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, 21 insertions, 0 deletions

diff --git a/lib/kunit/hooks.c b/lib/kunit/hooks.c
new file mode 100644
index 000000000..365d98d49
--- /dev/null
+++ b/lib/kunit/hooks.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit 'Hooks' implementation.
+ *
+ * This file contains code / structures which should be built-in even when
+ * KUnit itself is built as a module.
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: David Gow <davidgow@google.com>
+ */
+
+
+#include <kunit/test-bug.h>
+
+DEFINE_STATIC_KEY_FALSE(kunit_running);
+EXPORT_SYMBOL(kunit_running);
+
+/* Function pointers for hooks. */
+struct kunit_hooks_table kunit_hooks;
+EXPORT_SYMBOL(kunit_hooks);
+