-)

-- 
2.16.4

[RFC PATCH 1/2] 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 | 24 ++++++++++++++++++++++++
 include/crypto/public_key.h               |  1 +
 include/linux/oid_registry.h              |  5 +++++
 3 files changed, 30 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 26ec20ef4899..5179da8b7cd9 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -480,6 +480,8 @@ 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);
 
@@ -509,6 +511,28 @@ 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;
 }
 
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 11f535cfb810..7c7342648260 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 657d6bf2c064..cd448e9b02fc 100644
--- a/include/linux/oid_registry.h
+++ b/include/linux/oid_registry.h
@@ -107,9 +107,14 @@ enum OID {
 	OID_gostTC26Sign512B,		/* 1.2.643.7.1.2.1.2.2 */
 	OID_gostTC26Sign512C,		/* 1.2.643.7.1.2.1.2.3 */
 
+	/* 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);
-- 
2.16.4

[RFC PATCH 2/2] 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 extenstion 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       | 10 ++++++++++
 crypto/asymmetric_keys/pkcs7_trust.c | 37 +++++++++++++++++++++++++++++++++---
 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 798291177186..4104f5465d8a 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -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");
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index 1f1f004dc757..6e3de0c3b5f0 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -96,4 +96,14 @@ 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 extension when verifying the signature in PKCS#7. It
+	  affects kernel module verification and kexec PE binary verification
+	  now.
+
 endif # ASYMMETRIC_KEY_TYPE
diff --git a/crypto/asymmetric_keys/pkcs7_trust.c b/crypto/asymmetric_keys/pkcs7_trust.c
index 61af3c4d82cc..1d2318ff63db 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) {
@@ -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;
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

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

[Ben Boeckel]

On Tue, Oct 20, 2020 at 14:50:01 +0800, Lee, Chun-Yi wrote:
> +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 extension when verifying the signature in PKCS#7. It
> +	  affects kernel module verification and kexec PE binary verification
> +	  now.

Is the "now" necessary? Isn't it implied by the option's existence?

--Ben

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

[Randy Dunlap]

On 10/20/20 6:42 AM, Ben Boeckel wrote:
> On Tue, Oct 20, 2020 at 14:50:01 +0800, Lee, Chun-Yi wrote:
>> +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 extension when verifying the signature in PKCS#7. It

	  extended ... extension.
Can we drop one of those or reword it?

>> +	  affects kernel module verification and kexec PE binary verification
>> +	  now.
> 
> Is the "now" necessary? Isn't it implied by the option's existence?


-- 
~Randy

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

[joeyli]

Hi Ben,

On Tue, Oct 20, 2020 at 09:42:08AM -0400, Ben Boeckel wrote:
> On Tue, Oct 20, 2020 at 14:50:01 +0800, Lee, Chun-Yi wrote:
> > +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 extension when verifying the signature in PKCS#7. It
> > +	  affects kernel module verification and kexec PE binary verification
> > +	  now.
> 
> Is the "now" necessary? Isn't it implied by the option's existence?

Thanks for your review. I will remove the "now" in next version.

Joey Lee

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

[joeyli]

Hi Randy,

On Tue, Oct 20, 2020 at 07:56:29AM -0700, Randy Dunlap wrote:
> On 10/20/20 6:42 AM, Ben Boeckel wrote:
> > On Tue, Oct 20, 2020 at 14:50:01 +0800, Lee, Chun-Yi wrote:
> >> +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 extension when verifying the signature in PKCS#7. It
> 
> 	  extended ... extension.
> Can we drop one of those or reword it?

I will remove the _extension_ word in next version. Thanks for your review!

Joey Lee