[PATCH v2 00/10] Add CA enforcement keyring restrictions

[PATCH v2 00/10] Add CA enforcement keyring restrictions

[Eric Snowberg]

Prior to the introduction of the machine keyring, most distros simply 
allowed all keys contained within the platform keyring to be used
for both kernel and module verification.  This was done by an out of
tree patch.  Some distros took it even further and loaded all these keys
into the secondary trusted keyring.  This also allowed the system owner 
to add their own key for IMA usage.

Each distro contains similar documentation on how to sign kernel modules
and enroll the key into the MOK.  The process is fairly straightforward.
With the introduction of the machine keyring, the process remains
basically the same, without the need for any out of tree patches.

The machine keyring allowed distros to eliminate the out of tree patches
for kernel module signing.  However, it falls short in allowing the end 
user to add their own keys for IMA. Currently the machine keyring can not 
be used as another trust anchor for adding keys to the ima keyring, since 
CA enforcement does not currently exist.  This would expand the current 
integrity gap. The IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY 
Kconfig states that keys may be added to the ima keyrings if the key is 
validly signed by a CA cert in the system built-in or secondary trusted 
keyring.  Currently there is not code that enforces the "validly signed" 
CA cert. Any key in the builtin or secondary keyring can be used.  Also, 
the definition of "validly signed" has never been stated, leaving this up 
to multiple interpretations. 

To allow IMA to be enabled with the machine keyring, this series introduces
enforcement of key usage in the certificate. This series also defines a 
"validly signed" CA cert and applies the same definition across all
kernel keyrings.

The machine keyring shares  similarities with both the builtin and
secondary keyrings.  Similar to the builtin, no keys may be added to the
machine keyring following boot. The secondary keyring allows user
provided keys to be added following boot; however, a previously enrolled
kernel key must vouch for the key before it may be included. The system
owner may include their own keys into the machine keyring prior to boot.
If the end-user is not the system owner, they may not add their own keys
to the machine keyring.  

The machine keyring is only populated when Secure Boot is enabled.  A
system owner has the ability to control the entire Secure Boot keychain
(PK, KEK, DB, and DBX).  The system owner can also turn Secure Boot off.
With this control, they may use insert-sys-cert to include their own key 
and re-sign their kernel and have it boot.  The system owner also has 
control to include or exclude MOK keys. This series does not try to 
interpret how a system owner has configured their machine.  If the system 
owner has taken the steps to add their own MOK keys, they will be 
included in the machine keyring and used for verification, exactly 
the same way as keys contained in the builtin and secondary keyrings.
Since the system owner has the ability to add keys before booting to
either the machine or builtin keyrings, it is viewed as inconsequential 
if the key originated from one or the other.

This series introduces two different ways to configure the machine keyring.
By default, nothing changes and all MOK keys are loaded into it.  Whenever
a "validly signed" key is found within the machine, builtin, or
secondary, a flag indicating this is stored in the public key struct.
The other option is if the new Kconfig INTEGRITY_CA_MACHINE_KEYRING is 
enabled, only "validly signed" CA certs will be loaded into the machine 
keyring. All remaining MOK keys will be loaded into the platform keyring.

A "validly signed" CA cert shall be defined as any X509 certificate that
is self signed, contains the keyCertSign key usage and has the CA bit
set to true.

With this series applied, "validly signed" CA enforcement is in place
whenever IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY is enabled.
Meaning, before any key can be included into the ima keyring, it must be
vouched for by a "validly signed" CA key contained within the builtin,
secondary, or machine keyrings.

IMA allows userspace applications to be signed. The enduser may sign
their own application, however they may also want to use an application
provided by a 3rd party.  The entity building the kernel, may not be the
same entity building the userspace program.  The system owner may also
be a third entity.  If the system owner trusts the entity building the
userspace program, they will include their public key within the MOK.
This key would be used to sign the key added to the ima keyring. Not all
3rd party userspace providers have the capability to properly manage a
root CA.  Some may outsource to a different code signing provider.  Many
code signing providers use Intermediate CA certificates. Therefore, this
series also includes support for Intermediate CA certificates.  If a
"validly signed" CA can vouch for an Intermediate CA, and it contains
the keyCertSign key usage, it will also be flagged as being a "validly
signed" CA. The Intermediate CA certificates could be loaded into the
secondary keyring following boot. Afterwards, CA enforcement is
maintained for any key added to the ima keyring.

This series could be broken up into 3 different parts.  The first two
patches could be taken now.  They solve current issues that will be
triggered by the build robots.  Patches 3-8 add CA enforcement for the
ima keyring.  Patches 9-10 restrict the machine keyring to only load CA
certs into it.  Patches 9-10 require all the previous patches since
Intermediate CA enforcement is required. 

Eric Snowberg (10):
  KEYS: Create static version of public_key_verify_signature
  KEYS: Add missing function documentation
  KEYS: X.509: Parse Basic Constraints for CA
  KEYS: X.509: Parse Key Usage
  KEYS: Introduce a CA endorsed flag
  KEYS: Introduce keyring restriction that validates ca trust
  KEYS: X.509: Flag Intermediate CA certs as endorsed
  integrity: Use root of trust signature restriction
  KEYS: CA link restriction
  integrity: restrict INTEGRITY_KEYRING_MACHINE to restrict_link_by_ca

 certs/system_keyring.c                    | 30 ++++++++-
 crypto/asymmetric_keys/restrict.c         | 81 +++++++++++++++++++++++
 crypto/asymmetric_keys/x509_cert_parser.c | 31 +++++++++
 crypto/asymmetric_keys/x509_parser.h      |  2 +
 crypto/asymmetric_keys/x509_public_key.c  | 16 +++++
 include/crypto/public_key.h               | 30 +++++++++
 include/keys/system_keyring.h             | 12 +++-
 include/linux/ima.h                       | 11 +++
 include/linux/key-type.h                  |  3 +
 include/linux/key.h                       |  2 +
 security/integrity/Kconfig                | 11 ++-
 security/integrity/digsig.c               | 12 ++--
 security/integrity/ima/Kconfig            |  6 +-
 security/keys/key.c                       | 13 ++++
 14 files changed, 249 insertions(+), 11 deletions(-)


base-commit: 76dcd734eca23168cb008912c0f69ff408905235
-- 
2.27.0

[PATCH v2 01/10] KEYS: Create static version of public_key_verify_signature

[Eric Snowberg]

The kernel test robot reports undefined reference to
public_key_verify_signature when CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE is
not defined. Create a static version in this case and return -EINVAL.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
---
 include/crypto/public_key.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 68f7aa2a7e55..6d61695e1cde 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -80,7 +80,16 @@ extern int create_signature(struct kernel_pkey_params *, const void *, void *);
 extern int verify_signature(const struct key *,
 			    const struct public_key_signature *);
 
+#if IS_REACHABLE(CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE)
 int public_key_verify_signature(const struct public_key *pkey,
 				const struct public_key_signature *sig);
+#else
+static inline
+int public_key_verify_signature(const struct public_key *pkey,
+				const struct public_key_signature *sig)
+{
+	return -EINVAL;
+}
+#endif
 
 #endif /* _LINUX_PUBLIC_KEY_H */
-- 
2.27.0

[PATCH v2 02/10] KEYS: Add missing function documentation

[Eric Snowberg]

Compiling with 'W=1' results in warnings that 'Function parameter or member
not described'

Add the missing parameters for
restrict_link_by_builtin_and_secondary_trusted and
restrict_link_to_builtin_trusted.

Use /* instead of /** for get_builtin_and_secondary_restriction, since
it is a static function.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 certs/system_keyring.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index 5042cc54fa5e..250148298690 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -33,7 +33,11 @@ extern __initconst const unsigned long system_certificate_list_size;
 extern __initconst const unsigned long module_cert_size;
 
 /**
- * restrict_link_to_builtin_trusted - Restrict keyring addition by built in CA
+ * restrict_link_by_builtin_trusted - Restrict keyring addition by built in CA
+ * @dest_keyring: Keyring being linked to.
+ * @type: The type of key being added.
+ * @payload: The payload of the new key.
+ * @restriction_key: A ring of keys that can be used to vouch for the new cert.
  *
  * Restrict the addition of keys into a keyring based on the key-to-be-added
  * being vouched for by a key in the built in system keyring.
@@ -51,6 +55,10 @@ int restrict_link_by_builtin_trusted(struct key *dest_keyring,
 /**
  * restrict_link_by_builtin_and_secondary_trusted - Restrict keyring
  *   addition by both builtin and secondary keyrings
+ * @dest_keyring: Keyring being linked to.
+ * @type: The type of key being added.
+ * @payload: The payload of the new key.
+ * @restrict_key: A ring of keys that can be used to vouch for the new cert.
  *
  * Restrict the addition of keys into a keyring based on the key-to-be-added
  * being vouched for by a key in either the built-in or the secondary system
@@ -75,7 +83,7 @@ int restrict_link_by_builtin_and_secondary_trusted(
 					  secondary_trusted_keys);
 }
 
-/**
+/*
  * Allocate a struct key_restriction for the "builtin and secondary trust"
  * keyring. Only for use in system_trusted_keyring_init().
  */
-- 
2.27.0

[PATCH v2 03/10] KEYS: X.509: Parse Basic Constraints for CA

[Eric Snowberg]

Parse the X.509 Basic Constraints.  The basic constraints extension
identifies whether the subject of the certificate is a CA.

BasicConstraints ::= SEQUENCE {
        cA                      BOOLEAN DEFAULT FALSE,
        pathLenConstraint       INTEGER (0..MAX) OPTIONAL }

If the CA is true, store it in the x509_certificate.  This will be used
in a follow on patch that requires knowing if the public key is a CA.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
 crypto/asymmetric_keys/x509_parser.h      | 1 +
 2 files changed, 10 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 7a9b084e2043..b4443e507153 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -586,6 +586,15 @@ int x509_process_extension(void *context, size_t hdrlen,
 		return 0;
 	}
 
+	if (ctx->last_oid == OID_basicConstraints) {
+		if (vlen < 2 || v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
+			return -EBADMSG;
+		if (v[1] != vlen - 2)
+			return -EBADMSG;
+		if (vlen >= 4 && v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
+			ctx->cert->root_ca = true;
+	}
+
 	return 0;
 }
 
diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
index a299c9c56f40..7c5c0ad1c22e 100644
--- a/crypto/asymmetric_keys/x509_parser.h
+++ b/crypto/asymmetric_keys/x509_parser.h
@@ -38,6 +38,7 @@ struct x509_certificate {
 	bool		self_signed;		/* T if self-signed (check unsupported_sig too) */
 	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
 	bool		blacklisted;
+	bool		root_ca;		/* T if basic constraints CA is set */
 };
 
 /*
-- 
2.27.0

[PATCH v2 04/10] KEYS: X.509: Parse Key Usage

[Eric Snowberg]

Parse the X.509 Key Usage.  The key usage extension defines the purpose of
the key contained in the certificate.

   id-ce-keyUsage OBJECT IDENTIFIER ::=  { id-ce 15 }

      KeyUsage ::= BIT STRING {
           digitalSignature        (0),
           contentCommitment       (1),
           keyEncipherment         (2),
           dataEncipherment        (3),
           keyAgreement            (4),
           keyCertSign             (5),
           cRLSign                 (6),
           encipherOnly            (7),
           decipherOnly            (8) }

If the keyCertSign is set, store it in the x509_certificate structure.
This will be used in a follow on patch that requires knowing the
certificate key usage type.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 crypto/asymmetric_keys/x509_cert_parser.c | 22 ++++++++++++++++++++++
 crypto/asymmetric_keys/x509_parser.h      |  1 +
 2 files changed, 23 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index b4443e507153..edb22cf04eed 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -579,6 +579,28 @@ int x509_process_extension(void *context, size_t hdrlen,
 		return 0;
 	}
 
+	if (ctx->last_oid == OID_keyUsage) {
+		/*
+		 * Get hold of the keyUsage bit string to validate keyCertSign
+		 * v[1] is the encoding size
+		 *       (Expect either 0x02 or 0x03, making it 1 or 2 bytes)
+		 * v[2] is the number of unused bits in the bit string
+		 *       (If >= 3 keyCertSign is missing)
+		 * v[3] and possibly v[4] contain the bit string
+		 * 0x04 is where KeyCertSign lands in this bit string (from
+		 *      RFC 5280 4.2.1.3)
+		 */
+		if (v[0] != ASN1_BTS)
+			return -EBADMSG;
+		if (vlen < 4)
+			return -EBADMSG;
+		if (v[1] == 0x02 && v[2] <= 2 && (v[3] & 0x04))
+			ctx->cert->kcs_set = true;
+		else if (vlen > 4 && v[1] == 0x03 && (v[3] & 0x04))
+			ctx->cert->kcs_set = true;
+		return 0;
+	}
+
 	if (ctx->last_oid == OID_authorityKeyIdentifier) {
 		/* Get hold of the CA key fingerprint */
 		ctx->raw_akid = v;
diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
index 7c5c0ad1c22e..74a9f929e400 100644
--- a/crypto/asymmetric_keys/x509_parser.h
+++ b/crypto/asymmetric_keys/x509_parser.h
@@ -39,6 +39,7 @@ struct x509_certificate {
 	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
 	bool		blacklisted;
 	bool		root_ca;		/* T if basic constraints CA is set */
+	bool		kcs_set;		/* T if keyCertSign is set */
 };
 
 /*
-- 
2.27.0

[PATCH v2 05/10] KEYS: Introduce a CA endorsed flag

[Eric Snowberg]

Some subsystems are interested in knowing if a key has been endorsed
as a Certificate Authority (CA). From the data contained in struct
key, it is not possible to make this determination after the key
parsing is complete.  Introduce a new Endorsed Certificate Authority
flag called KEY_FLAG_ECA.

The first type of key to use this is X.509.  When a X.509 certificate
is self signed, has the keyCertSign Key Usage set and contains the
CA bit set, this new flag is set. In the future, other usage fields
could be added as flags, i.e. digitialSignature.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 crypto/asymmetric_keys/x509_public_key.c | 3 +++
 include/linux/key-type.h                 | 2 ++
 include/linux/key.h                      | 2 ++
 security/keys/key.c                      | 8 ++++++++
 4 files changed, 15 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index 0b4943a4592b..64cffedc4dd0 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -208,6 +208,9 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 		goto error_free_kids;
 	}
 
+	if (cert->kcs_set && cert->self_signed && cert->root_ca)
+		prep->payload_flags |= KEY_ALLOC_PECA;
+
 	/* We're pinning the module by being linked against it */
 	__module_get(public_key_subtype.owner);
 	prep->payload.data[asym_subtype] = &public_key_subtype;
diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index 7d985a1dfe4a..0b500578441c 100644
--- a/include/linux/key-type.h
+++ b/include/linux/key-type.h
@@ -36,6 +36,8 @@ struct key_preparsed_payload {
 	size_t		datalen;	/* Raw datalen */
 	size_t		quotalen;	/* Quota length for proposed payload */
 	time64_t	expiry;		/* Expiry time of key */
+	unsigned int	payload_flags;  /* Proposed payload flags */
+#define KEY_ALLOC_PECA	0x0001		/* Proposed Endorsed CA (ECA) key */
 } __randomize_layout;
 
 typedef int (*request_key_actor_t)(struct key *auth_key, void *aux);
diff --git a/include/linux/key.h b/include/linux/key.h
index d27477faf00d..21d5a13ee4a9 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -236,6 +236,7 @@ struct key {
 #define KEY_FLAG_ROOT_CAN_INVAL	7	/* set if key can be invalidated by root without permission */
 #define KEY_FLAG_KEEP		8	/* set if key should not be removed */
 #define KEY_FLAG_UID_KEYRING	9	/* set if key is a user or user session keyring */
+#define KEY_FLAG_ECA		10	/* set if key is an Endorsed CA key */
 
 	/* the key type and key description string
 	 * - the desc is used to match a key against search criteria
@@ -296,6 +297,7 @@ extern struct key *key_alloc(struct key_type *type,
 #define KEY_ALLOC_BYPASS_RESTRICTION	0x0008	/* Override the check on restricted keyrings */
 #define KEY_ALLOC_UID_KEYRING		0x0010	/* allocating a user or user session keyring */
 #define KEY_ALLOC_SET_KEEP		0x0020	/* Set the KEEP flag on the key/keyring */
+#define KEY_ALLOC_ECA			0x0040	/* Add Endorsed CA key */
 
 extern void key_revoke(struct key *key);
 extern void key_invalidate(struct key *key);
diff --git a/security/keys/key.c b/security/keys/key.c
index c45afdd1dfbb..e6b4946aca70 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -305,6 +305,8 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 		key->flags |= 1 << KEY_FLAG_UID_KEYRING;
 	if (flags & KEY_ALLOC_SET_KEEP)
 		key->flags |= 1 << KEY_FLAG_KEEP;
+	if (flags & KEY_ALLOC_ECA)
+		key->flags |= 1 << KEY_FLAG_ECA;
 
 #ifdef KEY_DEBUGGING
 	key->magic = KEY_DEBUG_MAGIC;
@@ -929,6 +931,12 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
 			perm |= KEY_POS_WRITE;
 	}
 
+	/* Only allow KEY_ALLOC_ECA flag to be set by preparser contents */
+	if (prep.payload_flags & KEY_ALLOC_PECA)
+		flags |= KEY_ALLOC_ECA;
+	else
+		flags &= ~KEY_ALLOC_ECA;
+
 	/* allocate a new key */
 	key = key_alloc(index_key.type, index_key.description,
 			cred->fsuid, cred->fsgid, cred, perm, flags, NULL);
-- 
2.27.0

[PATCH v2 06/10] KEYS: Introduce keyring restriction that validates ca trust

[Eric Snowberg]

The current keyring restrictions validate if a key can be vouched for by
another key already contained in a keyring.  Add a new restriction called
restrict_link_by_ca_and_signature that both vouches for the new key and
validates the vouching key is an endorsed certificate authority.

Two new system keyring restrictions are added to use
restrict_link_by_ca_and_signature.  The first restriction called
restrict_link_by_ca_builtin_trusted  uses the builtin_trusted_keys as
the restricted keyring.  The second system keyring restriction called
restrict_link_by_ca_builtin_and_secondary_trusted uses the
secondary_trusted_keys as the restricted keyring.  Should the machine
keyring be defined, it shall be validated too, since it is linked to
the secondary_trusted_keys keyring.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 certs/system_keyring.c            | 18 ++++++++++++++
 crypto/asymmetric_keys/restrict.c | 41 +++++++++++++++++++++++++++++++
 include/crypto/public_key.h       |  5 ++++
 include/keys/system_keyring.h     | 12 ++++++++-
 4 files changed, 75 insertions(+), 1 deletion(-)

diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index 250148298690..af5094ce9bcb 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -51,6 +51,14 @@ int restrict_link_by_builtin_trusted(struct key *dest_keyring,
 					  builtin_trusted_keys);
 }
 
+int restrict_link_by_ca_builtin_trusted(struct key *dest_keyring,
+					 const struct key_type *type,
+					 const union key_payload *payload,
+					 struct key *unused)
+{
+	return restrict_link_by_ca_and_signature(dest_keyring, type, payload,
+						  builtin_trusted_keys);
+}
 #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
 /**
  * restrict_link_by_builtin_and_secondary_trusted - Restrict keyring
@@ -83,6 +91,16 @@ int restrict_link_by_builtin_and_secondary_trusted(
 					  secondary_trusted_keys);
 }
 
+int restrict_link_by_ca_builtin_and_secondary_trusted(
+	struct key *dest_keyring,
+	const struct key_type *type,
+	const union key_payload *payload,
+	struct key *unused)
+{
+	return restrict_link_by_ca_and_signature(dest_keyring, type, payload,
+						  secondary_trusted_keys);
+}
+
 /*
  * Allocate a struct key_restriction for the "builtin and secondary trust"
  * keyring. Only for use in system_trusted_keyring_init().
diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
index 6b1ac5f5896a..005cb28969e4 100644
--- a/crypto/asymmetric_keys/restrict.c
+++ b/crypto/asymmetric_keys/restrict.c
@@ -108,6 +108,47 @@ int restrict_link_by_signature(struct key *dest_keyring,
 	return ret;
 }
 
+int restrict_link_by_ca_and_signature(struct key *dest_keyring,
+				       const struct key_type *type,
+				       const union key_payload *payload,
+				       struct key *trust_keyring)
+{
+	const struct public_key_signature *sig;
+	struct key *key;
+	int ret;
+
+	if (!trust_keyring)
+		return -ENOKEY;
+
+	if (type != &key_type_asymmetric)
+		return -EOPNOTSUPP;
+
+	sig = payload->data[asym_auth];
+	if (!sig)
+		return -ENOPKG;
+	if (!sig->auth_ids[0] && !sig->auth_ids[1] && !sig->auth_ids[2])
+		return -ENOKEY;
+
+	if (ca_keyid && !asymmetric_key_id_partial(sig->auth_ids[1], ca_keyid))
+		return -EPERM;
+
+	/* See if we have a key that signed this one. */
+	key = find_asymmetric_key(trust_keyring,
+				  sig->auth_ids[0], sig->auth_ids[1],
+				  sig->auth_ids[2], false);
+	if (IS_ERR(key))
+		return -ENOKEY;
+
+	if (!test_bit(KEY_FLAG_ECA, &key->flags))
+		ret = -ENOKEY;
+	else if (use_builtin_keys && !test_bit(KEY_FLAG_BUILTIN, &key->flags))
+		ret = -ENOKEY;
+	else
+		ret = verify_signature(key, sig);
+	key_put(key);
+	return ret;
+}
+
 static bool match_either_id(const struct asymmetric_key_id **pair,
 			    const struct asymmetric_key_id *single)
 {
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 6d61695e1cde..e51bbc5ffe17 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -71,6 +71,11 @@ extern int restrict_link_by_key_or_keyring_chain(struct key *trust_keyring,
 						 const union key_payload *payload,
 						 struct key *trusted);
 
+extern int restrict_link_by_ca_and_signature(struct key *dest_keyring,
+					      const struct key_type *type,
+					      const union key_payload *payload,
+					      struct key *unused);
+
 extern int query_asymmetric_key(const struct kernel_pkey_params *,
 				struct kernel_pkey_query *);
 
diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
index 91e080efb918..4e94bf72b998 100644
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -24,9 +24,13 @@ extern int restrict_link_by_builtin_trusted(struct key *keyring,
 					    const union key_payload *payload,
 					    struct key *restriction_key);
 extern __init int load_module_cert(struct key *keyring);
-
+extern int restrict_link_by_ca_builtin_trusted(struct key *keyring,
+						const struct key_type *type,
+						const union key_payload *payload,
+						struct key *unused);
 #else
 #define restrict_link_by_builtin_trusted restrict_link_reject
+#define restrict_link_by_ca_builtin_trusted restrict_link_reject
 
 static inline __init int load_module_cert(struct key *keyring)
 {
@@ -41,8 +45,14 @@ extern int restrict_link_by_builtin_and_secondary_trusted(
 	const struct key_type *type,
 	const union key_payload *payload,
 	struct key *restriction_key);
+extern int restrict_link_by_ca_builtin_and_secondary_trusted(
+	struct key *dest_keyring,
+	const struct key_type *type,
+	const union key_payload *payload,
+	struct key *restrict_key);
 #else
 #define restrict_link_by_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
+#define restrict_link_by_ca_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
 #endif
 
 #ifdef CONFIG_INTEGRITY_MACHINE_KEYRING
-- 
2.27.0

[PATCH v2 07/10] KEYS: X.509: Flag Intermediate CA certs as endorsed

[Eric Snowberg]

Currently X.509 Intermediate CA certs do not have the endorsed CA
(KEY_FLAG_ECA) set. Allow intermediate CA certs to be added.  Requirements
for an intermediate CA include: Usage extension defined as keyCertSign,
Basic Constrains for CA is false, and Intermediate CA cert is signed by a
current endorsed CA.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 crypto/asymmetric_keys/x509_public_key.c | 14 ++++++++++++--
 include/linux/ima.h                      | 11 +++++++++++
 include/linux/key-type.h                 |  1 +
 security/keys/key.c                      |  5 +++++
 4 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index 64cffedc4dd0..7a87d5c0c32b 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -208,8 +208,18 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 		goto error_free_kids;
 	}
 
-	if (cert->kcs_set && cert->self_signed && cert->root_ca)
-		prep->payload_flags |= KEY_ALLOC_PECA;
+	if (cert->kcs_set) {
+		if (cert->self_signed && cert->root_ca)
+			prep->payload_flags |= KEY_ALLOC_PECA;
+		/*
+		 * In this case it could be an Intermediate CA.  Set
+		 * KEY_MAYBE_PECA for now.  If the restriction check
+		 * passes later, the key will be allocated with the
+		 * correct CA flag
+		 */
+		else if (!cert->self_signed && !cert->root_ca)
+			prep->payload_flags |= KEY_MAYBE_PECA;
+	}
 
 	/* We're pinning the module by being linked against it */
 	__module_get(public_key_subtype.owner);
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 81708ca0ebc7..6597081b6b1a 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -12,6 +12,7 @@
 #include <linux/security.h>
 #include <linux/kexec.h>
 #include <crypto/hash_info.h>
+#include <keys/system_keyring.h>
 struct linux_binprm;
 
 #ifdef CONFIG_IMA
@@ -181,6 +182,16 @@ static inline void ima_post_key_create_or_update(struct key *keyring,
 						 bool create) {}
 #endif  /* CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS */
 
+#ifdef CONFIG_ASYMMETRIC_KEY_TYPE
+#ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
+#define ima_validate_builtin_ca restrict_link_by_ca_builtin_and_secondary_trusted
+#else
+#define ima_validate_builtin_ca restrict_link_by_ca_builtin_trusted
+#endif
+#else
+#define ima_validate_builtin_ca restrict_link_reject
+#endif
+
 #ifdef CONFIG_IMA_APPRAISE
 extern bool is_ima_appraise_enabled(void);
 extern void ima_inode_post_setattr(struct user_namespace *mnt_userns,
diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index 0b500578441c..0d2f95f6b8a1 100644
--- a/include/linux/key-type.h
+++ b/include/linux/key-type.h
@@ -38,6 +38,7 @@ struct key_preparsed_payload {
 	time64_t	expiry;		/* Expiry time of key */
 	unsigned int	payload_flags;  /* Proposed payload flags */
 #define KEY_ALLOC_PECA	0x0001		/* Proposed Endorsed CA (ECA) key */
+#define KEY_MAYBE_PECA	0x0002		/* Proposed possible ECA key */
 } __randomize_layout;
 
 typedef int (*request_key_actor_t)(struct key *auth_key, void *aux);
diff --git a/security/keys/key.c b/security/keys/key.c
index e6b4946aca70..69d5f143683f 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -900,6 +900,11 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
 		}
 	}
 
+	/* Previous restriction check passed therefore try to validate endorsed ca */
+	if ((prep.payload_flags & KEY_MAYBE_PECA) &&
+	   !(ima_validate_builtin_ca(keyring, index_key.type, &prep.payload, NULL)))
+		prep.payload_flags |= KEY_ALLOC_PECA;
+
 	/* if we're going to allocate a new key, we're going to have
 	 * to modify the keyring */
 	ret = key_permission(keyring_ref, KEY_NEED_WRITE);
-- 
2.27.0

[PATCH v2 08/10] integrity: Use root of trust signature restriction

[Eric Snowberg]

Keys added to the IMA keyring must be vouched for by keys contained
within the builtin or secondary keyrings.  These keys must also be self
signed, have the CA bit set and have the keyCertSign KeyUsage bit set.
Or they could be validated by a properly formed intermediate CA.
Currently these restrictions are not enforced. Use the new
restrict_link_by_ca_builtin_and_secondary_trusted and
restrict_link_by_ca_builtin_trusted to enforce the missing
CA restrictions when adding keys to the IMA keyring. With the
CA restrictions enforced, allow the machine keyring to be
enabled with IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 security/integrity/Kconfig     | 1 -
 security/integrity/digsig.c    | 4 ++--
 security/integrity/ima/Kconfig | 6 +++---
 3 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
index 599429f99f99..14cc3c767270 100644
--- a/security/integrity/Kconfig
+++ b/security/integrity/Kconfig
@@ -68,7 +68,6 @@ config INTEGRITY_MACHINE_KEYRING
 	depends on INTEGRITY_ASYMMETRIC_KEYS
 	depends on SYSTEM_BLACKLIST_KEYRING
 	depends on LOAD_UEFI_KEYS
-	depends on !IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
 	help
 	 If set, provide a keyring to which Machine Owner Keys (MOK) may
 	 be added. This keyring shall contain just MOK keys.  Unlike keys
diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index 8a82a6c7f48a..1fe8d1ed6e0b 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -34,9 +34,9 @@ static const char * const keyring_name[INTEGRITY_KEYRING_MAX] = {
 };
 
 #ifdef CONFIG_IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
-#define restrict_link_to_ima restrict_link_by_builtin_and_secondary_trusted
+#define restrict_link_to_ima restrict_link_by_ca_builtin_and_secondary_trusted
 #else
-#define restrict_link_to_ima restrict_link_by_builtin_trusted
+#define restrict_link_to_ima restrict_link_by_ca_builtin_trusted
 #endif
 
 static struct key *integrity_keyring_from_id(const unsigned int id)
diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 7249f16257c7..6fe3bd0e5c82 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -269,13 +269,13 @@ config IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
 	default n
 	help
 	  Keys may be added to the IMA or IMA blacklist keyrings, if the
-	  key is validly signed by a CA cert in the system built-in or
-	  secondary trusted keyrings.
+	  key is validly signed by a CA cert in the system built-in,
+	  secondary trusted, or machine keyrings.
 
 	  Intermediate keys between those the kernel has compiled in and the
 	  IMA keys to be added may be added to the system secondary keyring,
 	  provided they are validly signed by a key already resident in the
-	  built-in or secondary trusted keyrings.
+	  built-in, secondary trusted or machine keyrings.
 
 config IMA_BLACKLIST_KEYRING
 	bool "Create IMA machine owner blacklist keyrings (EXPERIMENTAL)"
-- 
2.27.0

[PATCH v2 09/10] KEYS: CA link restriction

[Eric Snowberg]

Add a new link restriction.  Restrict the addition of keys in a keyring
based on the key to be added being a CA.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 crypto/asymmetric_keys/restrict.c        | 40 ++++++++++++++++++++++++
 crypto/asymmetric_keys/x509_public_key.c |  5 ++-
 include/crypto/public_key.h              | 16 ++++++++++
 3 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
index 005cb28969e4..ac0a6efafb03 100644
--- a/crypto/asymmetric_keys/restrict.c
+++ b/crypto/asymmetric_keys/restrict.c
@@ -108,6 +108,46 @@ int restrict_link_by_signature(struct key *dest_keyring,
 	return ret;
 }
 
+/**
+ * restrict_link_by_ca - Restrict additions to a ring of CA keys
+ * @dest_keyring: Keyring being linked to.
+ * @type: The type of key being added.
+ * @payload: The payload of the new key.
+ * @trust_keyring: Unused.
+ *
+ * Check if the new certificate is a CA. If it is a CA, then mark the new
+ * certificate as being ok to link.
+ *
+ * Returns 0 if the new certificate was accepted, -ENOKEY if the
+ * certificate is not a CA. -ENOPKG if the signature uses unsupported
+ * crypto, or some other error if there is a matching certificate but
+ * the signature check cannot be performed.
+ */
+int restrict_link_by_ca(struct key *dest_keyring,
+			const struct key_type *type,
+			const union key_payload *payload,
+			struct key *trust_keyring)
+{
+	const struct public_key_signature *sig;
+	const struct public_key *pkey;
+
+	if (type != &key_type_asymmetric)
+		return -EOPNOTSUPP;
+
+	sig = payload->data[asym_auth];
+	if (!sig)
+		return -ENOPKG;
+
+	pkey = payload->data[asym_crypto];
+	if (!pkey)
+		return -ENOPKG;
+
+	if (!pkey->key_is_ca)
+		return -ENOKEY;
+
+	return public_key_verify_signature(pkey, sig);
+}
+
 int restrict_link_by_ca_and_signature(struct key *dest_keyring,
 				       const struct key_type *type,
 				       const union key_payload *payload,
diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index 7a87d5c0c32b..9c2909fea63e 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -209,8 +209,11 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 	}
 
 	if (cert->kcs_set) {
-		if (cert->self_signed && cert->root_ca)
+		if (cert->self_signed && cert->root_ca) {
 			prep->payload_flags |= KEY_ALLOC_PECA;
+			cert->pub->key_is_ca = true;
+		}
+
 		/*
 		 * In this case it could be an Intermediate CA.  Set
 		 * KEY_MAYBE_PECA for now.  If the restriction check
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index e51bbc5ffe17..3de0f8a68914 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -26,6 +26,7 @@ struct public_key {
 	void *params;
 	u32 paramlen;
 	bool key_is_private;
+	bool key_is_ca;
 	const char *id_type;
 	const char *pkey_algo;
 };
@@ -76,6 +77,21 @@ extern int restrict_link_by_ca_and_signature(struct key *dest_keyring,
 					      const union key_payload *payload,
 					      struct key *unused);
 
+#if IS_REACHABLE(CONFIG_ASYMMETRIC_KEY_TYPE)
+extern int restrict_link_by_ca(struct key *dest_keyring,
+			       const struct key_type *type,
+			       const union key_payload *payload,
+			       struct key *trust_keyring);
+#else
+static inline int restrict_link_by_ca(struct key *dest_keyring,
+				      const struct key_type *type,
+				      const union key_payload *payload,
+				      struct key *trust_keyring)
+{
+	return 0;
+}
+#endif
+
 extern int query_asymmetric_key(const struct kernel_pkey_params *,
 				struct kernel_pkey_query *);
 
-- 
2.27.0

[PATCH v2 10/10] integrity: restrict INTEGRITY_KEYRING_MACHINE to restrict_link_by_ca

[Eric Snowberg]

Set the restriction check for INTEGRITY_KEYRING_MACHINE keys to
restrict_link_by_ca.  This will only allow CA keys into the machine
keyring.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 security/integrity/Kconfig  | 10 ++++++++++
 security/integrity/digsig.c |  8 ++++++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
index 14cc3c767270..3357883fa5a8 100644
--- a/security/integrity/Kconfig
+++ b/security/integrity/Kconfig
@@ -74,6 +74,16 @@ config INTEGRITY_MACHINE_KEYRING
 	 in the platform keyring, keys contained in the .machine keyring will
 	 be trusted within the kernel.
 
+config INTEGRITY_CA_MACHINE_KEYRING
+	bool "Only allow CA keys into the Machine Keyring"
+	depends on INTEGRITY_MACHINE_KEYRING
+	help
+	 If set, only Machine Owner Keys (MOK) that are Certificate
+	 Authority (CA) keys will be added to the .machine keyring. All
+	 other MOK keys will be added to the .platform keyring.  After
+	 booting, any other key signed by the CA key can be added to the
+	 secondary_trusted_keys keyring.
+
 config LOAD_UEFI_KEYS
        depends on INTEGRITY_PLATFORM_KEYRING
        depends on EFI
diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index 1fe8d1ed6e0b..b0ec615745e3 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -131,7 +131,8 @@ int __init integrity_init_keyring(const unsigned int id)
 		| KEY_USR_READ | KEY_USR_SEARCH;
 
 	if (id == INTEGRITY_KEYRING_PLATFORM ||
-	    id == INTEGRITY_KEYRING_MACHINE) {
+	    (id == INTEGRITY_KEYRING_MACHINE &&
+	    !IS_ENABLED(CONFIG_INTEGRITY_CA_MACHINE_KEYRING))) {
 		restriction = NULL;
 		goto out;
 	}
@@ -143,7 +144,10 @@ int __init integrity_init_keyring(const unsigned int id)
 	if (!restriction)
 		return -ENOMEM;
 
-	restriction->check = restrict_link_to_ima;
+	if (id == INTEGRITY_KEYRING_MACHINE)
+		restriction->check = restrict_link_by_ca;
+	else
+		restriction->check = restrict_link_to_ima;
 
 	/*
 	 * MOK keys can only be added through a read-only runtime services
-- 
2.27.0

Re: [PATCH v2 01/10] KEYS: Create static version of public_key_verify_signature

[Petr Vorel]

Hi Eric,

Reviewed-by: Petr Vorel <pvorel@suse.cz>

Kind regards,
Petr

Re: [PATCH v2 02/10] KEYS: Add missing function documentation

[Petr Vorel]

Hi Eric,

> Compiling with 'W=1' results in warnings that 'Function parameter or member
> not described'

> Add the missing parameters for
> restrict_link_by_builtin_and_secondary_trusted and
> restrict_link_to_builtin_trusted.

> Use /* instead of /** for get_builtin_and_secondary_restriction, since
> it is a static function.

> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
> ---
>  certs/system_keyring.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)

> diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> index 5042cc54fa5e..250148298690 100644
> --- a/certs/system_keyring.c
> +++ b/certs/system_keyring.c
> @@ -33,7 +33,11 @@ extern __initconst const unsigned long system_certificate_list_size;
>  extern __initconst const unsigned long module_cert_size;

>  /**
> - * restrict_link_to_builtin_trusted - Restrict keyring addition by built in CA
> + * restrict_link_by_builtin_trusted - Restrict keyring addition by built in CA
Hm, wrong function name restrict_link_to_builtin_trusted brought by:
d3bfe84129f6 ("certs: Add a secondary system keyring that can be added to dynamically")

> + * @dest_keyring: Keyring being linked to.
> + * @type: The type of key being added.
> + * @payload: The payload of the new key.
> + * @restriction_key: A ring of keys that can be used to vouch for the new cert.
>   *
>   * Restrict the addition of keys into a keyring based on the key-to-be-added
>   * being vouched for by a key in the built in system keyring.
> @@ -51,6 +55,10 @@ int restrict_link_by_builtin_trusted(struct key *dest_keyring,
>  /**
>   * restrict_link_by_builtin_and_secondary_trusted - Restrict keyring
>   *   addition by both builtin and secondary keyrings
nit: missing dot at the end of the sentence (maybe can be fixed before merge).

Obviously correct.

Reviewed-by: Petr Vorel <pvorel@suse.cz>

Kind regards,
Petr

> + * @dest_keyring: Keyring being linked to.
> + * @type: The type of key being added.
> + * @payload: The payload of the new key.
> + * @restrict_key: A ring of keys that can be used to vouch for the new cert.
>   *
>   * Restrict the addition of keys into a keyring based on the key-to-be-added
>   * being vouched for by a key in either the built-in or the secondary system
> @@ -75,7 +83,7 @@ int restrict_link_by_builtin_and_secondary_trusted(
>  					  secondary_trusted_keys);
>  }

> -/**
> +/*
>   * Allocate a struct key_restriction for the "builtin and secondary trust"
>   * keyring. Only for use in system_trusted_keyring_init().
>   */

Re: [PATCH v2 00/10] Add CA enforcement keyring restrictions

[Coiby Xu]

Hi Eric,

Thanks for your work! The patch set looks good to me except for the
requirement of an intermediate CA certificate should be vouched for by a
root CA certificate before it can vouch for other certificates. What if
users only want to enroll an intermediate CA certificate into the MOK?
If this requirement could be dropped, the code could be simplified and
some issues could be resolved automatically,

1. "[PATCH v2 03/10] KEYS: X.509: Parse Basic Constraints for CA" added
    a root_ca filed to a certificate to indicate the subject of the
    certificate is a CA. The name root_ca implies it's also a root CA. But
    according to [1], both an intermediate and root CA will have
    root_ca=True. For example, the intermediate certificate of
    https://www.kernel.org/ has "Certificate Authority=Yes" in the basic
    constraints. Btw, a root CA certificate by definition is self-signed,
    so the following code in "[PATCH v2 05/10] KEYS: Introduce a CA
    endorsed flag" looks a bit strange to me,
     if (cert->kcs_set && cert->self_signed && cert->root_ca)
         prep->payload_flags |= KEY_ALLOC_PECA;

2. Since an intermediate CA certificate also has root_ca=True,
    "[PATCH v2 07/10] KEYS: X.509: Flag Intermediate CA certs as
    endorsed" won't work as intended i.e. this following else branch
    will never be reached,
    else if (!cert->self_signed && !cert->root_ca)
            prep->payload_flags |= KEY_MAYBE_PECA;

3. I see nowhere public_key->key_is_ca is set to true for an intermediate
    CA certificate after it gains the KEY_ALLOC_PECA flag. So it will fail
    restrict_link_by_ca even if the KEY_MAYBE_PECA flag is added.

[1] https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.9

On Wed, Dec 07, 2022 at 12:12:28PM -0500, Eric Snowberg wrote:
>Prior to the introduction of the machine keyring, most distros simply
>allowed all keys contained within the platform keyring to be used
>for both kernel and module verification.  This was done by an out of
>tree patch.  Some distros took it even further and loaded all these keys
>into the secondary trusted keyring.  This also allowed the system owner
>to add their own key for IMA usage.
>
>Each distro contains similar documentation on how to sign kernel modules
>and enroll the key into the MOK.  The process is fairly straightforward.
>With the introduction of the machine keyring, the process remains
>basically the same, without the need for any out of tree patches.
>
>The machine keyring allowed distros to eliminate the out of tree patches
>for kernel module signing.  However, it falls short in allowing the end
>user to add their own keys for IMA. Currently the machine keyring can not
>be used as another trust anchor for adding keys to the ima keyring, since
>CA enforcement does not currently exist.  This would expand the current
>integrity gap. The IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
>Kconfig states that keys may be added to the ima keyrings if the key is
>validly signed by a CA cert in the system built-in or secondary trusted
>keyring.  Currently there is not code that enforces the "validly signed"
>CA cert. Any key in the builtin or secondary keyring can be used.  Also,
>the definition of "validly signed" has never been stated, leaving this up
>to multiple interpretations.
>
>To allow IMA to be enabled with the machine keyring, this series introduces
>enforcement of key usage in the certificate. This series also defines a
>"validly signed" CA cert and applies the same definition across all
>kernel keyrings.
>
>The machine keyring shares  similarities with both the builtin and
>secondary keyrings.  Similar to the builtin, no keys may be added to the
>machine keyring following boot. The secondary keyring allows user
>provided keys to be added following boot; however, a previously enrolled
>kernel key must vouch for the key before it may be included. The system
>owner may include their own keys into the machine keyring prior to boot.
>If the end-user is not the system owner, they may not add their own keys
>to the machine keyring.
>
>The machine keyring is only populated when Secure Boot is enabled.  A
>system owner has the ability to control the entire Secure Boot keychain
>(PK, KEK, DB, and DBX).  The system owner can also turn Secure Boot off.
>With this control, they may use insert-sys-cert to include their own key
>and re-sign their kernel and have it boot.  The system owner also has
>control to include or exclude MOK keys. This series does not try to
>interpret how a system owner has configured their machine.  If the system
>owner has taken the steps to add their own MOK keys, they will be
>included in the machine keyring and used for verification, exactly
>the same way as keys contained in the builtin and secondary keyrings.
>Since the system owner has the ability to add keys before booting to
>either the machine or builtin keyrings, it is viewed as inconsequential
>if the key originated from one or the other.
>
>This series introduces two different ways to configure the machine keyring.
>By default, nothing changes and all MOK keys are loaded into it.  Whenever
>a "validly signed" key is found within the machine, builtin, or
>secondary, a flag indicating this is stored in the public key struct.
>The other option is if the new Kconfig INTEGRITY_CA_MACHINE_KEYRING is
>enabled, only "validly signed" CA certs will be loaded into the machine
>keyring. All remaining MOK keys will be loaded into the platform keyring.
>
>A "validly signed" CA cert shall be defined as any X509 certificate that
>is self signed, contains the keyCertSign key usage and has the CA bit
>set to true.
>
>With this series applied, "validly signed" CA enforcement is in place
>whenever IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY is enabled.
>Meaning, before any key can be included into the ima keyring, it must be
>vouched for by a "validly signed" CA key contained within the builtin,
>secondary, or machine keyrings.
>
>IMA allows userspace applications to be signed. The enduser may sign
>their own application, however they may also want to use an application
>provided by a 3rd party.  The entity building the kernel, may not be the
>same entity building the userspace program.  The system owner may also
>be a third entity.  If the system owner trusts the entity building the
>userspace program, they will include their public key within the MOK.
>This key would be used to sign the key added to the ima keyring. Not all
>3rd party userspace providers have the capability to properly manage a
>root CA.  Some may outsource to a different code signing provider.  Many
>code signing providers use Intermediate CA certificates. Therefore, this
>series also includes support for Intermediate CA certificates.  If a
>"validly signed" CA can vouch for an Intermediate CA, and it contains
>the keyCertSign key usage, it will also be flagged as being a "validly
>signed" CA. The Intermediate CA certificates could be loaded into the
>secondary keyring following boot. Afterwards, CA enforcement is
>maintained for any key added to the ima keyring.
>
>This series could be broken up into 3 different parts.  The first two
>patches could be taken now.  They solve current issues that will be
>triggered by the build robots.  Patches 3-8 add CA enforcement for the
>ima keyring.  Patches 9-10 restrict the machine keyring to only load CA
>certs into it.  Patches 9-10 require all the previous patches since
>Intermediate CA enforcement is required.
>
>Eric Snowberg (10):
>  KEYS: Create static version of public_key_verify_signature
>  KEYS: Add missing function documentation
>  KEYS: X.509: Parse Basic Constraints for CA
>  KEYS: X.509: Parse Key Usage
>  KEYS: Introduce a CA endorsed flag
>  KEYS: Introduce keyring restriction that validates ca trust
>  KEYS: X.509: Flag Intermediate CA certs as endorsed
>  integrity: Use root of trust signature restriction
>  KEYS: CA link restriction
>  integrity: restrict INTEGRITY_KEYRING_MACHINE to restrict_link_by_ca
>
> certs/system_keyring.c                    | 30 ++++++++-
> crypto/asymmetric_keys/restrict.c         | 81 +++++++++++++++++++++++
> crypto/asymmetric_keys/x509_cert_parser.c | 31 +++++++++
> crypto/asymmetric_keys/x509_parser.h      |  2 +
> crypto/asymmetric_keys/x509_public_key.c  | 16 +++++
> include/crypto/public_key.h               | 30 +++++++++
> include/keys/system_keyring.h             | 12 +++-
> include/linux/ima.h                       | 11 +++
> include/linux/key-type.h                  |  3 +
> include/linux/key.h                       |  2 +
> security/integrity/Kconfig                | 11 ++-
> security/integrity/digsig.c               | 12 ++--
> security/integrity/ima/Kconfig            |  6 +-
> security/keys/key.c                       | 13 ++++
> 14 files changed, 249 insertions(+), 11 deletions(-)
>
>
>base-commit: 76dcd734eca23168cb008912c0f69ff408905235
>-- 
>2.27.0
>

-- 
Best regards,
Coiby

Re: [PATCH v2 00/10] Add CA enforcement keyring restrictions

[Eric Snowberg]

> On Dec 9, 2022, at 3:26 AM, Coiby Xu <coxu@redhat.com> wrote:
> 
> Thanks for your work! The patch set looks good to me except for the
> requirement of an intermediate CA certificate should be vouched for by a
> root CA certificate before it can vouch for other certificates. What if
> users only want to enroll an intermediate CA certificate into the MOK?

This question would need to be answered by the maintainers.  The intermediate 
requirement was based on my understanding of previous discussions requiring
there be a way to validate root of trust all the way back to the root CA.

> If this requirement could be dropped, the code could be simplified and
> some issues could be resolved automatically,

Agreed. I will make sure the issue below is resolved one way or the other,
once we have an agreement on the requirements. 

> 1. "[PATCH v2 03/10] KEYS: X.509: Parse Basic Constraints for CA" added
>   a root_ca filed to a certificate to indicate the subject of the
>   certificate is a CA. The name root_ca implies it's also a root CA. But
>   according to [1], both an intermediate and root CA will have
>   root_ca=True. For example, the intermediate certificate of
>   https://www.kernel.org/ has "Certificate Authority=Yes" in the basic
>   constraints. Btw, a root CA certificate by definition is self-signed,
>   so the following code in "[PATCH v2 05/10] KEYS: Introduce a CA
>   endorsed flag" looks a bit strange to me,
>    if (cert->kcs_set && cert->self_signed && cert->root_ca)
>        prep->payload_flags |= KEY_ALLOC_PECA;
> 
> 2. Since an intermediate CA certificate also has root_ca=True,
>   "[PATCH v2 07/10] KEYS: X.509: Flag Intermediate CA certs as
>   endorsed" won't work as intended i.e. this following else branch
>   will never be reached,
>   else if (!cert->self_signed && !cert->root_ca)
>           prep->payload_flags |= KEY_MAYBE_PECA;
> 
> 3. I see nowhere public_key->key_is_ca is set to true for an intermediate
>   CA certificate after it gains the KEY_ALLOC_PECA flag. So it will fail
>   restrict_link_by_ca even if the KEY_MAYBE_PECA flag is added.
> 
> [1] https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.9

Thanks for reviewing the series.

Re: [PATCH v2 00/10] Add CA enforcement keyring restrictions

[Mimi Zohar]

Hi Eric, Coiby,

On Fri, 2022-12-09 at 15:44 +0000, Eric Snowberg wrote:
> > On Dec 9, 2022, at 3:26 AM, Coiby Xu <coxu@redhat.com> wrote:
> > 
> > Thanks for your work! The patch set looks good to me except for the
> > requirement of an intermediate CA certificate should be vouched for by a
> > root CA certificate before it can vouch for other certificates. What if
> > users only want to enroll an intermediate CA certificate into the MOK?
> 
> This question would need to be answered by the maintainers.  The intermediate 
> requirement was based on my understanding of previous discussions requiring
> there be a way to validate root of trust all the way back to the root CA.

That definitely did not come from me.  My requirement all along has
been to support a single self-signed CA certificate for the end
user/customer use case, so that they could create and load their own
public key, signed by that CA, onto the trusted IMA/EVM keyrings.

> 
> > If this requirement could be dropped, the code could be simplified and
> > some issues could be resolved automatically,
> 
> Agreed. I will make sure the issue below is resolved one way or the other,
> once we have an agreement on the requirements. 

I totally agree with Coiby that there is no need for intermediate CA
certificates be vouched for by a root CA certificate.  In fact the
closer the CA certificate is to the leaf code signing certificate, the
better.  As much as possible we want to limit the CA keys being loaded
onto the machine keyring to those that are absolutely required.

thanks,

Mimi

> 
> > 1. "[PATCH v2 03/10] KEYS: X.509: Parse Basic
> >   a root_ca filed to a certificate to indicate the subject of the
> >   certificate is a CA. The name root_ca implies it's also a root CA. But
> >   according to [1], both an intermediate and root CA will have
> >   root_ca=True. For example, the intermediate certificate of
> >   https://www.kernel.org/ has "Certificate Authority=Yes" in the basic
> >   constraints. Btw, a root CA certificate by definition is self-signed,
> >   so the following code in "[PATCH v2 05/10] KEYS: Introduce a CA
> >   endorsed flag" looks a bit strange to me,
> >    if (cert->kcs_set && cert->self_signed && cert->root_ca)
> >        prep->payload_flags |= KEY_ALLOC_PECA;
> > 
> > 2. Since an intermediate CA certificate also has root_ca=True,
> >   "[PATCH v2 07/10] KEYS: X.509: Flag Intermediate CA certs as
> >   endorsed" won't work as intended i.e. this following else branch
> >   will never be reached,
> >   else if (!cert->self_signed && !cert->root_ca)
> >           prep->payload_flags |= KEY_MAYBE_PECA;
> > 
> > 3. I see nowhere public_key->key_is_ca is set to true for an intermediate
> >   CA certificate after it gains the KEY_ALLOC_PECA flag. So it will fail
> >   restrict_link_by_ca even if the KEY_MAYBE_PECA flag is added.
> > 
> > [1] https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.9
> 
> Thanks for reviewing the series.
> 

Re: [PATCH v2 00/10] Add CA enforcement keyring restrictions

[Eric Snowberg]

> On Dec 12, 2022, at 2:44 PM, Mimi Zohar <zohar@linux.ibm.com> wrote:
> 
> Hi Eric, Coiby,
> 
> On Fri, 2022-12-09 at 15:44 +0000, Eric Snowberg wrote:
>>> On Dec 9, 2022, at 3:26 AM, Coiby Xu <coxu@redhat.com> wrote:
>>> 
>>> Thanks for your work! The patch set looks good to me except for the
>>> requirement of an intermediate CA certificate should be vouched for by a
>>> root CA certificate before it can vouch for other certificates. What if
>>> users only want to enroll an intermediate CA certificate into the MOK?
>> 
>> This question would need to be answered by the maintainers.  The intermediate 
>> requirement was based on my understanding of previous discussions requiring
>> there be a way to validate root of trust all the way back to the root CA.
> 
> That definitely did not come from me.  My requirement all along has
> been to support a single self-signed CA certificate for the end
> user/customer use case, so that they could create and load their own
> public key, signed by that CA, onto the trusted IMA/EVM keyrings.
> 
>> 
>>> If this requirement could be dropped, the code could be simplified and
>>> some issues could be resolved automatically,
>> 
>> Agreed. I will make sure the issue below is resolved one way or the other,
>> once we have an agreement on the requirements. 
> 
> I totally agree with Coiby that there is no need for intermediate CA
> certificates be vouched for by a root CA certificate.  In fact the
> closer the CA certificate is to the leaf code signing certificate, the
> better.  As much as possible we want to limit the CA keys being loaded
> onto the machine keyring to those that are absolutely required.

Ok, I will change this in the next round.  The confusion around the requirement 
comes from the request to validate the cert is self-signed.  The intermediate in this
case will not be self signed.  As long as this check is not necessary, I will drop it from
the code and allow the intermediate to vouch for the ima key without the root being 
present.  Thanks for clearing this up.