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, 64 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-block-rnbd b/Documentation/ABI/testing/sysfs-block-rnbd
new file mode 100644
index 000000000..80b420b5d
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-block-rnbd
@@ -0,0 +1,64 @@
+What:		/sys/block/rnbd<N>/rnbd/unmap_device
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	To unmap a volume, "normal" or "force" has to be written to:
+		/sys/block/rnbd<N>/rnbd/unmap_device
+
+		When "normal" is used, the operation will fail with EBUSY if any process
+		is using the device.  When "force" is used, the device is also unmapped
+		when device is in use.  All I/Os that are in progress will fail.
+
+		Example::
+
+		  # echo "normal" > /sys/block/rnbd0/rnbd/unmap_device
+
+What:		/sys/block/rnbd<N>/rnbd/state
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	The file contains the current state of the block device. The state file
+		returns "open" when the device is successfully mapped from the server
+		and accepting I/O requests. When the connection to the server gets
+		disconnected in case of an error (e.g. link failure), the state file
+		returns "closed" and all I/O requests submitted to it will fail with -EIO.
+
+What:		/sys/block/rnbd<N>/rnbd/session
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	RNBD uses RTRS session to transport the data between client and
+		server.  The entry "session" contains the name of the session, that
+		was used to establish the RTRS session.  It's the same name that
+		was passed as server parameter to the map_device entry.
+
+What:		/sys/block/rnbd<N>/rnbd/mapping_path
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the path that was passed as "device_path" to the map_device
+		operation.
+
+What:		/sys/block/rnbd<N>/rnbd/access_mode
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the device access mode: ro, rw or migration.
+
+What:		/sys/block/rnbd<N>/rnbd/resize
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Write the number of sectors to change the size of the disk.
+
+What:		/sys/block/rnbd<N>/rnbd/remap_device
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Remap the disconnected device if the session is not destroyed yet.
+
+What:		/sys/block/rnbd<N>/rnbd/nr_poll_queues
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the number of poll-mode queues