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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: Mon, 28 Sep 2020 20:08:41 +0200
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Subject: [PATCH] acpi: Don't register the acpi command when locked down
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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The command is not allowed when lockdown is enforced. Otherwise an
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attacker can instruct the GRUB to load an SSDT table to overwrite
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the kernel lockdown configuration and later load and execute
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unsigned code.
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Fixes: CVE-2020-14372
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Reported-by: Máté Kukri <km@mkukri.xyz>
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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/acpi.c | 15 ++++++++-------
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docs/grub.texi | 5 +++++
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2 files changed, 13 insertions(+), 7 deletions(-)
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diff --git a/grub-core/commands/acpi.c b/grub-core/commands/acpi.c
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index 5a1499aa0e3..1215f2a62ef 100644
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--- a/grub-core/commands/acpi.c
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+++ b/grub-core/commands/acpi.c
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@@ -27,6 +27,7 @@
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#include <grub/mm.h>
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#include <grub/memory.h>
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#include <grub/i18n.h>
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+#include <grub/lockdown.h>
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#ifdef GRUB_MACHINE_EFI
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#include <grub/efi/efi.h>
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@@ -775,13 +776,13 @@ static grub_extcmd_t cmd;
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GRUB_MOD_INIT(acpi)
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{
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- cmd = grub_register_extcmd ("acpi", grub_cmd_acpi, 0,
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- N_("[-1|-2] [--exclude=TABLE1,TABLE2|"
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- "--load-only=TABLE1,TABLE2] FILE1"
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- " [FILE2] [...]"),
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- N_("Load host ACPI tables and tables "
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- "specified by arguments."),
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- options);
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+ cmd = grub_register_extcmd_lockdown ("acpi", grub_cmd_acpi, 0,
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+ N_("[-1|-2] [--exclude=TABLE1,TABLE2|"
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+ "--load-only=TABLE1,TABLE2] FILE1"
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+ " [FILE2] [...]"),
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+ N_("Load host ACPI tables and tables "
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+ "specified by arguments."),
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+ options);
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}
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GRUB_MOD_FINI(acpi)
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diff --git a/docs/grub.texi b/docs/grub.texi
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index 755de88d7d8..01acf672b80 100644
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--- a/docs/grub.texi
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+++ b/docs/grub.texi
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@@ -4038,6 +4038,11 @@ Normally, this command will replace the Root System Description Pointer
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(RSDP) in the Extended BIOS Data Area to point to the new tables. If the
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@option{--no-ebda} option is used, the new tables will be known only to
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GRUB, but may be used by GRUB's EFI emulation.
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+
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+Note: The command is not allowed when lockdown is enforced (@pxref{Lockdown}).
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+ Otherwise an attacker can instruct the GRUB to load an SSDT table to
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+ overwrite the kernel lockdown configuration and later load and execute
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+ unsigned code.
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@end deffn
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