Linux-Fsdevel Archive on lore.kernel.org
 help / color / Atom feed
From: Lokesh Gidra <lokeshgidra@google.com>
To: Kees Cook <keescook@chromium.org>,
	Jonathan Corbet <corbet@lwn.net>, Peter Xu <peterx@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Stephen Smalley <stephen.smalley.work@gmail.com>,
	Eric Biggers <ebiggers@kernel.org>,
	Lokesh Gidra <lokeshgidra@google.com>,
	Daniel Colascione <dancol@dancol.org>,
	"Joel Fernandes (Google)" <joel@joelfernandes.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-doc@vger.kernel.org, kaleshsingh@google.com,
	calin@google.com, surenb@google.com, nnk@google.com,
	jeffv@google.com, kernel-team@android.com,
	Mike Rapoport <rppt@linux.vnet.ibm.com>, Shaohua Li <shli@fb.com>,
	Jerome Glisse <jglisse@redhat.com>,
	Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Nitin Gupta <nigupta@nvidia.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Iurii Zaikin <yzaikin@google.com>,
	Luis Chamberlain <mcgrof@kernel.org>
Subject: [PATCH v5 0/2] Control over userfaultfd kernel-fault handling
Date: Sat, 10 Oct 2020 23:24:54 -0700
Message-ID: <20201011062456.4065576-1-lokeshgidra@google.com> (raw)

This patch series is split from [1]. The other series enables SELinux
support for userfaultfd file descriptors so that its creation and
movement can be controlled.

It has been demonstrated on various occasions that suspending kernel
code execution for an arbitrary amount of time at any access to
userspace memory (copy_from_user()/copy_to_user()/...) can be exploited
to change the intended behavior of the kernel. For instance, handling
page faults in kernel-mode using userfaultfd has been exploited in [2, 3].
Likewise, FUSE, which is similar to userfaultfd in this respect, has been
exploited in [4, 5] for similar outcome.

This small patch series adds a new flag to userfaultfd(2) that allows
callers to give up the ability to handle kernel-mode faults with the
resulting UFFD file object. It then adds a 'user-mode only' option to
the unprivileged_userfaultfd sysctl knob to require unprivileged
callers to use this new flag.

The purpose of this new interface is to decrease the chance of an
unprivileged userfaultfd user taking advantage of userfaultfd to
enhance security vulnerabilities by lengthening the race window in
kernel code.

[1] https://lore.kernel.org/lkml/20200211225547.235083-1-dancol@google.com/
[2] https://duasynt.com/blog/linux-kernel-heap-spray
[3] https://duasynt.com/blog/cve-2016-6187-heap-off-by-one-exploit
[4] https://googleprojectzero.blogspot.com/2016/06/exploiting-recursion-in-linux-kernel_20.html
[5] https://bugs.chromium.org/p/project-zero/issues/detail?id=808

Changes since v4:

  - Added warning when bailing out from handling kernel fault.

Changes since v3:

  - Modified the meaning of value '0' of unprivileged_userfaultfd
    sysctl knob. Setting this knob to '0' now allows unprivileged users
    to use userfaultfd, but can handle page faults in user-mode only.
  - The default value of unprivileged_userfaultfd sysctl knob is changed
    to '0'.

Changes since v2:

  - Removed 'uffd_flags' and directly used 'UFFD_USER_MODE_ONLY' in
    userfaultfd().

Changes since v1:

  - Added external references to the threats from allowing unprivileged
    users to handle page faults from kernel-mode.
  - Removed the new sysctl knob restricting handling of page
    faults from kernel-mode, and added an option for the same
    in the existing 'unprivileged_userfaultfd' knob.

Lokesh Gidra (2):
  Add UFFD_USER_MODE_ONLY
  Add user-mode only option to unprivileged_userfaultfd sysctl knob

 Documentation/admin-guide/sysctl/vm.rst | 15 ++++++++++-----
 fs/userfaultfd.c                        | 16 +++++++++++++---
 include/uapi/linux/userfaultfd.h        |  9 +++++++++
 3 files changed, 32 insertions(+), 8 deletions(-)

-- 
2.28.0.1011.ga647a8990f-goog


             reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-11  6:24 Lokesh Gidra [this message]
2020-10-11  6:24 ` [PATCH v5 1/2] Add UFFD_USER_MODE_ONLY Lokesh Gidra
2020-10-24  2:08   ` Andrea Arcangeli
2020-10-11  6:24 ` [PATCH v5 2/2] Add user-mode only option to unprivileged_userfaultfd sysctl knob Lokesh Gidra
2020-10-24  2:48   ` Andrea Arcangeli
2020-10-24  4:08     ` Lokesh Gidra

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20201011062456.4065576-1-lokeshgidra@google.com \
    --to=lokeshgidra@google.com \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=bigeasy@linutronix.de \
    --cc=calin@google.com \
    --cc=corbet@lwn.net \
    --cc=dancol@dancol.org \
    --cc=ebiggers@kernel.org \
    --cc=hannes@cmpxchg.org \
    --cc=jeffv@google.com \
    --cc=jglisse@redhat.com \
    --cc=joel@joelfernandes.org \
    --cc=kaleshsingh@google.com \
    --cc=keescook@chromium.org \
    --cc=kernel-team@android.com \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mcgrof@kernel.org \
    --cc=mchehab+huawei@kernel.org \
    --cc=mgorman@techsingularity.net \
    --cc=nigupta@nvidia.com \
    --cc=nnk@google.com \
    --cc=peterx@redhat.com \
    --cc=rppt@linux.vnet.ibm.com \
    --cc=shli@fb.com \
    --cc=stephen.smalley.work@gmail.com \
    --cc=surenb@google.com \
    --cc=vbabka@suse.cz \
    --cc=viro@zeniv.linux.org.uk \
    --cc=yzaikin@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Fsdevel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-fsdevel/0 linux-fsdevel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-fsdevel linux-fsdevel/ https://lore.kernel.org/linux-fsdevel \
		linux-fsdevel@vger.kernel.org
	public-inbox-index linux-fsdevel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-fsdevel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git