From: Andrea Parri (Microsoft) <parri.and...@gmail.com> 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 <juv...@microsoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.and...@gmail.com>
> ---
> 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 <mikel...@microsoft.com>
