Re: [PATCH v3] certs: Add EFI_CERT_X509_GUID support for dbx entries

On Sep 14, 2020, at 12:12 PM, Jarkko Sakkinen [off-list ref] wrote:

On Fri, Sep 11, 2020 at 02:22:30PM -0400, Eric Snowberg wrote:

quoted

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.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
v3:
Fixed an issue when CONFIG_PKCS7_MESSAGE_PARSER is not builtin and defined
as a module instead, pointed out by Randy Dunlap

v2: 
Fixed build issue reported by kernel test robot [off-list ref]
Commit message update (suggested by Jarkko Sakkinen)
---
certs/blacklist.c                             | 33 +++++++++++++++++++
certs/blacklist.h                             | 12 +++++++
certs/system_keyring.c                        |  6 ++++
include/keys/system_keyring.h                 | 11 +++++++
.../platform_certs/keyring_handler.c          | 11 +++++++
5 files changed, 73 insertions(+)

diff --git a/certs/blacklist.c b/certs/blacklist.c
index 6514f9ebc943..3d1514ba5d47 100644
--- a/certs/blacklist.c
+++ b/certs/blacklist.c

@@ -100,6 +100,39 @@ int mark_hash_blacklisted(const char *hash)

	return 0;
}

+int mark_key_revocationlisted(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;
+}
+
+int is_key_revocationlisted(struct pkcs7_message *pkcs7)
+{
+	int ret;
+
+	ret = validate_trust(pkcs7, blacklist_keyring);
+
+	if (ret == 0)
+		return -EKEYREJECTED;
+
+	return -ENOKEY;
+}
+EXPORT_SYMBOL_GPL(is_key_revocationlisted);

Hmm... ignore my previous comment about this. Export symbol is called
only by system keyring code.

Would be best if the commit message would explicitly reason new exports.

I don’t see a good reason to keep the export now, I’ll remove it from the
next version.  Thanks.