efi: Make it possible to disable efivar_ssdt entirely

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>

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index e6fc022..3939699 100644 (file)
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -278,3 +278,14 @@ config EFI_EARLYCON
        depends on SERIAL_EARLYCON && !ARM && !IA64
        select FONT_SUPPORT
        select ARCH_USE_MEMREMAP_PROT
+
+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.

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index edc5d36..5114cae 100644 (file)
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -189,7 +189,7 @@ 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)