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, 18 insertions, 0 deletions

diff --git a/drivers/net/arcnet/com9026.h b/drivers/net/arcnet/com9026.h
new file mode 100644
index 000000000..6adbc1871
--- /dev/null
+++ b/drivers/net/arcnet/com9026.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __COM9026_H
+#define __COM9026_H
+
+/* COM 9026 controller chip --> ARCnet register addresses */
+
+#define COM9026_REG_W_INTMASK	0	/* writable */
+#define COM9026_REG_R_STATUS	0	/* readable */
+#define COM9026_REG_W_COMMAND	1	/* writable, returns random vals on read (?) */
+#define COM9026_REG_RW_CONFIG	2	/* Configuration register */
+#define COM9026_REG_R_RESET	8	/* software reset (on read) */
+#define COM9026_REG_RW_MEMDATA	12	/* Data port for IO-mapped memory */
+#define COM9026_REG_W_ADDR_LO	14	/* Control registers for said */
+#define COM9026_REG_W_ADDR_HI	15
+
+#define COM9026_REG_R_STATION	1	/* Station ID */
+
+#endif