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, 66 insertions, 0 deletions

diff --git a/net/xdp/xsk_queue.c b/net/xdp/xsk_queue.c
new file mode 100644
index 000000000..4dd01b7d8
--- /dev/null
+++ b/net/xdp/xsk_queue.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/* XDP user-space ring structure
+ * Copyright(c) 2018 Intel Corporation.
+ */
+
+#include <linux/log2.h>
+#include <linux/slab.h>
+#include <linux/overflow.h>
+#include <linux/vmalloc.h>
+#include <net/xdp_sock_drv.h>
+
+#include "xsk_queue.h"
+
+static size_t xskq_get_ring_size(struct xsk_queue *q, bool umem_queue)
+{
+	struct xdp_umem_ring *umem_ring;
+	struct xdp_rxtx_ring *rxtx_ring;
+
+	if (umem_queue)
+		return struct_size(umem_ring, desc, q->nentries);
+	return struct_size(rxtx_ring, desc, q->nentries);
+}
+
+struct xsk_queue *xskq_create(u32 nentries, bool umem_queue)
+{
+	struct xsk_queue *q;
+	size_t size;
+
+	q = kzalloc_obj(*q);
+	if (!q)
+		return NULL;
+
+	q->nentries = nentries;
+	q->ring_mask = nentries - 1;
+
+	size = xskq_get_ring_size(q, umem_queue);
+
+	/* size which is overflowing or close to SIZE_MAX will become 0 in
+	 * PAGE_ALIGN(), checking SIZE_MAX is enough due to the previous
+	 * is_power_of_2(), the rest will be handled by vmalloc_user()
+	 */
+	if (unlikely(size == SIZE_MAX)) {
+		kfree(q);
+		return NULL;
+	}
+
+	size = PAGE_ALIGN(size);
+
+	q->ring = vmalloc_user(size);
+	if (!q->ring) {
+		kfree(q);
+		return NULL;
+	}
+
+	q->ring_vmalloc_size = size;
+	return q;
+}
+
+void xskq_destroy(struct xsk_queue *q)
+{
+	if (!q)
+		return;
+
+	vfree(q->ring);
+	kfree(q);
+}