[Qemu-devel] [RFC v2 04/12] Add vhost-user-backend

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

Create a vhost-user-backend object that holds a connection to a
vhost-user backend and can be referenced from virtio devices that
support it. See later patches for input & gpu usage.

A chardev can be specified to communicate with the vhost-user backend,
ex: -chardev socket,id=char0,path=/tmp/foo.sock -object
vhost-user-backend,id=vuid,chardev=char0.

Alternatively, an executable with its arguments may be given as 'cmd'
property, ex: -object
vhost-user-backend,id=vui,cmd="./vhost-user-input /dev/input..". The
executable is then spawn and, by convention, the vhost-user socket is
passed as fd=3. It may be considered a security breach to allow
creating processes that may execute arbitrary executables, so this may
be restricted to some known executables (via signature etc) or
directory.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 include/sysemu/vhost-user-backend.h |  58 +++++
 backends/vhost-user.c               | 330 ++++++++++++++++++++++++++++
 vl.c                                |   3 +-
 backends/Makefile.objs              |   4 +
 4 files changed, 394 insertions(+), 1 deletion(-)
 create mode 100644 include/sysemu/vhost-user-backend.h
 create mode 100644 backends/vhost-user.c

diff --git a/include/sysemu/vhost-user-backend.h b/include/sysemu/vhost-user-backend.h
new file mode 100644
index 0000000000..890db176fd
--- /dev/null
+++ b/include/sysemu/vhost-user-backend.h
@@ -0,0 +1,58 @@
+/*
+ * QEMU vhost-user backend
+ *
+ * Copyright (C) 2018 Red Hat Inc
+ *
+ * Authors:
+ *  Marc-André Lureau <marcandre.lureau@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+#ifndef QEMU_VHOST_USER_BACKEND_H
+#define QEMU_VHOST_USER_BACKEND_H
+
+#include "qom/object.h"
+#include "exec/memory.h"
+#include "qemu/option.h"
+#include "qemu/bitmap.h"
+#include "hw/virtio/vhost.h"
+#include "chardev/char-fe.h"
+#include "io/channel.h"
+
+#define TYPE_VHOST_USER_BACKEND "vhost-user-backend"
+#define VHOST_USER_BACKEND(obj) \
+    OBJECT_CHECK(VhostUserBackend, (obj), TYPE_VHOST_USER_BACKEND)
+#define VHOST_USER_BACKEND_GET_CLASS(obj) \
+    OBJECT_GET_CLASS(VhostUserBackendClass, (obj), TYPE_VHOST_USER_BACKEND)
+#define VHOST_USER_BACKEND_CLASS(klass) \
+    OBJECT_CLASS_CHECK(VhostUserBackendClass, (klass), TYPE_VHOST_USER_BACKEND)
+
+typedef struct VhostUserBackend VhostUserBackend;
+typedef struct VhostUserBackendClass VhostUserBackendClass;
+
+struct VhostUserBackendClass {
+    ObjectClass parent_class;
+};
+
+struct VhostUserBackend {
+    /* private */
+    Object parent;
+
+    char *cmd;
+    char *chr_name;
+
+    CharBackend chr;
+    struct vhost_dev dev;
+    QIOChannel *child;
+    VirtIODevice *vdev;
+    bool started;
+    bool completed;
+};
+
+int vhost_user_backend_dev_init(VhostUserBackend *b, VirtIODevice *vdev,
+                                unsigned nvqs, Error **errp);
+void vhost_user_backend_start(VhostUserBackend *b);
+void vhost_user_backend_stop(VhostUserBackend *b);
+
+#endif
diff --git a/backends/vhost-user.c b/backends/vhost-user.c
new file mode 100644
index 0000000000..ae40dee373
--- /dev/null
+++ b/backends/vhost-user.c
@@ -0,0 +1,330 @@
+/*
+ * QEMU vhost-user backend
+ *
+ * Copyright (C) 2018 Red Hat Inc
+ *
+ * Authors:
+ *  Marc-André Lureau <marcandre.lureau@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+
+#include "qemu/osdep.h"
+#include "hw/qdev.h"
+#include "qapi/error.h"
+#include "qapi/qmp/qerror.h"
+#include "qemu/error-report.h"
+#include "qom/object_interfaces.h"
+#include "sysemu/vhost-user-backend.h"
+#include "sysemu/kvm.h"
+#include "io/channel-command.h"
+#include "hw/virtio/virtio-bus.h"
+
+static bool
+ioeventfd_enabled(void)
+{
+    return kvm_enabled() && kvm_eventfds_enabled();
+}
+
+int
+vhost_user_backend_dev_init(VhostUserBackend *b, VirtIODevice *vdev,
+                            unsigned nvqs, Error **errp)
+{
+    int ret;
+
+    assert(!b->vdev && vdev);
+
+    if (!ioeventfd_enabled()) {
+        error_setg(errp, "vhost initialization failed: requires kvm");
+        return -1;
+    }
+
+    b->vdev = vdev;
+    b->dev.nvqs = nvqs;
+    b->dev.vqs = g_new(struct vhost_virtqueue, nvqs);
+
+    ret = vhost_dev_init(&b->dev, &b->chr, VHOST_BACKEND_TYPE_USER, 0);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "vhost initialization failed");
+        return -1;
+    }
+
+    return 0;
+}
+
+void
+vhost_user_backend_start(VhostUserBackend *b)
+{
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(b->vdev)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+    int ret, i ;
+
+    if (b->started) {
+        return;
+    }
+
+    if (!k->set_guest_notifiers) {
+        error_report("binding does not support guest notifiers");
+        return;
+    }
+
+    ret = vhost_dev_enable_notifiers(&b->dev, b->vdev);
+    if (ret < 0) {
+        return;
+    }
+
+    ret = k->set_guest_notifiers(qbus->parent, b->dev.nvqs, true);
+    if (ret < 0) {
+        error_report("Error binding guest notifier");
+        goto err_host_notifiers;
+    }
+
+    b->dev.acked_features = b->vdev->guest_features;
+    ret = vhost_dev_start(&b->dev, b->vdev);
+    if (ret < 0) {
+        error_report("Error start vhost dev");
+        goto err_guest_notifiers;
+    }
+
+    /* guest_notifier_mask/pending not used yet, so just unmask
+     * everything here.  virtio-pci will do the right thing by
+     * enabling/disabling irqfd.
+     */
+    for (i = 0; i < b->dev.nvqs; i++) {
+        vhost_virtqueue_mask(&b->dev, b->vdev,
+                             b->dev.vq_index + i, false);
+    }
+
+    b->started = true;
+    return;
+
+err_guest_notifiers:
+    k->set_guest_notifiers(qbus->parent, b->dev.nvqs, false);
+err_host_notifiers:
+    vhost_dev_disable_notifiers(&b->dev, b->vdev);
+}
+
+void
+vhost_user_backend_stop(VhostUserBackend *b)
+{
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(b->vdev)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+    int ret = 0;
+
+    if (!b->started) {
+        return;
+    }
+
+    vhost_dev_stop(&b->dev, b->vdev);
+
+    if (k->set_guest_notifiers) {
+        ret = k->set_guest_notifiers(qbus->parent,
+                                     b->dev.nvqs, false);
+        if (ret < 0) {
+            error_report("vhost guest notifier cleanup failed: %d", ret);
+        }
+    }
+    assert(ret >= 0);
+
+    vhost_dev_disable_notifiers(&b->dev, b->vdev);
+    b->started = false;
+}
+
+static int
+vhost_user_backend_spawn_cmd(VhostUserBackend *b, int vhostfd, Error **errp)
+{
+    int devnull = open("/dev/null", O_RDWR);
+    pid_t pid;
+
+    assert(!b->child);
+
+    if (!b->cmd) {
+        error_setg_errno(errp, errno, "Missing cmd property");
+        return -1;
+    }
+    if (devnull < 0) {
+        error_setg_errno(errp, errno, "Unable to open /dev/null");
+        return -1;
+    }
+
+    pid = qemu_fork(errp);
+    if (pid < 0) {
+        close(devnull);
+        return -1;
+    }
+
+    if (pid == 0) { /* child */
+        int fd, maxfd = sysconf(_SC_OPEN_MAX);
+
+        dup2(devnull, STDIN_FILENO);
+        dup2(devnull, STDOUT_FILENO);
+        dup2(vhostfd, 3);
+
+        signal(SIGINT, SIG_IGN);
+
+        for (fd = 4; fd < maxfd; fd++) {
+            close(fd);
+        }
+
+        execlp("/bin/sh", "sh", "-c", b->cmd, NULL);
+        _exit(1);
+    }
+
+    b->child = QIO_CHANNEL(qio_channel_command_new_pid(devnull, devnull, pid));
+
+    return 0;
+}
+
+static void
+vhost_user_backend_complete(UserCreatable *uc, Error **errp)
+{
+    VhostUserBackend *b = VHOST_USER_BACKEND(uc);
+    Chardev *chr;
+
+    if (!!b->chr_name + !!b->cmd != 1) {
+        error_setg(errp, "You may specificy only one of 'chardev' or 'cmd'.");
+        return;
+    }
+
+    if (b->chr_name) {
+        chr = qemu_chr_find(b->chr_name);
+        if (chr == NULL) {
+            error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
+                      "Chardev '%s' not found", b->chr_name);
+            return;
+        }
+
+        if (!qemu_chr_fe_init(&b->chr, chr, errp)) {
+            return;
+        }
+    } else {
+        int sv[2];
+
+        if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
+            error_setg_errno(errp, errno, "socketpair() failed");
+            return;
+        }
+
+        chr = CHARDEV(object_new(TYPE_CHARDEV_SOCKET));
+        if (!chr || qemu_chr_add_client(chr, sv[0]) == -1) {
+            error_setg(errp, "Failed to make socket chardev");
+            object_unref(OBJECT(chr));
+            return;
+        }
+
+        if (!qemu_chr_fe_init(&b->chr, chr, errp)) {
+            return;
+        }
+
+        vhost_user_backend_spawn_cmd(b, sv[1], errp);
+
+        close(sv[1]);
+    }
+
+    b->completed = true;
+    /* could vhost_dev_init() happen here, so early vhost-user message
+     * can be exchanged */
+}
+
+static char *get_cmd(Object *obj, Error **errp)
+{
+    VhostUserBackend *b = VHOST_USER_BACKEND(obj);
+
+    return g_strdup(b->cmd);
+}
+
+static void set_cmd(Object *obj, const char *str, Error **errp)
+{
+    VhostUserBackend *b = VHOST_USER_BACKEND(obj);
+
+    if (b->child) {
+        error_setg(errp, "cannot change property value");
+        return;
+    }
+
+    g_free(b->cmd);
+    b->cmd = g_strdup(str);
+}
+
+static void set_chardev(Object *obj, const char *value, Error **errp)
+{
+    VhostUserBackend *b = VHOST_USER_BACKEND(obj);
+
+    if (b->completed) {
+        error_setg(errp, QERR_PERMISSION_DENIED);
+    } else {
+        g_free(b->chr_name);
+        b->chr_name = g_strdup(value);
+    }
+}
+
+static char *get_chardev(Object *obj, Error **errp)
+{
+    VhostUserBackend *b = VHOST_USER_BACKEND(obj);
+    Chardev *chr = qemu_chr_fe_get_driver(&b->chr);
+
+    if (chr && chr->label) {
+        return g_strdup(chr->label);
+    }
+
+    return NULL;
+}
+
+static void vhost_user_backend_init(Object *obj)
+{
+    object_property_add_str(obj, "cmd", get_cmd, set_cmd, NULL);
+    object_property_add_str(obj, "chardev", get_chardev, set_chardev, NULL);
+}
+
+static void vhost_user_backend_finalize(Object *obj)
+{
+    VhostUserBackend *b = VHOST_USER_BACKEND(obj);
+
+    g_free(b->dev.vqs);
+    g_free(b->cmd);
+    g_free(b->chr_name);
+
+    qemu_chr_fe_deinit(&b->chr, true);
+
+    if (b->child) {
+        object_unref(OBJECT(b->child));
+    }
+}
+
+static bool
+vhost_user_backend_can_be_deleted(UserCreatable *uc)
+{
+    return true;
+}
+
+static void
+vhost_user_backend_class_init(ObjectClass *oc, void *data)
+{
+    UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
+
+    ucc->complete = vhost_user_backend_complete;
+    ucc->can_be_deleted = vhost_user_backend_can_be_deleted;
+}
+
+static const TypeInfo vhost_user_backend_info = {
+    .name = TYPE_VHOST_USER_BACKEND,
+    .parent = TYPE_OBJECT,
+    .instance_size = sizeof(VhostUserBackend),
+    .instance_init = vhost_user_backend_init,
+    .instance_finalize = vhost_user_backend_finalize,
+    .class_size = sizeof(VhostUserBackendClass),
+    .class_init = vhost_user_backend_class_init,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_USER_CREATABLE },
+        { }
+    }
+};
+
+static void register_types(void)
+{
+    type_register_static(&vhost_user_backend_info);
+}
+
+type_init(register_types);
diff --git a/vl.c b/vl.c
index c4fe25560c..4ed094dd71 100644
--- a/vl.c
+++ b/vl.c
@@ -2833,7 +2833,8 @@ static bool object_create_initial(const char *type)
     }
 
 #if defined(CONFIG_VHOST_USER) && defined(CONFIG_LINUX)
-    if (g_str_equal(type, "cryptodev-vhost-user")) {
+    if (g_str_equal(type, "cryptodev-vhost-user") ||
+        g_str_equal(type, "vhost-user-backend")) {
         return false;
     }
 #endif
diff --git a/backends/Makefile.objs b/backends/Makefile.objs
index ad7c0325ed..bac27de11b 100644
--- a/backends/Makefile.objs
+++ b/backends/Makefile.objs
@@ -16,3 +16,7 @@ common-obj-$(call land,$(CONFIG_VHOST_USER),$(CONFIG_LINUX)) += \
 endif
 
 common-obj-$(CONFIG_LINUX) += hostmem-memfd.o
+
+ifdef CONFIG_LINUX
+common-obj-$(CONFIG_VIRTIO) += vhost-user.o
+endif
-- 
2.17.1.906.g10fd178552