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, 28 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/gpio-cdev b/Documentation/ABI/testing/gpio-cdev
new file mode 100644
index 000000000..c9689b2a6
--- /dev/null
+++ b/Documentation/ABI/testing/gpio-cdev
@@ -0,0 +1,28 @@
+What:		/dev/gpiochip[0-9]+
+Date:		November 2015
+KernelVersion:	4.4
+Contact:	linux-gpio@vger.kernel.org
+Description:
+		The character device files /dev/gpiochip* are the interface
+		between GPIO chips and userspace.
+
+		The ioctl(2)-based ABI is defined in
+		[include/uapi]<linux/gpio.h> and documented in
+		Documentation/userspace-api/gpio/chardev.rst.
+
+		The following file operations are supported:
+
+		open(2)
+		  Currently the only useful flags are O_RDWR.
+
+		ioctl(2)
+		  Initiate various actions.
+
+		  See Documentation/userspace-api/gpio/chardev.rst
+		  for a description of all ioctls.
+
+		close(2)
+		  Stops and free up the I/O contexts that was associated
+		  with the file descriptor.
+
+Users:		TBD