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, 44 insertions, 0 deletions

diff --git a/drivers/video/videomode.c b/drivers/video/videomode.c
new file mode 100644
index 000000000..2ecf80c08
--- /dev/null
+++ b/drivers/video/videomode.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * generic display timing functions
+ *
+ * Copyright (c) 2012 Steffen Trumtrar <s.trumtrar@pengutronix.de>, Pengutronix
+ */
+
+#include <linux/errno.h>
+#include <linux/export.h>
+#include <video/display_timing.h>
+#include <video/videomode.h>
+
+void videomode_from_timing(const struct display_timing *dt,
+			  struct videomode *vm)
+{
+	vm->pixelclock = dt->pixelclock.typ;
+	vm->hactive = dt->hactive.typ;
+	vm->hfront_porch = dt->hfront_porch.typ;
+	vm->hback_porch = dt->hback_porch.typ;
+	vm->hsync_len = dt->hsync_len.typ;
+
+	vm->vactive = dt->vactive.typ;
+	vm->vfront_porch = dt->vfront_porch.typ;
+	vm->vback_porch = dt->vback_porch.typ;
+	vm->vsync_len = dt->vsync_len.typ;
+
+	vm->flags = dt->flags;
+}
+EXPORT_SYMBOL_GPL(videomode_from_timing);
+
+int videomode_from_timings(const struct display_timings *disp,
+			  struct videomode *vm, unsigned int index)
+{
+	struct display_timing *dt;
+
+	dt = display_timings_get(disp, index);
+	if (!dt)
+		return -EINVAL;
+
+	videomode_from_timing(dt, vm);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(videomode_from_timings);