[tip: efi/urgent] efi: Make it possible to disable efivar_ssdt entirely

[tip-bot2 for Peter Jones]

The following commit has been merged into the efi/urgent branch of tip:

Commit-ID:     435d1a471598752446a72ad1201b3c980526d869
Gitweb:        https://git.kernel.org/tip/435d1a471598752446a72ad1201b3c980526d869
Author:        Peter Jones <pjones@xxxxxxxxxx>
AuthorDate:    Mon, 15 Jun 2020 16:24:08 -04:00
Committer:     Ard Biesheuvel <ardb@xxxxxxxxxx>
CommitterDate: Tue, 16 Jun 2020 11:01:07 +02:00

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@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Jones <pjones@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200615202408.2242614-1-pjones@xxxxxxxxxx
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---
 drivers/firmware/efi/Kconfig | 11 +++++++++++
 drivers/firmware/efi/efi.c   |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index e6fc022..3939699 100644
--- 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
--- 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)