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, 78 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/numeric.h b/drivers/md/dm-vdo/numeric.h
new file mode 100644
index 000000000..f568dc59e
--- /dev/null
+++ b/drivers/md/dm-vdo/numeric.h
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef UDS_NUMERIC_H
+#define UDS_NUMERIC_H
+
+#include <linux/unaligned.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+
+/*
+ * These utilities encode or decode a number from an offset in a larger data buffer and then
+ * advance the offset pointer to the next field in the buffer.
+ */
+
+static inline void decode_s64_le(const u8 *buffer, size_t *offset, s64 *decoded)
+{
+	*decoded = get_unaligned_le64(buffer + *offset);
+	*offset += sizeof(s64);
+}
+
+static inline void encode_s64_le(u8 *data, size_t *offset, s64 to_encode)
+{
+	put_unaligned_le64(to_encode, data + *offset);
+	*offset += sizeof(s64);
+}
+
+static inline void decode_u64_le(const u8 *buffer, size_t *offset, u64 *decoded)
+{
+	*decoded = get_unaligned_le64(buffer + *offset);
+	*offset += sizeof(u64);
+}
+
+static inline void encode_u64_le(u8 *data, size_t *offset, u64 to_encode)
+{
+	put_unaligned_le64(to_encode, data + *offset);
+	*offset += sizeof(u64);
+}
+
+static inline void decode_s32_le(const u8 *buffer, size_t *offset, s32 *decoded)
+{
+	*decoded = get_unaligned_le32(buffer + *offset);
+	*offset += sizeof(s32);
+}
+
+static inline void encode_s32_le(u8 *data, size_t *offset, s32 to_encode)
+{
+	put_unaligned_le32(to_encode, data + *offset);
+	*offset += sizeof(s32);
+}
+
+static inline void decode_u32_le(const u8 *buffer, size_t *offset, u32 *decoded)
+{
+	*decoded = get_unaligned_le32(buffer + *offset);
+	*offset += sizeof(u32);
+}
+
+static inline void encode_u32_le(u8 *data, size_t *offset, u32 to_encode)
+{
+	put_unaligned_le32(to_encode, data + *offset);
+	*offset += sizeof(u32);
+}
+
+static inline void decode_u16_le(const u8 *buffer, size_t *offset, u16 *decoded)
+{
+	*decoded = get_unaligned_le16(buffer + *offset);
+	*offset += sizeof(u16);
+}
+
+static inline void encode_u16_le(u8 *data, size_t *offset, u16 to_encode)
+{
+	put_unaligned_le16(to_encode, data + *offset);
+	*offset += sizeof(u16);
+}
+
+#endif /* UDS_NUMERIC_H */