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 <[email protected]> Acked-by: Ard Biesheuvel <[email protected]> Reviewed-by: Kees Cook <[email protected]> Cc: Ard Biesheuvel <[email protected]> Cc: [email protected] Signed-off-by: James Morris <[email protected]>
endlessm · Aug 20, 2019 · 1957a85 · 1957a85
1 parent ccbd54f
commit 1957a85
Showing 1 changed file with 6 additions and 0 deletions.
diff --git 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 +242,11 @@ 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