ivshmem: add check on protocol version in QEMU

Send a protocol version as the first message from server, clients must
close communication if they don't support this protocol version.  Older
QEMUs should be fine with this change in the protocol since they
overrides their own vm_id on reception of an id associated to no
eventfd.

Signed-off-by: David Marchand <[email protected]>
Signed-off-by: Marc-André Lureau <[email protected]>
[use fifo_update_and_get()]
Reviewed-by: Claudio Fontana <[email protected]>

Author: David Marchand

contrib/ivshmem-client/ivshmem-client.c

@@ -206,10 +206,17 @@ ivshmem_client_connect(IvshmemClient *client)
         goto err_close;
     }
 
-    /* first, we expect our index + a fd == -1 */
+    /* first, we expect a protocol version */
+    if (ivshmem_client_read_one_msg(client, &tmp, &fd) < 0 ||
+        (tmp != IVSHMEM_PROTOCOL_VERSION) || fd != -1) {
+        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server\n");
+        goto err_close;
+    }
+
+    /* then, we expect our index + a fd == -1 */
     if (ivshmem_client_read_one_msg(client, &client->local.id, &fd) < 0 ||
         client->local.id < 0 || fd != -1) {
-        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server\n");
+        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server (2)\n");
         goto err_close;
     }
     IVSHMEM_CLIENT_DEBUG(client, "our_id=%ld\n", client->local.id);
@@ -221,7 +228,7 @@ ivshmem_client_connect(IvshmemClient *client)
         if (fd >= 0) {
             close(fd);
         }
-        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server (2)\n");
+        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server (3)\n");
         goto err_close;
     }
     client->shm_fd = fd;

contrib/ivshmem-client/ivshmem-client.h

@@ -23,6 +23,7 @@
 #include <sys/select.h>
 
 #include "qemu/queue.h"
+#include "hw/misc/ivshmem.h"
 
 /**
  * Maximum number of notification vectors supported by the client

contrib/ivshmem-server/ivshmem-server.c

@@ -101,6 +101,15 @@ ivshmem_server_send_initial_info(IvshmemServer *server, IvshmemServerPeer *peer)
 {
     int ret;
 
+    /* send our protocol version first */
+    ret = ivshmem_server_send_one_msg(peer->sock_fd, IVSHMEM_PROTOCOL_VERSION,
+                                      -1);
+    if (ret < 0) {
+        IVSHMEM_SERVER_DEBUG(server, "cannot send version: %s\n",
+                             strerror(errno));
+        return -1;
+    }
+
     /* send the peer id to the client */
     ret = ivshmem_server_send_one_msg(peer->sock_fd, peer->id, -1);
     if (ret < 0) {

contrib/ivshmem-server/ivshmem-server.h

@@ -33,6 +33,7 @@
 
 #include "qemu/event_notifier.h"
 #include "qemu/queue.h"
+#include "hw/misc/ivshmem.h"
 
 /**
  * Maximum number of notification vectors supported by the server

docs/specs/ivshmem_device_spec.txt

@@ -64,6 +64,8 @@ It creates a shared memory object then waits for clients to connect on a unix
 socket.
 
 For each client (QEMU process) that connects to the server:
+- the server sends a protocol version, if client does not support it, the client
+  closes the communication,
 - the server assigns an ID for this client and sends this ID to him as the first
   message,
 - the server sends a fd to the shared memory object to this client,
@@ -86,9 +88,10 @@ been provided in qemu.git/contrib/ivshmem-client for debug.
 
 *QEMU as an ivshmem client*
 
-At initialisation, when creating the ivshmem device, QEMU gets its ID from the
-server then makes it available through BAR0 IVPosition register for the VM to
-use (see 'PCI device registers' subsection).
+At initialisation, when creating the ivshmem device, QEMU first receives a
+protocol version and closes communication with server if it does not match.
+Then, QEMU gets its ID from the server then makes it available through BAR0
+IVPosition register for the VM to use (see 'PCI device registers' subsection).
 QEMU then uses the fd to the shared memory to map it to BAR2.
 eventfds for all other clients received from the server are stored to implement
 BAR0 Doorbell register (see 'PCI device registers' subsection).

hw/misc/ivshmem.c

@@ -27,6 +27,8 @@
 #include "qemu/fifo8.h"
 #include "sysemu/char.h"
 
+#include "hw/misc/ivshmem.h"
+
 #include <sys/mman.h>
 #include <sys/types.h>
 #include <limits.h>
@@ -596,6 +598,31 @@ static void ivshmem_read(void *opaque, const uint8_t *buf, int size)
     }
 }
 
+static void ivshmem_check_version(void *opaque, const uint8_t * buf, int size)
+{
+    IVShmemState *s = opaque;
+    int tmp;
+    long version;
+
+    if (!fifo_update_and_get(s, buf, size,
+                             &version, sizeof(version))) {
+        return;
+    }
+
+    tmp = qemu_chr_fe_get_msgfd(s->server_chr);
+    if (tmp != -1 || version != IVSHMEM_PROTOCOL_VERSION) {
+        fprintf(stderr, "incompatible version, you are connecting to a ivshmem-"
+                "server using a different protocol please check your setup\n");
+        qemu_chr_delete(s->server_chr);
+        s->server_chr = NULL;
+        return;
+    }
+
+    IVSHMEM_DPRINTF("version check ok, switch to real chardev handler\n");
+    qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive, ivshmem_read,
+                          ivshmem_event, s);
+}
+
 /* Select the MSI-X vectors used by device.
  * ivshmem maps events to vectors statically, so
  * we just enable all vectors on init and after reset. */
@@ -769,8 +796,8 @@ static void pci_ivshmem_realize(PCIDevice *dev, Error **errp)
 
         s->eventfd_chr = g_malloc0(s->vectors * sizeof(CharDriverState *));
 
-        qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive, ivshmem_read,
-                     ivshmem_event, s);
+        qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive,
+                              ivshmem_check_version, ivshmem_event, s);
     } else {
         /* just map the file immediately, we're not using a server */
         int fd;

include/hw/misc/ivshmem.h

@@ -0,0 +1,25 @@
+
+/*
+ * Inter-VM Shared Memory PCI device.
+ *
+ * Author:
+ *      Cam Macdonell <[email protected]>
+ *
+ * Based On: cirrus_vga.c
+ *          Copyright (c) 2004 Fabrice Bellard
+ *          Copyright (c) 2004 Makoto Suzuki (suzu)
+ *
+ *      and rtl8139.c
+ *          Copyright (c) 2006 Igor Kovalenko
+ *
+ * This code is licensed under the GNU GPL v2.
+ *
+ * Contributions after 2012-01-13 are licensed under the terms of the
+ * GNU GPL, version 2 or (at your option) any later version.
+ */
+#ifndef IVSHMEM_H
+#define IVSHMEM_H
+
+#define IVSHMEM_PROTOCOL_VERSION 0
+
+#endif /* IVSHMEM_H */