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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8E45AC433EF for ; Fri, 29 Oct 2021 22:48:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6E68260200 for ; Fri, 29 Oct 2021 22:48:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231132AbhJ2WvX (ORCPT ); Fri, 29 Oct 2021 18:51:23 -0400 Received: from mga02.intel.com ([134.134.136.20]:5762 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229441AbhJ2WvW (ORCPT ); Fri, 29 Oct 2021 18:51:22 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10152"; a="217951556" X-IronPort-AV: E=Sophos;i="5.87,194,1631602800"; d="scan'208";a="217951556" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Oct 2021 15:48:51 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.87,194,1631602800"; d="scan'208";a="448274950" Received: from gupta-dev2.jf.intel.com (HELO gupta-dev2.localdomain) ([10.54.74.119]) by orsmga006.jf.intel.com with ESMTP; 29 Oct 2021 15:48:50 -0700 Date: Fri, 29 Oct 2021 15:51:09 -0700 From: Pawan Gupta To: "Russell King (Oracle)" Cc: Mark Rutland , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Kees Cook , Andrew Morton , Masahiro Yamada , "Peter Zijlstra (Intel)" , Sami Tolvanen , Colin Ian King , Frederic Weisbecker , Mike Rapoport , YiFei Zhu , "Steven Rostedt (VMware)" , Viresh Kumar , Andrey Konovalov , Wang Kefeng , Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= , Nathan Chancellor , Nick Desaulniers , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Alexei Starovoitov , Daniel Borkmann , bpf@vger.kernel.org Subject: Re: [PATCH v2 1/2] arch/Kconfig: Make CONFIG_CPU_SPECTRE available for all architectures Message-ID: <20211029225109.d3m2q4kuuzhzs2cv@gupta-dev2.localdomain> References: <232b692cd79e4f6e4c3ee7055b5f02792a28d2c4.1635383031.git.pawan.kumar.gupta@linux.intel.com> <20211028134918.GB48435@lakrids.cambridge.arm.com> <20211028193658.7n2oehp6yogyqbwq@gupta-dev2.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 29.10.2021 11:08, Russell King (Oracle) wrote: >On Thu, Oct 28, 2021 at 12:36:58PM -0700, Pawan Gupta wrote: >> Isn't ARM already using CPU_SPECTRE for selecting things: >> >> config HARDEN_BRANCH_PREDICTOR >> bool "Harden the branch predictor against aliasing attacks" if EXPERT >> depends on CPU_SPECTRE >> >> This was the whole motivation for doing the same for x86. >> >> Adding a condition for all architectures is also okay, but its going to >> a little messier: >> >> config BPF_UNPRIV_DEFAULT_OFF >> default y if X86 || ARM || ... > >It doesn't have to be (but sadly we end up repeating "DEFAULT"): > >config BPF_UNPRIV_DEFAULT_OFF_DEFAULT > bool > >config BPF_UNPRIV_DEFAULT_OFF > bool "Disable unprivileged BPF by default" > default BPF_UNPRIV_DEFAULT_OFF_DEFAULT > >Then architectures can select BPF_UNPRIV_DEFAULT_OFF_DEFAULT if they >wish this to be defaulted to "yes". Looks like we are settling on unconditional 'default y' for now [1]. I have sent a v3 with 'default y' [2]. >However, please note that this has limited use given that the >BPF_UNPRIV_DEFAULT_OFF option has been around for a while now. Any >existing configuration that mentions this symbol will override any >default specified in the Kconfig files if the option is user-visible. Yes, existing configurations will have to toggle this manually. However, many distros already have BPF_UNPRIV_DEFAULT_OFF=y in their configuration. >So, IMHO, defaults need to be set correctly from the point in time >that the option is introduced. Agree. [1] https://lore.kernel.org/lkml/6130e55f-4d84-5ada-4e86-5b678e3eaf5e@iogearbox.net/ [2] https://lore.kernel.org/lkml/0ace9ce3f97656d5f62d11093ad7ee81190c3c25.1635535215.git.pawan.kumar.gupta@linux.intel.com/