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, 25 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-devfreq-event b/Documentation/ABI/testing/sysfs-class-devfreq-event
new file mode 100644
index 000000000..dbe48495e
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-devfreq-event
@@ -0,0 +1,25 @@
+What:		/sys/class/devfreq-event/event<x>/
+Date:		January 2017
+Contact:	Chanwoo Choi <cw00.choi@samsung.com>
+Description:
+		Provide a place in sysfs for the devfreq-event objects.
+		This allows accessing various devfreq-event specific variables.
+		The name of devfreq-event object denoted as 'event<x>' which
+		includes the unique number of 'x' for each devfreq-event object.
+
+What:		/sys/class/devfreq-event/event<x>/name
+Date:		January 2017
+Contact:	Chanwoo Choi <cw00.choi@samsung.com>
+Description:
+		The /sys/class/devfreq-event/event<x>/name attribute contains
+		the name of the devfreq-event object. This attribute is
+		read-only.
+
+What:		/sys/class/devfreq-event/event<x>/enable_count
+Date:		January 2017
+Contact:	Chanwoo Choi <cw00.choi@samsung.com>
+Description:
+		The /sys/class/devfreq-event/event<x>/enable_count attribute
+		contains the reference count to enable the devfreq-event
+		object. If the device is enabled, the value of attribute is
+		greater than zero.