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, 51 insertions, 0 deletions

diff --git a/arch/mips/cobalt/rtc.c b/arch/mips/cobalt/rtc.c
new file mode 100644
index 000000000..0f9ca45da
--- /dev/null
+++ b/arch/mips/cobalt/rtc.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Registration of Cobalt RTC platform device.
+ *
+ *  Copyright (C) 2007  Yoichi Yuasa <yuasa@linux-mips.org>
+ */
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/ioport.h>
+#include <linux/mc146818rtc.h>
+#include <linux/platform_device.h>
+
+static struct resource cobalt_rtc_resource[] __initdata = {
+	{
+		.start	= 0x70,
+		.end	= 0x77,
+		.flags	= IORESOURCE_IO,
+	},
+	{
+		.start	= RTC_IRQ,
+		.end	= RTC_IRQ,
+		.flags	= IORESOURCE_IRQ,
+	},
+};
+
+static __init int cobalt_rtc_add(void)
+{
+	struct platform_device *pdev;
+	int retval;
+
+	pdev = platform_device_alloc("rtc_cmos", -1);
+	if (!pdev)
+		return -ENOMEM;
+
+	retval = platform_device_add_resources(pdev, cobalt_rtc_resource,
+					       ARRAY_SIZE(cobalt_rtc_resource));
+	if (retval)
+		goto err_free_device;
+
+	retval = platform_device_add(pdev);
+	if (retval)
+		goto err_free_device;
+
+	return 0;
+
+err_free_device:
+	platform_device_put(pdev);
+
+	return retval;
+}
+device_initcall(cobalt_rtc_add);