boot: skip loading DTBs in type 1 when secure boot is enabled

The kernel loads the DTB from EFI before ExitBootServices():

https://github.com/torvalds/linux/blob/v6.5/drivers/firmware/efi/libstub/fdt.c#L245

DTBs can map and assign arbitrary memory ranges. The kernel refuses
to load one from the dtb= kernel command line parameter when secure
boot is enabled, as it's not safe. Let's do the same for type 1
entries, as they are unverified.

This only affects arm64 and riscv64, firmwares do not support DTB
on x86.

(cherry picked from commit 4b4d612)
(cherry picked from commit c1404ff)
(cherry picked from commit 7844c65)
(cherry picked from commit f381320)
(cherry picked from commit 3c97ff5)

Author: bluca

src/boot/efi/boot.c

@@ -2185,7 +2185,9 @@ static EFI_STATUS image_start(
         if (EFI_ERROR(err))
                 return log_error_status_stall(err, L"Error loading %s: %r", entry->loader, err);
 
-        if (entry->devicetree) {
+        /* DTBs are loaded by the kernel before ExitBootServices, and they can be used to map and assign
+         * arbitrary memory ranges, so skip it when secure boot is enabled as the DTB here is unverified. */
+        if (entry->devicetree && !secure_boot_enabled()) {
                 err = devicetree_install(&dtstate, root_dir, entry->devicetree);
                 if (EFI_ERROR(err))
                         return log_error_status_stall(err, L"Error loading %s: %r", entry->devicetree, err);