certs: Add EFI_CERT_X509_GUID support for dbx entries

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/
Link: https://lore.kernel.org/r/20200909172736.73003-1-eric.snowberg@oracle.com/
Link: https://lore.kernel.org/r/20200911182230.62266-1-eric.snowberg@oracle.com/
Link: https://lore.kernel.org/r/20200916004927.64276-1-eric.snowberg@oracle.com/
Link: https://lore.kernel.org/r/20210122181054.32635-2-eric.snowberg@oracle.com/
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/
Link: https://lore.kernel.org/r/161529605075.163428.14625520893961300757.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/bc2c24e3-ed68-2521-0bf4-a1f6be4a895d@infradead.org/
Link: https://lore.kernel.org/r/20210225125638.1841436-1-arnd@kernel.org/

diff --git a/certs/Kconfig b/certs/Kconfig
index c94e93d8bccf038f4684c4cce93d558d9e7269ff..76e469b56a773ccd1c2163f04a541fde0faf2672 100644 (file)
--- 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 bffe4c6f4a9e204d215119278d419bb491d2d7c8..2b8644123d5fd58cdbffad1645207bea414426a6 100644 (file)
--- a/certs/blacklist.c
+++ b/certs/blacklist.c
@@ -145,6 +145,49 @@ 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 1efd6fa0dc608c2a3d598b56c798f3e772a2bdbc..51b320cf85749e7a82788ed54a301b8a63243f1e 100644 (file)
--- 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 4b693da488f14bcc66b452789f2eab92da959f9f..ed98754d5795a3f0582640f11ee3923ebe1d292a 100644 (file)
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -242,6 +242,12 @@ 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 fb8b07daa9d15519370e1731b8cf4c726bf83a17..875e002a41804726f712948e5ed9acb1c7402706 100644 (file)
--- 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 c5ba695c10e3a5afd1633fc5bd765c0f1bf7a303..5604bd57c99077d8238cde7b5e6335a13cf16dce 100644 (file)
--- 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;
 }