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, 16 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/debugfs-olpc b/Documentation/ABI/testing/debugfs-olpc
new file mode 100644
index 000000000..bd76cc6d5
--- /dev/null
+++ b/Documentation/ABI/testing/debugfs-olpc
@@ -0,0 +1,16 @@
+What:		/sys/kernel/debug/olpc-ec/cmd
+Date:		Dec 2011
+KernelVersion:	3.4
+Contact:	devel@lists.laptop.org
+Description:
+
+A generic interface for executing OLPC Embedded Controller commands and
+reading their responses.
+
+To execute a command, write data with the format: CC:N A A A A
+CC is the (hex) command, N is the count of expected reply bytes, and A A A A
+are optional (hex) arguments.
+
+To read the response (if any), read from the generic node after executing
+a command. Hex reply bytes will be returned, *whether or not* they came from
+the immediately previous command.