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virtio: force vring descriptors to be allocated from lowmem 

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.

Cc: stable@kernel.org
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Will Deacon 2012-10-19 14:03:33 +01:00 committed by Rusty Russell
parent b9cdc88df8
commit b92b1b89a3
1 changed files with 7 additions and 0 deletions
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7
drivers/virtio/virtio_ring.c
View File

@ -135,6 +135,13 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
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;