linux-kernel - [PATCH 4/7] KEYS: Introduce a builtin root of trust key flag

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Message-Id: <20220406015337.4000739-5-eric.snowberg@oracle.com>
Date:   Tue,  5 Apr 2022 21:53:34 -0400
From:   Eric Snowberg <eric.snowberg@...cle.com>
To:     dhowells@...hat.com, dwmw2@...radead.org, jarkko@...nel.org,
        zohar@...ux.ibm.com, linux-integrity@...r.kernel.org
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com,
        roberto.sassu@...wei.com, nramas@...ux.microsoft.com,
        eric.snowberg@...cle.com, pvorel@...e.cz, tiwai@...e.de,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: [PATCH 4/7] KEYS: Introduce a builtin root of trust key flag

Some subsystems are interested in knowing if keys within a keyring could
be used as a foundation of a root of trust.  Introduce a new builtin root
of trust key flag.

The first type of key to use this is X.509.  When a X.509 certificate
is self signed, has the kernCertSign Key Usage set and contains the
CA bit set this new flag is set.

Signed-off-by: Eric Snowberg <eric.snowberg@...cle.com>
---
 crypto/asymmetric_keys/x509_public_key.c | 2 ++
 include/linux/key-type.h                 | 2 ++
 include/linux/key.h                      | 2 ++
 security/keys/key.c                      | 8 ++++++++
 4 files changed, 14 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index 91a4ad50dea2..7290e765f46b 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -215,6 +215,8 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 	prep->payload.data[asym_auth] = cert->sig;
 	prep->description = desc;
 	prep->quotalen = 100;
+	if (cert->is_kcs_set && cert->self_signed && cert->is_root_ca)
+		prep->payload_flags |= KEY_ALLOC_ROT;
 
 	/* We've finished with the certificate */
 	cert->pub = NULL;
diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index 7d985a1dfe4a..ed0aaad3849b 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_ROT	0x0001		/* Proposed Root of Trust (ROT) 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 7febc4881363..97f6a1f86a27 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -230,6 +230,7 @@ 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_BUILTIN_ROT	10	/* set if key is a builtin Root of Trust key */
 
 	/* the key type and key description string
 	 * - the desc is used to match a key against search criteria
@@ -290,6 +291,7 @@ 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_BUILT_IN_ROT		0x0040  /* Add builtin root of trust 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..732bb837fc51 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_BUILT_IN_ROT)
+		key->flags |= 1 << KEY_FLAG_BUILTIN_ROT;
 
 #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_BUILT_IN_ROT flag to be set by preparser contents */
+	if (prep.payload_flags & KEY_ALLOC_ROT)
+		flags |= KEY_ALLOC_BUILT_IN_ROT;
+	else
+		flags &= ~KEY_ALLOC_BUILT_IN_ROT;
+
 	/* allocate a new key */
 	key = key_alloc(index_key.type, index_key.description,
 			cred->fsuid, cred->fsgid, cred, perm, flags, NULL);
-- 
2.27.0