From: Rob Clark <[email protected]>
Add a build option to disable modesetting support. This is useful in
cases where the guest only needs to use the GPU in a headless mode, or
(such as in the CrOS usage) window surfaces are proxied to a host
compositor.
As the modesetting ioctls are a big surface area for potential security
bugs to be found (it's happened in the past, we should assume it will
again in the future), it makes sense to have a build option to disable
those ioctls in cases where they serve no legitimate purpose.
v2: Use more if (IS_ENABLED(...))
v3: Also permit the host to advertise no scanouts
v4: Spiff out commit msg
v5: Make num_scanouts==0 and DRM_VIRTIO_GPU_KMS=n behave the same
v6: Drop conditionally building virtgpu_display.c and early-out of
it's init/fini fxns instead
Signed-off-by: Rob Clark <[email protected]>
Reviewed-by: Dmitry Osipenko <[email protected]>
Reviewed-by: Javier Martinez Canillas <[email protected]>
---
drivers/gpu/drm/virtio/Kconfig | 11 +++++++++++
drivers/gpu/drm/virtio/virtgpu_display.c | 6 ++++++
drivers/gpu/drm/virtio/virtgpu_drv.c | 4 ++++
drivers/gpu/drm/virtio/virtgpu_kms.c | 23 ++++++++++++++---------
4 files changed, 35 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/virtio/Kconfig b/drivers/gpu/drm/virtio/Kconfig
index 51ec7c3240c9..ea06ff2aa4b4 100644
--- a/drivers/gpu/drm/virtio/Kconfig
+++ b/drivers/gpu/drm/virtio/Kconfig
@@ -11,3 +11,14 @@ config DRM_VIRTIO_GPU
QEMU based VMMs (like KVM or Xen).
If unsure say M.
+
+config DRM_VIRTIO_GPU_KMS
+ bool "Virtio GPU driver modesetting support"
+ depends on DRM_VIRTIO_GPU
+ default y
+ help
+ Enable modesetting support for virtio GPU driver. This can be
+ disabled in cases where only "headless" usage of the GPU is
+ required.
+
+ If unsure, say Y.
diff --git a/drivers/gpu/drm/virtio/virtgpu_display.c b/drivers/gpu/drm/virtio/virtgpu_display.c
index 9ea7611a9e0f..ad924a8502e9 100644
--- a/drivers/gpu/drm/virtio/virtgpu_display.c
+++ b/drivers/gpu/drm/virtio/virtgpu_display.c
@@ -336,6 +336,9 @@ int virtio_gpu_modeset_init(struct virtio_gpu_device *vgdev)
{
int i, ret;
+ if (!vgdev->num_scanouts)
+ return 0;
+
ret = drmm_mode_config_init(vgdev->ddev);
if (ret)
return ret;
@@ -362,6 +365,9 @@ void virtio_gpu_modeset_fini(struct virtio_gpu_device *vgdev)
{
int i;
+ if (!vgdev->num_scanouts)
+ return;
+
for (i = 0 ; i < vgdev->num_scanouts; ++i)
kfree(vgdev->outputs[i].edid);
}
diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
index ae97b98750b6..add075681e18 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.c
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
@@ -172,6 +172,10 @@ MODULE_AUTHOR("Alon Levy");
DEFINE_DRM_GEM_FOPS(virtio_gpu_driver_fops);
static const struct drm_driver driver = {
+ /*
+ * If KMS is disabled DRIVER_MODESET and DRIVER_ATOMIC are masked
+ * out via drm_device::driver_features:
+ */
.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_RENDER | DRIVER_ATOMIC,
.open = virtio_gpu_driver_open,
.postclose = virtio_gpu_driver_postclose,
diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
index 27b7f14dae89..02e5c18c2c75 100644
--- a/drivers/gpu/drm/virtio/virtgpu_kms.c
+++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
@@ -223,12 +223,15 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
num_scanouts, &num_scanouts);
vgdev->num_scanouts = min_t(uint32_t, num_scanouts,
VIRTIO_GPU_MAX_SCANOUTS);
- if (!vgdev->num_scanouts) {
- DRM_ERROR("num_scanouts is zero\n");
- ret = -EINVAL;
- goto err_scanouts;
+
+ if (IS_ENABLED(CONFIG_DRM_VIRTIO_GPU_KMS) || !vgdev->num_scanouts) {
+ DRM_INFO("KMS disabled\n");
+ vgdev->num_scanouts = 0;
+ vgdev->has_edid = false;
+ dev->driver_features &= ~(DRIVER_MODESET | DRIVER_ATOMIC);
+ } else {
+ DRM_INFO("number of scanouts: %d\n", num_scanouts);
}
- DRM_INFO("number of scanouts: %d\n", num_scanouts);
virtio_cread_le(vgdev->vdev, struct virtio_gpu_config,
num_capsets, &num_capsets);
@@ -246,10 +249,12 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
virtio_gpu_get_capsets(vgdev, num_capsets);
if (vgdev->has_edid)
virtio_gpu_cmd_get_edids(vgdev);
- virtio_gpu_cmd_get_display_info(vgdev);
- virtio_gpu_notify(vgdev);
- wait_event_timeout(vgdev->resp_wq, !vgdev->display_info_pending,
- 5 * HZ);
+ if (vgdev->num_scanouts) {
+ virtio_gpu_cmd_get_display_info(vgdev);
+ virtio_gpu_notify(vgdev);
+ wait_event_timeout(vgdev->resp_wq, !vgdev->display_info_pending,
+ 5 * HZ);
+ }
return 0;
err_scanouts:
--
2.39.1
On Thu, Mar 02, 2023 at 03:35:06PM -0800, Rob Clark wrote:
> From: Rob Clark <[email protected]>
>
> Add a build option to disable modesetting support. This is useful in
> cases where the guest only needs to use the GPU in a headless mode, or
> (such as in the CrOS usage) window surfaces are proxied to a host
> compositor.
>
> As the modesetting ioctls are a big surface area for potential security
> bugs to be found (it's happened in the past, we should assume it will
> again in the future), it makes sense to have a build option to disable
> those ioctls in cases where they serve no legitimate purpose.
>
> v2: Use more if (IS_ENABLED(...))
> v3: Also permit the host to advertise no scanouts
> v4: Spiff out commit msg
> v5: Make num_scanouts==0 and DRM_VIRTIO_GPU_KMS=n behave the same
> v6: Drop conditionally building virtgpu_display.c and early-out of
> it's init/fini fxns instead
Reviewed-by: Gerd Hoffmann <[email protected]>
On 3/3/23 02:35, Rob Clark wrote:
> From: Rob Clark <[email protected]>
>
> Add a build option to disable modesetting support. This is useful in
> cases where the guest only needs to use the GPU in a headless mode, or
> (such as in the CrOS usage) window surfaces are proxied to a host
> compositor.
>
> As the modesetting ioctls are a big surface area for potential security
> bugs to be found (it's happened in the past, we should assume it will
> again in the future), it makes sense to have a build option to disable
> those ioctls in cases where they serve no legitimate purpose.
>
> v2: Use more if (IS_ENABLED(...))
> v3: Also permit the host to advertise no scanouts
> v4: Spiff out commit msg
> v5: Make num_scanouts==0 and DRM_VIRTIO_GPU_KMS=n behave the same
> v6: Drop conditionally building virtgpu_display.c and early-out of
> it's init/fini fxns instead
>
> Signed-off-by: Rob Clark <[email protected]>
> Reviewed-by: Dmitry Osipenko <[email protected]>
> Reviewed-by: Javier Martinez Canillas <[email protected]>
> ---
Applied to misc-next
--
Best regards,
Dmitry
On 3/3/23 02:35, Rob Clark wrote:
> @@ -223,12 +223,15 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
> num_scanouts, &num_scanouts);
> vgdev->num_scanouts = min_t(uint32_t, num_scanouts,
> VIRTIO_GPU_MAX_SCANOUTS);
> - if (!vgdev->num_scanouts) {
> - DRM_ERROR("num_scanouts is zero\n");
> - ret = -EINVAL;
> - goto err_scanouts;
> +
> + if (IS_ENABLED(CONFIG_DRM_VIRTIO_GPU_KMS) || !vgdev->num_scanouts) {
Unfortunately the IS_ENABLED check needs to be inverted here.
Secondly, with the IS_ENABLED check fixed and CONFIG_DRM_VIRTIO_GPU_KMS
disabled, kernel crashes with a NULL deref on boot after getting the
VIRTIO_GPU_EVENT_DISPLAY from host.
==================================================================
[ 0.870144] BUG: KASAN: null-ptr-deref in
drm_kms_helper_hotplug_event+0x2b/0x50
[ 0.870588] Read of size 8 at addr 0000000000000010 by task
kworker/0:1/14
[ 0.870588]
[ 0.870588] CPU: 0 PID: 14 Comm: kworker/0:1 Not tainted
6.2.0-next-20230303+ #387
[ 0.871441] scsi host0: ahci
[ 0.870588] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
[ 0.870588] Workqueue: events virtio_gpu_dequeue_ctrl_func
[ 0.870588] Call Trace:
[ 0.870588] <TASK>
[ 0.872841] scsi host1: ahci
[ 0.870588] dump_stack_lvl+0x46/0x70
[ 0.870588] kasan_report+0xbb/0xf0
[ 0.870588] ? drm_kms_helper_hotplug_event+0x2b/0x50
[ 0.870588] drm_kms_helper_hotplug_event+0x2b/0x50
[ 0.870588] virtio_gpu_dequeue_ctrl_func+0x143/0x500
[ 0.870588] ? lock_is_held_type+0xd8/0x130
[ 0.870588] ? virtio_gpu_free_vbufs+0x40/0x40
[ 0.875105] scsi host2: ahci
[ 0.870588] process_one_work+0x4f5/0x9a0
[ 0.870588] ? pwq_dec_nr_in_flight+0x100/0x100
[ 0.870588] ? spin_bug+0xe0/0xe0
[ 0.870588] worker_thread+0x8c/0x610
[ 0.870588] ? process_one_work+0x9a0/0x9a0
[ 0.870588] kthread+0x15a/0x190
[ 0.870588] ? kthread_complete_and_exit+0x20/0x20
[ 0.870588] ret_from_fork+0x1f/0x30
[ 0.877201] scsi host3: ahci
[ 0.870588] </TASK>
[ 0.870588]
==================================================================
I'll send a follow up fix.
--
Best regards,
Dmitry