drivers/firmware/efi/libstub/secureboot.c

   1 /*
   2  * Secure boot handling.
   3  *
   4  * Copyright (C) 2013,2014 Linaro Limited
   5  *     Roy Franz <roy.franz@linaro.org
   6  * Copyright (C) 2013 Red Hat, Inc.
   7  *     Mark Salter <msalter@redhat.com>
   8  *
   9  * This file is part of the Linux kernel, and is made available under the
  10  * terms of the GNU General Public License version 2.
  11  */
  12 #include <linux/efi.h>
  13 #include <asm/efi.h>
  14
  15 #include "efistub.h"
  16
  17 /* BIOS variables */
  18 static const efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
  19 static const efi_char16_t const efi_SecureBoot_name[] = {
  20         'S', 'e', 'c', 'u', 'r', 'e', 'B', 'o', 'o', 't', 0
  21 };
  22 static const efi_char16_t const efi_SetupMode_name[] = {
  23         'S', 'e', 't', 'u', 'p', 'M', 'o', 'd', 'e', 0
  24 };
  25
  26 /* SHIM variables */
  27 static const efi_guid_t shim_guid = EFI_SHIM_LOCK_GUID;
  28 static efi_char16_t const shim_MokSBState_name[] = {
  29         'M', 'o', 'k', 'S', 'B', 'S', 't', 'a', 't', 'e', 0
  30 };
  31
  32 #define get_efi_var(name, vendor, ...) \
  33         efi_call_runtime(get_variable, \
  34                          (efi_char16_t *)(name), (efi_guid_t *)(vendor), \
  35                          __VA_ARGS__);
  36
  37 /*
  38  * Determine whether we're in secure boot mode.
  39  */
  40 enum efi_secureboot_mode efi_get_secureboot(efi_system_table_t *sys_table_arg)
  41 {
  42         u32 attr;
  43         u8 secboot, setupmode, moksbstate;
  44         unsigned long size;
  45         efi_status_t status;
  46
  47         size = sizeof(secboot);
  48         status = get_efi_var(efi_SecureBoot_name, &efi_variable_guid,
  49                              NULL, &size, &secboot);
  50         if (status == EFI_NOT_FOUND)
  51                 return efi_secureboot_mode_disabled;
  52         if (status != EFI_SUCCESS)
  53                 goto out_efi_err;
  54
  55         size = sizeof(setupmode);
  56         status = get_efi_var(efi_SetupMode_name, &efi_variable_guid,
  57                              NULL, &size, &setupmode);
  58         if (status != EFI_SUCCESS)
  59                 goto out_efi_err;
  60
  61         if (secboot == 0 || setupmode == 1)
  62                 return efi_secureboot_mode_disabled;
  63
  64         /*
  65          * See if a user has put the shim into insecure mode. If so, and if the
  66          * variable doesn't have the runtime attribute set, we might as well
  67          * honor that.
  68          */
  69         size = sizeof(moksbstate);
  70         status = get_efi_var(shim_MokSBState_name, &shim_guid,
  71                              &attr, &size, &moksbstate);
  72
  73         /* If it fails, we don't care why. Default to secure */
  74         if (status != EFI_SUCCESS)
  75                 goto secure_boot_enabled;
  76         if (!(attr & EFI_VARIABLE_RUNTIME_ACCESS) && moksbstate == 1)
  77                 return efi_secureboot_mode_disabled;
  78
  79 secure_boot_enabled:
  80         pr_efi(sys_table_arg, "UEFI Secure Boot is enabled.\n");
  81         return efi_secureboot_mode_enabled;
  82
  83 out_efi_err:
  84         pr_efi_err(sys_table_arg, "Could not determine UEFI Secure Boot status.\n");
  85         return efi_secureboot_mode_unknown;
  86 }