Drivers: hv: vmbus: Copy packets sent by Hyper-V out of the ring buffer

Pointers to ring-buffer packets sent by Hyper-V are used within the
guest VM. Hyper-V can send packets with erroneous values or modify
packet fields after they are processed by the guest. To defend
against these scenarios, return a copy of the incoming VMBus packet
after validating its length and offset fields in hv_pkt_iter_first().
In this way, the packet can no longer be modified by the host.

Signed-off-by: Andres Beltran <lkmlabelt@gmail.com>
Co-developed-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20210408161439.341988-1-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

Author: Andres Beltran

drivers/hv/channel.c

@@ -662,12 +662,15 @@ static int __vmbus_open(struct vmbus_channel *newchannel,
 	newchannel->onchannel_callback = onchannelcallback;
 	newchannel->channel_callback_context = context;
 
-	err = hv_ringbuffer_init(&newchannel->outbound, page, send_pages);
+	if (!newchannel->max_pkt_size)
+		newchannel->max_pkt_size = VMBUS_DEFAULT_MAX_PKT_SIZE;
+
+	err = hv_ringbuffer_init(&newchannel->outbound, page, send_pages, 0);
 	if (err)
 		goto error_clean_ring;
 
-	err = hv_ringbuffer_init(&newchannel->inbound,
-				 &page[send_pages], recv_pages);
+	err = hv_ringbuffer_init(&newchannel->inbound, &page[send_pages],
+				 recv_pages, newchannel->max_pkt_size);
 	if (err)
 		goto error_clean_ring;
 

drivers/hv/hv_fcopy.c

@@ -349,6 +349,7 @@ int hv_fcopy_init(struct hv_util_service *srv)
 {
 	recv_buffer = srv->recv_buffer;
 	fcopy_transaction.recv_channel = srv->channel;
+	fcopy_transaction.recv_channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;
 
 	/*
 	 * When this driver loads, the user level daemon that

drivers/hv/hv_kvp.c

@@ -757,6 +757,7 @@ hv_kvp_init(struct hv_util_service *srv)
 {
 	recv_buffer = srv->recv_buffer;
 	kvp_transaction.recv_channel = srv->channel;
+	kvp_transaction.recv_channel->max_pkt_size = HV_HYP_PAGE_SIZE * 4;
 
 	/*
 	 * When this driver loads, the user level daemon that

drivers/hv/hyperv_vmbus.h

@@ -174,7 +174,7 @@ extern int hv_synic_cleanup(unsigned int cpu);
 void hv_ringbuffer_pre_init(struct vmbus_channel *channel);
 
 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
-		       struct page *pages, u32 pagecnt);
+		       struct page *pages, u32 pagecnt, u32 max_pkt_size);
 
 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info);
 

drivers/hv/ring_buffer.c

@@ -181,7 +181,7 @@ void hv_ringbuffer_pre_init(struct vmbus_channel *channel)
 
 /* Initialize the ring buffer. */
 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
-		       struct page *pages, u32 page_cnt)
+		       struct page *pages, u32 page_cnt, u32 max_pkt_size)
 {
 	int i;
 	struct page **pages_wraparound;
@@ -223,6 +223,14 @@ int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
 		sizeof(struct hv_ring_buffer);
 	ring_info->priv_read_index = 0;
 
+	/* Initialize buffer that holds copies of incoming packets */
+	if (max_pkt_size) {
+		ring_info->pkt_buffer = kzalloc(max_pkt_size, GFP_KERNEL);
+		if (!ring_info->pkt_buffer)
+			return -ENOMEM;
+		ring_info->pkt_buffer_size = max_pkt_size;
+	}
+
 	spin_lock_init(&ring_info->ring_lock);
 
 	return 0;
@@ -235,6 +243,9 @@ void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
 	vunmap(ring_info->ring_buffer);
 	ring_info->ring_buffer = NULL;
 	mutex_unlock(&ring_info->ring_buffer_mutex);
+
+	kfree(ring_info->pkt_buffer);
+	ring_info->pkt_buffer_size = 0;
 }
 
 /* Write to the ring buffer. */
@@ -375,7 +386,7 @@ int hv_ringbuffer_read(struct vmbus_channel *channel,
 	memcpy(buffer, (const char *)desc + offset, packetlen);
 
 	/* Advance ring index to next packet descriptor */
-	__hv_pkt_iter_next(channel, desc);
+	__hv_pkt_iter_next(channel, desc, true);
 
 	/* Notify host of update */
 	hv_pkt_iter_close(channel);
@@ -401,6 +412,22 @@ static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
 		return (rbi->ring_datasize - priv_read_loc) + write_loc;
 }
 
+/*
+ * Get first vmbus packet without copying it out of the ring buffer
+ */
+struct vmpacket_descriptor *hv_pkt_iter_first_raw(struct vmbus_channel *channel)
+{
+	struct hv_ring_buffer_info *rbi = &channel->inbound;
+
+	hv_debug_delay_test(channel, MESSAGE_DELAY);
+
+	if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
+		return NULL;
+
+	return (struct vmpacket_descriptor *)(hv_get_ring_buffer(rbi) + rbi->priv_read_index);
+}
+EXPORT_SYMBOL_GPL(hv_pkt_iter_first_raw);
+
 /*
  * Get first vmbus packet from ring buffer after read_index
  *
@@ -409,17 +436,49 @@ static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
 struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
 {
 	struct hv_ring_buffer_info *rbi = &channel->inbound;
-	struct vmpacket_descriptor *desc;
+	struct vmpacket_descriptor *desc, *desc_copy;
+	u32 bytes_avail, pkt_len, pkt_offset;
 
-	hv_debug_delay_test(channel, MESSAGE_DELAY);
-	if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
+	desc = hv_pkt_iter_first_raw(channel);
+	if (!desc)
 		return NULL;
 
-	desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
-	if (desc)
-		prefetch((char *)desc + (desc->len8 << 3));
+	bytes_avail = min(rbi->pkt_buffer_size, hv_pkt_iter_avail(rbi));
+
+	/*
+	 * Ensure the compiler does not use references to incoming Hyper-V values (which
+	 * could change at any moment) when reading local variables later in the code
+	 */
+	pkt_len = READ_ONCE(desc->len8) << 3;
+	pkt_offset = READ_ONCE(desc->offset8) << 3;
+
+	/*
+	 * If pkt_len is invalid, set it to the smaller of hv_pkt_iter_avail() and
+	 * rbi->pkt_buffer_size
+	 */
+	if (pkt_len < sizeof(struct vmpacket_descriptor) || pkt_len > bytes_avail)
+		pkt_len = bytes_avail;
+
+	/*
+	 * If pkt_offset is invalid, arbitrarily set it to
+	 * the size of vmpacket_descriptor
+	 */
+	if (pkt_offset < sizeof(struct vmpacket_descriptor) || pkt_offset > pkt_len)
+		pkt_offset = sizeof(struct vmpacket_descriptor);
+
+	/* Copy the Hyper-V packet out of the ring buffer */
+	desc_copy = (struct vmpacket_descriptor *)rbi->pkt_buffer;
+	memcpy(desc_copy, desc, pkt_len);
+
+	/*
+	 * Hyper-V could still change len8 and offset8 after the earlier read.
+	 * Ensure that desc_copy has legal values for len8 and offset8 that
+	 * are consistent with the copy we just made
+	 */
+	desc_copy->len8 = pkt_len >> 3;
+	desc_copy->offset8 = pkt_offset >> 3;
 
-	return desc;
+	return desc_copy;
 }
 EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
 
@@ -431,7 +490,8 @@ EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
  */
 struct vmpacket_descriptor *
 __hv_pkt_iter_next(struct vmbus_channel *channel,
-		   const struct vmpacket_descriptor *desc)
+		   const struct vmpacket_descriptor *desc,
+		   bool copy)
 {
 	struct hv_ring_buffer_info *rbi = &channel->inbound;
 	u32 packetlen = desc->len8 << 3;
@@ -444,7 +504,7 @@ __hv_pkt_iter_next(struct vmbus_channel *channel,
 		rbi->priv_read_index -= dsize;
 
 	/* more data? */
-	return hv_pkt_iter_first(channel);
+	return copy ? hv_pkt_iter_first(channel) : hv_pkt_iter_first_raw(channel);
 }
 EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
 

drivers/net/hyperv/hyperv_net.h

@@ -895,9 +895,16 @@ static inline u32 netvsc_rqstor_size(unsigned long ringbytes)
 		ringbytes / NETVSC_MIN_IN_MSG_SIZE;
 }
 
+/* XFER PAGE packets can specify a maximum of 375 ranges for NDIS >= 6.0
+ * and a maximum of 64 ranges for NDIS < 6.0 with no RSC; with RSC, this
+ * limit is raised to 562 (= NVSP_RSC_MAX).
+ */
+#define NETVSC_MAX_XFER_PAGE_RANGES NVSP_RSC_MAX
 #define NETVSC_XFER_HEADER_SIZE(rng_cnt) \
 		(offsetof(struct vmtransfer_page_packet_header, ranges) + \
 		(rng_cnt) * sizeof(struct vmtransfer_page_range))
+#define NETVSC_MAX_PKT_SIZE (NETVSC_XFER_HEADER_SIZE(NETVSC_MAX_XFER_PAGE_RANGES) + \
+		sizeof(struct nvsp_message) + (sizeof(u32) * VRSS_SEND_TAB_SIZE))
 
 struct multi_send_data {
 	struct sk_buff *skb; /* skb containing the pkt */

drivers/net/hyperv/netvsc.c

@@ -1650,6 +1650,8 @@ struct netvsc_device *netvsc_device_add(struct hv_device *device,
 
 	/* Open the channel */
 	device->channel->rqstor_size = netvsc_rqstor_size(netvsc_ring_bytes);
+	device->channel->max_pkt_size = NETVSC_MAX_PKT_SIZE;
+
 	ret = vmbus_open(device->channel, netvsc_ring_bytes,
 			 netvsc_ring_bytes,  NULL, 0,
 			 netvsc_channel_cb, net_device->chan_table);

drivers/net/hyperv/rndis_filter.c

@@ -1260,6 +1260,8 @@ static void netvsc_sc_open(struct vmbus_channel *new_sc)
 	nvchan->channel = new_sc;
 
 	new_sc->rqstor_size = netvsc_rqstor_size(netvsc_ring_bytes);
+	new_sc->max_pkt_size = NETVSC_MAX_PKT_SIZE;
+
 	ret = vmbus_open(new_sc, netvsc_ring_bytes,
 			 netvsc_ring_bytes, NULL, 0,
 			 netvsc_channel_cb, nvchan);

drivers/scsi/storvsc_drv.c

@@ -406,6 +406,14 @@ static void storvsc_on_channel_callback(void *context);
 #define STORVSC_IDE_MAX_TARGETS				1
 #define STORVSC_IDE_MAX_CHANNELS			1
 
+/*
+ * Upper bound on the size of a storvsc packet. vmscsi_size_delta is not
+ * included in the calculation because it is set after STORVSC_MAX_PKT_SIZE
+ * is used in storvsc_connect_to_vsp
+ */
+#define STORVSC_MAX_PKT_SIZE (sizeof(struct vmpacket_descriptor) +\
+			      sizeof(struct vstor_packet))
+
 struct storvsc_cmd_request {
 	struct scsi_cmnd *cmd;
 
@@ -701,6 +709,7 @@ static void handle_sc_creation(struct vmbus_channel *new_sc)
 		return;
 
 	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
+	new_sc->max_pkt_size = STORVSC_MAX_PKT_SIZE;
 
 	/*
 	 * The size of vmbus_requestor is an upper bound on the number of requests
@@ -1294,6 +1303,7 @@ static int storvsc_connect_to_vsp(struct hv_device *device, u32 ring_size,
 
 	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
 
+	device->channel->max_pkt_size = STORVSC_MAX_PKT_SIZE;
 	/*
 	 * The size of vmbus_requestor is an upper bound on the number of requests
 	 * that can be in-progress at any one time across all channels.

include/linux/hyperv.h

@@ -181,6 +181,10 @@ struct hv_ring_buffer_info {
 	 * being freed while the ring buffer is being accessed.
 	 */
 	struct mutex ring_buffer_mutex;
+
+	/* Buffer that holds a copy of an incoming host packet */
+	void *pkt_buffer;
+	u32 pkt_buffer_size;
 };
 
 
@@ -799,6 +803,8 @@ struct vmbus_device {
 	bool allowed_in_isolated;
 };
 
+#define VMBUS_DEFAULT_MAX_PKT_SIZE 4096
+
 struct vmbus_channel {
 	struct list_head listentry;
 
@@ -1021,6 +1027,9 @@ struct vmbus_channel {
 	/* request/transaction ids for VMBus */
 	struct vmbus_requestor requestor;
 	u32 rqstor_size;
+
+	/* The max size of a packet on this channel */
+	u32 max_pkt_size;
 };
 
 u64 vmbus_next_request_id(struct vmbus_requestor *rqstor, u64 rqst_addr);
@@ -1662,32 +1671,55 @@ static inline u32 hv_pkt_datalen(const struct vmpacket_descriptor *desc)
 }
 
 
+struct vmpacket_descriptor *
+hv_pkt_iter_first_raw(struct vmbus_channel *channel);
+
 struct vmpacket_descriptor *
 hv_pkt_iter_first(struct vmbus_channel *channel);
 
 struct vmpacket_descriptor *
 __hv_pkt_iter_next(struct vmbus_channel *channel,
-		   const struct vmpacket_descriptor *pkt);
+		   const struct vmpacket_descriptor *pkt,
+		   bool copy);
 
 void hv_pkt_iter_close(struct vmbus_channel *channel);
 
-/*
- * Get next packet descriptor from iterator
- * If at end of list, return NULL and update host.
- */
 static inline struct vmpacket_descriptor *
-hv_pkt_iter_next(struct vmbus_channel *channel,
-		 const struct vmpacket_descriptor *pkt)
+hv_pkt_iter_next_pkt(struct vmbus_channel *channel,
+		     const struct vmpacket_descriptor *pkt,
+		     bool copy)
 {
 	struct vmpacket_descriptor *nxt;
 
-	nxt = __hv_pkt_iter_next(channel, pkt);
+	nxt = __hv_pkt_iter_next(channel, pkt, copy);
 	if (!nxt)
 		hv_pkt_iter_close(channel);
 
 	return nxt;
 }
 
+/*
+ * Get next packet descriptor without copying it out of the ring buffer
+ * If at end of list, return NULL and update host.
+ */
+static inline struct vmpacket_descriptor *
+hv_pkt_iter_next_raw(struct vmbus_channel *channel,
+		     const struct vmpacket_descriptor *pkt)
+{
+	return hv_pkt_iter_next_pkt(channel, pkt, false);
+}
+
+/*
+ * Get next packet descriptor from iterator
+ * If at end of list, return NULL and update host.
+ */
+static inline struct vmpacket_descriptor *
+hv_pkt_iter_next(struct vmbus_channel *channel,
+		 const struct vmpacket_descriptor *pkt)
+{
+	return hv_pkt_iter_next_pkt(channel, pkt, true);
+}
+
 #define foreach_vmbus_pkt(pkt, channel) \
 	for (pkt = hv_pkt_iter_first(channel); pkt; \
 	    pkt = hv_pkt_iter_next(channel, pkt))