Drivers: hv: vmbus: Copy the hv_message in vmbus_on_msg_dpc()

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@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20201209070827.29335-4-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 9749cbc..4b0f206 100644 (file)
--- 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