5f56a74cc0
We currently check the MokSBState variable to decide whether we should treat UEFI secure boot as being disabled, even if the firmware thinks otherwise. This is used by shim to indicate that it is not checking signatures on boot images. In the kernel, we use this to relax lockdown policies. However, in cases where shim is not even being used, we don't want this variable to interfere with lockdown, given that the variable may be non-volatile and therefore persist across a reboot. This means setting it once will persistently disable lockdown checks on a given system. So switch to the mirrored version of this variable, called MokSBStateRT, which is supposed to be volatile, and this is something we can check. Cc: <stable@vger.kernel.org> # v4.19+ Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> Reviewed-by: Peter Jones <pjones@redhat.com>
62 lines
1.7 KiB
C
62 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Secure boot handling.
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*
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* Copyright (C) 2013,2014 Linaro Limited
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* Roy Franz <roy.franz@linaro.org
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* Copyright (C) 2013 Red Hat, Inc.
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* Mark Salter <msalter@redhat.com>
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*/
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#include <linux/efi.h>
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#include <asm/efi.h>
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#include "efistub.h"
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/* SHIM variables */
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static const efi_guid_t shim_guid = EFI_SHIM_LOCK_GUID;
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static const efi_char16_t shim_MokSBState_name[] = L"MokSBStateRT";
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static efi_status_t get_var(efi_char16_t *name, efi_guid_t *vendor, u32 *attr,
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unsigned long *data_size, void *data)
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{
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return get_efi_var(name, vendor, attr, data_size, data);
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}
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/*
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* Determine whether we're in secure boot mode.
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*/
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enum efi_secureboot_mode efi_get_secureboot(void)
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{
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u32 attr;
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unsigned long size;
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enum efi_secureboot_mode mode;
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efi_status_t status;
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u8 moksbstate;
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mode = efi_get_secureboot_mode(get_var);
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if (mode == efi_secureboot_mode_unknown) {
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efi_err("Could not determine UEFI Secure Boot status.\n");
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return efi_secureboot_mode_unknown;
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}
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if (mode != efi_secureboot_mode_enabled)
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return mode;
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/*
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* See if a user has put the shim into insecure mode. If so, and if the
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* variable doesn't have the non-volatile attribute set, we might as
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* well honor that.
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*/
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size = sizeof(moksbstate);
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status = get_efi_var(shim_MokSBState_name, &shim_guid,
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&attr, &size, &moksbstate);
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/* If it fails, we don't care why. Default to secure */
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if (status != EFI_SUCCESS)
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goto secure_boot_enabled;
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if (!(attr & EFI_VARIABLE_NON_VOLATILE) && moksbstate == 1)
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return efi_secureboot_mode_disabled;
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secure_boot_enabled:
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efi_info("UEFI Secure Boot is enabled.\n");
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return efi_secureboot_mode_enabled;
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}
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