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/cuboot.c b/arch/powerpc/boot/cuboot.c
new file mode 100644
index 000000000..7f186658f
--- /dev/null
+++ b/arch/powerpc/boot/cuboot.c
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Compatibility for old (not device tree aware) U-Boot versions
+ *
+ * Author: Scott Wood <scottwood@freescale.com>
+ * Consolidated using macros by David Gibson <david@gibson.dropbear.id.au>
+ *
+ * Copyright 2007 David Gibson, IBM Corporation.
+ * Copyright (c) 2007 Freescale Semiconductor, Inc.
+ */
+
+#include "ops.h"
+#include "stdio.h"
+
+#include "ppcboot.h"
+
+void cuboot_init(unsigned long r4, unsigned long r5,
+		 unsigned long r6, unsigned long r7,
+		 unsigned long end_of_ram)
+{
+	unsigned long avail_ram = end_of_ram - (unsigned long)_end;
+
+	loader_info.initrd_addr = r4;
+	loader_info.initrd_size = r4 ? r5 - r4 : 0;
+	loader_info.cmdline = (char *)r6;
+	loader_info.cmdline_len = r7 - r6;
+
+	simple_alloc_init(_end, avail_ram - 1024*1024, 32, 64);
+}