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

Andrea Parri (Microsoft)
2022-04-07T04:32:36Z

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..c1322ac37cda9 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_warn_ratelimited(&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