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, 47 insertions, 0 deletions

diff --git a/Documentation/dev-tools/testing-devices.rst b/Documentation/dev-tools/testing-devices.rst
new file mode 100644
index 000000000..ab26adb99
--- /dev/null
+++ b/Documentation/dev-tools/testing-devices.rst
@@ -0,0 +1,47 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright (c) 2024 Collabora Ltd
+
+=============================
+Device testing with kselftest
+=============================
+
+
+There are a few different kselftests available for testing devices generically,
+with some overlap in coverage and different requirements. This document aims to
+give an overview of each one.
+
+Note: Paths in this document are relative to the kselftest folder
+(``tools/testing/selftests``).
+
+Device oriented kselftests:
+
+* Devicetree (``dt``)
+
+  * **Coverage**: Probe status for devices described in Devicetree
+  * **Requirements**: None
+
+* Error logs (``devices/error_logs``)
+
+  * **Coverage**: Error (or more critical) log messages presence coming from any
+    device
+  * **Requirements**: None
+
+* Discoverable bus (``devices/probe``)
+
+  * **Coverage**: Presence and probe status of USB or PCI devices that have been
+    described in the reference file
+  * **Requirements**: Manually describe the devices that should be tested in a
+    YAML reference file (see ``devices/probe/boards/google,spherion.yaml`` for
+    an example)
+
+* Exist (``devices/exist``)
+
+  * **Coverage**: Presence of all devices
+  * **Requirements**: Generate the reference (see ``devices/exist/README.rst``
+    for details) on a known-good kernel
+
+Therefore, the suggestion is to enable the error log and devicetree tests on all
+(DT-based) platforms, since they don't have any requirements. Then to greatly
+improve coverage, generate the reference for each platform and enable the exist
+test. The discoverable bus test can be used to verify the probe status of
+specific USB or PCI devices, but is probably not worth it for most cases.