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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8AB49C433EF for ; Fri, 15 Jul 2022 12:52:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233088AbiGOMwh (ORCPT ); Fri, 15 Jul 2022 08:52:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35228 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229480AbiGOMwe (ORCPT ); Fri, 15 Jul 2022 08:52:34 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 4D2B93F33E for ; Fri, 15 Jul 2022 05:52:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1657889552; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Bn/sNX4ffBRjzNPcS5PuemUEc8YHP6wFTJGbO8K7n3w=; b=WpbSfuuHowHosc0Bba5f0Ag39IqrH7Vlzs3Kl5Pa/aQnaNPg1kxjBtcDTEErgMGVlyAOg6 /pHNhx79fZ+gVb6Uu6OgZdB4gHRyLyescDXVgmgtu8OhoMl664JNumN5gFHzlpYrFXX8Zs JDRhTQ81JUGc0xyJanaAtGpJ8/mgkqk= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-312-C_Sj2__HN3qa7syAvV4R6g-1; Fri, 15 Jul 2022 08:52:29 -0400 X-MC-Unique: C_Sj2__HN3qa7syAvV4R6g-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E7BD285A581; Fri, 15 Jul 2022 12:52:28 +0000 (UTC) Received: from samus.usersys.redhat.com (unknown [10.43.17.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7138F40315D; Fri, 15 Jul 2022 12:52:27 +0000 (UTC) Date: Fri, 15 Jul 2022 14:52:25 +0200 From: Artem Savkov To: Alexei Starovoitov Cc: Song Liu , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , bpf , Networking , open list , Andrea Arcangeli , dvacek@redhat.com Subject: Re: [RFC PATCH bpf-next 3/4] bpf: add bpf_panic() helper Message-ID: Mail-Followup-To: Alexei Starovoitov , Song Liu , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , bpf , Networking , open list , Andrea Arcangeli , dvacek@redhat.com References: <20220711083220.2175036-1-asavkov@redhat.com> <20220711083220.2175036-4-asavkov@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 13, 2022 at 03:20:22PM -0700, Alexei Starovoitov wrote: > On Wed, Jul 13, 2022 at 6:31 AM Artem Savkov wrote: > > > > On Tue, Jul 12, 2022 at 11:08:54AM -0700, Alexei Starovoitov wrote: > > > On Tue, Jul 12, 2022 at 10:53 AM Song Liu wrote: > > > > > > > > > > > > > > +BPF_CALL_1(bpf_panic, const char *, msg) > > > > > +{ > > > > > + panic(msg); > > > > > > > > I think we should also check > > > > > > > > capable(CAP_SYS_BOOT) && destructive_ebpf_enabled() > > > > > > > > here. Or at least, destructive_ebpf_enabled(). Otherwise, we > > > > may trigger panic after the sysctl is disabled. > > > > > > > > In general, I don't think sysctl is a good API, as it is global, and > > > > the user can easily forget to turn it back off. If possible, I would > > > > rather avoid adding new BPF related sysctls. > > > > > > +1. New syscal isn't warranted here. > > > Just CAP_SYS_BOOT would be enough here. > > > > Point taken, I'll remove sysctl knob in any further versions. > > > > > Also full blown panic() seems unnecessary. > > > If the motivation is to get a memory dump then crash_kexec() helper > > > would be more suitable. > > > If the goal is to reboot the system then the wrapper of sys_reboot() > > > is better. > > > Unfortunately the cover letter lacks these details. > > > > The main goal is to get the memory dump, so crash_kexec() should be enough. > > However panic() is a bit more versatile and it's consequences are configurable > > to some extent. Are there any downsides to using it? > > versatile? In what sense? That it does a lot more than kexec? > That's a disadvantage. > We should provide bpf with minimal building blocks and let > bpf program decide what to do. > If dmesg (that is part of panic) is useful it should be its > own kfunc. > If halt is necessary -> separate kfunc as well. > reboot -> another kfunc. > > Also panic() is not guaranteed to do kexec and just > panic is not what you stated is the goal of the helper. Alright, if the aim is to provide the smallest building blocks then crash_kexec() is a better choice. > > > > > Why this destructive action cannot be delegated to user space? > > > > Going through userspace adds delays and makes it impossible to hit "exactly > > the right moment" thus making it unusable in most cases. > > What would be an example of that? > kexec is not instant either. With kexec at least the thread it got called in is in a proper state. I guess it is possible to achieve this by signalling userspace to do kexec/panic and then block the thread somehow but that won't work in a single-cpu case. Or am I missing something? -- Artem