1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Secure boot handling.
4  *
5  * Copyright (C) 2013,2014 Linaro Limited
6  *     Roy Franz <roy.franz@linaro.org
7  * Copyright (C) 2013 Red Hat, Inc.
8  *     Mark Salter <msalter@redhat.com>
9  */
10 #include <linux/efi.h>
11 #include <asm/efi.h>
12 
13 #include "efistub.h"
14 
15 /* SHIM variables */
16 static const efi_guid_t shim_guid = EFI_SHIM_LOCK_GUID;
17 static const efi_char16_t shim_MokSBState_name[] = L"MokSBState";
18 
19 static efi_status_t get_var(efi_char16_t *name, efi_guid_t *vendor, u32 *attr,
20 			    unsigned long *data_size, void *data)
21 {
22 	return get_efi_var(name, vendor, attr, data_size, data);
23 }
24 
25 /*
26  * Determine whether we're in secure boot mode.
27  */
28 enum efi_secureboot_mode efi_get_secureboot(void)
29 {
30 	u32 attr;
31 	unsigned long size;
32 	enum efi_secureboot_mode mode;
33 	efi_status_t status;
34 	u8 moksbstate;
35 
36 	mode = efi_get_secureboot_mode(get_var);
37 	if (mode == efi_secureboot_mode_unknown) {
38 		efi_err("Could not determine UEFI Secure Boot status.\n");
39 		return efi_secureboot_mode_unknown;
40 	}
41 	if (mode != efi_secureboot_mode_enabled)
42 		return mode;
43 
44 	/*
45 	 * See if a user has put the shim into insecure mode. If so, and if the
46 	 * variable doesn't have the runtime attribute set, we might as well
47 	 * honor that.
48 	 */
49 	size = sizeof(moksbstate);
50 	status = get_efi_var(shim_MokSBState_name, &shim_guid,
51 			     &attr, &size, &moksbstate);
52 
53 	/* If it fails, we don't care why. Default to secure */
54 	if (status != EFI_SUCCESS)
55 		goto secure_boot_enabled;
56 	if (!(attr & EFI_VARIABLE_RUNTIME_ACCESS) && moksbstate == 1)
57 		return efi_secureboot_mode_disabled;
58 
59 secure_boot_enabled:
60 	efi_info("UEFI Secure Boot is enabled.\n");
61 	return efi_secureboot_mode_enabled;
62 }
63