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/ # 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]
This commit is contained in:
Eric Snowberg 2021-01-22 13:10:51 -05:00 committed by David Howells
parent 8f0bfc25c9
commit 56c5812623
6 changed files with 86 additions and 0 deletions

View File

@ -83,4 +83,13 @@ config SYSTEM_BLACKLIST_HASH_LIST
wrapper to incorporate the list into the kernel. Each <hash> should wrapper to incorporate the list into the kernel. Each <hash> should
be a string of hex digits. 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 endmenu

View File

@ -145,6 +145,49 @@ int is_binary_blacklisted(const u8 *hash, size_t hash_len)
} }
EXPORT_SYMBOL_GPL(is_binary_blacklisted); 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 * Initialise the blacklist
*/ */

View File

@ -1,3 +1,5 @@
#include <linux/kernel.h> #include <linux/kernel.h>
#include <linux/errno.h>
#include <crypto/pkcs7.h>
extern const char __initconst *const blacklist_hashes[]; extern const char __initconst *const blacklist_hashes[];

View File

@ -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"); pr_devel("PKCS#7 platform keyring is not available\n");
goto error; 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); ret = pkcs7_validate_trust(pkcs7, trusted_keys);
if (ret < 0) { if (ret < 0) {

View File

@ -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 #define restrict_link_by_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
#endif #endif
extern struct pkcs7_message *pkcs7;
#ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING #ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING
extern int mark_hash_blacklisted(const char *hash); extern int mark_hash_blacklisted(const char *hash);
extern int is_hash_blacklisted(const u8 *hash, size_t hash_len, 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 #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 #ifdef CONFIG_IMA_BLACKLIST_KEYRING
extern struct key *ima_blacklist_keyring; extern struct key *ima_blacklist_keyring;

View File

@ -55,6 +55,15 @@ static __init void uefi_blacklist_binary(const char *source,
uefi_blacklist_hash(source, data, len, "bin:", 4); 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 * Return the appropriate handler for particular signature list types found in
* the UEFI db and MokListRT tables. * 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; return uefi_blacklist_x509_tbs;
if (efi_guidcmp(*sig_type, efi_cert_sha256_guid) == 0) if (efi_guidcmp(*sig_type, efi_cert_sha256_guid) == 0)
return uefi_blacklist_binary; return uefi_blacklist_binary;
if (efi_guidcmp(*sig_type, efi_cert_x509_guid) == 0)
return uefi_revocation_list_x509;
return 0; return 0;
} }