tools/pygrub: Remove unnecessary hypercall

There's a hypercall being issued in order to determine whether PV64 is
supported, but since Xen 4.3 that's strictly true so it's not required.

Plus, this way we can avoid mapping the privcmd interface altogether in the
depriv pygrub.

This is part of XSA-443 / CVE-2023-34325

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
(cherry picked from commit f4b504c617)

tools/pygrub/src/pygrub

@@ -18,7 +18,6 @@ import os, sys, string, struct, tempfile, re, traceback, stat, errno
 import copy
 import logging
 import platform
-import xen.lowlevel.xc
 
 import curses, _curses, curses.textpad, curses.ascii
 import getopt
@@ -668,14 +667,6 @@ def run_grub(file, entry, fs, cfg_args):
 
     return grubcfg
 
-def supports64bitPVguest():
-    xc = xen.lowlevel.xc.xc()
-    caps = xc.xeninfo()['xen_caps'].split(" ")
-    for cap in caps:
-        if cap == "xen-3.0-x86_64":
-            return True
-    return False
-
 # If nothing has been specified, look for a Solaris domU. If found, perform the
 # necessary tweaks.
 def sniff_solaris(fs, cfg):
@@ -684,8 +675,7 @@ def sniff_solaris(fs, cfg):
         return cfg
 
     if not cfg["kernel"]:
-        if supports64bitPVguest() and \
-          fs.file_exists("/platform/i86xpv/kernel/amd64/unix"):
+        if fs.file_exists("/platform/i86xpv/kernel/amd64/unix"):
             cfg["kernel"] = "/platform/i86xpv/kernel/amd64/unix"
             cfg["ramdisk"] = "/platform/i86pc/amd64/boot_archive"
         elif fs.file_exists("/platform/i86xpv/kernel/unix"):