[PATCH V36 28/29] efi: Restrict efivar_ssdt_load when the kernel is locked down

[Matthew Garrett]

efivar_ssdt_load allows the kernel to import arbitrary ACPI code from an
EFI variable, which gives arbitrary code execution in ring 0. Prevent
that when the kernel is locked down.

Signed-off-by: Matthew Garrett <mj...@google.com>
Acked-by: Ard Biesheuvel <ard.biesheu...@linaro.org>
Reviewed-by: Kees Cook <keesc...@chromium.org>
Cc: Ard Biesheuvel <ard.biesheu...@linaro.org>
Cc: linux-...@vger.kernel.org
---
 drivers/firmware/efi/efi.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index ad3b1f4866b3..776f479e5499 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -30,6 +30,7 @@
 #include <linux/acpi.h>
 #include <linux/ucs2_string.h>
 #include <linux/memblock.h>
+#include <linux/security.h>
 
 #include <asm/early_ioremap.h>
 
@@ -242,6 +243,11 @@ static void generic_ops_unregister(void)
 static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
 static int __init efivar_ssdt_setup(char *str)
 {
+       int ret = security_locked_down(LOCKDOWN_ACPI_TABLES);
+
+       if (ret)
+               return ret;
+
        if (strlen(str) < sizeof(efivar_ssdt))
                memcpy(efivar_ssdt, str, strlen(str));
        else
-- 
2.22.0.510.g264f2c817a-goog