[PATCH v4 2/3] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

[PATCH v4 2/3] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

[Andres Beltran]

Currently, pointers to guest memory are passed to Hyper-V as
transaction IDs in storvsc. In the face of errors or malicious
behavior in Hyper-V, storvsc 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 requests
(transaction) IDs.

Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Andres Beltran <lkmlabelt@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
---
Changes in v2:
        - Add casts to unsigned long to fix warnings on 32bit.

 drivers/scsi/storvsc_drv.c | 85 +++++++++++++++++++++++++++++++++-----
 1 file changed, 74 insertions(+), 11 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 624467e2590a..6d2df1f0fe6d 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -399,6 +399,7 @@ static int storvsc_timeout = 180;
 static struct scsi_transport_template *fc_transport_template;
 #endif
 
+static struct scsi_host_template scsi_driver;
 static void storvsc_on_channel_callback(void *context);
 
 #define STORVSC_MAX_LUNS_PER_TARGET			255
@@ -698,6 +699,12 @@ static void handle_sc_creation(struct vmbus_channel *new_sc)
 
 	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
 
+	/*
+	 * 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.
+	 */
+	new_sc->rqstor_size = scsi_driver.can_queue;
+
 	ret = vmbus_open(new_sc,
 			 storvsc_ringbuffer_size,
 			 storvsc_ringbuffer_size,
@@ -726,6 +733,7 @@ static void  handle_multichannel_storage(struct hv_device *device, int max_chns)
 	struct storvsc_cmd_request *request;
 	struct vstor_packet *vstor_packet;
 	int ret, t;
+	u64 rqst_id;
 
 	/*
 	 * If the number of CPUs is artificially restricted, such as
@@ -760,14 +768,23 @@ static void  handle_multichannel_storage(struct hv_device *device, int max_chns)
 	vstor_packet->flags = REQUEST_COMPLETION_FLAG;
 	vstor_packet->sub_channel_count = num_sc;
 
+	rqst_id = vmbus_next_request_id(&device->channel->requestor,
+					(unsigned long)request);
+	if (rqst_id == VMBUS_RQST_ERROR) {
+		dev_err(dev, "No request id available\n");
+		return;
+	}
+
 	ret = vmbus_sendpacket(device->channel, vstor_packet,
 			       (sizeof(struct vstor_packet) -
 			       vmscsi_size_delta),
-			       (unsigned long)request,
+			       rqst_id,
 			       VM_PKT_DATA_INBAND,
 			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
 
 	if (ret != 0) {
+		/* Reclaim request ID to avoid leak of IDs */
+		vmbus_request_addr(&device->channel->requestor, rqst_id);
 		dev_err(dev, "Failed to create sub-channel: err=%d\n", ret);
 		return;
 	}
@@ -818,20 +835,31 @@ static int storvsc_execute_vstor_op(struct hv_device *device,
 {
 	struct vstor_packet *vstor_packet;
 	int ret, t;
+	u64 rqst_id;
 
 	vstor_packet = &request->vstor_packet;
 
 	init_completion(&request->wait_event);
 	vstor_packet->flags = REQUEST_COMPLETION_FLAG;
 
+	rqst_id = vmbus_next_request_id(&device->channel->requestor,
+					(unsigned long)request);
+	if (rqst_id == VMBUS_RQST_ERROR) {
+		dev_err(&device->device, "No request id available\n");
+		return -EAGAIN;
+	}
+
 	ret = vmbus_sendpacket(device->channel, vstor_packet,
 			       (sizeof(struct vstor_packet) -
 			       vmscsi_size_delta),
-			       (unsigned long)request,
+			       rqst_id,
 			       VM_PKT_DATA_INBAND,
 			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
-	if (ret != 0)
+	if (ret != 0) {
+		/* Reclaim request ID to avoid leak of IDs */
+		vmbus_request_addr(&device->channel->requestor, rqst_id);
 		return ret;
+	}
 
 	t = wait_for_completion_timeout(&request->wait_event, 5*HZ);
 	if (t == 0)
@@ -1233,9 +1261,17 @@ static void storvsc_on_channel_callback(void *context)
 	foreach_vmbus_pkt(desc, channel) {
 		void *packet = hv_pkt_data(desc);
 		struct storvsc_cmd_request *request;
+		u64 cmd_rqst;
 
-		request = (struct storvsc_cmd_request *)
-			((unsigned long)desc->trans_id);
+		cmd_rqst = vmbus_request_addr(&channel->requestor,
+					      desc->trans_id);
+		if (cmd_rqst == VMBUS_RQST_ERROR) {
+			dev_err(&device->device,
+				"Incorrect transaction id\n");
+			continue;
+		}
+
+		request = (struct storvsc_cmd_request *)(unsigned long)cmd_rqst;
 
 		if (request == &stor_device->init_request ||
 		    request == &stor_device->reset_request) {
@@ -1256,6 +1292,12 @@ static int storvsc_connect_to_vsp(struct hv_device *device, u32 ring_size,
 
 	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
 
+	/*
+	 * 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.
+	 */
+	device->channel->rqstor_size = scsi_driver.can_queue;
+
 	ret = vmbus_open(device->channel,
 			 ring_size,
 			 ring_size,
@@ -1369,6 +1411,7 @@ static int storvsc_do_io(struct hv_device *device,
 	int ret = 0;
 	const struct cpumask *node_mask;
 	int tgt_cpu;
+	u64 rqst_id;
 
 	vstor_packet = &request->vstor_packet;
 	stor_device = get_out_stor_device(device);
@@ -1463,6 +1506,13 @@ static int storvsc_do_io(struct hv_device *device,
 
 	vstor_packet->operation = VSTOR_OPERATION_EXECUTE_SRB;
 
+	rqst_id = vmbus_next_request_id(&outgoing_channel->requestor,
+					(unsigned long)request);
+	if (rqst_id == VMBUS_RQST_ERROR) {
+		dev_err(&device->device, "No request id available\n");
+		return -EAGAIN;
+	}
+
 	if (request->payload->range.len) {
 
 		ret = vmbus_sendpacket_mpb_desc(outgoing_channel,
@@ -1470,18 +1520,21 @@ static int storvsc_do_io(struct hv_device *device,
 				vstor_packet,
 				(sizeof(struct vstor_packet) -
 				vmscsi_size_delta),
-				(unsigned long)request);
+				rqst_id);
 	} else {
 		ret = vmbus_sendpacket(outgoing_channel, vstor_packet,
 			       (sizeof(struct vstor_packet) -
 				vmscsi_size_delta),
-			       (unsigned long)request,
+			       rqst_id,
 			       VM_PKT_DATA_INBAND,
 			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
 	}
 
-	if (ret != 0)
+	if (ret != 0) {
+		/* Reclaim request ID to avoid leak of IDs */
+		vmbus_request_addr(&outgoing_channel->requestor, rqst_id);
 		return ret;
+	}
 
 	atomic_inc(&stor_device->num_outstanding_req);
 
@@ -1562,7 +1615,7 @@ static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
 	struct storvsc_cmd_request *request;
 	struct vstor_packet *vstor_packet;
 	int ret, t;
-
+	u64 rqst_id;
 
 	stor_device = get_out_stor_device(device);
 	if (!stor_device)
@@ -1577,14 +1630,24 @@ static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
 	vstor_packet->flags = REQUEST_COMPLETION_FLAG;
 	vstor_packet->vm_srb.path_id = stor_device->path_id;
 
+	rqst_id = vmbus_next_request_id(&device->channel->requestor,
+					(unsigned long)&stor_device->reset_request);
+	if (rqst_id == VMBUS_RQST_ERROR) {
+		dev_err(&device->device, "No request id available\n");
+		return FAILED;
+	}
+
 	ret = vmbus_sendpacket(device->channel, vstor_packet,
 			       (sizeof(struct vstor_packet) -
 				vmscsi_size_delta),
-			       (unsigned long)&stor_device->reset_request,
+			       rqst_id,
 			       VM_PKT_DATA_INBAND,
 			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
-	if (ret != 0)
+	if (ret != 0) {
+		/* Reclaim request ID to avoid leak of IDs */
+		vmbus_request_addr(&device->channel->requestor, rqst_id);
 		return FAILED;
+	}
 
 	t = wait_for_completion_timeout(&request->wait_event, 5*HZ);
 	if (t == 0)
-- 
2.25.1

Re: [PATCH v4 2/3] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

[Wei Liu]

On Tue, Jun 30, 2020 at 08:12:20PM -0400, Andres Beltran wrote:
> Currently, pointers to guest memory are passed to Hyper-V as
> transaction IDs in storvsc. In the face of errors or malicious
> behavior in Hyper-V, storvsc 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 requests
> (transaction) IDs.
> 
> Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
> Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
> Cc: linux-scsi@vger.kernel.org

James and Martin, FYI I'm going to take this patch via hyperv tree
because it depends on the first patch.

Wei.

Re: [PATCH v4 2/3] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

[Martin K. Petersen]

Andres,

> Currently, pointers to guest memory are passed to Hyper-V as
> transaction IDs in storvsc. In the face of errors or malicious
> behavior in Hyper-V, storvsc 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
> requests (transaction) IDs.

Acked-by: Martin K. Petersen <martin.petersen@oracle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: [PATCH v4 2/3] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

[Nathan Chancellor]

Hi Andres,

On Tue, Jun 30, 2020 at 08:12:20PM -0400, Andres Beltran wrote:
> Currently, pointers to guest memory are passed to Hyper-V as
> transaction IDs in storvsc. In the face of errors or malicious
> behavior in Hyper-V, storvsc 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 requests
> (transaction) IDs.
> 
> Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
> Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
> Cc: linux-scsi@vger.kernel.org
> Signed-off-by: Andres Beltran <lkmlabelt@gmail.com>
> Reviewed-by: Michael Kelley <mikelley@microsoft.com>
> ---
> Changes in v2:
>         - Add casts to unsigned long to fix warnings on 32bit.
> 
>  drivers/scsi/storvsc_drv.c | 85 +++++++++++++++++++++++++++++++++-----
>  1 file changed, 74 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index 624467e2590a..6d2df1f0fe6d 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -399,6 +399,7 @@ static int storvsc_timeout = 180;
>  static struct scsi_transport_template *fc_transport_template;
>  #endif
>  
> +static struct scsi_host_template scsi_driver;
>  static void storvsc_on_channel_callback(void *context);
>  
>  #define STORVSC_MAX_LUNS_PER_TARGET			255
> @@ -698,6 +699,12 @@ static void handle_sc_creation(struct vmbus_channel *new_sc)
>  
>  	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
>  
> +	/*
> +	 * 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.
> +	 */
> +	new_sc->rqstor_size = scsi_driver.can_queue;
> +
>  	ret = vmbus_open(new_sc,
>  			 storvsc_ringbuffer_size,
>  			 storvsc_ringbuffer_size,
> @@ -726,6 +733,7 @@ static void  handle_multichannel_storage(struct hv_device *device, int max_chns)
>  	struct storvsc_cmd_request *request;
>  	struct vstor_packet *vstor_packet;
>  	int ret, t;
> +	u64 rqst_id;
>  
>  	/*
>  	 * If the number of CPUs is artificially restricted, such as
> @@ -760,14 +768,23 @@ static void  handle_multichannel_storage(struct hv_device *device, int max_chns)
>  	vstor_packet->flags = REQUEST_COMPLETION_FLAG;
>  	vstor_packet->sub_channel_count = num_sc;
>  
> +	rqst_id = vmbus_next_request_id(&device->channel->requestor,
> +					(unsigned long)request);
> +	if (rqst_id == VMBUS_RQST_ERROR) {
> +		dev_err(dev, "No request id available\n");
> +		return;
> +	}
> +
>  	ret = vmbus_sendpacket(device->channel, vstor_packet,
>  			       (sizeof(struct vstor_packet) -
>  			       vmscsi_size_delta),
> -			       (unsigned long)request,
> +			       rqst_id,
>  			       VM_PKT_DATA_INBAND,
>  			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
>  
>  	if (ret != 0) {
> +		/* Reclaim request ID to avoid leak of IDs */
> +		vmbus_request_addr(&device->channel->requestor, rqst_id);
>  		dev_err(dev, "Failed to create sub-channel: err=%d\n", ret);
>  		return;
>  	}
> @@ -818,20 +835,31 @@ static int storvsc_execute_vstor_op(struct hv_device *device,
>  {
>  	struct vstor_packet *vstor_packet;
>  	int ret, t;
> +	u64 rqst_id;
>  
>  	vstor_packet = &request->vstor_packet;
>  
>  	init_completion(&request->wait_event);
>  	vstor_packet->flags = REQUEST_COMPLETION_FLAG;
>  
> +	rqst_id = vmbus_next_request_id(&device->channel->requestor,
> +					(unsigned long)request);
> +	if (rqst_id == VMBUS_RQST_ERROR) {
> +		dev_err(&device->device, "No request id available\n");
> +		return -EAGAIN;
> +	}
> +
>  	ret = vmbus_sendpacket(device->channel, vstor_packet,
>  			       (sizeof(struct vstor_packet) -
>  			       vmscsi_size_delta),
> -			       (unsigned long)request,
> +			       rqst_id,
>  			       VM_PKT_DATA_INBAND,
>  			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
> -	if (ret != 0)
> +	if (ret != 0) {
> +		/* Reclaim request ID to avoid leak of IDs */
> +		vmbus_request_addr(&device->channel->requestor, rqst_id);
>  		return ret;
> +	}
>  
>  	t = wait_for_completion_timeout(&request->wait_event, 5*HZ);
>  	if (t == 0)
> @@ -1233,9 +1261,17 @@ static void storvsc_on_channel_callback(void *context)
>  	foreach_vmbus_pkt(desc, channel) {
>  		void *packet = hv_pkt_data(desc);
>  		struct storvsc_cmd_request *request;
> +		u64 cmd_rqst;
>  
> -		request = (struct storvsc_cmd_request *)
> -			((unsigned long)desc->trans_id);
> +		cmd_rqst = vmbus_request_addr(&channel->requestor,
> +					      desc->trans_id);
> +		if (cmd_rqst == VMBUS_RQST_ERROR) {
> +			dev_err(&device->device,
> +				"Incorrect transaction id\n");
> +			continue;
> +		}
> +
> +		request = (struct storvsc_cmd_request *)(unsigned long)cmd_rqst;
>  
>  		if (request == &stor_device->init_request ||
>  		    request == &stor_device->reset_request) {
> @@ -1256,6 +1292,12 @@ static int storvsc_connect_to_vsp(struct hv_device *device, u32 ring_size,
>  
>  	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
>  
> +	/*
> +	 * 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.
> +	 */
> +	device->channel->rqstor_size = scsi_driver.can_queue;
> +
>  	ret = vmbus_open(device->channel,
>  			 ring_size,
>  			 ring_size,
> @@ -1369,6 +1411,7 @@ static int storvsc_do_io(struct hv_device *device,
>  	int ret = 0;
>  	const struct cpumask *node_mask;
>  	int tgt_cpu;
> +	u64 rqst_id;
>  
>  	vstor_packet = &request->vstor_packet;
>  	stor_device = get_out_stor_device(device);
> @@ -1463,6 +1506,13 @@ static int storvsc_do_io(struct hv_device *device,
>  
>  	vstor_packet->operation = VSTOR_OPERATION_EXECUTE_SRB;
>  
> +	rqst_id = vmbus_next_request_id(&outgoing_channel->requestor,
> +					(unsigned long)request);
> +	if (rqst_id == VMBUS_RQST_ERROR) {
> +		dev_err(&device->device, "No request id available\n");
> +		return -EAGAIN;
> +	}
> +
>  	if (request->payload->range.len) {
>  
>  		ret = vmbus_sendpacket_mpb_desc(outgoing_channel,
> @@ -1470,18 +1520,21 @@ static int storvsc_do_io(struct hv_device *device,
>  				vstor_packet,
>  				(sizeof(struct vstor_packet) -
>  				vmscsi_size_delta),
> -				(unsigned long)request);
> +				rqst_id);
>  	} else {
>  		ret = vmbus_sendpacket(outgoing_channel, vstor_packet,
>  			       (sizeof(struct vstor_packet) -
>  				vmscsi_size_delta),
> -			       (unsigned long)request,
> +			       rqst_id,
>  			       VM_PKT_DATA_INBAND,
>  			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
>  	}
>  
> -	if (ret != 0)
> +	if (ret != 0) {
> +		/* Reclaim request ID to avoid leak of IDs */
> +		vmbus_request_addr(&outgoing_channel->requestor, rqst_id);
>  		return ret;
> +	}
>  
>  	atomic_inc(&stor_device->num_outstanding_req);
>  
> @@ -1562,7 +1615,7 @@ static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
>  	struct storvsc_cmd_request *request;
>  	struct vstor_packet *vstor_packet;
>  	int ret, t;
> -
> +	u64 rqst_id;
>  
>  	stor_device = get_out_stor_device(device);
>  	if (!stor_device)
> @@ -1577,14 +1630,24 @@ static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
>  	vstor_packet->flags = REQUEST_COMPLETION_FLAG;
>  	vstor_packet->vm_srb.path_id = stor_device->path_id;
>  
> +	rqst_id = vmbus_next_request_id(&device->channel->requestor,
> +					(unsigned long)&stor_device->reset_request);
> +	if (rqst_id == VMBUS_RQST_ERROR) {
> +		dev_err(&device->device, "No request id available\n");
> +		return FAILED;
> +	}
> +
>  	ret = vmbus_sendpacket(device->channel, vstor_packet,
>  			       (sizeof(struct vstor_packet) -
>  				vmscsi_size_delta),
> -			       (unsigned long)&stor_device->reset_request,
> +			       rqst_id,
>  			       VM_PKT_DATA_INBAND,
>  			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
> -	if (ret != 0)
> +	if (ret != 0) {
> +		/* Reclaim request ID to avoid leak of IDs */
> +		vmbus_request_addr(&device->channel->requestor, rqst_id);
>  		return FAILED;
> +	}
>  
>  	t = wait_for_completion_timeout(&request->wait_event, 5*HZ);
>  	if (t == 0)
> -- 
> 2.25.1
> 

This patch has landed in linux-next as of next-20200707 and now I can no
longer boot the WSL2 lightweight VM.

PS C:\Users\natec> wsl -d ubuntu
The virtual machine or container was forcefully exited.

$ git bisect log
# bad: [5b2a702f85b3285fcde0309aadacc13a36c70fc7] Add linux-next specific files for 20200707
# good: [bfe91da29bfad9941d5d703d45e29f0812a20724] Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
git bisect start 'origin/master' 'origin/stable'
# good: [885913a4d03f7f5fbd2c75121ea8c42f58185cc5] Merge remote-tracking branch 'crypto/master'
git bisect good 885913a4d03f7f5fbd2c75121ea8c42f58185cc5
# good: [4a902a00a463f60b1630577a32e142800707c576] Merge remote-tracking branch 'regulator/for-next'
git bisect good 4a902a00a463f60b1630577a32e142800707c576
# good: [e48c950eb83e19d532ea49112211b01c6210377a] Merge remote-tracking branch 'thunderbolt/next'
git bisect good e48c950eb83e19d532ea49112211b01c6210377a
# good: [0a299abc3a2127d9711517904a1e5c751985b5a5] Merge remote-tracking branch 'rtc/rtc-next'
git bisect good 0a299abc3a2127d9711517904a1e5c751985b5a5
# good: [6de62f5629875029fbd8d79d7fa9c45e8dbea966] kcov: make some symbols static
git bisect good 6de62f5629875029fbd8d79d7fa9c45e8dbea966
# bad: [9103b615924bf7594a7651a9777e0cf177201dbd] Merge remote-tracking branch 'auxdisplay/auxdisplay'
git bisect bad 9103b615924bf7594a7651a9777e0cf177201dbd
# good: [ed0e825a5c0f00aec12f79e8aef4b37dbb5a94f1] Merge remote-tracking branch 'kspp/for-next/kspp'
git bisect good ed0e825a5c0f00aec12f79e8aef4b37dbb5a94f1
# good: [563bebf9d7625b579a13b79a4981fdd3097d9bce] Merge remote-tracking branch 'nvmem/for-next'
git bisect good 563bebf9d7625b579a13b79a4981fdd3097d9bce
# good: [efd8e353a542e79995681d98a4849eeeb1ce3809] Drivers: hv: vmbus: Add vmbus_requestor data structure for VMBus hardening
git bisect good efd8e353a542e79995681d98a4849eeeb1ce3809
# good: [27586ca786a729cda6c807621a1494900a56e7bc] XArray: Handle retry entries within xas_find_marked
git bisect good 27586ca786a729cda6c807621a1494900a56e7bc
# bad: [11478f56f20e3be6d11043b501f3090375af4492] hv_netvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening
git bisect bad 11478f56f20e3be6d11043b501f3090375af4492
# bad: [8e569d774e1e73afabf1fbf40d11fcb8462ddffa] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardeninggit bisect bad 8e569d774e1e73afabf1fbf40d11fcb8462ddffa
# first bad commit: [8e569d774e1e73afabf1fbf40d11fcb8462ddffa] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

If I revert this commit, everything works fine:

PS C:\Users\natec> wsl --shutdown
PS C:\Users\natec> wsl -d ubuntu -- /bin/bash
nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ cat /proc/version
Linux version 5.8.0-rc4-next-20200707-microsoft-standard+ (nathan@Ryzen-9-3900X) (gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #1 SMP Tue Jul 7 16:35:06 MST 2020
nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ git -C ~/src/linux-next lo -2
0ff017dff922 (HEAD -> master) Revert "scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening"
5b2a702f85b3 (tag: next-20200707, origin/master, origin/HEAD) Add linux-next specific files for 20200707
nathan@Ryzen-9-3900X:/mnt/c/Users/natec$

The kernel was built using the following commands:

$ mkdir -p out/x86_64

$ curl -LSso out/x86_64/.config https://github.com/microsoft/WSL2-Linux-Kernel/raw/linux-msft-wsl-4.19.y/Microsoft/config-wsl

$ scripts/config --file out/x86_64/.config -d RAID6_PQ_BENCHMARK -e NET_9P_VIRTIO

$ make -skj"$(nproc)" O=out/x86_64 olddefconfig bzImage

I don't really know how to get more information than this as WSL seems
rather opaque but I am happy to provide any information.

Cheers,
Nathan

Re: [PATCH v4 2/3] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

[Wei Liu]

On Tue, Jul 07, 2020 at 04:47:00PM -0700, Nathan Chancellor wrote:
> Hi Andres,
> 
> On Tue, Jun 30, 2020 at 08:12:20PM -0400, Andres Beltran wrote:
> > Currently, pointers to guest memory are passed to Hyper-V as
> > transaction IDs in storvsc. In the face of errors or malicious
> > behavior in Hyper-V, storvsc 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 requests
> > (transaction) IDs.
> > 
> > Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
> > Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
> > Cc: linux-scsi@vger.kernel.org
> > Signed-off-by: Andres Beltran <lkmlabelt@gmail.com>
> > Reviewed-by: Michael Kelley <mikelley@microsoft.com>
> > ---
> > Changes in v2:
> >         - Add casts to unsigned long to fix warnings on 32bit.
> > 
> >  drivers/scsi/storvsc_drv.c | 85 +++++++++++++++++++++++++++++++++-----
> >  1 file changed, 74 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> > index 624467e2590a..6d2df1f0fe6d 100644
> > --- a/drivers/scsi/storvsc_drv.c
> > +++ b/drivers/scsi/storvsc_drv.c
> > @@ -399,6 +399,7 @@ static int storvsc_timeout = 180;
> >  static struct scsi_transport_template *fc_transport_template;
> >  #endif
> >  
> > +static struct scsi_host_template scsi_driver;
> >  static void storvsc_on_channel_callback(void *context);
> >  
> >  #define STORVSC_MAX_LUNS_PER_TARGET			255
> > @@ -698,6 +699,12 @@ static void handle_sc_creation(struct vmbus_channel *new_sc)
> >  
> >  	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
> >  
> > +	/*
> > +	 * 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.
> > +	 */
> > +	new_sc->rqstor_size = scsi_driver.can_queue;
> > +
> >  	ret = vmbus_open(new_sc,
> >  			 storvsc_ringbuffer_size,
> >  			 storvsc_ringbuffer_size,
> > @@ -726,6 +733,7 @@ static void  handle_multichannel_storage(struct hv_device *device, int max_chns)
> >  	struct storvsc_cmd_request *request;
> >  	struct vstor_packet *vstor_packet;
> >  	int ret, t;
> > +	u64 rqst_id;
> >  
> >  	/*
> >  	 * If the number of CPUs is artificially restricted, such as
> > @@ -760,14 +768,23 @@ static void  handle_multichannel_storage(struct hv_device *device, int max_chns)
> >  	vstor_packet->flags = REQUEST_COMPLETION_FLAG;
> >  	vstor_packet->sub_channel_count = num_sc;
> >  
> > +	rqst_id = vmbus_next_request_id(&device->channel->requestor,
> > +					(unsigned long)request);
> > +	if (rqst_id == VMBUS_RQST_ERROR) {
> > +		dev_err(dev, "No request id available\n");
> > +		return;
> > +	}
> > +
> >  	ret = vmbus_sendpacket(device->channel, vstor_packet,
> >  			       (sizeof(struct vstor_packet) -
> >  			       vmscsi_size_delta),
> > -			       (unsigned long)request,
> > +			       rqst_id,
> >  			       VM_PKT_DATA_INBAND,
> >  			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
> >  
> >  	if (ret != 0) {
> > +		/* Reclaim request ID to avoid leak of IDs */
> > +		vmbus_request_addr(&device->channel->requestor, rqst_id);
> >  		dev_err(dev, "Failed to create sub-channel: err=%d\n", ret);
> >  		return;
> >  	}
> > @@ -818,20 +835,31 @@ static int storvsc_execute_vstor_op(struct hv_device *device,
> >  {
> >  	struct vstor_packet *vstor_packet;
> >  	int ret, t;
> > +	u64 rqst_id;
> >  
> >  	vstor_packet = &request->vstor_packet;
> >  
> >  	init_completion(&request->wait_event);
> >  	vstor_packet->flags = REQUEST_COMPLETION_FLAG;
> >  
> > +	rqst_id = vmbus_next_request_id(&device->channel->requestor,
> > +					(unsigned long)request);
> > +	if (rqst_id == VMBUS_RQST_ERROR) {
> > +		dev_err(&device->device, "No request id available\n");
> > +		return -EAGAIN;
> > +	}
> > +
> >  	ret = vmbus_sendpacket(device->channel, vstor_packet,
> >  			       (sizeof(struct vstor_packet) -
> >  			       vmscsi_size_delta),
> > -			       (unsigned long)request,
> > +			       rqst_id,
> >  			       VM_PKT_DATA_INBAND,
> >  			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
> > -	if (ret != 0)
> > +	if (ret != 0) {
> > +		/* Reclaim request ID to avoid leak of IDs */
> > +		vmbus_request_addr(&device->channel->requestor, rqst_id);
> >  		return ret;
> > +	}
> >  
> >  	t = wait_for_completion_timeout(&request->wait_event, 5*HZ);
> >  	if (t == 0)
> > @@ -1233,9 +1261,17 @@ static void storvsc_on_channel_callback(void *context)
> >  	foreach_vmbus_pkt(desc, channel) {
> >  		void *packet = hv_pkt_data(desc);
> >  		struct storvsc_cmd_request *request;
> > +		u64 cmd_rqst;
> >  
> > -		request = (struct storvsc_cmd_request *)
> > -			((unsigned long)desc->trans_id);
> > +		cmd_rqst = vmbus_request_addr(&channel->requestor,
> > +					      desc->trans_id);
> > +		if (cmd_rqst == VMBUS_RQST_ERROR) {
> > +			dev_err(&device->device,
> > +				"Incorrect transaction id\n");
> > +			continue;
> > +		}
> > +
> > +		request = (struct storvsc_cmd_request *)(unsigned long)cmd_rqst;
> >  
> >  		if (request == &stor_device->init_request ||
> >  		    request == &stor_device->reset_request) {
> > @@ -1256,6 +1292,12 @@ static int storvsc_connect_to_vsp(struct hv_device *device, u32 ring_size,
> >  
> >  	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
> >  
> > +	/*
> > +	 * 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.
> > +	 */
> > +	device->channel->rqstor_size = scsi_driver.can_queue;
> > +
> >  	ret = vmbus_open(device->channel,
> >  			 ring_size,
> >  			 ring_size,
> > @@ -1369,6 +1411,7 @@ static int storvsc_do_io(struct hv_device *device,
> >  	int ret = 0;
> >  	const struct cpumask *node_mask;
> >  	int tgt_cpu;
> > +	u64 rqst_id;
> >  
> >  	vstor_packet = &request->vstor_packet;
> >  	stor_device = get_out_stor_device(device);
> > @@ -1463,6 +1506,13 @@ static int storvsc_do_io(struct hv_device *device,
> >  
> >  	vstor_packet->operation = VSTOR_OPERATION_EXECUTE_SRB;
> >  
> > +	rqst_id = vmbus_next_request_id(&outgoing_channel->requestor,
> > +					(unsigned long)request);
> > +	if (rqst_id == VMBUS_RQST_ERROR) {
> > +		dev_err(&device->device, "No request id available\n");
> > +		return -EAGAIN;
> > +	}
> > +
> >  	if (request->payload->range.len) {
> >  
> >  		ret = vmbus_sendpacket_mpb_desc(outgoing_channel,
> > @@ -1470,18 +1520,21 @@ static int storvsc_do_io(struct hv_device *device,
> >  				vstor_packet,
> >  				(sizeof(struct vstor_packet) -
> >  				vmscsi_size_delta),
> > -				(unsigned long)request);
> > +				rqst_id);
> >  	} else {
> >  		ret = vmbus_sendpacket(outgoing_channel, vstor_packet,
> >  			       (sizeof(struct vstor_packet) -
> >  				vmscsi_size_delta),
> > -			       (unsigned long)request,
> > +			       rqst_id,
> >  			       VM_PKT_DATA_INBAND,
> >  			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
> >  	}
> >  
> > -	if (ret != 0)
> > +	if (ret != 0) {
> > +		/* Reclaim request ID to avoid leak of IDs */
> > +		vmbus_request_addr(&outgoing_channel->requestor, rqst_id);
> >  		return ret;
> > +	}
> >  
> >  	atomic_inc(&stor_device->num_outstanding_req);
> >  
> > @@ -1562,7 +1615,7 @@ static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
> >  	struct storvsc_cmd_request *request;
> >  	struct vstor_packet *vstor_packet;
> >  	int ret, t;
> > -
> > +	u64 rqst_id;
> >  
> >  	stor_device = get_out_stor_device(device);
> >  	if (!stor_device)
> > @@ -1577,14 +1630,24 @@ static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
> >  	vstor_packet->flags = REQUEST_COMPLETION_FLAG;
> >  	vstor_packet->vm_srb.path_id = stor_device->path_id;
> >  
> > +	rqst_id = vmbus_next_request_id(&device->channel->requestor,
> > +					(unsigned long)&stor_device->reset_request);
> > +	if (rqst_id == VMBUS_RQST_ERROR) {
> > +		dev_err(&device->device, "No request id available\n");
> > +		return FAILED;
> > +	}
> > +
> >  	ret = vmbus_sendpacket(device->channel, vstor_packet,
> >  			       (sizeof(struct vstor_packet) -
> >  				vmscsi_size_delta),
> > -			       (unsigned long)&stor_device->reset_request,
> > +			       rqst_id,
> >  			       VM_PKT_DATA_INBAND,
> >  			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
> > -	if (ret != 0)
> > +	if (ret != 0) {
> > +		/* Reclaim request ID to avoid leak of IDs */
> > +		vmbus_request_addr(&device->channel->requestor, rqst_id);
> >  		return FAILED;
> > +	}
> >  
> >  	t = wait_for_completion_timeout(&request->wait_event, 5*HZ);
> >  	if (t == 0)
> > -- 
> > 2.25.1
> > 
> 
> This patch has landed in linux-next as of next-20200707 and now I can no
> longer boot the WSL2 lightweight VM.
> 
> PS C:\Users\natec> wsl -d ubuntu
> The virtual machine or container was forcefully exited.
> 
> $ git bisect log
> # bad: [5b2a702f85b3285fcde0309aadacc13a36c70fc7] Add linux-next specific files for 20200707
> # good: [bfe91da29bfad9941d5d703d45e29f0812a20724] Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
> git bisect start 'origin/master' 'origin/stable'
> # good: [885913a4d03f7f5fbd2c75121ea8c42f58185cc5] Merge remote-tracking branch 'crypto/master'
> git bisect good 885913a4d03f7f5fbd2c75121ea8c42f58185cc5
> # good: [4a902a00a463f60b1630577a32e142800707c576] Merge remote-tracking branch 'regulator/for-next'
> git bisect good 4a902a00a463f60b1630577a32e142800707c576
> # good: [e48c950eb83e19d532ea49112211b01c6210377a] Merge remote-tracking branch 'thunderbolt/next'
> git bisect good e48c950eb83e19d532ea49112211b01c6210377a
> # good: [0a299abc3a2127d9711517904a1e5c751985b5a5] Merge remote-tracking branch 'rtc/rtc-next'
> git bisect good 0a299abc3a2127d9711517904a1e5c751985b5a5
> # good: [6de62f5629875029fbd8d79d7fa9c45e8dbea966] kcov: make some symbols static
> git bisect good 6de62f5629875029fbd8d79d7fa9c45e8dbea966
> # bad: [9103b615924bf7594a7651a9777e0cf177201dbd] Merge remote-tracking branch 'auxdisplay/auxdisplay'
> git bisect bad 9103b615924bf7594a7651a9777e0cf177201dbd
> # good: [ed0e825a5c0f00aec12f79e8aef4b37dbb5a94f1] Merge remote-tracking branch 'kspp/for-next/kspp'
> git bisect good ed0e825a5c0f00aec12f79e8aef4b37dbb5a94f1
> # good: [563bebf9d7625b579a13b79a4981fdd3097d9bce] Merge remote-tracking branch 'nvmem/for-next'
> git bisect good 563bebf9d7625b579a13b79a4981fdd3097d9bce
> # good: [efd8e353a542e79995681d98a4849eeeb1ce3809] Drivers: hv: vmbus: Add vmbus_requestor data structure for VMBus hardening
> git bisect good efd8e353a542e79995681d98a4849eeeb1ce3809
> # good: [27586ca786a729cda6c807621a1494900a56e7bc] XArray: Handle retry entries within xas_find_marked
> git bisect good 27586ca786a729cda6c807621a1494900a56e7bc
> # bad: [11478f56f20e3be6d11043b501f3090375af4492] hv_netvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening
> git bisect bad 11478f56f20e3be6d11043b501f3090375af4492
> # bad: [8e569d774e1e73afabf1fbf40d11fcb8462ddffa] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardeninggit bisect bad 8e569d774e1e73afabf1fbf40d11fcb8462ddffa
> # first bad commit: [8e569d774e1e73afabf1fbf40d11fcb8462ddffa] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening
> 
> If I revert this commit, everything works fine:
> 
> PS C:\Users\natec> wsl --shutdown
> PS C:\Users\natec> wsl -d ubuntu -- /bin/bash
> nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ cat /proc/version
> Linux version 5.8.0-rc4-next-20200707-microsoft-standard+ (nathan@Ryzen-9-3900X) (gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #1 SMP Tue Jul 7 16:35:06 MST 2020
> nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ git -C ~/src/linux-next lo -2
> 0ff017dff922 (HEAD -> master) Revert "scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening"
> 5b2a702f85b3 (tag: next-20200707, origin/master, origin/HEAD) Add linux-next specific files for 20200707
> nathan@Ryzen-9-3900X:/mnt/c/Users/natec$
> 
> The kernel was built using the following commands:
> 
> $ mkdir -p out/x86_64
> 
> $ curl -LSso out/x86_64/.config https://github.com/microsoft/WSL2-Linux-Kernel/raw/linux-msft-wsl-4.19.y/Microsoft/config-wsl
> 
> $ scripts/config --file out/x86_64/.config -d RAID6_PQ_BENCHMARK -e NET_9P_VIRTIO
> 
> $ make -skj"$(nproc)" O=out/x86_64 olddefconfig bzImage
> 
> I don't really know how to get more information than this as WSL seems
> rather opaque but I am happy to provide any information.

Linux kernel uses Hyper-V's crash reporting facility to spit out
information when it dies. It is said that you can see that information
in the "Event Viewer" program.

(I've never tried this though -- not using WSL2)

Wei.

> 
> Cheers,
> Nathan

Re: [PATCH v4 2/3] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

[Wei Liu]

On Wed, Jul 08, 2020 at 09:21:05AM +0000, Wei Liu wrote:
[...]
> > If I revert this commit, everything works fine:
> > 
> > PS C:\Users\natec> wsl --shutdown
> > PS C:\Users\natec> wsl -d ubuntu -- /bin/bash
> > nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ cat /proc/version
> > Linux version 5.8.0-rc4-next-20200707-microsoft-standard+ (nathan@Ryzen-9-3900X) (gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #1 SMP Tue Jul 7 16:35:06 MST 2020
> > nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ git -C ~/src/linux-next lo -2
> > 0ff017dff922 (HEAD -> master) Revert "scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening"
> > 5b2a702f85b3 (tag: next-20200707, origin/master, origin/HEAD) Add linux-next specific files for 20200707
> > nathan@Ryzen-9-3900X:/mnt/c/Users/natec$
> > 
> > The kernel was built using the following commands:
> > 
> > $ mkdir -p out/x86_64
> > 
> > $ curl -LSso out/x86_64/.config https://github.com/microsoft/WSL2-Linux-Kernel/raw/linux-msft-wsl-4.19.y/Microsoft/config-wsl
> > 
> > $ scripts/config --file out/x86_64/.config -d RAID6_PQ_BENCHMARK -e NET_9P_VIRTIO
> > 
> > $ make -skj"$(nproc)" O=out/x86_64 olddefconfig bzImage
> > 
> > I don't really know how to get more information than this as WSL seems
> > rather opaque but I am happy to provide any information.
> 
> Linux kernel uses Hyper-V's crash reporting facility to spit out
> information when it dies. It is said that you can see that information
> in the "Event Viewer" program.
> 
> (I've never tried this though -- not using WSL2)
> 

If this doesn't work, another idea is to install a traditional VM on
Hyper-V and replace the kernel with your own.

With such setup, you should be able to add an emulated serial port to
the VM and grab more information.

Wei.

Re: [PATCH v4 2/3] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

[Wei Liu]

On Wed, Jul 08, 2020 at 09:25:12AM +0000, Wei Liu wrote:
> On Wed, Jul 08, 2020 at 09:21:05AM +0000, Wei Liu wrote:
> [...]
> > > If I revert this commit, everything works fine:
> > > 
> > > PS C:\Users\natec> wsl --shutdown
> > > PS C:\Users\natec> wsl -d ubuntu -- /bin/bash
> > > nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ cat /proc/version
> > > Linux version 5.8.0-rc4-next-20200707-microsoft-standard+ (nathan@Ryzen-9-3900X) (gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #1 SMP Tue Jul 7 16:35:06 MST 2020
> > > nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ git -C ~/src/linux-next lo -2
> > > 0ff017dff922 (HEAD -> master) Revert "scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening"
> > > 5b2a702f85b3 (tag: next-20200707, origin/master, origin/HEAD) Add linux-next specific files for 20200707
> > > nathan@Ryzen-9-3900X:/mnt/c/Users/natec$
> > > 
> > > The kernel was built using the following commands:
> > > 
> > > $ mkdir -p out/x86_64
> > > 
> > > $ curl -LSso out/x86_64/.config https://github.com/microsoft/WSL2-Linux-Kernel/raw/linux-msft-wsl-4.19.y/Microsoft/config-wsl
> > > 
> > > $ scripts/config --file out/x86_64/.config -d RAID6_PQ_BENCHMARK -e NET_9P_VIRTIO
> > > 
> > > $ make -skj"$(nproc)" O=out/x86_64 olddefconfig bzImage
> > > 
> > > I don't really know how to get more information than this as WSL seems
> > > rather opaque but I am happy to provide any information.
> > 
> > Linux kernel uses Hyper-V's crash reporting facility to spit out
> > information when it dies. It is said that you can see that information
> > in the "Event Viewer" program.
> > 
> > (I've never tried this though -- not using WSL2)
> > 
> 
> If this doesn't work, another idea is to install a traditional VM on
> Hyper-V and replace the kernel with your own.
> 
> With such setup, you should be able to add an emulated serial port to
> the VM and grab more information.

Hi Nathan, do you need more help on this?

MSFT is also working on reproducing this internally.

We're ~2 weeks away from the next merge window so it would be good if we
can get to the bottom of this as quickly as possible.

Wei.

> 
> Wei.

RE: [PATCH v4 2/3] scsi: storvsc: Use vmbus_requestor to generate transaction IDs for VMBus hardening

[Michael Kelley]

From: Wei Liu <wei.liu@kernel.org>  Sent: Friday, July 17, 2020 3:46 AM
> On Wed, Jul 08, 2020 at 09:25:12AM +0000, Wei Liu wrote:
> > On Wed, Jul 08, 2020 at 09:21:05AM +0000, Wei Liu wrote:
> > [...]
> > > > If I revert this commit, everything works fine:
> > > >
> > > > PS C:\Users\natec> wsl --shutdown
> > > > PS C:\Users\natec> wsl -d ubuntu -- /bin/bash
> > > > nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ cat /proc/version
> > > > Linux version 5.8.0-rc4-next-20200707-microsoft-standard+ (nathan@Ryzen-9-3900X)
> (gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #1 SMP Tue Jul
> 7 16:35:06 MST 2020
> > > > nathan@Ryzen-9-3900X:/mnt/c/Users/natec$ git -C ~/src/linux-next lo -2
> > > > 0ff017dff922 (HEAD -> master) Revert "scsi: storvsc: Use vmbus_requestor to
> generate transaction IDs for VMBus hardening"
> > > > 5b2a702f85b3 (tag: next-20200707, origin/master, origin/HEAD) Add linux-next specific
> files for 20200707
> > > > nathan@Ryzen-9-3900X:/mnt/c/Users/natec$
> > > >
> > > > The kernel was built using the following commands:
> > > >
> > > > $ mkdir -p out/x86_64
> > > >
> > > > $ curl -LSso out/x86_64/.config
> https://raw.githubusercontent.com/microsoft/WSL2-Linux-Kernel/linux-msft-wsl-4.19.y/Microsoft/config-wsl
> > > >
> > > > $ scripts/config --file out/x86_64/.config -d RAID6_PQ_BENCHMARK -e
> NET_9P_VIRTIO
> > > >
> > > > $ make -skj"$(nproc)" O=out/x86_64 olddefconfig bzImage
> > > >
> > > > I don't really know how to get more information than this as WSL seems
> > > > rather opaque but I am happy to provide any information.
> > >
> > > Linux kernel uses Hyper-V's crash reporting facility to spit out
> > > information when it dies. It is said that you can see that information
> > > in the "Event Viewer" program.
> > >
> > > (I've never tried this though -- not using WSL2)
> > >
> >
> > If this doesn't work, another idea is to install a traditional VM on
> > Hyper-V and replace the kernel with your own.
> >
> > With such setup, you should be able to add an emulated serial port to
> > the VM and grab more information.
> 
> Hi Nathan, do you need more help on this?
> 
> MSFT is also working on reproducing this internally.
> 
> We're ~2 weeks away from the next merge window so it would be good if we
> can get to the bottom of this as quickly as possible.
> 

On the Microsoft side we now have a repro of the problem when running
in WSLv2.  The symptoms match exactly what Nathan has reported.  We
will debug it from here.  Thanks for reporting this!

Michael