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, 33 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-vduse b/Documentation/ABI/testing/sysfs-class-vduse
new file mode 100644
index 000000000..2f2bc5c8f
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-vduse
@@ -0,0 +1,33 @@
+What:		/sys/class/vduse/
+Date:		Oct 2021
+KernelVersion:	5.15
+Contact:	Yongji Xie <xieyongji@bytedance.com>
+Description:
+		The vduse/ class sub-directory belongs to the VDUSE
+		framework and provides a sysfs interface for configuring
+		VDUSE devices.
+
+What:		/sys/class/vduse/control/
+Date:		Oct 2021
+KernelVersion:	5.15
+Contact:	Yongji Xie <xieyongji@bytedance.com>
+Description:
+		This directory entry is created for the control device
+		of VDUSE framework.
+
+What:		/sys/class/vduse/<device-name>/
+Date:		Oct 2021
+KernelVersion:	5.15
+Contact:	Yongji Xie <xieyongji@bytedance.com>
+Description:
+		This directory entry is created when a VDUSE device is
+		created via the control device.
+
+What:		/sys/class/vduse/<device-name>/msg_timeout
+Date:		Oct 2021
+KernelVersion:	5.15
+Contact:	Yongji Xie <xieyongji@bytedance.com>
+Description:
+		(RW) The timeout (in seconds) for waiting for the control
+		message's response from userspace. Default value is 30s.
+		Writing a '0' to the file means to disable the timeout.