stub: don't override LoaderDevicePartUUID EFI var

We document and all our code assumes that LoaderDevicePartUUID is
initialized to the ESP's UUID. Let's hence not override the variable if
it is already set, in order to not confuse userspace if the kernel's EFI
image is run from a different partition than the ESP.

This matches behaviour for all other variables set by the EFI stub, in
particular the closely related LoaderImageIdentifier variable.

diff --git a/src/boot/efi/stub.c b/src/boot/efi/stub.c
index d0a9acf5d20e0cc2a1015255804a921507878d61..26c204fb438a1757083699eced8373f066b53444 100644 (file)
--- a/src/boot/efi/stub.c
+++ b/src/boot/efi/stub.c
@@ -87,9 +87,10 @@ EFI_STATUS efi_main(EFI_HANDLE image, EFI_SYSTEM_TABLE *sys_table) {
 #endif
         }
 
-        /* export the device path this image is started from */
-        if (disk_get_part_uuid(loaded_image->DeviceHandle, uuid) == EFI_SUCCESS)
-                efivar_set(L"LoaderDevicePartUUID", uuid, FALSE);
+        /* Export the device path this image is started from, if it's not set yet */
+        if (efivar_get_raw(&loader_guid, L"LoaderDevicePartUUID", NULL, NULL) != EFI_SUCCESS)
+                if (disk_get_part_uuid(loaded_image->DeviceHandle, uuid) == EFI_SUCCESS)
+                        efivar_set(L"LoaderDevicePartUUID", uuid, FALSE);
 
         /* if LoaderImageIdentifier is not set, assume the image with this stub was loaded directly from UEFI */
         if (efivar_get_raw(&loader_guid, L"LoaderImageIdentifier", NULL, NULL) != EFI_SUCCESS) {