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, 41 insertions, 0 deletions

diff --git a/lib/raid/raid6/algos.h b/lib/raid/raid6/algos.h
new file mode 100644
index 000000000..43f636be1
--- /dev/null
+++ b/lib/raid/raid6/algos.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright 2003 H. Peter Anvin - All Rights Reserved
+ */
+#ifndef _PQ_IMPL_H
+#define _PQ_IMPL_H
+
+#include <linux/init.h>
+#include <linux/raid/pq_tables.h>
+
+/* Routine choices */
+struct raid6_calls {
+	const char *name;
+	void (*gen_syndrome)(int disks, size_t bytes, void **ptrs);
+	void (*xor_syndrome)(int disks, int start, int stop, size_t bytes,
+			void **ptrs);
+};
+
+struct raid6_recov_calls {
+	const char *name;
+	void (*data2)(int disks, size_t bytes, int faila, int failb,
+			void **ptrs);
+	void (*datap)(int disks, size_t bytes, int faila, void **ptrs);
+};
+
+void __init raid6_algo_add(const struct raid6_calls *algo);
+void __init raid6_algo_add_default(void);
+void __init raid6_recov_algo_add(const struct raid6_recov_calls *algo);
+
+/* for the kunit test */
+const struct raid6_calls *raid6_algo_find(unsigned int idx);
+const struct raid6_recov_calls *raid6_recov_algo_find(unsigned int idx);
+
+/* generic implementations */
+extern const struct raid6_calls raid6_intx1;
+extern const struct raid6_calls raid6_intx2;
+extern const struct raid6_calls raid6_intx4;
+extern const struct raid6_calls raid6_intx8;
+extern const struct raid6_recov_calls raid6_recov_intx1;
+
+#endif /* _PQ_IMPL_H */