efi: Allow the "db" UEFI variable to be suppressed

If a user tells shim to not use the certs/hashes in the UEFI db variable
for verification purposes, shim will set a UEFI variable called
MokIgnoreDB. Have the uefi import code look for this and ignore the db
variable if it is found.

[zohar@linux.ibm.com: removed reference to "secondary" keyring comment]
Signed-off-by: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Nayna Jain <nayna@linux.ibm.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: James Morris <james.morris@microsoft.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

diff --git a/security/integrity/platform_certs/load_uefi.c b/security/integrity/platform_certs/load_uefi.c
index 8ceafa5..81b19c5 100644 (file)
--- a/security/integrity/platform_certs/load_uefi.c
+++ b/security/integrity/platform_certs/load_uefi.c
@@ -15,6 +15,26 @@ static efi_guid_t efi_cert_x509_sha256_guid __initdata =
        EFI_CERT_X509_SHA256_GUID;
 static efi_guid_t efi_cert_sha256_guid __initdata = EFI_CERT_SHA256_GUID;
 
+/*
+ * Look to see if a UEFI variable called MokIgnoreDB exists and return true if
+ * it does.
+ *
+ * This UEFI variable is set by the shim if a user tells the shim to not use
+ * the certs/hashes in the UEFI db variable for verification purposes.  If it
+ * is set, we should ignore the db variable also and the true return indicates
+ * this.
+ */
+static __init bool uefi_check_ignore_db(void)
+{
+       efi_status_t status;
+       unsigned int db = 0;
+       unsigned long size = sizeof(db);
+       efi_guid_t guid = EFI_SHIM_LOCK_GUID;
+
+       status = efi.get_variable(L"MokIgnoreDB", &guid, NULL, &size, &db);
+       return status == EFI_SUCCESS;
+}
+
 /*
  * Get a certificate list blob from the named EFI variable.
  */
@@ -114,7 +134,9 @@ static __init efi_element_handler_t get_handler_for_dbx(const efi_guid_t *
 }
 
 /*
- * Load the certs contained in the UEFI databases
+ * Load the certs contained in the UEFI databases into the platform trusted
+ * keyring and the UEFI blacklisted X.509 cert SHA256 hashes into the blacklist
+ * keyring.
  */
 static int __init load_uefi_certs(void)
 {
@@ -130,15 +152,18 @@ static int __init load_uefi_certs(void)
        /* Get db, MokListRT, and dbx.  They might not exist, so it isn't
         * an error if we can't get them.
         */
-       db = get_cert_list(L"db", &secure_var, &dbsize);
-       if (!db) {
-               pr_err("Couldn't get UEFI db list\n");
-       } else {
-               rc = parse_efi_signature_list("UEFI:db",
-                                             db, dbsize, get_handler_for_db);
-               if (rc)
-                       pr_err("Couldn't parse db signatures: %d\n", rc);
-               kfree(db);
+       if (!uefi_check_ignore_db()) {
+               db = get_cert_list(L"db", &secure_var, &dbsize);
+               if (!db) {
+                       pr_err("MODSIGN: Couldn't get UEFI db list\n");
+               } else {
+                       rc = parse_efi_signature_list("UEFI:db",
+                                       db, dbsize, get_handler_for_db);
+                       if (rc)
+                               pr_err("Couldn't parse db signatures: %d\n",
+                                      rc);
+                       kfree(db);
+               }
        }
 
        mok = get_cert_list(L"MokListRT", &mok_var, &moksize);