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, 29 insertions, 0 deletions

diff --git a/lib/kunit/try-catch-impl.h b/lib/kunit/try-catch-impl.h
new file mode 100644
index 000000000..6f401b97c
--- /dev/null
+++ b/lib/kunit/try-catch-impl.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Internal kunit try catch implementation to be shared with tests.
+ *
+ * Copyright (C) 2019, Google LLC.
+ * Author: Brendan Higgins <brendanhiggins@google.com>
+ */
+
+#ifndef _KUNIT_TRY_CATCH_IMPL_H
+#define _KUNIT_TRY_CATCH_IMPL_H
+
+#include <kunit/try-catch.h>
+#include <linux/types.h>
+
+struct kunit;
+
+static inline void kunit_try_catch_init(struct kunit_try_catch *try_catch,
+					struct kunit *test,
+					kunit_try_catch_func_t try,
+					kunit_try_catch_func_t catch,
+					unsigned long timeout)
+{
+	try_catch->test = test;
+	try_catch->try = try;
+	try_catch->catch = catch;
+	try_catch->timeout = timeout;
+}
+
+#endif /* _KUNIT_TRY_CATCH_IMPL_H */