PCI: hv: Add validation for untrusted Hyper-V values

PCI: hv: Add validation for untrusted Hyper-V values

For additional robustness in the face of Hyper-V errors or malicious
behavior, validate all values that originate from packets that Hyper-V
has sent to the guest in the host-to-guest ring buffer.  Ensure that
invalid values cannot cause data being copied out of the bounds of the
source buffer in hv_pci_onchannelcallback().

While at it, remove a redundant validation in hv_pci_generic_compl():
hv_pci_onchannelcallback() already ensures that all processed incoming
packets are "at least as large as [in fact larger than] a response".

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Link: https://lore.kernel.org/r/20220511223207.3386-2-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>