From patchwork Wed Jan 17 10:17:37 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jesper Dangaard Brouer X-Patchwork-Id: 862158 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 3zM31m0FMrz9sNV for ; Wed, 17 Jan 2018 21:17:48 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752409AbeAQKRo (ORCPT ); Wed, 17 Jan 2018 05:17:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49716 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752338AbeAQKRm (ORCPT ); Wed, 17 Jan 2018 05:17:42 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 88D4CC058EB0; Wed, 17 Jan 2018 10:17:42 +0000 (UTC) Received: from firesoul.localdomain (ovpn-200-22.brq.redhat.com [10.40.200.22]) by smtp.corp.redhat.com (Postfix) with ESMTP id 161E76EE70; Wed, 17 Jan 2018 10:17:39 +0000 (UTC) Received: from [192.168.42.3] (localhost [IPv6:::1]) by firesoul.localdomain (Postfix) with ESMTP id 043B530736C72; Wed, 17 Jan 2018 11:17:38 +0100 (CET) Subject: [bpf-next PATCH] samples/bpf: xdp2skb_meta comment explain why pkt-data pointers are invalidated From: Jesper Dangaard Brouer To: Daniel Borkmann , Alexei Starovoitov Cc: netdev@vger.kernel.org, Jesper Dangaard Brouer Date: Wed, 17 Jan 2018 11:17:37 +0100 Message-ID: <151618425790.21568.15367415527676574003.stgit@firesoul> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Wed, 17 Jan 2018 10:17:42 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Improve the 'unknown reason' comment, with an actual explaination of why the ctx pkt-data pointers need to be loaded after the helper function bpf_xdp_adjust_meta(). Based on the explaination Daniel gave. Fixes: 36e04a2d78d9 ("samples/bpf: xdp2skb_meta shows transferring info from XDP to SKB") Reported-by: Daniel Borkmann Signed-off-by: Jesper Dangaard Brouer --- samples/bpf/xdp2skb_meta_kern.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/samples/bpf/xdp2skb_meta_kern.c b/samples/bpf/xdp2skb_meta_kern.c index 12e1024069c2..0c12048ac79f 100644 --- a/samples/bpf/xdp2skb_meta_kern.c +++ b/samples/bpf/xdp2skb_meta_kern.c @@ -35,15 +35,17 @@ int _xdp_mark(struct xdp_md *ctx) void *data, *data_end; int ret; - /* Reserve space in-front data pointer for our meta info. + /* Reserve space in-front of data pointer for our meta info. * (Notice drivers not supporting data_meta will fail here!) */ ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(*meta)); if (ret < 0) return XDP_ABORTED; - /* For some unknown reason, these ctx pointers must be read - * after bpf_xdp_adjust_meta, else verifier will reject prog. + /* Notice: Kernel-side verifier requires that loading of + * ctx->data MUST happen _after_ helper bpf_xdp_adjust_meta(), + * as pkt-data pointers are invalidated. Helpers that require + * this are determined/marked by bpf_helper_changes_pkt_data() */ data = (void *)(unsigned long)ctx->data;