On 2023/12/21 10:33, Jason Wang wrote: > On Wed, Dec 20, 2023 at 8:45 PM Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote: >> >> On 2023/12/12 12:35, Jason Wang wrote:>>>> +done: >>>>>> + backend.fd = tun_alloc(); >>>>>> + assert(backend.fd >= 0); >>>>>> + vdev_info_init(&dev, features); >>>>>> + vq_info_add(&dev, 256); >>>>>> + run_test(&dev, &dev.vqs[0], delayed, batch, reset, nbufs); >>>>> >>>>> I'd expect we are testing some basic traffic here. E.g can we use a >>>>> packet socket then we can test both tx and rx? >>>> >>>> Yes, only rx for tun is tested. >>>> Do you have an idea how to test the tx too? As I am not familar enough >>>> with vhost_net and tun yet. >>> >>> Maybe you can have a packet socket to bind to the tun/tap. Then you can test: >>> >>> 1) TAP RX: by write a packet via virtqueue through vhost_net and read >>> it from packet socket >>> 2) TAP TX: by write via packet socket and read it from the virtqueue >>> through vhost_net >> >> When implementing the TAP TX by adding VHOST_NET_F_VIRTIO_NET_HDR, >> I found one possible use of uninitialized data in vhost_net_build_xdp(). >> >> And vhost_hlen is set to sizeof(struct virtio_net_hdr_mrg_rxbuf) and >> sock_hlen is set to zero in vhost_net_set_features() for both tx and rx >> queue. >> >> For vhost_net_build_xdp() called by handle_tx_copy(): >> >> The (gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) checking below may cause a >> read of uninitialized data if sock_hlen is zero. > > Which data is uninitialized here? The 'gso', as the sock_hlen is zero, there is no copying for: copied = copy_page_from_iter(alloc_frag->page, alloc_frag->offset + offsetof(struct tun_xdp_hdr, gso), sock_hlen, from); > >> >> And it seems vhost_hdr is skipped in get_tx_bufs(): >> https://elixir.bootlin.com/linux/latest/source/drivers/vhost/net.c#L616 >> >> static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq, >> struct iov_iter *from) >> { >> ... >> buflen += SKB_DATA_ALIGN(len + pad); >> alloc_frag->offset = ALIGN((u64)alloc_frag->offset, SMP_CACHE_BYTES); >> if (unlikely(!vhost_net_page_frag_refill(net, buflen, >> alloc_frag, GFP_KERNEL))) >> return -ENOMEM; >> >> buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset; >> copied = copy_page_from_iter(alloc_frag->page, >> alloc_frag->offset + >> offsetof(struct tun_xdp_hdr, gso), >> sock_hlen, from); >> if (copied != sock_hlen) >> return -EFAULT; >> >> hdr = buf; >> gso = &hdr->gso; >> >> if ((gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && >> vhost16_to_cpu(vq, gso->csum_start) + >> vhost16_to_cpu(vq, gso->csum_offset) + 2 > >> vhost16_to_cpu(vq, gso->hdr_len)) { >> ... >> } >> >> I seems the handle_tx_copy() does not handle the VHOST_NET_F_VIRTIO_NET_HDR >> case correctly, Or do I miss something obvious here? > > In get_tx_bufs() we did: > > *len = init_iov_iter(vq, &msg->msg_iter, nvq->vhost_hlen, *out); > > Which covers this case? It does not seems to cover it, as the vhost_hdr is just skipped without any handling in get_tx_bufs(): https://elixir.bootlin.com/linux/v6.7-rc6/source/drivers/vhost/net.c#L616 > > Thanks