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, 48 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/siox/eckelmann,siox-gpio.yaml b/Documentation/devicetree/bindings/siox/eckelmann,siox-gpio.yaml
new file mode 100644
index 000000000..2ff204109
--- /dev/null
+++ b/Documentation/devicetree/bindings/siox/eckelmann,siox-gpio.yaml
@@ -0,0 +1,48 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/siox/eckelmann,siox-gpio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Eckelmann SIOX GPIO bus
+
+maintainers:
+  - Frank Li <Frank.Li@nxp.com>
+
+properties:
+  compatible:
+    const: eckelmann,siox-gpio
+
+  din-gpios:
+    maxItems: 1
+
+  dout-gpios:
+    maxItems: 1
+
+  dclk-gpios:
+    maxItems: 1
+
+  dld-gpios:
+    maxItems: 1
+
+required:
+  - compatible
+  - din-gpios
+  - dout-gpios
+  - dclk-gpios
+  - dld-gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    siox {
+        compatible = "eckelmann,siox-gpio";
+        pinctrl-names = "default";
+        pinctrl-0 = <&pinctrl_siox>;
+
+        din-gpios = <&gpio6 11 0>;
+        dout-gpios = <&gpio6 8 0>;
+        dclk-gpios = <&gpio6 9 0>;
+        dld-gpios = <&gpio6 10 0>;
+    };