acpi: Ignore acpi_rsdp kernel parameter when module loading is restricted

BugLink: http://bugs.launchpad.net/bugs/1566221

This option allows userspace to pass the RSDP address to the kernel, which
makes it possible for a user to circumvent any restrictions imposed on
loading modules. Disable it in that case.
Signed-off-by: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/acpi/osl.c

@@ -40,6 +40,7 @@
 #include <linux/list.h>
 #include <linux/jiffies.h>
 #include <linux/semaphore.h>
+#include <linux/module.h>
 
 #include <asm/io.h>
 #include <asm/uaccess.h>
@@ -252,7 +253,7 @@ early_param("acpi_rsdp", setup_acpi_rsdp);
 acpi_physical_address __init acpi_os_get_root_pointer(void)
 {
 #ifdef CONFIG_KEXEC
-	if (acpi_rsdp)
+	if (acpi_rsdp && !secure_modules())
 		return acpi_rsdp;
 #endif