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, 14 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-sun b/Documentation/ABI/testing/sysfs-devices-sun
new file mode 100644
index 000000000..625ce4b63
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-sun
@@ -0,0 +1,14 @@
+What:		/sys/devices/.../sun
+Date:		October 2012
+Contact:	Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
+Description:
+		The file contains a Slot-unique ID which provided by the _SUN
+		method in the ACPI namespace. The value is written in Advanced
+		Configuration and Power Interface Specification as follows:
+
+		"The _SUN value is required to be unique among the slots of
+		the same type. It is also recommended that this number match
+		the slot number printed on the physical slot whenever possible."
+
+		So reading the sysfs file, we can identify a physical position
+		of the slot in the system.