• David Hildenbrand's avatar
    device-dax: don't leak kernel memory to user space after unloading kmem · 60858c00
    David Hildenbrand authored
    Assume we have kmem configured and loaded:
    
      [root@localhost ~]# cat /proc/iomem
      ...
      140000000-33fffffff : Persistent Memory$
        140000000-1481fffff : namespace0.0
        150000000-33fffffff : dax0.0
          150000000-33fffffff : System RAM
    
    Assume we try to unload kmem. This force-unloading will work, even if
    memory cannot get removed from the system.
    
      [root@localhost ~]# rmmod kmem
      [   86.380228] removing memory fails, because memory [0x0000000150000000-0x0000000157ffffff] is onlined
      ...
      [   86.431225] kmem dax0.0: DAX region [mem 0x150000000-0x33fffffff] cannot be hotremoved until the next reboot
    
    Now, we can reconfigure the namespace:
    
      [root@localhost ~]# ndctl create-namespace --force --reconfig=namespace0.0 --mode=devdax
      [  131.409351] nd_pmem namespace0.0: could not reserve region [mem 0x140000000-0x33fffffff]dax
      [  131.410147] nd_pmem: probe of namespace0.0 failed with error -16namespace0.0 --mode=devdax
      ...
    
    This fails as expected due to the busy memory resource, and the memory
    cannot be used.  However, the dax0.0 device is removed, and along its
    name.
    
    The name of the memory resource now points at freed memory (name of the
    device):
    
      [root@localhost ~]# cat /proc/iomem
      ...
      140000000-33fffffff : Persistent Memory
        140000000-1481fffff : namespace0.0
        150000000-33fffffff : �_�^7_��/_��wR��WQ���^��� ...
        150000000-33fffffff : System RAM
    
    We have to make sure to duplicate the string.  While at it, remove the
    superfluous setting of the name and fixup a stale comment.
    
    Fixes: 9f960da7 ("device-dax: "Hotremove" persistent memory that is used like normal RAM")
    Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: Vishal Verma <vishal.l.verma@intel.com>
    Cc: Dave Jiang <dave.jiang@intel.com>
    Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: <stable@vger.kernel.org>	[5.3]
    Link: http://lkml.kernel.org/r/20200508084217.9160-2-david@redhat.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    60858c00
kmem.c 4.08 KB