RE: [PATCH 1/2] PCI: hv: Add validation for untrusted Hyper-V values

["Michael Kelley (LINUX)" <mikelley@microsoft.com>]

From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Sent: Wednesday, May 4, 2022 5:51 AM
> 
> 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>
> ---
>  drivers/pci/controller/pci-hyperv.c | 27 ++++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index cf2fe5754fde4..9a3e17b682eb7 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -981,11 +981,7 @@ static void hv_pci_generic_compl(void *context, struct
> pci_response *resp,
>  {
>  	struct hv_pci_compl *comp_pkt = context;
> 
> -	if (resp_packet_size >= offsetofend(struct pci_response, status))
> -		comp_pkt->completion_status = resp->status;
> -	else
> -		comp_pkt->completion_status = -1;
> -
> +	comp_pkt->completion_status = resp->status;
>  	complete(&comp_pkt->host_event);
>  }
> 
> @@ -1602,8 +1598,13 @@ static void hv_pci_compose_compl(void *context, struct
> pci_response *resp,
>  	struct pci_create_int_response *int_resp =
>  		(struct pci_create_int_response *)resp;
> 
> +	if (resp_packet_size < sizeof(*int_resp)) {
> +		comp_pkt->comp_pkt.completion_status = -1;
> +		goto out;
> +	}
>  	comp_pkt->comp_pkt.completion_status = resp->status;
>  	comp_pkt->int_desc = int_resp->int_desc;
> +out:
>  	complete(&comp_pkt->comp_pkt.host_event);
>  }
> 
> @@ -2806,7 +2807,8 @@ static void hv_pci_onchannelcallback(void *context)
>  			case PCI_BUS_RELATIONS:
> 
>  				bus_rel = (struct pci_bus_relations *)buffer;
> -				if (bytes_recvd <
> +				if (bytes_recvd < sizeof(*bus_rel) ||
> +				    bytes_recvd <
>  					struct_size(bus_rel, func,
>  						    bus_rel->device_count)) {
>  					dev_err(&hbus->hdev->device,
> @@ -2820,7 +2822,8 @@ static void hv_pci_onchannelcallback(void *context)
>  			case PCI_BUS_RELATIONS2:
> 
>  				bus_rel2 = (struct pci_bus_relations2 *)buffer;
> -				if (bytes_recvd <
> +				if (bytes_recvd < sizeof(*bus_rel2) ||
> +				    bytes_recvd <
>  					struct_size(bus_rel2, func,
>  						    bus_rel2->device_count)) {
>  					dev_err(&hbus->hdev->device,
> @@ -2834,6 +2837,11 @@ static void hv_pci_onchannelcallback(void *context)
>  			case PCI_EJECT:
> 
>  				dev_message = (struct pci_dev_incoming *)buffer;
> +				if (bytes_recvd < sizeof(*dev_message)) {
> +					dev_err(&hbus->hdev->device,
> +						"eject message too small\n");
> +					break;
> +				}
>  				hpdev = get_pcichild_wslot(hbus,
>  						      dev_message->wslot.slot);
>  				if (hpdev) {
> @@ -2845,6 +2853,11 @@ static void hv_pci_onchannelcallback(void *context)
>  			case PCI_INVALIDATE_BLOCK:
> 
>  				inval = (struct pci_dev_inval_block *)buffer;
> +				if (bytes_recvd < sizeof(*inval)) {
> +					dev_err(&hbus->hdev->device,
> +						"invalidate message too small\n");
> +					break;
> +				}
>  				hpdev = get_pcichild_wslot(hbus,
>  							   inval->wslot.slot);
>  				if (hpdev) {
> --
> 2.25.1

I don't see any issues with the code here.  But check the function
q_resource_requirements().  Doesn't it need the same treatment as you've
done above with hv_pci_compose_compl()?   For completeness, the
fix for q_resource_requirements() should be included in this patch as well.

Michael