[PATCH v3 1/4] certs: Add EFI_CERT_X509_GUID support for dbx entries
David Howells
dhowells at redhat.com
Tue Mar 9 13:20:50 UTC 2021
From: Eric Snowberg <eric.snowberg at oracle.com>
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.
- Moved the functions out from the middle of the blacklist functions.
- Added kerneldoc comments.]
Signed-off-by: Eric Snowberg <eric.snowberg at oracle.com>
Signed-off-by: David Howells <dhowells at redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko at kernel.org>
cc: Randy Dunlap <rdunlap at infradead.org>
cc: Mickaël Salaün <mic at digikod.net>
cc: Arnd Bergmann <arnd at kernel.org>
cc: keyrings at 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/ # 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/2660556.1610545213@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/20210122181054.32635-2-eric.snowberg@oracle.com/ # v5
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/
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
---
certs/Kconfig | 9 ++++
certs/blacklist.c | 43 ++++++++++++++++++++
certs/blacklist.h | 2 +
certs/system_keyring.c | 6 +++
include/keys/system_keyring.h | 15 +++++++
.../integrity/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 bffe4c6f4a9e..2b8644123d5f 100644
--- 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 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 4b693da488f1..ed98754d5795 100644
--- 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 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;
}
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