From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH] ebpf: emit correct src_reg for conditional jumps Date: Fri, 11 Sep 2015 10:45:29 +0200 Message-ID: <55F294A9.9020005@iogearbox.net> References: <1441931107-17673-1-git-send-email-tycho.andersen@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: Tycho Andersen , Alexei Starovoitov , "David S. Miller" Return-path: Received: from www62.your-server.de ([213.133.104.62]:39438 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751064AbbIKIpi (ORCPT ); Fri, 11 Sep 2015 04:45:38 -0400 In-Reply-To: <1441931107-17673-1-git-send-email-tycho.andersen@canonical.com> Sender: netdev-owner@vger.kernel.org List-ID: On 09/11/2015 02:25 AM, Tycho Andersen wrote: > Instead of always emitting BPF_REG_X, let's emit BPF_REG_X only when the > source actually is BPF_X. This causes programs generated by the classic > converter to not be importable via bpf(), as the eBPF verifier checks that > the src_reg is correct or 0. While not a problem yet, this will be a > problem when BPF_PROG_DUMP lands, and we can potentially dump and re-import > programs generated by the converter. > > Signed-off-by: Tycho Andersen > CC: Alexei Starovoitov > CC: Daniel Borkmann I think the description at the beginning could have been a bit clearer. I.e. it's safe to zero insn->src_reg for BPF_SRC(fp->code) that is not X, because we can either have X or K for classic jump compares, and in case of K we're only interested in the immediate value, but not a possible src_reg, of course, so eBPF converter should have zeroed it. Yeah, it was never really the aim of the converter to cover something like that requirement you seem to have: load classic BPF -> transform into eBPF -> dump that eBPF result to uspace -> load that eBPF via bpf(2) Anyway, it doesn't cause an issue in the current code as stated, but it's good if we fix it up nevertheless. Looks good to me: Acked-by: Daniel Borkmann