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, 20 insertions, 0 deletions

diff --git a/Documentation/admin-guide/media/raspberrypi-pisp-be.dot b/Documentation/admin-guide/media/raspberrypi-pisp-be.dot
new file mode 100644
index 000000000..55671dc1d
--- /dev/null
+++ b/Documentation/admin-guide/media/raspberrypi-pisp-be.dot
@@ -0,0 +1,20 @@
+digraph board {
+	rankdir=TB
+	n00000001 [label="{{<port0> 0 | <port1> 1 | <port2> 2 | <port7> 7} | pispbe\n | {<port3> 3 | <port4> 4 | <port5> 5 | <port6> 6}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000001:port3 -> n0000001c [style=bold]
+	n00000001:port4 -> n00000022 [style=bold]
+	n00000001:port5 -> n00000028 [style=bold]
+	n00000001:port6 -> n0000002e [style=bold]
+	n0000000a [label="pispbe-input\n/dev/video0", shape=box, style=filled, fillcolor=yellow]
+	n0000000a -> n00000001:port0 [style=bold]
+	n00000010 [label="pispbe-tdn_input\n/dev/video1", shape=box, style=filled, fillcolor=yellow]
+	n00000010 -> n00000001:port1 [style=bold]
+	n00000016 [label="pispbe-stitch_input\n/dev/video2", shape=box, style=filled, fillcolor=yellow]
+	n00000016 -> n00000001:port2 [style=bold]
+	n0000001c [label="pispbe-output0\n/dev/video3", shape=box, style=filled, fillcolor=yellow]
+	n00000022 [label="pispbe-output1\n/dev/video4", shape=box, style=filled, fillcolor=yellow]
+	n00000028 [label="pispbe-tdn_output\n/dev/video5", shape=box, style=filled, fillcolor=yellow]
+	n0000002e [label="pispbe-stitch_output\n/dev/video6", shape=box, style=filled, fillcolor=yellow]
+	n00000034 [label="pispbe-config\n/dev/video7", shape=box, style=filled, fillcolor=yellow]
+	n00000034 -> n00000001:port7 [style=bold]
+}