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, 43 insertions, 0 deletions

diff --git a/arch/powerpc/boot/ofconsole.c b/arch/powerpc/boot/ofconsole.c
new file mode 100644
index 000000000..8eb0f1c45
--- /dev/null
+++ b/arch/powerpc/boot/ofconsole.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * OF console routines
+ *
+ * Copyright (C) Paul Mackerras 1997.
+ */
+#include <stddef.h>
+#include "types.h"
+#include "elf.h"
+#include "string.h"
+#include "stdio.h"
+#include "page.h"
+#include "ops.h"
+
+#include "of.h"
+
+static unsigned int of_stdout_handle;
+
+static int of_console_open(void)
+{
+	void *devp;
+
+	if (((devp = of_finddevice("/chosen")) != NULL)
+	    && (of_getprop(devp, "stdout", &of_stdout_handle,
+			   sizeof(of_stdout_handle))
+		== sizeof(of_stdout_handle))) {
+		of_stdout_handle = be32_to_cpu(of_stdout_handle);
+		return 0;
+	}
+
+	return -1;
+}
+
+static void of_console_write(const char *buf, int len)
+{
+	of_call_prom("write", 3, 1, of_stdout_handle, buf, len);
+}
+
+void of_console_init(void)
+{
+	console_ops.open = of_console_open;
+	console_ops.write = of_console_write;
+}