relocator: Protect grub_relocator_alloc_chunk_align() max_addr against integer underflow

This commit introduces integer underflow mitigation in max_addr calculation
in grub_relocator_alloc_chunk_align() invocation.

It consists of 2 fixes:
  1. Introduced grub_relocator_alloc_chunk_align_safe() wrapper function to perform
     sanity check for min/max and size values, and to make safe invocation of
     grub_relocator_alloc_chunk_align() with validated max_addr value. Replace all
     invocations such as grub_relocator_alloc_chunk_align(..., min_addr, max_addr - size, size, ...)
     by grub_relocator_alloc_chunk_align_safe(..., min_addr, max_addr, size, ...).
  2. Introduced UP_TO_TOP32(s) macro for the cases where max_addr is 32-bit top
     address (0xffffffff - size + 1) or similar.

Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/loader/i386/multiboot_mbi.c

@@ -466,10 +466,9 @@ grub_multiboot_make_mbi (grub_uint32_t *target)
 
   bufsize = grub_multiboot_get_mbi_size ();
 
-  err = grub_relocator_alloc_chunk_align (grub_multiboot_relocator, &ch,
-					  0x10000, 0xa0000 - bufsize,
-					  bufsize, 4,
-					  GRUB_RELOCATOR_PREFERENCE_NONE, 0);
+  err = grub_relocator_alloc_chunk_align_safe (grub_multiboot_relocator, &ch,
+					       0x10000, 0xa0000, bufsize, 4,
+					       GRUB_RELOCATOR_PREFERENCE_NONE, 0);
   if (err)
     return err;
   ptrorig = get_virtual_current_address (ch);