[PATCH 5.4 69/71] certs: Add EFI_CERT_X509_GUID support for dbx entries

[PATCH 5.4 69/71] certs: Add EFI_CERT_X509_GUID support for dbx entries

[Sasha Levin]

From: Eric Snowberg <eric.snowberg@oracle.com>

[ Upstream commit 56c5812623f95313f6a46fbf0beee7fa17c68bbf ]

This fixes CVE-2020-26541.

The Secure Boot Forbidden Signature Database, dbx, contains a list of now
revoked signatures and keys previously approved to boot with UEFI Secure
Boot enabled.  The dbx is capable of containing any number of
EFI_CERT_X509_SHA256_GUID, EFI_CERT_SHA256_GUID, and EFI_CERT_X509_GUID
entries.

Currently when EFI_CERT_X509_GUID are contained in the dbx, the entries are
skipped.

Add support for EFI_CERT_X509_GUID dbx entries. When a EFI_CERT_X509_GUID
is found, it is added as an asymmetrical key to the .blacklist keyring.
Anytime the .platform keyring is used, the keys in the .blacklist keyring
are referenced, if a matching key is found, the key will be rejected.

[DH: Made the following changes:
 - Added to have a config option to enable the facility.  This allows a
   Kconfig solution to make sure that pkcs7_validate_trust() is
   enabled.[1][2]
 - Moved the functions out from the middle of the blacklist functions.
 - Added kerneldoc comments.]

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
cc: Randy Dunlap <rdunlap@infradead.org>
cc: Mickaël Salaün <mic@digikod.net>
cc: Arnd Bergmann <arnd@kernel.org>
cc: keyrings@vger.kernel.org
Link: https://lore.kernel.org/r/20200901165143.10295-1-eric.snowberg@oracle.com/ # rfc
Link: https://lore.kernel.org/r/20200909172736.73003-1-eric.snowberg@oracle.com/ # v2
Link: https://lore.kernel.org/r/20200911182230.62266-1-eric.snowberg@oracle.com/ # v3
Link: https://lore.kernel.org/r/20200916004927.64276-1-eric.snowberg@oracle.com/ # v4
Link: https://lore.kernel.org/r/20210122181054.32635-2-eric.snowberg@oracle.com/ # v5
Link: https://lore.kernel.org/r/161428672051.677100.11064981943343605138.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/161433310942.902181.4901864302675874242.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161529605075.163428.14625520893961300757.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/bc2c24e3-ed68-2521-0bf4-a1f6be4a895d@infradead.org/ [1]
Link: https://lore.kernel.org/r/20210225125638.1841436-1-arnd@kernel.org/ [2]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 certs/Kconfig                                 |  9 ++++
 certs/blacklist.c                             | 43 +++++++++++++++++++
 certs/blacklist.h                             |  2 +
 certs/system_keyring.c                        |  6 +++
 include/keys/system_keyring.h                 | 15 +++++++
 .../platform_certs/keyring_handler.c          | 11 +++++
 6 files changed, 86 insertions(+)

diff --git a/certs/Kconfig b/certs/Kconfig
index c94e93d8bccf..76e469b56a77 100644
--- a/certs/Kconfig
+++ b/certs/Kconfig
@@ -83,4 +83,13 @@ config SYSTEM_BLACKLIST_HASH_LIST
 	  wrapper to incorporate the list into the kernel.  Each <hash> should
 	  be a string of hex digits.
 
+config SYSTEM_REVOCATION_LIST
+	bool "Provide system-wide ring of revocation certificates"
+	depends on SYSTEM_BLACKLIST_KEYRING
+	depends on PKCS7_MESSAGE_PARSER=y
+	help
+	  If set, this allows revocation certificates to be stored in the
+	  blacklist keyring and implements a hook whereby a PKCS#7 message can
+	  be checked to see if it matches such a certificate.
+
 endmenu
diff --git a/certs/blacklist.c b/certs/blacklist.c
index f1c434b04b5e..59b2f106b294 100644
--- a/certs/blacklist.c
+++ b/certs/blacklist.c
@@ -144,6 +144,49 @@ int is_binary_blacklisted(const u8 *hash, size_t hash_len)
 }
 EXPORT_SYMBOL_GPL(is_binary_blacklisted);
 
+#ifdef CONFIG_SYSTEM_REVOCATION_LIST
+/**
+ * add_key_to_revocation_list - Add a revocation certificate to the blacklist
+ * @data: The data blob containing the certificate
+ * @size: The size of data blob
+ */
+int add_key_to_revocation_list(const char *data, size_t size)
+{
+	key_ref_t key;
+
+	key = key_create_or_update(make_key_ref(blacklist_keyring, true),
+				   "asymmetric",
+				   NULL,
+				   data,
+				   size,
+				   ((KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW),
+				   KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN);
+
+	if (IS_ERR(key)) {
+		pr_err("Problem with revocation key (%ld)\n", PTR_ERR(key));
+		return PTR_ERR(key);
+	}
+
+	return 0;
+}
+
+/**
+ * is_key_on_revocation_list - Determine if the key for a PKCS#7 message is revoked
+ * @pkcs7: The PKCS#7 message to check
+ */
+int is_key_on_revocation_list(struct pkcs7_message *pkcs7)
+{
+	int ret;
+
+	ret = pkcs7_validate_trust(pkcs7, blacklist_keyring);
+
+	if (ret == 0)
+		return -EKEYREJECTED;
+
+	return -ENOKEY;
+}
+#endif
+
 /*
  * Initialise the blacklist
  */
diff --git a/certs/blacklist.h b/certs/blacklist.h
index 1efd6fa0dc60..51b320cf8574 100644
--- a/certs/blacklist.h
+++ b/certs/blacklist.h
@@ -1,3 +1,5 @@
 #include <linux/kernel.h>
+#include <linux/errno.h>
+#include <crypto/pkcs7.h>
 
 extern const char __initconst *const blacklist_hashes[];
diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index 798291177186..cc165b359ea3 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -241,6 +241,12 @@ int verify_pkcs7_message_sig(const void *data, size_t len,
 			pr_devel("PKCS#7 platform keyring is not available\n");
 			goto error;
 		}
+
+		ret = is_key_on_revocation_list(pkcs7);
+		if (ret != -ENOKEY) {
+			pr_devel("PKCS#7 platform key is on revocation list\n");
+			goto error;
+		}
 	}
 	ret = pkcs7_validate_trust(pkcs7, trusted_keys);
 	if (ret < 0) {
diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
index fb8b07daa9d1..875e002a4180 100644
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -31,6 +31,7 @@ extern int restrict_link_by_builtin_and_secondary_trusted(
 #define restrict_link_by_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
 #endif
 
+extern struct pkcs7_message *pkcs7;
 #ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING
 extern int mark_hash_blacklisted(const char *hash);
 extern int is_hash_blacklisted(const u8 *hash, size_t hash_len,
@@ -49,6 +50,20 @@ static inline int is_binary_blacklisted(const u8 *hash, size_t hash_len)
 }
 #endif
 
+#ifdef CONFIG_SYSTEM_REVOCATION_LIST
+extern int add_key_to_revocation_list(const char *data, size_t size);
+extern int is_key_on_revocation_list(struct pkcs7_message *pkcs7);
+#else
+static inline int add_key_to_revocation_list(const char *data, size_t size)
+{
+	return 0;
+}
+static inline int is_key_on_revocation_list(struct pkcs7_message *pkcs7)
+{
+	return -ENOKEY;
+}
+#endif
+
 #ifdef CONFIG_IMA_BLACKLIST_KEYRING
 extern struct key *ima_blacklist_keyring;
 
diff --git a/security/integrity/platform_certs/keyring_handler.c b/security/integrity/platform_certs/keyring_handler.c
index c5ba695c10e3..5604bd57c990 100644
--- a/security/integrity/platform_certs/keyring_handler.c
+++ b/security/integrity/platform_certs/keyring_handler.c
@@ -55,6 +55,15 @@ static __init void uefi_blacklist_binary(const char *source,
 	uefi_blacklist_hash(source, data, len, "bin:", 4);
 }
 
+/*
+ * Add an X509 cert to the revocation list.
+ */
+static __init void uefi_revocation_list_x509(const char *source,
+					     const void *data, size_t len)
+{
+	add_key_to_revocation_list(data, len);
+}
+
 /*
  * Return the appropriate handler for particular signature list types found in
  * the UEFI db and MokListRT tables.
@@ -76,5 +85,7 @@ __init efi_element_handler_t get_handler_for_dbx(const efi_guid_t *sig_type)
 		return uefi_blacklist_x509_tbs;
 	if (efi_guidcmp(*sig_type, efi_cert_sha256_guid) == 0)
 		return uefi_blacklist_binary;
+	if (efi_guidcmp(*sig_type, efi_cert_x509_guid) == 0)
+		return uefi_revocation_list_x509;
 	return 0;
 }
-- 
2.30.2

[PATCH 5.4 70/71] certs: Move load_system_certificate_list to a common function

[Sasha Levin]

From: Eric Snowberg <eric.snowberg@oracle.com>

[ Upstream commit 2565ca7f5ec1a98d51eea8860c4ab923f1ca2c85 ]

Move functionality within load_system_certificate_list to a common
function, so it can be reused in the future.

DH Changes:
 - Added inclusion of common.h to common.c (Eric [1]).

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: keyrings@vger.kernel.org
Link: https://lore.kernel.org/r/EDA280F9-F72D-4181-93C7-CDBE95976FF7@oracle.com/ [1]
Link: https://lore.kernel.org/r/20200930201508.35113-2-eric.snowberg@oracle.com/
Link: https://lore.kernel.org/r/20210122181054.32635-3-eric.snowberg@oracle.com/ # v5
Link: https://lore.kernel.org/r/161428672825.677100.7545516389752262918.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/161433311696.902181.3599366124784670368.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161529605850.163428.7786675680201528556.stgit@warthog.procyon.org.uk/ # v3
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 certs/Makefile         |  2 +-
 certs/common.c         | 57 ++++++++++++++++++++++++++++++++++++++++++
 certs/common.h         |  9 +++++++
 certs/system_keyring.c | 49 +++---------------------------------
 4 files changed, 70 insertions(+), 47 deletions(-)
 create mode 100644 certs/common.c
 create mode 100644 certs/common.h

diff --git a/certs/Makefile b/certs/Makefile
index f4c25b67aad9..f4b90bad8690 100644
--- a/certs/Makefile
+++ b/certs/Makefile
@@ -3,7 +3,7 @@
 # Makefile for the linux kernel signature checking certificates.
 #
 
-obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o
+obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o common.o
 obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist.o
 ifneq ($(CONFIG_SYSTEM_BLACKLIST_HASH_LIST),"")
 obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist_hashes.o
diff --git a/certs/common.c b/certs/common.c
new file mode 100644
index 000000000000..16a220887a53
--- /dev/null
+++ b/certs/common.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/kernel.h>
+#include <linux/key.h>
+#include "common.h"
+
+int load_certificate_list(const u8 cert_list[],
+			  const unsigned long list_size,
+			  const struct key *keyring)
+{
+	key_ref_t key;
+	const u8 *p, *end;
+	size_t plen;
+
+	p = cert_list;
+	end = p + list_size;
+	while (p < end) {
+		/* Each cert begins with an ASN.1 SEQUENCE tag and must be more
+		 * than 256 bytes in size.
+		 */
+		if (end - p < 4)
+			goto dodgy_cert;
+		if (p[0] != 0x30 &&
+		    p[1] != 0x82)
+			goto dodgy_cert;
+		plen = (p[2] << 8) | p[3];
+		plen += 4;
+		if (plen > end - p)
+			goto dodgy_cert;
+
+		key = key_create_or_update(make_key_ref(keyring, 1),
+					   "asymmetric",
+					   NULL,
+					   p,
+					   plen,
+					   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
+					   KEY_USR_VIEW | KEY_USR_READ),
+					   KEY_ALLOC_NOT_IN_QUOTA |
+					   KEY_ALLOC_BUILT_IN |
+					   KEY_ALLOC_BYPASS_RESTRICTION);
+		if (IS_ERR(key)) {
+			pr_err("Problem loading in-kernel X.509 certificate (%ld)\n",
+			       PTR_ERR(key));
+		} else {
+			pr_notice("Loaded X.509 cert '%s'\n",
+				  key_ref_to_ptr(key)->description);
+			key_ref_put(key);
+		}
+		p += plen;
+	}
+
+	return 0;
+
+dodgy_cert:
+	pr_err("Problem parsing in-kernel X.509 certificate list\n");
+	return 0;
+}
diff --git a/certs/common.h b/certs/common.h
new file mode 100644
index 000000000000..abdb5795936b
--- /dev/null
+++ b/certs/common.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _CERT_COMMON_H
+#define _CERT_COMMON_H
+
+int load_certificate_list(const u8 cert_list[], const unsigned long list_size,
+			  const struct key *keyring);
+
+#endif
diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index cc165b359ea3..a44a8915c94c 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -15,6 +15,7 @@
 #include <keys/asymmetric-type.h>
 #include <keys/system_keyring.h>
 #include <crypto/pkcs7.h>
+#include "common.h"
 
 static struct key *builtin_trusted_keys;
 #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
@@ -136,54 +137,10 @@ device_initcall(system_trusted_keyring_init);
  */
 static __init int load_system_certificate_list(void)
 {
-	key_ref_t key;
-	const u8 *p, *end;
-	size_t plen;
-
 	pr_notice("Loading compiled-in X.509 certificates\n");
 
-	p = system_certificate_list;
-	end = p + system_certificate_list_size;
-	while (p < end) {
-		/* Each cert begins with an ASN.1 SEQUENCE tag and must be more
-		 * than 256 bytes in size.
-		 */
-		if (end - p < 4)
-			goto dodgy_cert;
-		if (p[0] != 0x30 &&
-		    p[1] != 0x82)
-			goto dodgy_cert;
-		plen = (p[2] << 8) | p[3];
-		plen += 4;
-		if (plen > end - p)
-			goto dodgy_cert;
-
-		key = key_create_or_update(make_key_ref(builtin_trusted_keys, 1),
-					   "asymmetric",
-					   NULL,
-					   p,
-					   plen,
-					   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
-					   KEY_USR_VIEW | KEY_USR_READ),
-					   KEY_ALLOC_NOT_IN_QUOTA |
-					   KEY_ALLOC_BUILT_IN |
-					   KEY_ALLOC_BYPASS_RESTRICTION);
-		if (IS_ERR(key)) {
-			pr_err("Problem loading in-kernel X.509 certificate (%ld)\n",
-			       PTR_ERR(key));
-		} else {
-			pr_notice("Loaded X.509 cert '%s'\n",
-				  key_ref_to_ptr(key)->description);
-			key_ref_put(key);
-		}
-		p += plen;
-	}
-
-	return 0;
-
-dodgy_cert:
-	pr_err("Problem parsing in-kernel X.509 certificate list\n");
-	return 0;
+	return load_certificate_list(system_certificate_list, system_certificate_list_size,
+				     builtin_trusted_keys);
 }
 late_initcall(load_system_certificate_list);
 
-- 
2.30.2