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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Javier Martinez Canillas <javierm@redhat.com>
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Date: Wed, 24 Feb 2021 09:00:05 +0100
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Subject: [PATCH] commands: Restrict commands that can load BIOS or DT blobs
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when locked down
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There are some more commands that should be restricted when the GRUB is
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locked down. Following is the list of commands and reasons to restrict:
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* fakebios: creates BIOS-like structures for backward compatibility with
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existing OSes. This should not be allowed when locked down.
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* loadbios: reads a BIOS dump from storage and loads it. This action
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should not be allowed when locked down.
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* devicetree: loads a Device Tree blob and passes it to the OS. It replaces
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any Device Tree provided by the firmware. This also should
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not be allowed when locked down.
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Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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---
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grub-core/commands/efi/loadbios.c | 14 +++++++-------
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grub-core/loader/arm/linux.c | 6 +++---
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grub-core/loader/efi/fdt.c | 4 ++--
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docs/grub.texi | 6 ++++--
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4 files changed, 16 insertions(+), 14 deletions(-)
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diff --git a/grub-core/commands/efi/loadbios.c b/grub-core/commands/efi/loadbios.c
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index d41d521a4..5c7725f8b 100644
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--- a/grub-core/commands/efi/loadbios.c
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+++ b/grub-core/commands/efi/loadbios.c
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@@ -205,14 +205,14 @@ static grub_command_t cmd_fakebios, cmd_loadbios;
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GRUB_MOD_INIT(loadbios)
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{
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- cmd_fakebios = grub_register_command ("fakebios", grub_cmd_fakebios,
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- 0, N_("Create BIOS-like structures for"
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- " backward compatibility with"
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- " existing OS."));
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+ cmd_fakebios = grub_register_command_lockdown ("fakebios", grub_cmd_fakebios,
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+ 0, N_("Create BIOS-like structures for"
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+ " backward compatibility with"
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+ " existing OS."));
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- cmd_loadbios = grub_register_command ("loadbios", grub_cmd_loadbios,
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- N_("BIOS_DUMP [INT10_DUMP]"),
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- N_("Load BIOS dump."));
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+ cmd_loadbios = grub_register_command_lockdown ("loadbios", grub_cmd_loadbios,
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+ N_("BIOS_DUMP [INT10_DUMP]"),
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+ N_("Load BIOS dump."));
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}
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GRUB_MOD_FINI(loadbios)
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diff --git a/grub-core/loader/arm/linux.c b/grub-core/loader/arm/linux.c
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index 1e944a2b6..653f2e076 100644
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--- a/grub-core/loader/arm/linux.c
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+++ b/grub-core/loader/arm/linux.c
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@@ -493,9 +493,9 @@ GRUB_MOD_INIT (linux)
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0, N_("Load Linux."));
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cmd_initrd = grub_register_command ("initrd", grub_cmd_initrd,
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0, N_("Load initrd."));
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- cmd_devicetree = grub_register_command ("devicetree", grub_cmd_devicetree,
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- /* TRANSLATORS: DTB stands for device tree blob. */
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- 0, N_("Load DTB file."));
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+ cmd_devicetree = grub_register_command_lockdown ("devicetree", grub_cmd_devicetree,
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+ /* TRANSLATORS: DTB stands for device tree blob. */
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+ 0, N_("Load DTB file."));
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my_mod = mod;
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current_fdt = (const void *) grub_arm_firmware_get_boot_data ();
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machine_type = grub_arm_firmware_get_machine_type ();
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diff --git a/grub-core/loader/efi/fdt.c b/grub-core/loader/efi/fdt.c
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index e3ee3ad79..64c560f56 100644
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--- a/grub-core/loader/efi/fdt.c
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+++ b/grub-core/loader/efi/fdt.c
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@@ -167,8 +167,8 @@ static grub_command_t cmd_devicetree;
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GRUB_MOD_INIT (fdt)
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{
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cmd_devicetree =
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- grub_register_command ("devicetree", grub_cmd_devicetree, 0,
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- N_("Load DTB file."));
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+ grub_register_command_lockdown ("devicetree", grub_cmd_devicetree, 0,
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+ N_("Load DTB file."));
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}
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GRUB_MOD_FINI (fdt)
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diff --git a/docs/grub.texi b/docs/grub.texi
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index f1675b614..c55452307 100644
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--- a/docs/grub.texi
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+++ b/docs/grub.texi
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@@ -4281,13 +4281,15 @@ hour, minute, and second unchanged.
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@node devicetree
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-@subsection linux
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+@subsection devicetree
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@deffn Command devicetree file
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Load a device tree blob (.dtb) from a filesystem, for later use by a Linux
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kernel. Does not perform merging with any device tree supplied by firmware,
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but rather replaces it completely.
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-@ref{GNU/Linux}.
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+
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+Note: The command is not allowed when lockdown is enforced (@pxref{Lockdown}).
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+ This is done to prevent subverting various security mechanisms.
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@end deffn
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@node distrust
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