From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E82C2C18E5B for ; Thu, 2 Apr 2020 01:23:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BFDE220675 for ; Thu, 2 Apr 2020 01:23:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733222AbgDBBXY (ORCPT ); Wed, 1 Apr 2020 21:23:24 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:49440 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732462AbgDBBXX (ORCPT ); Wed, 1 Apr 2020 21:23:23 -0400 Received: from DGGEMS406-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 4C5354C9FB92A9B66279; Thu, 2 Apr 2020 09:23:17 +0800 (CST) Received: from [127.0.0.1] (10.173.223.60) by DGGEMS406-HUB.china.huawei.com (10.3.19.206) with Microsoft SMTP Server id 14.3.487.0; Thu, 2 Apr 2020 09:23:12 +0800 Subject: Re: [PATCH net v2] veth: xdp: use head instead of hard_start To: Jesper Dangaard Brouer , Toshiaki Makita CC: , , , , , , , , , , , , , , , , References: <20200331060641.79999-1-maowenan@huawei.com> <7a1d55ad-1427-67fe-f204-4d4a0ab2c4b1@gmail.com> <20200401181419.7acd2aa6@carbon> From: maowenan Message-ID: <348d193e-cc68-3be4-ae39-dd73dbba635c@huawei.com> Date: Thu, 2 Apr 2020 09:23:11 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <20200401181419.7acd2aa6@carbon> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.173.223.60] X-CFilter-Loop: Reflected Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2020/4/2 0:15, Jesper Dangaard Brouer wrote: > On Tue, 31 Mar 2020 15:16:22 +0900 > Toshiaki Makita wrote: > >> On 2020/03/31 15:06, Mao Wenan wrote: >>> xdp.data_hard_start is equal to first address of >>> struct xdp_frame, which is mentioned in >>> convert_to_xdp_frame(). But the pointer hard_start >>> in veth_xdp_rcv_one() is 32 bytes offset of frame, >>> so it should use head instead of hard_start to >>> set xdp.data_hard_start. Otherwise, if BPF program >>> calls helper_function such as bpf_xdp_adjust_head, it >>> will be confused for xdp_frame_end. >> >> I think you should discuss this more with Jesper before >> submitting v2. >> He does not like this to be included now due to merge conflict risk. >> Basically I agree with him that we don't need to hurry with this fix. >> >> Toshiaki Makita >> >>> >>> Fixes: 9fc8d518d9d5 ("veth: Handle xdp_frames in xdp napi ring") >>> Signed-off-by: Mao Wenan >>> --- >>> v2: add fixes tag, as well as commit log. >>> drivers/net/veth.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/net/veth.c b/drivers/net/veth.c >>> index d4cbb9e8c63f..5ea550884bf8 100644 >>> --- a/drivers/net/veth.c >>> +++ b/drivers/net/veth.c >>> @@ -506,7 +506,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, >>> struct xdp_buff xdp; >>> u32 act; >>> >>> - xdp.data_hard_start = hard_start; >>> + xdp.data_hard_start = head; >>> xdp.data = frame->data; >>> xdp.data_end = frame->data + frame->len; >>> xdp.data_meta = frame->data - frame->metasize; >>> > > Below is the patch that I have in my queue. I've added a Reported-by > tag to give you some credit, even-though I already had plans to fix > this, as part of my XDP frame_sz work. thanks for reported-by. Actually the fault is found by reviewing veth code two weeks ago, when I debugged another warning bpf_warn_invalid_xdp_action associated veth module, and there is no chance to send such fix patch as quick. > > > [PATCH RFC net-next] veth: adjust hard_start offset on redirect XDP frames > > When native XDP redirect into a veth device, the frame arrives in the > xdp_frame structure. It is then processed in veth_xdp_rcv_one(), > which can run a new XDP bpf_prog on the packet. Doing so requires > converting xdp_frame to xdp_buff, but the tricky part is that > xdp_frame memory area is located in the top (data_hard_start) memory > area that xdp_buff will point into. > > The current code tried to protect the xdp_frame area, by assigning > xdp_buff.data_hard_start past this memory. This results in 32 bytes > less headroom to expand into via BPF-helper bpf_xdp_adjust_head(). > > This protect step is actually not needed, because BPF-helper > bpf_xdp_adjust_head() already reserve this area, and don't allow > BPF-prog to expand into it. Thus, it is safe to point data_hard_start > directly at xdp_frame memory area. > > Cc: Toshiaki Makita > Fixes: 9fc8d518d9d5 ("veth: Handle xdp_frames in xdp napi ring") > Reported-by: Mao Wenan > Signed-off-by: Jesper Dangaard Brouer > --- > drivers/net/veth.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/net/veth.c b/drivers/net/veth.c > index 8cdc4415fa70..2edc04a8ab8e 100644 > --- a/drivers/net/veth.c > +++ b/drivers/net/veth.c > @@ -493,13 +493,15 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, > struct veth_xdp_tx_bq *bq) > { > void *hard_start = frame->data - frame->headroom; > - void *head = hard_start - sizeof(struct xdp_frame); > int len = frame->len, delta = 0; > struct xdp_frame orig_frame; > struct bpf_prog *xdp_prog; > unsigned int headroom; > struct sk_buff *skb; > > + /* bpf_xdp_adjust_head() assures BPF cannot access xdp_frame area */ > + hard_start -= sizeof(struct xdp_frame); > + > rcu_read_lock(); > xdp_prog = rcu_dereference(rq->xdp_prog); > if (likely(xdp_prog)) { > @@ -521,7 +523,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, > break; > case XDP_TX: > orig_frame = *frame; > - xdp.data_hard_start = head; > xdp.rxq->mem = frame->mem; > if (unlikely(veth_xdp_tx(rq->dev, &xdp, bq) < 0)) { > trace_xdp_exception(rq->dev, xdp_prog, act); > @@ -533,7 +534,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, > goto xdp_xmit; > case XDP_REDIRECT: > orig_frame = *frame; > - xdp.data_hard_start = head; > xdp.rxq->mem = frame->mem; > if (xdp_do_redirect(rq->dev, &xdp, xdp_prog)) { > frame = &orig_frame; > @@ -555,7 +555,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, > rcu_read_unlock(); > > headroom = sizeof(struct xdp_frame) + frame->headroom - delta; > - skb = veth_build_skb(head, headroom, len, 0); > + skb = veth_build_skb(hard_start, headroom, len, 0); > if (!skb) { > xdp_return_frame(frame); > goto err; > >