Check codeSigning extended key usage extension

index 6d003096b5bc..996db9419474 100644
@@ -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;
 }
 

index 47accec68cb0..1ccaebe2a28b 100644
@@ -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);

index 461b7aa587ba..8c8935f0eb73 100644
@@ -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);

index 0c9a4795e847..302ca0555e75 100644
@@ -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");

index b531df2013c4..7c27bf81aca9 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) {

@@ -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;

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