DF-0862 — fix validation: SAME PoC (su_btotal=0xFFFFC001 crafted HPFS image) on the
SINGLE-FIX hpfs.ko module.  (Kernel text unchanged: #0 6.5-DEVELOPMENT; the bug lives
entirely in the hpfs.ko module, so the fix is the rebuilt module:
/boot/kernel/hpfs.ko sha256 d5dbde0c50f7deee435641cd9855d128b5c3fae2b8087daa4a713c58ce6e4a33.)

Run 1 (timeout 30s, returned promptly):
---------------------------------------------------------------------------
DEV=vn4
ABOUT_TO_MOUNT_FIXED_MODULE_v2
mount_hpfs: /dev/vn4: Invalid argument
MOUNT_RC=71 (nonzero, no panic => fix VALIDATED)
GUEST_STILL_UP
swap low/high-water marks set to 41940/62910
vn4: MBR magic not found; assume a COMPATIBILITY_SLICE (s0)
hpfs_mountfs: su_btotal 4294950913 exceeds device capacity 262144
RUN_RC=0 (0=returned promptly, 124=timeout/hang)
guest status: up
---------------------------------------------------------------------------

Run 2 (determinism check):
---------------------------------------------------------------------------
RUN2 DEV=vn5
mount_hpfs: /dev/vn5: Invalid argument
RUN2_MOUNT_RC=71
RUN2_GUEST_STILL_UP
 4:30PM  up 10 mins, 0 users, load averages: 1.09, 3.04, 1.91
guest status: up
---------------------------------------------------------------------------

CONTRAST (before/after):
  BEFORE (unpatched hpfs.ko):  Fatal trap 12 page fault, VA=0xfffffffffffffff8,
                               Stopped at hpfs_bminit+0x230  -> kernel PANIC, guest DOWN.
  AFTER  (fixed hpfs.ko):      mount returns EINVAL (71) promptly, guest UP,
                               dmesg "hpfs_mountfs: su_btotal 4294950913 exceeds
                               device capacity 262144"  -> clean rejection, NO panic.

=> The fix closes the bug.  fix_status: fixed.