efi/arm64: ignore dtb= when UEFI SecureBoot is enabled

Loading unauthenticated FDT blobs directly from storage is a security hazard,
so this should only be allowed when running with UEFI Secure Boot disabled.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

diff --git a/drivers/firmware/efi/arm-stub.c b/drivers/firmware/efi/arm-stub.c
index 19239a9..41114ce 100644 (file)
--- a/drivers/firmware/efi/arm-stub.c
+++ b/drivers/firmware/efi/arm-stub.c
@@ -12,6 +12,30 @@
  *
  */
 
+static int __init efi_secureboot_enabled(efi_system_table_t *sys_table_arg)
+{
+       static efi_guid_t const var_guid __initconst = EFI_GLOBAL_VARIABLE_GUID;
+       static efi_char16_t const var_name[] __initconst = {
+               'S', 'e', 'c', 'u', 'r', 'e', 'B', 'o', 'o', 't', 0 };
+
+       efi_get_variable_t *f_getvar = sys_table_arg->runtime->get_variable;
+       unsigned long size = sizeof(u8);
+       efi_status_t status;
+       u8 val;
+
+       status = f_getvar((efi_char16_t *)var_name, (efi_guid_t *)&var_guid,
+                         NULL, &size, &val);
+
+       switch (status) {
+       case EFI_SUCCESS:
+               return val;
+       case EFI_NOT_FOUND:
+               return 0;
+       default:
+               return 1;
+       }
+}
+
 static efi_status_t efi_open_volume(efi_system_table_t *sys_table_arg,
                                    void *__image, void **__fh)
 {
@@ -144,7 +168,7 @@ unsigned long __init efi_entry(void *handle, efi_system_table_t *sys_table,
        /* addr/point and size pairs for memory management*/
        unsigned long initrd_addr;
        u64 initrd_size = 0;
-       unsigned long fdt_addr;  /* Original DTB */
+       unsigned long fdt_addr = 0;  /* Original DTB */
        u64 fdt_size = 0;  /* We don't get size from configuration table */
        char *cmdline_ptr = NULL;
        int cmdline_size = 0;
@@ -196,9 +220,13 @@ unsigned long __init efi_entry(void *handle, efi_system_table_t *sys_table,
                goto fail_free_image;
        }
 
-       /* Load a device tree from the configuration table, if present. */
-       fdt_addr = (uintptr_t)get_fdt(sys_table);
-       if (!fdt_addr) {
+       /*
+        * Unauthenticated device tree data is a security hazard, so
+        * ignore 'dtb=' unless UEFI Secure Boot is disabled.
+        */
+       if (efi_secureboot_enabled(sys_table)) {
+               pr_efi(sys_table, "UEFI Secure Boot is enabled.\n");
+       } else {
                status = handle_cmdline_files(sys_table, image, cmdline_ptr,
                                              "dtb=",
                                              ~0UL, (unsigned long *)&fdt_addr,
@@ -209,6 +237,9 @@ unsigned long __init efi_entry(void *handle, efi_system_table_t *sys_table,
                        goto fail_free_cmdline;
                }
        }
+       if (!fdt_addr)
+               /* Look for a device tree configuration table entry. */
+               fdt_addr = (uintptr_t)get_fdt(sys_table);
 
        status = handle_cmdline_files(sys_table, image, cmdline_ptr,
                                      "initrd=", dram_base + SZ_512M,