[PATCH 2/3 Xenial SRU] UBUNTU: SAUCE: (noup) efi: Disable secure boot if shim is in insecure mode

[tim.gardner at canonical.com]

From: Josh Boyer <jwboyer at fedoraproject.org>

BugLink: http://bugs.launchpad.net/bugs/1571691

A user can manually tell the shim boot loader to disable validation of
images it loads.  When a user does this, it creates a UEFI variable called
MokSBState that does not have the runtime attribute set.  Given that the
user explicitly disabled validation, we can honor that and not enable
secure boot mode if that variable is set.

Signed-off-by: Josh Boyer <jwboyer at fedoraproject.org>
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 arch/x86/boot/compressed/eboot.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index ca120ac..665b202 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -850,8 +850,9 @@ out:
 
 static int get_secure_boot(void)
 {
-	u8 sb, setup;
+	u8 sb, setup, moksbstate;
 	unsigned long datasize = sizeof(sb);
+	u32 attr;
 	efi_guid_t var_guid = EFI_GLOBAL_VARIABLE_GUID;
 	efi_status_t status;
 
@@ -875,6 +876,23 @@ static int get_secure_boot(void)
 	if (setup == 1)
 		return 0;
 
+	/* See if a user has put shim into insecure_mode.  If so, and the variable
+	 * doesn't have the runtime attribute set, we might as well honor that.
+	 */
+	var_guid = EFI_SHIM_LOCK_GUID;
+	status = efi_early->call((unsigned long)sys_table->runtime->get_variable,
+				L"MokSBState", &var_guid, &attr, &datasize,
+				&moksbstate);
+
+	/* If it fails, we don't care why.  Default to secure */
+	if (status != EFI_SUCCESS)
+		return 1;
+
+	if (!(attr & EFI_VARIABLE_RUNTIME_ACCESS)) {
+		if (moksbstate == 1)
+			return 0;
+	}
+
 	return 1;
 }
 
-- 
1.9.1