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, 66 insertions, 0 deletions

diff --git a/Documentation/fb/pvr2fb.rst b/Documentation/fb/pvr2fb.rst
new file mode 100644
index 000000000..315ce085a
--- /dev/null
+++ b/Documentation/fb/pvr2fb.rst
@@ -0,0 +1,66 @@
+===============================================
+pvr2fb - PowerVR 2 graphics frame buffer driver
+===============================================
+
+This is a driver for PowerVR 2 based graphics frame buffers, such as the
+one found in the Dreamcast.
+
+Advantages:
+
+ * It provides a nice large console (128 cols + 48 lines with 1024x768)
+   without using tiny, unreadable fonts (NOT on the Dreamcast)
+ * You can run XF86_FBDev on top of /dev/fb0
+ * Most important: boot logo :-)
+
+Disadvantages:
+
+ * Driver is largely untested on non-Dreamcast systems.
+
+Configuration
+=============
+
+You can pass kernel command line options to pvr2fb with
+`video=pvr2fb:option1,option2:value2,option3` (multiple options should be
+separated by comma, values are separated from options by `:`).
+
+Accepted options:
+
+==========  ==================================================================
+font:X      default font to use. All fonts are supported, including the
+	    SUN12x22 font which is very nice at high resolutions.
+
+
+mode:X      default video mode with format [xres]x[yres]-<bpp>@<refresh rate>
+	    The following video modes are supported:
+	    640x640-16@60, 640x480-24@60, 640x480-32@60. The Dreamcast
+	    defaults to 640x480-16@60. At the time of writing the
+	    24bpp and 32bpp modes function poorly. Work to fix that is
+	    ongoing
+
+	    Note: the 640x240 mode is currently broken, and should not be
+	    used for any reason. It is only mentioned here as a reference.
+
+inverse     invert colors on screen (for LCD displays)
+
+nomtrr      disables write combining on frame buffer. This slows down driver
+	    but there is reported minor incompatibility between GUS DMA and
+	    XFree under high loads if write combining is enabled (sound
+	    dropouts). MTRR is enabled by default on systems that have it
+	    configured and that support it.
+
+cable:X     cable type. This can be any of the following: vga, rgb, and
+	    composite. If none is specified, we guess.
+
+output:X    output type. This can be any of the following: pal, ntsc, and
+	    vga. If none is specified, we guess.
+==========  ==================================================================
+
+X11
+===
+
+XF86_FBDev has been shown to work on the Dreamcast in the past - though not yet
+on any 2.6 series kernel.
+
+Paul Mundt <lethal@linuxdc.org>
+
+Updated by Adrian McMenamin <adrian@mcmen.demon.co.uk>