[PATCH] drm/virtio: reject mappable HOST3D blobs without host-visible memory

[Henry Martin <bsdhenrymartin@gmail.com>]

virtio_gpu_resource_create_blob_ioctl() -> verify_blob() validates
blob flags, memory type, context and alignment, but never checks
VIRTGPU_BLOB_FLAG_USE_MAPPABLE against vgdev->has_host_visible.

For blob_mem == VIRTGPU_BLOB_MEM_HOST3D the blob is created via
virtio_gpu_vram_create(), and on a device without host-visible
memory (plain virtio-gpu-pci,blob=on with no hostmem) the failure
comes too late: the GEM object has been allocated, a host resource
id taken and the create_blob command issued when
virtio_gpu_vram_map() returns -EINVAL, and the cleanup calls
virtio_gpu_vram_free(), which is a no-op while bo->created is still
false (the host response has not been processed yet).  Every such
blob creation permanently leaks the vram object and its resource
id; /dev/dri/renderD* is reachable by unprivileged users.

Guest-backed blobs (VIRTGPU_BLOB_MEM_GUEST and
VIRTGPU_BLOB_MEM_HOST3D_GUEST) mmap through the shmem path and do
not need host-visible memory, so only the HOST3D case is rejected.

Commit 036d28db1818a ("drm/virtio: release the GEM object on
virtio_gpu_vram_create() errors") fixed the sibling error paths but
missed this one.  Reject the impossible combination at ioctl entry,
making the failure mode unreachable.

This issue was discovered by Tencent CodeBuddy Security.

Cc: stable@vger.kernel.org
Fixes: 16845c5d5409 ("drm/virtio: implement blob resources: implement vram object")
Signed-off-by: Henry Martin <bsdhenrymartin@gmail.com>
---
 drivers/gpu/drm/virtio/virtgpu_ioctl.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index 81e70a12b3569..e3edade4a62dd 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -533,6 +533,11 @@ static int verify_blob(struct virtio_gpu_device *vgdev,
 			return -EINVAL;
 	}
 
+	if ((rc_blob->blob_flags & VIRTGPU_BLOB_FLAG_USE_MAPPABLE) &&
+	    rc_blob->blob_mem == VIRTGPU_BLOB_MEM_HOST3D &&
+	    !vgdev->has_host_visible)
+		return -EINVAL;
+
 	params->blob_mem = rc_blob->blob_mem;
 	params->size = rc_blob->size;
 	params->blob = true;
-- 
2.43.7