video/efi_gop: Require shadow if PixelBltOnly

If the EFI graphics pixel format is PixelBltOnly, we cannot write directly
to the frame buffer. We need the shadow frame buffer which we copy via
the BitBlt operation to the hardware.

If the pixel format is PixelBltOnly and allocation of the shadow frame
buffer fails, we must raise an error to signal that the EFI GOP protocol
is not usable.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/video/efi_gop.c

@@ -480,6 +480,10 @@ grub_video_gop_setup (unsigned int width, unsigned int height,
   if (!buffer)
     {
       grub_dprintf ("video", "GOP: couldn't allocate shadow\n");
+
+      if (info->pixel_format == GRUB_EFI_GOT_BLT_ONLY)
+        return grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
+
       grub_errno = 0;
       grub_video_gop_fill_mode_info (gop->mode->mode, info,
 				     &framebuffer.mode_info);