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, 38 insertions, 0 deletions

diff --git a/Documentation/admin-guide/braille-console.rst b/Documentation/admin-guide/braille-console.rst
new file mode 100644
index 000000000..153472e93
--- /dev/null
+++ b/Documentation/admin-guide/braille-console.rst
@@ -0,0 +1,38 @@
+Linux Braille Console
+=====================
+
+To get early boot messages on a braille device (before userspace screen
+readers can start), you first need to compile the support for the usual serial
+console (see :ref:`Documentation/admin-guide/serial-console.rst <serial_console>`), and
+for braille device
+(in :menuselection:`Device Drivers --> Accessibility support --> Console on braille device`).
+
+Then you need to specify a ``console=brl``, option on the kernel command line, the
+format is::
+
+	console=brl,serial_options...
+
+where ``serial_options...`` are the same as described in
+:ref:`Documentation/admin-guide/serial-console.rst <serial_console>`.
+
+So for instance you can use ``console=brl,ttyS0`` if the braille device is connected to the first serial port, and ``console=brl,ttyS0,115200`` to
+override the baud rate to 115200, etc.
+
+By default, the braille device will just show the last kernel message (console
+mode).  To review previous messages, press the Insert key to switch to the VT
+review mode.  In review mode, the arrow keys permit to browse in the VT content,
+`PAGE-UP`/`PAGE-DOWN` keys go at the top/bottom of the screen, and
+the `HOME` key goes back
+to the cursor, hence providing very basic screen reviewing facility.
+
+Sound feedback can be obtained by adding the ``braille_console.sound=1`` kernel
+parameter.
+
+For simplicity, only one braille console can be enabled, other uses of
+``console=brl,...`` will be discarded.  Also note that it does not interfere with
+the console selection mechanism described in
+:ref:`Documentation/admin-guide/serial-console.rst <serial_console>`.
+
+For now, only the VisioBraille device is supported.
+
+Samuel Thibault <samuel.thibault@ens-lyon.org>