ACPI: configfs: Disallow loading ACPI tables when locked down

commit 75b0cea7bf307f362057cc778efe89af4c615354 upstream.

Like other vectors already patched, this one here allows the root
user to load ACPI tables, which enables arbitrary physical address
writes, which in turn makes it possible to disable lockdown.

Prevents this by checking the lockdown status before allowing a new
ACPI table to be installed. The link in the trailer shows a PoC of
how this might be used.

Link: https://git.zx2c4.com/american-unsigned-language/tree/american-unsigned-language-2.sh
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/acpi/acpi_configfs.c b/drivers/acpi/acpi_configfs.c
index 57d9d574d4dde6e448e83d12f3f66265fbc13398..01738d8e888e30ae0a86ca197ddb63412681a15f 100644 (file)
--- a/drivers/acpi/acpi_configfs.c
+++ b/drivers/acpi/acpi_configfs.c
@@ -11,6 +11,7 @@
 #include <linux/module.h>
 #include <linux/configfs.h>
 #include <linux/acpi.h>
+#include <linux/security.h>
 
 #include "acpica/accommon.h"
 #include "acpica/actables.h"
@@ -28,7 +29,10 @@ static ssize_t acpi_table_aml_write(struct config_item *cfg,
 {
        const struct acpi_table_header *header = data;
        struct acpi_table *table;
-       int ret;
+       int ret = security_locked_down(LOCKDOWN_ACPI_TABLES);
+
+       if (ret)
+               return ret;
 
        table = container_of(cfg, struct acpi_table, cfg);