openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 87 insertions, 0 deletions

diff --git a/Documentation/admin-guide/binderfs.rst b/Documentation/admin-guide/binderfs.rst
new file mode 100644
index 000000000..41a4db00d
--- /dev/null
+++ b/Documentation/admin-guide/binderfs.rst
@@ -0,0 +1,87 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+The Android binderfs Filesystem
+===============================
+
+Android binderfs is a filesystem for the Android binder IPC mechanism.  It
+allows to dynamically add and remove binder devices at runtime.  Binder devices
+located in a new binderfs instance are independent of binder devices located in
+other binderfs instances.  Mounting a new binderfs instance makes it possible
+to get a set of private binder devices.
+
+Mounting binderfs
+-----------------
+
+Android binderfs can be mounted with::
+
+  mkdir /dev/binderfs
+  mount -t binder binder /dev/binderfs
+
+at which point a new instance of binderfs will show up at ``/dev/binderfs``.
+In a fresh instance of binderfs no binder devices will be present.  There will
+only be a ``binder-control`` device which serves as the request handler for
+binderfs. Mounting another binderfs instance at a different location will
+create a new and separate instance from all other binderfs mounts.  This is
+identical to the behavior of e.g. ``devpts`` and ``tmpfs``. The Android
+binderfs filesystem can be mounted in user namespaces.
+
+Options
+-------
+max
+  binderfs instances can be mounted with a limit on the number of binder
+  devices that can be allocated. The ``max=<count>`` mount option serves as
+  a per-instance limit. If ``max=<count>`` is set then only ``<count>`` number
+  of binder devices can be allocated in this binderfs instance.
+
+stats
+  Using ``stats=global`` enables global binder statistics.
+  ``stats=global`` is only available for a binderfs instance mounted in the
+  initial user namespace. An attempt to use the option to mount a binderfs
+  instance in another user namespace will return a permission error.
+
+Allocating binder Devices
+-------------------------
+
+.. _ioctl: http://man7.org/linux/man-pages/man2/ioctl.2.html
+
+To allocate a new binder device in a binderfs instance a request needs to be
+sent through the ``binder-control`` device node.  A request is sent in the form
+of an `ioctl() <ioctl_>`_.
+
+What a program needs to do is to open the ``binder-control`` device node and
+send a ``BINDER_CTL_ADD`` request to the kernel.  Users of binderfs need to
+tell the kernel which name the new binder device should get.  By default a name
+can only contain up to ``BINDERFS_MAX_NAME`` chars including the terminating
+zero byte.
+
+Once the request is made via an `ioctl() <ioctl_>`_ passing a ``struct
+binder_device`` with the name to the kernel it will allocate a new binder
+device and return the major and minor number of the new device in the struct
+(This is necessary because binderfs allocates a major device number
+dynamically.).  After the `ioctl() <ioctl_>`_ returns there will be a new
+binder device located under /dev/binderfs with the chosen name.
+
+Deleting binder Devices
+-----------------------
+
+.. _unlink: http://man7.org/linux/man-pages/man2/unlink.2.html
+.. _rm: http://man7.org/linux/man-pages/man1/rm.1.html
+
+Binderfs binder devices can be deleted via `unlink() <unlink_>`_.  This means
+that the `rm() <rm_>`_ tool can be used to delete them. Note that the
+``binder-control`` device cannot be deleted since this would make the binderfs
+instance unusable.  The ``binder-control`` device will be deleted when the
+binderfs instance is unmounted and all references to it have been dropped.
+
+Binder features
+---------------
+
+Assuming an instance of binderfs has been mounted at ``/dev/binderfs``, the
+features supported by the binder driver can be located under
+``/dev/binderfs/features/``. The presence of individual files can be tested
+to determine whether a particular feature is supported by the driver.
+
+Example::
+
+        cat /dev/binderfs/features/oneway_spam_detection
+        1