[PATCH v2 2/6] PCI: hv: Use vmbus_requestor to generate transaction IDs for VMbus hardening

["Andrea Parri (Microsoft)" <parri.andrea@gmail.com>]

Currently, pointers to guest memory are passed to Hyper-V as transaction
IDs in hv_pci.  In the face of errors or malicious behavior in Hyper-V,
hv_pci should not expose or trust the transaction IDs returned by
Hyper-V to be valid guest memory addresses.  Instead, use small integers
generated by vmbus_requestor as request (transaction) IDs.

Suggested-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
---
 drivers/pci/controller/pci-hyperv.c | 39 +++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 88b3b56d05228..0252b4bbc8d15 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -91,6 +91,13 @@ static enum pci_protocol_version_t pci_protocol_versions[] = {
 /* space for 32bit serial number as string */
 #define SLOT_NAME_SIZE 11
 
+/*
+ * Size of requestor for VMbus; the value is based on the observation
+ * that having more than one request outstanding is 'rare', and so 64
+ * should be generous in ensuring that we don't ever run out.
+ */
+#define HV_PCI_RQSTOR_SIZE 64
+
 /*
  * Message Types
  */
@@ -1407,7 +1414,7 @@ static void hv_int_desc_free(struct hv_pci_dev *hpdev,
 	int_pkt->wslot.slot = hpdev->desc.win_slot.slot;
 	int_pkt->int_desc = *int_desc;
 	vmbus_sendpacket(hpdev->hbus->hdev->channel, int_pkt, sizeof(*int_pkt),
-			 (unsigned long)&ctxt.pkt, VM_PKT_DATA_INBAND, 0);
+			 0, VM_PKT_DATA_INBAND, 0);
 	kfree(int_desc);
 }
 
@@ -2649,7 +2656,7 @@ static void hv_eject_device_work(struct work_struct *work)
 	ejct_pkt->message_type.type = PCI_EJECTION_COMPLETE;
 	ejct_pkt->wslot.slot = hpdev->desc.win_slot.slot;
 	vmbus_sendpacket(hbus->hdev->channel, ejct_pkt,
-			 sizeof(*ejct_pkt), (unsigned long)&ctxt.pkt,
+			 sizeof(*ejct_pkt), 0,
 			 VM_PKT_DATA_INBAND, 0);
 
 	/* For the get_pcichild() in hv_pci_eject_device() */
@@ -2696,8 +2703,9 @@ static void hv_pci_onchannelcallback(void *context)
 	const int packet_size = 0x100;
 	int ret;
 	struct hv_pcibus_device *hbus = context;
+	struct vmbus_channel *chan = hbus->hdev->channel;
 	u32 bytes_recvd;
-	u64 req_id;
+	u64 req_id, req_addr;
 	struct vmpacket_descriptor *desc;
 	unsigned char *buffer;
 	int bufferlen = packet_size;
@@ -2715,8 +2723,8 @@ static void hv_pci_onchannelcallback(void *context)
 		return;
 
 	while (1) {
-		ret = vmbus_recvpacket_raw(hbus->hdev->channel, buffer,
-					   bufferlen, &bytes_recvd, &req_id);
+		ret = vmbus_recvpacket_raw(chan, buffer, bufferlen,
+					   &bytes_recvd, &req_id);
 
 		if (ret == -ENOBUFS) {
 			kfree(buffer);
@@ -2743,11 +2751,14 @@ static void hv_pci_onchannelcallback(void *context)
 		switch (desc->type) {
 		case VM_PKT_COMP:
 
-			/*
-			 * The host is trusted, and thus it's safe to interpret
-			 * this transaction ID as a pointer.
-			 */
-			comp_packet = (struct pci_packet *)req_id;
+			req_addr = chan->request_addr_callback(chan, req_id);
+			if (req_addr == VMBUS_RQST_ERROR) {
+				dev_err(&hbus->hdev->device,
+					"Invalid transaction ID %llx\n",
+					req_id);
+				break;
+			}
+			comp_packet = (struct pci_packet *)req_addr;
 			response = (struct pci_response *)buffer;
 			comp_packet->completion_func(comp_packet->compl_ctxt,
 						     response,
@@ -3428,6 +3439,10 @@ static int hv_pci_probe(struct hv_device *hdev,
 		goto free_dom;
 	}
 
+	hdev->channel->next_request_id_callback = vmbus_next_request_id;
+	hdev->channel->request_addr_callback = vmbus_request_addr;
+	hdev->channel->rqstor_size = HV_PCI_RQSTOR_SIZE;
+
 	ret = vmbus_open(hdev->channel, pci_ring_size, pci_ring_size, NULL, 0,
 			 hv_pci_onchannelcallback, hbus);
 	if (ret)
@@ -3758,6 +3773,10 @@ static int hv_pci_resume(struct hv_device *hdev)
 
 	hbus->state = hv_pcibus_init;
 
+	hdev->channel->next_request_id_callback = vmbus_next_request_id;
+	hdev->channel->request_addr_callback = vmbus_request_addr;
+	hdev->channel->rqstor_size = HV_PCI_RQSTOR_SIZE;
+
 	ret = vmbus_open(hdev->channel, pci_ring_size, pci_ring_size, NULL, 0,
 			 hv_pci_onchannelcallback, hbus);
 	if (ret)
-- 
2.25.1