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, 163 insertions, 0 deletions

diff --git a/drivers/misc/ibmasm/event.c b/drivers/misc/ibmasm/event.c
new file mode 100644
index 000000000..3990bf2b1
--- /dev/null
+++ b/drivers/misc/ibmasm/event.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * IBM ASM Service Processor Device Driver
+ *
+ * Copyright (C) IBM Corporation, 2004
+ *
+ * Author: Max Asböck <amax@us.ibm.com>
+ */
+
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include "ibmasm.h"
+#include "lowlevel.h"
+
+/*
+ * ASM service processor event handling routines.
+ *
+ * Events are signalled to the device drivers through interrupts.
+ * They have the format of dot commands, with the type field set to
+ * sp_event.
+ * The driver does not interpret the events, it simply stores them in a
+ * circular buffer.
+ */
+
+static void wake_up_event_readers(struct service_processor *sp)
+{
+	struct event_reader *reader;
+
+	list_for_each_entry(reader, &sp->event_buffer->readers, node)
+                wake_up_interruptible(&reader->wait);
+}
+
+/*
+ * receive_event
+ * Called by the interrupt handler when a dot command of type sp_event is
+ * received.
+ * Store the event in the circular event buffer, wake up any sleeping
+ * event readers.
+ * There is no reader marker in the buffer, therefore readers are
+ * responsible for keeping up with the writer, or they will lose events.
+ */
+void ibmasm_receive_event(struct service_processor *sp, void *data, unsigned int data_size)
+{
+	struct event_buffer *buffer = sp->event_buffer;
+	struct ibmasm_event *event;
+	unsigned long flags;
+
+	data_size = min(data_size, IBMASM_EVENT_MAX_SIZE);
+
+	spin_lock_irqsave(&sp->lock, flags);
+	/* copy the event into the next slot in the circular buffer */
+	event = &buffer->events[buffer->next_index];
+	memcpy_fromio(event->data, data, data_size);
+	event->data_size = data_size;
+	event->serial_number = buffer->next_serial_number;
+
+	/* advance indices in the buffer */
+	buffer->next_index = (buffer->next_index + 1) % IBMASM_NUM_EVENTS;
+	buffer->next_serial_number++;
+	spin_unlock_irqrestore(&sp->lock, flags);
+
+	wake_up_event_readers(sp);
+}
+
+static inline int event_available(struct event_buffer *b, struct event_reader *r)
+{
+	return (r->next_serial_number < b->next_serial_number);
+}
+
+/*
+ * get_next_event
+ * Called by event readers (initiated from user space through the file
+ * system).
+ * Sleeps until a new event is available.
+ */
+int ibmasm_get_next_event(struct service_processor *sp, struct event_reader *reader)
+{
+	struct event_buffer *buffer = sp->event_buffer;
+	struct ibmasm_event *event;
+	unsigned int index;
+	unsigned long flags;
+
+	reader->cancelled = 0;
+
+	if (wait_event_interruptible(reader->wait,
+			event_available(buffer, reader) || reader->cancelled))
+		return -ERESTARTSYS;
+
+	if (!event_available(buffer, reader))
+		return 0;
+
+	spin_lock_irqsave(&sp->lock, flags);
+
+	index = buffer->next_index;
+	event = &buffer->events[index];
+	while (event->serial_number < reader->next_serial_number) {
+		index = (index + 1) % IBMASM_NUM_EVENTS;
+		event = &buffer->events[index];
+	}
+	memcpy(reader->data, event->data, event->data_size);
+	reader->data_size = event->data_size;
+	reader->next_serial_number = event->serial_number + 1;
+
+	spin_unlock_irqrestore(&sp->lock, flags);
+
+	return event->data_size;
+}
+
+void ibmasm_cancel_next_event(struct event_reader *reader)
+{
+        reader->cancelled = 1;
+        wake_up_interruptible(&reader->wait);
+}
+
+void ibmasm_event_reader_register(struct service_processor *sp, struct event_reader *reader)
+{
+	unsigned long flags;
+
+	reader->next_serial_number = sp->event_buffer->next_serial_number;
+	init_waitqueue_head(&reader->wait);
+	spin_lock_irqsave(&sp->lock, flags);
+	list_add(&reader->node, &sp->event_buffer->readers);
+	spin_unlock_irqrestore(&sp->lock, flags);
+}
+
+void ibmasm_event_reader_unregister(struct service_processor *sp, struct event_reader *reader)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&sp->lock, flags);
+	list_del(&reader->node);
+	spin_unlock_irqrestore(&sp->lock, flags);
+}
+
+int ibmasm_event_buffer_init(struct service_processor *sp)
+{
+	struct event_buffer *buffer;
+	struct ibmasm_event *event;
+	int i;
+
+	buffer = kmalloc_obj(struct event_buffer);
+	if (!buffer)
+		return -ENOMEM;
+
+	buffer->next_index = 0;
+	buffer->next_serial_number = 1;
+
+	event = buffer->events;
+	for (i=0; i<IBMASM_NUM_EVENTS; i++, event++)
+		event->serial_number = 0;
+
+	INIT_LIST_HEAD(&buffer->readers);
+
+	sp->event_buffer = buffer;
+
+	return 0;
+}
+
+void ibmasm_event_buffer_exit(struct service_processor *sp)
+{
+	kfree(sp->event_buffer);
+}