Patch "virtio: force vring descriptors to be allocated from lowmem" has been added to the 3.0-stable tree

This is a note to let you know that I've just added the patch titled

virtio: force vring descriptors to be allocated from lowmem

to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
virtio-force-vring-descriptors-to-be-allocated-from-lowmem.patch
and it can be found in the queue-3.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Will Deacon <[email protected]>
Date: Fri, 19 Oct 2012 14:03:33 +0100
Subject: virtio: force vring descriptors to be allocated from lowmem

From: Will Deacon <[email protected]>

commit b92b1b89a33c172c075edccf6afb0edc41d851fd upstream.

Virtio devices may attempt to add descriptors to a virtqueue from atomic context using GFP_ATOMIC allocation. This is problematic because such allocations can fall outside of the lowmem mapping, causing virt_to_phys to report bogus physical addresses which are subsequently passed to userspace via the buffers for the virtual device.

This patch masks out __GFP_HIGH and __GFP_HIGHMEM from the requested flags when allocating descriptors for a virtqueue. If an atomic allocation is requested and later fails, we will return -ENOSPC which will be handled by the driver.

---
 drivers/virtio/virtio_ring.c |    7 +++++++
 1 file changed, 7 insertions(+)

@@ -120,6 +120,13 @@ static int vring_add_indirect(struct vri
 	unsigned head;
 	int i;
 
+	/*
+	 * We require lowmem mappings for the descriptors because
+	 * otherwise virt_to_phys will give us bogus addresses in the
+	 * virtqueue.
+	 */
+	gfp &= ~(__GFP_HIGHMEM | __GFP_HIGH);
+
 	desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
 	if (!desc)
 		return -ENOMEM;

Patches currently in stable-queue which might be from [email protected] are

queue-3.0/virtio-force-vring-descriptors-to-be-allocated-from-lowmem.patch