libvhost-user: Support across-memory-boundary access

The sg list/indirect descriptor table may be contigious
in GPA but not in HVA address space. But libvhost-user
wasn't aware of that. This would cause out-of-bounds
access. Even a malicious guest could use it to get
information from the vhost-user backend.

Introduce a plen parameter in vu_gpa_to_va() so we can
handle this case, returning the actual mapped length.

Signed-off-by: Yongji Xie <xieyongji@baidu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
2 files changed