EFI: refine cfgfile buffer allocation

Use of AllocateMaxAddress requires that the variable pointed to by the
last argument of ->AllocatePages() is initialized. For cfgfile buffers we
don't need AllocateMaxAddress though, at which point initialization of
"addr" also isn't necessary anymore.

Mirror the lack of address constraint also to the main / central buffer
allocation in read_file().

Fixes: df75f77092 ("EFI: avoid OOB config file reads")
Assisted-by: Sashiko + Opus 5.0
Reported-by: George Dunlap <dunlapg@umich.edu>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Daniel P. Smith <dpsmith@apertussolutions.com>

xen/common/efi/boot.c

@@ -878,8 +878,13 @@ static bool __init read_file(EFI_FILE_HANDLE dir_handle, CHAR16 *name,
     what = L"Allocation";
     file->addr = min(1UL << (32 + PAGE_SHIFT),
                      HYPERVISOR_VIRT_END - DIRECTMAP_VIRT_START);
-    /* For config files allocate an extra byte to put a NUL there. */
-    ret = efi_bs->AllocatePages(AllocateMaxAddress, EfiLoaderData,
+    /*
+     * For config files allocate an extra byte to put a NUL there.  There's
+     * also no constraint on addresses for them.
+     */
+    ret = efi_bs->AllocatePages(file != &cfg ? AllocateMaxAddress
+                                             : AllocateAnyPages,
+                                EfiLoaderData,
                                 PFN_UP(size + (file == &cfg)), &file->addr);
     if ( EFI_ERROR(ret) )
         goto fail;
@@ -931,7 +936,7 @@ static bool __init read_section(const EFI_LOADED_IMAGE *image,
     if ( file == &cfg && file->size && !iscntrl(file->str[file->size - 1]) )
     {
         EFI_PHYSICAL_ADDRESS addr;
-        EFI_STATUS ret = efi_bs->AllocatePages(AllocateMaxAddress,
+        EFI_STATUS ret = efi_bs->AllocatePages(AllocateAnyPages,
                                                EfiLoaderData,
                                                PFN_UP(file->size + 1), &addr);