RE: [PATCH v3 3/6] Drivers: hv: vmbus: Copy the hv_message in vmbus_on_msg_dpc()

[Michael Kelley]

From: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Sent: Tuesday, December 8, 2020 11:08 PM
> 
> Since the message is in memory shared with the host, an erroneous or a
> malicious Hyper-V could 'corrupt' the message while vmbus_on_msg_dpc()
> or individual message handlers are executing.  To prevent it, copy the
> message into private memory.
> 
> Reported-by: Juan Vazquez <juvazq@xxxxxxxxxxxxx>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> ---
> Changes since v2:
>   - Revisit commit message and inline comment
> 
>  drivers/hv/vmbus_drv.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 44bcf9ccdaf5f..b1c5a89d75f9d 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1054,14 +1054,14 @@ void vmbus_on_msg_dpc(unsigned long data)
>  {
>  	struct hv_per_cpu_context *hv_cpu = (void *)data;
>  	void *page_addr = hv_cpu->synic_message_page;
> -	struct hv_message *msg = (struct hv_message *)page_addr +
> +	struct hv_message msg_copy, *msg = (struct hv_message *)page_addr +
>  				  VMBUS_MESSAGE_SINT;
>  	struct vmbus_channel_message_header *hdr;
>  	enum vmbus_channel_message_type msgtype;
>  	const struct vmbus_channel_message_table_entry *entry;
>  	struct onmessage_work_context *ctx;
> -	u32 message_type = msg->header.message_type;
>  	__u8 payload_size;
> +	u32 message_type;
> 
>  	/*
>  	 * 'enum vmbus_channel_message_type' is supposed to always be 'u32' as
> @@ -1070,11 +1070,20 @@ void vmbus_on_msg_dpc(unsigned long data)
>  	 */
>  	BUILD_BUG_ON(sizeof(enum vmbus_channel_message_type) != sizeof(u32));
> 
> +	/*
> +	 * Since the message is in memory shared with the host, an erroneous or
> +	 * malicious Hyper-V could modify the message while vmbus_on_msg_dpc()
> +	 * or individual message handlers are executing; to prevent this, copy
> +	 * the message into private memory.
> +	 */
> +	memcpy(&msg_copy, msg, sizeof(struct hv_message));
> +
> +	message_type = msg_copy.header.message_type;
>  	if (message_type == HVMSG_NONE)
>  		/* no msg */
>  		return;
> 
> -	hdr = (struct vmbus_channel_message_header *)msg->u.payload;
> +	hdr = (struct vmbus_channel_message_header *)msg_copy.u.payload;
>  	msgtype = hdr->msgtype;
> 
>  	trace_vmbus_on_msg_dpc(hdr);
> @@ -1084,7 +1093,7 @@ void vmbus_on_msg_dpc(unsigned long data)
>  		goto msg_handled;
>  	}
> 
> -	payload_size = msg->header.payload_size;
> +	payload_size = msg_copy.header.payload_size;
>  	if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT) {
>  		WARN_ONCE(1, "payload size is too large (%d)\n", payload_size);
>  		goto msg_handled;
> @@ -1106,7 +1115,7 @@ void vmbus_on_msg_dpc(unsigned long data)
>  			return;
> 
>  		INIT_WORK(&ctx->work, vmbus_onmessage_work);
> -		memcpy(&ctx->msg, msg, sizeof(msg->header) + payload_size);
> +		memcpy(&ctx->msg, &msg_copy, sizeof(msg->header) + payload_size);
> 
>  		/*
>  		 * The host can generate a rescind message while we
> --
> 2.25.1

Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>