[PATCH 9/9] MODSIGN: Allow the "db" UEFI variable to be suppressed

David Howells
2016-11-16T18:12:29Z

From: Josh Boyer <jwboyer@fedoraproject.org>

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.

Signed-off-by: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: David Howells <dhowells@redhat.com>
---

certs/load_uefi.c | 44 ++++++++++++++++++++++++++++++++++----------
1 file changed, 34 insertions(+), 10 deletions(-)

diff --git a/certs/load_uefi.c b/certs/load_uefi.c
index b44e464c3ff4..3d8845986019 100644
--- a/certs/load_uefi.c
+++ b/certs/load_uefi.c
@@ -13,6 +13,26 @@ static __initdata efi_guid_t efi_cert_x509_sha256_guid = EFI_CERT_X509_SHA256_GU
static __initdata efi_guid_t efi_cert_sha256_guid = 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.
*/
static __init void *get_cert_list(efi_char16_t *name, efi_guid_t *guid,
@@ -113,7 +133,9 @@ static __init efi_element_handler_t get_handler_for_dbx(const efi_guid_t *sig_ty
}

/*
- * Load the certs contained in the UEFI databases
+ * Load the certs contained in the UEFI databases into the secondary trusted
+ * keyring and the UEFI blacklisted X.509 cert SHA256 hashes into the blacklist
+ * keyring.
*/
static int __init load_uefi_certs(void)
{
@@ -129,15 +151,17 @@ 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("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);
+ 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);