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/arch/powerpc/boot/treeboot-ebony.c b/arch/powerpc/boot/treeboot-ebony.c
new file mode 100644
index 000000000..332e28659
--- /dev/null
+++ b/arch/powerpc/boot/treeboot-ebony.c
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Old U-boot compatibility for Ebony
+ *
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ *
+ * Copyright 2007 David Gibson, IBM Corporatio.
+ *   Based on cuboot-83xx.c, which is:
+ * Copyright (c) 2007 Freescale Semiconductor, Inc.
+ */
+
+#include "ops.h"
+#include "stdio.h"
+#include "44x.h"
+
+BSS_STACK(4096);
+
+#define OPENBIOS_MAC_BASE	0xfffffe0c
+#define OPENBIOS_MAC_OFFSET	0xc
+
+void platform_init(void)
+{
+	unsigned long end_of_ram = 0x8000000;
+	unsigned long avail_ram = end_of_ram - (unsigned long)_end;
+
+	simple_alloc_init(_end, avail_ram, 32, 64);
+	ebony_init((u8 *)OPENBIOS_MAC_BASE,
+		   (u8 *)(OPENBIOS_MAC_BASE + OPENBIOS_MAC_OFFSET));
+}