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M. Vefa Bicakci 49bb053b1e xen/gntdev: Prevent leaking grants 
commit 0991028cd4 upstream.

Prior to this commit, if a grant mapping operation failed partially,
some of the entries in the map_ops array would be invalid, whereas all
of the entries in the kmap_ops array would be valid. This in turn would
cause the following logic in gntdev_map_grant_pages to become invalid:

  for (i = 0; i < map->count; i++) {
    if (map->map_ops[i].status == GNTST_okay) {
      map->unmap_ops[i].handle = map->map_ops[i].handle;
      if (!use_ptemod)
        alloced++;
    }
    if (use_ptemod) {
      if (map->kmap_ops[i].status == GNTST_okay) {
        if (map->map_ops[i].status == GNTST_okay)
          alloced++;
        map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
      }
    }
  }
  ...
  atomic_add(alloced, &map->live_grants);

Assume that use_ptemod is true (i.e., the domain mapping the granted
pages is a paravirtualized domain). In the code excerpt above, note that
the "alloced" variable is only incremented when both kmap_ops[i].status
and map_ops[i].status are set to GNTST_okay (i.e., both mapping
operations are successful).  However, as also noted above, there are
cases where a grant mapping operation fails partially, breaking the
assumption of the code excerpt above.

The aforementioned causes map->live_grants to be incorrectly set. In
some cases, all of the map_ops mappings fail, but all of the kmap_ops
mappings succeed, meaning that live_grants may remain zero. This in turn
makes it impossible to unmap the successfully grant-mapped pages pointed
to by kmap_ops, because unmap_grant_pages has the following snippet of
code at its beginning:

  if (atomic_read(&map->live_grants) == 0)
    return; /* Nothing to do */

In other cases where only some of the map_ops mappings fail but all
kmap_ops mappings succeed, live_grants is made positive, but when the
user requests unmapping the grant-mapped pages, __unmap_grant_pages_done
will then make map->live_grants negative, because the latter function
does not check if all of the pages that were requested to be unmapped
were actually unmapped, and the same function unconditionally subtracts
"data->count" (i.e., a value that can be greater than map->live_grants)
from map->live_grants. The side effects of a negative live_grants value
have not been studied.

The net effect of all of this is that grant references are leaked in one
of the above conditions. In Qubes OS v4.1 (which uses Xen's grant
mechanism extensively for X11 GUI isolation), this issue manifests
itself with warning messages like the following to be printed out by the
Linux kernel in the VM that had granted pages (that contain X11 GUI
window data) to dom0: "g.e. 0x1234 still pending", especially after the
user rapidly resizes GUI VM windows (causing some grant-mapping
operations to partially or completely fail, due to the fact that the VM
unshares some of the pages as part of the window resizing, making the
pages impossible to grant-map from dom0).

The fix for this issue involves counting all successful map_ops and
kmap_ops mappings separately, and then adding the sum to live_grants.
During unmapping, only the number of successfully unmapped grants is
subtracted from live_grants. The code is also modified to check for
negative live_grants values after the subtraction and warn the user.

Link: https://github.com/QubesOS/qubes-issues/issues/7631
Fixes: dbe97cff7d ("xen/gntdev: Avoid blocking in unmap_grant_pages()")
Cc: stable@vger.kernel.org
Signed-off-by: M. Vefa Bicakci <m.v.b@runbox.com>
Acked-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20221002222006.2077-2-m.v.b@runbox.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-11-03 23:50:54 +09:00
arch s390/futex: add missing EX_TABLE entry to __futex_atomic_op() 2022-11-03 23:50:53 +09:00
block block-map: add __GFP_ZERO flag for alloc_page in function bio_copy_kern 2022-06-06 08:20:57 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-25 11:46:44 +02:00
crypto crypto: drbg - make reseeding from get_random_bytes() synchronous 2022-06-25 11:46:41 +02:00
Documentation arm64: errata: Remove AES hwcap for COMPAT tasks 2022-11-03 23:50:50 +09:00
drivers xen/gntdev: Prevent leaking grants 2022-11-03 23:50:54 +09:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:20:30 +01:00
fs kernfs: fix use-after-free in __kernfs_remove 2022-11-03 23:50:53 +09:00
include x86/bugs: Report AMD retbleed vulnerability 2022-11-01 19:14:44 +01:00
init random: handle latent entropy and command line from random_init() 2022-06-25 11:46:40 +02:00
ipc ipc: WARN if trying to remove ipc object which is absent 2021-12-08 08:46:53 +01:00
kernel gcov: support GCC 12.1 and newer compilers 2022-10-26 13:16:58 +02:00
lib dyndbg: let query-modname override actual module name 2022-10-26 13:17:04 +02:00
mm mm/migrate_device.c: flush TLB while holding PTL 2022-10-26 13:16:50 +02:00
net mac802154: Fix LQI recording 2022-11-03 23:50:53 +09:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-26 11:40:31 +01:00
scripts selinux: use "grep -E" instead of "egrep" 2022-10-26 13:16:58 +02:00
security apparmor: fix reference count leak in aa_pivotroot() 2022-08-25 11:11:32 +02:00
sound ALSA: au88x0: use explicitly signed char 2022-11-03 23:50:52 +09:00
tools tools: iio: iio_utils: fix digit calculation 2022-11-03 23:50:53 +09:00
usr initramfs: restore default compression behavior 2020-04-13 10:34:19 +02:00
virt KVM: arm64: vgic: Fix exit condition in scan_its_table() 2022-11-03 23:50:50 +09:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS MAINTAINERS: co-maintain random.c 2022-06-25 11:46:29 +02:00
Makefile Linux 4.14.297 2022-11-01 19:14:46 +01:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.