efi: Make it possible to disable efivar_ssdt entirely

commit 435d1a471598752446a72ad1201b3c980526d869 upstream.

In most cases, such as CONFIG_ACPI_CUSTOM_DSDT and
CONFIG_ACPI_TABLE_UPGRADE, boot-time modifications to firmware tables
are tied to specific Kconfig options.  Currently this is not the case
for modifying the ACPI SSDT via the efivar_ssdt kernel command line
option and associated EFI variable.

This patch adds CONFIG_EFI_CUSTOM_SSDT_OVERLAYS, which defaults
disabled, in order to allow enabling or disabling that feature during
the build.

Cc: <stable@vger.kernel.org>
Signed-off-by: Peter Jones <pjones@redhat.com>
Link: https://lore.kernel.org/r/20200615202408.2242614-1-pjones@redhat.com
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 86210f75d23331899f6454eb6b1c20de0e0ae992..a4fadd42221d36223a2bc676342daf8705e7c3ad 100644 (file)
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -164,6 +164,17 @@ config RESET_ATTACK_MITIGATION
          have been evicted, since otherwise it will trigger even on clean
          reboots.
 
+config EFI_CUSTOM_SSDT_OVERLAYS
+       bool "Load custom ACPI SSDT overlay from an EFI variable"
+       depends on EFI_VARS && ACPI
+       default ACPI_TABLE_UPGRADE
+       help
+         Allow loading of an ACPI SSDT overlay from an EFI variable specified
+         by a kernel command line option.
+
+         See Documentation/admin-guide/acpi/ssdt-overlays.rst for more
+         information.endmenu
+
 endmenu
 
 config UEFI_CPER

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index b39b7e6d4e4dc1a6bcbde746472714b82f5ad521..a3dc6cb7326a5b8e07db9284ca086e867dc4dfc1 100644 (file)
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -221,7 +221,7 @@ static void generic_ops_unregister(void)
        efivars_unregister(&generic_efivars);
 }
 
-#if IS_ENABLED(CONFIG_ACPI)
+#ifdef CONFIG_EFI_CUSTOM_SSDT_OVERLAYS
 #define EFIVAR_SSDT_NAME_MAX   16
 static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
 static int __init efivar_ssdt_setup(char *str)