acpi: Disable ACPI table override if securelevel is set

From the kernel documentation (initrd_table_override.txt):

  If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible
  to override nearly any ACPI table provided by the BIOS with an
  instrumented, modified one.

When securelevel is set, the kernel should disallow any unauthenticated
changes to kernel space. ACPI tables contain code invoked by the kernel, so
do not allow ACPI tables to be overridden if securelevel is set.

Signed-off-by: Linn Crosetto <linn@hpe.com>
static u32 acpi_osi_handler(acpi_string interface, u32 supported)
{
	if (!strcmp("Linux", interface)) {

		printk_once(KERN_NOTICE FW_BUG PREFIX
			"BIOS _OSI(Linux) query %s%s\n",
			osi_linux.enable ? "honored" : "ignored",
			osi_linux.cmdline ? " via cmdline" :
			osi_linux.dmi ? " via DMI" : "");
	}

	if (!strcmp("Darwin", interface)) {
		/*
		 * Apple firmware will behave poorly if it receives positive
		 * answers to "Darwin" and any other OS. Respond positively
		 * to Darwin and then disable all other vendor strings.
		 */
		acpi_update_interfaces(ACPI_DISABLE_ALL_VENDOR_STRINGS);
		supported = ACPI_UINT32_MAX;
	}

	return supported;
}

static u32 acpi_osi_handler(acpi_string interface, u32 supported)
{
	if (!strcmp("Linux", interface)) {

		printk_once(KERN_NOTICE FW_BUG PREFIX
			"BIOS _OSI(Linux) query %s%s\n",
			osi_linux.enable ? "honored" : "ignored",
			osi_linux.cmdline ? " via cmdline" :
			osi_linux.dmi ? " via DMI" : "");
	}

	if (!strcmp("Darwin", interface)) {
		/*
		 * Apple firmware will behave poorly if it receives positive
		 * answers to "Darwin" and any other OS. Respond positively
		 * to Darwin and then disable all other vendor strings.
		 */
		acpi_update_interfaces(ACPI_DISABLE_ALL_VENDOR_STRINGS);
		supported = ACPI_UINT32_MAX;
	}

	return supported;
}
