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sb.c
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sb.c
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/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2020 Free Software Foundation, Inc.
*
* GRUB is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* GRUB is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GRUB. If not, see <http://www.gnu.org/licenses/>.
*
* UEFI Secure Boot related checkings.
*/
#include <grub/efi/efi.h>
#include <grub/efi/pe32.h>
#include <grub/efi/sb.h>
#include <grub/env.h>
#include <grub/err.h>
#include <grub/file.h>
#include <grub/i386/linux.h>
#include <grub/kernel.h>
#include <grub/mm.h>
#include <grub/types.h>
#include <grub/verify.h>
static grub_efi_guid_t shim_lock_guid = GRUB_EFI_SHIM_LOCK_GUID;
/*
* Determine whether we're in secure boot mode.
*
* Please keep the logic in sync with the Linux kernel,
* drivers/firmware/efi/libstub/secureboot.c:efi_get_secureboot().
*/
grub_uint8_t
grub_efi_get_secureboot (void)
{
static grub_efi_guid_t efi_variable_guid = GRUB_EFI_GLOBAL_VARIABLE_GUID;
grub_efi_status_t status;
grub_efi_uint32_t attr = 0;
grub_size_t size = 0;
grub_uint8_t *secboot = NULL;
grub_uint8_t *setupmode = NULL;
grub_uint8_t *moksbstate = NULL;
grub_uint8_t secureboot = GRUB_EFI_SECUREBOOT_MODE_UNKNOWN;
const char *secureboot_str = "UNKNOWN";
status = grub_efi_get_variable ("SecureBoot", &efi_variable_guid,
&size, (void **) &secboot);
if (status == GRUB_EFI_NOT_FOUND)
{
secureboot = GRUB_EFI_SECUREBOOT_MODE_DISABLED;
goto out;
}
if (status != GRUB_EFI_SUCCESS)
goto out;
status = grub_efi_get_variable ("SetupMode", &efi_variable_guid,
&size, (void **) &setupmode);
if (status != GRUB_EFI_SUCCESS)
goto out;
if ((*secboot == 0) || (*setupmode == 1))
{
secureboot = GRUB_EFI_SECUREBOOT_MODE_DISABLED;
goto out;
}
/*
* See if a user has put the shim into insecure mode. If so, and if the
* variable doesn't have the runtime attribute set, we might as well
* honor that.
*/
status = grub_efi_get_variable_with_attributes ("MokSBState", &shim_lock_guid,
&size, (void **) &moksbstate, &attr);
/* If it fails, we don't care why. Default to secure. */
if (status != GRUB_EFI_SUCCESS)
{
secureboot = GRUB_EFI_SECUREBOOT_MODE_ENABLED;
goto out;
}
if (!(attr & GRUB_EFI_VARIABLE_RUNTIME_ACCESS) && *moksbstate == 1)
{
secureboot = GRUB_EFI_SECUREBOOT_MODE_DISABLED;
goto out;
}
secureboot = GRUB_EFI_SECUREBOOT_MODE_ENABLED;
out:
grub_free (moksbstate);
grub_free (setupmode);
grub_free (secboot);
if (secureboot == GRUB_EFI_SECUREBOOT_MODE_DISABLED)
secureboot_str = "Disabled";
else if (secureboot == GRUB_EFI_SECUREBOOT_MODE_ENABLED)
secureboot_str = "Enabled";
grub_dprintf ("efi", "UEFI Secure Boot state: %s\n", secureboot_str);
return secureboot;
}
static grub_err_t
shim_lock_verifier_init (grub_file_t io __attribute__ ((unused)),
enum grub_file_type type,
void **context __attribute__ ((unused)),
enum grub_verify_flags *flags)
{
*flags = GRUB_VERIFY_FLAGS_NONE;
switch (type & GRUB_FILE_TYPE_MASK)
{
/* Files we check. */
case GRUB_FILE_TYPE_LINUX_KERNEL:
case GRUB_FILE_TYPE_MULTIBOOT_KERNEL:
case GRUB_FILE_TYPE_BSD_KERNEL:
case GRUB_FILE_TYPE_XNU_KERNEL:
case GRUB_FILE_TYPE_PLAN9_KERNEL:
case GRUB_FILE_TYPE_EFI_CHAINLOADED_IMAGE:
*flags = GRUB_VERIFY_FLAGS_SINGLE_CHUNK;
return GRUB_ERR_NONE;
/* Files that do not affect secureboot state. */
case GRUB_FILE_TYPE_NONE:
case GRUB_FILE_TYPE_LOOPBACK:
case GRUB_FILE_TYPE_LINUX_INITRD:
case GRUB_FILE_TYPE_OPENBSD_RAMDISK:
case GRUB_FILE_TYPE_XNU_RAMDISK:
case GRUB_FILE_TYPE_SIGNATURE:
case GRUB_FILE_TYPE_PUBLIC_KEY:
case GRUB_FILE_TYPE_PUBLIC_KEY_TRUST:
case GRUB_FILE_TYPE_PRINT_BLOCKLIST:
case GRUB_FILE_TYPE_TESTLOAD:
case GRUB_FILE_TYPE_GET_SIZE:
case GRUB_FILE_TYPE_ZFS_ENCRYPTION_KEY:
case GRUB_FILE_TYPE_CAT:
case GRUB_FILE_TYPE_HEXCAT:
case GRUB_FILE_TYPE_CMP:
case GRUB_FILE_TYPE_HASHLIST:
case GRUB_FILE_TYPE_TO_HASH:
case GRUB_FILE_TYPE_KEYBOARD_LAYOUT:
case GRUB_FILE_TYPE_PIXMAP:
case GRUB_FILE_TYPE_GRUB_MODULE_LIST:
case GRUB_FILE_TYPE_CONFIG:
case GRUB_FILE_TYPE_THEME:
case GRUB_FILE_TYPE_GETTEXT_CATALOG:
case GRUB_FILE_TYPE_FS_SEARCH:
case GRUB_FILE_TYPE_LOADENV:
case GRUB_FILE_TYPE_SAVEENV:
case GRUB_FILE_TYPE_VERIFY_SIGNATURE:
*flags = GRUB_VERIFY_FLAGS_SKIP_VERIFICATION;
return GRUB_ERR_NONE;
/* Other files. */
default:
return grub_error (GRUB_ERR_ACCESS_DENIED, N_("prohibited by secure boot policy"));
}
}
static grub_err_t
shim_lock_verifier_write (void *context __attribute__ ((unused)), void *buf, grub_size_t size)
{
grub_efi_shim_lock_protocol_t *sl = grub_efi_locate_protocol (&shim_lock_guid, 0);
if (!sl)
return grub_error (GRUB_ERR_ACCESS_DENIED, N_("shim_lock protocol not found"));
if (sl->verify (buf, size) != GRUB_EFI_SUCCESS)
return grub_error (GRUB_ERR_BAD_SIGNATURE, N_("bad shim signature"));
return GRUB_ERR_NONE;
}
struct grub_file_verifier shim_lock_verifier =
{
.name = "shim_lock_verifier",
.init = shim_lock_verifier_init,
.write = shim_lock_verifier_write
};
void
grub_shim_lock_verifier_setup (void)
{
struct grub_module_header *header;
grub_efi_shim_lock_protocol_t *sl =
grub_efi_locate_protocol (&shim_lock_guid, 0);
/* shim_lock is missing, check if GRUB image is built with --disable-shim-lock. */
if (!sl)
{
FOR_MODULES (header)
{
if (header->type == OBJ_TYPE_DISABLE_SHIM_LOCK)
return;
}
}
/* Secure Boot is off. Do not load shim_lock. */
if (grub_efi_get_secureboot () != GRUB_EFI_SECUREBOOT_MODE_ENABLED)
return;
/* Enforce shim_lock_verifier. */
grub_verifier_register (&shim_lock_verifier);
grub_env_set ("shim_lock", "y");
grub_env_export ("shim_lock");
}