efi: Restrict efivar_ssdt_load when the kernel is locked down

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 <mjg59@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: linux-efi@vger.kernel.org
[bwh: Convert back to the non-LSM lockdown API]

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0032-efi-Restrict-efivar_ssdt_load-when-the-kernel-is-loc.patch

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 4b7cf7bc0ded9cbfd279dea2072198b38b0f3c34..8fc1c04a0414249ed653282bd50665556e0680b6 100644 (file)
--- 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>
 
@@ -241,6 +242,9 @@ static void generic_ops_unregister(void)
 static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
 static int __init efivar_ssdt_setup(char *str)
 {
+       if (kernel_is_locked_down("ACPI tables"))
+               return -EPERM;
+
        if (strlen(str) < sizeof(efivar_ssdt))
                memcpy(efivar_ssdt, str, strlen(str));
        else