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578c95298b
When the GRUB starts on a secure boot platform, some commands can be
used to subvert the protections provided by the verification mechanism and
could lead to booting untrusted system.
To prevent that situation, allow GRUB to be locked down. That way the code
may check if GRUB has been locked down and further restrict the commands
that are registered or what subset of their functionality could be used.
The lockdown support adds the following components:
* The grub_lockdown() function which can be used to lockdown GRUB if,
e.g., UEFI Secure Boot is enabled.
* The grub_is_lockdown() function which can be used to check if the GRUB
was locked down.
* A verifier that flags OS kernels, the GRUB modules, Device Trees and ACPI
tables as GRUB_VERIFY_FLAGS_DEFER_AUTH to defer verification to other
verifiers. These files are only successfully verified if another registered
verifier returns success. Otherwise, the whole verification process fails.
For example, PE/COFF binaries verification can be done by the shim_lock
verifier which validates the signatures using the shim_lock protocol.
However, the verification is not deferred directly to the shim_lock verifier.
The shim_lock verifier is hooked into the verification process instead.
* A set of grub_{command,extcmd}_lockdown functions that can be used by
code registering command handlers, to only register unsafe commands if
the GRUB has not been locked down.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
81 lines
2.2 KiB
C
81 lines
2.2 KiB
C
/*
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* GRUB -- GRand Unified Bootloader
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* Copyright (C) 2020 Free Software Foundation, Inc.
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*
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* GRUB is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* GRUB is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GRUB. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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#include <grub/dl.h>
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#include <grub/file.h>
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#include <grub/lockdown.h>
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#include <grub/verify.h>
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static int lockdown = GRUB_LOCKDOWN_DISABLED;
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static grub_err_t
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lockdown_verifier_init (grub_file_t io __attribute__ ((unused)),
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enum grub_file_type type,
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void **context __attribute__ ((unused)),
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enum grub_verify_flags *flags)
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{
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*flags = GRUB_VERIFY_FLAGS_SKIP_VERIFICATION;
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switch (type & GRUB_FILE_TYPE_MASK)
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{
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case GRUB_FILE_TYPE_GRUB_MODULE:
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case GRUB_FILE_TYPE_LINUX_KERNEL:
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case GRUB_FILE_TYPE_MULTIBOOT_KERNEL:
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case GRUB_FILE_TYPE_XEN_HYPERVISOR:
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case GRUB_FILE_TYPE_BSD_KERNEL:
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case GRUB_FILE_TYPE_XNU_KERNEL:
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case GRUB_FILE_TYPE_PLAN9_KERNEL:
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case GRUB_FILE_TYPE_NTLDR:
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case GRUB_FILE_TYPE_TRUECRYPT:
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case GRUB_FILE_TYPE_FREEDOS:
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case GRUB_FILE_TYPE_PXECHAINLOADER:
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case GRUB_FILE_TYPE_PCCHAINLOADER:
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case GRUB_FILE_TYPE_COREBOOT_CHAINLOADER:
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case GRUB_FILE_TYPE_EFI_CHAINLOADED_IMAGE:
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case GRUB_FILE_TYPE_ACPI_TABLE:
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case GRUB_FILE_TYPE_DEVICE_TREE_IMAGE:
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*flags = GRUB_VERIFY_FLAGS_DEFER_AUTH;
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/* Fall through. */
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default:
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return GRUB_ERR_NONE;
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}
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}
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struct grub_file_verifier lockdown_verifier =
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{
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.name = "lockdown_verifier",
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.init = lockdown_verifier_init,
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};
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void
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grub_lockdown (void)
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{
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lockdown = GRUB_LOCKDOWN_ENABLED;
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grub_verifier_register (&lockdown_verifier);
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}
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int
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grub_is_lockdown (void)
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{
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return lockdown;
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}
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