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=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 D095CC31E40 for ; Mon, 12 Aug 2019 18:06:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A1B3720842 for ; Mon, 12 Aug 2019 18:06:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="Pm/i5Awv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726823AbfHLSGU (ORCPT ); Mon, 12 Aug 2019 14:06:20 -0400 Received: from mail-pg1-f194.google.com ([209.85.215.194]:45968 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726506AbfHLSGS (ORCPT ); Mon, 12 Aug 2019 14:06:18 -0400 Received: by mail-pg1-f194.google.com with SMTP id o13so49865290pgp.12 for ; Mon, 12 Aug 2019 11:06:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=rkibUktkvDgvPaKzYudHbYv+zssBd9BVnmORpFK5sIM=; b=Pm/i5Awv+1wuEbKCQ7G++ON3VKecwo9wUwhdvsO4/YJuS0PP46xEGXgjDrgypxhqB1 EZV4gC90lHCBFaUda5gn9lCqVYK6cLjjx5kHklAdvsV2533UxL6qZ5kKKQzdvSVhs8Yt 0baWDmWgyor6cBKVrjFhiZkMlh5ninhAuqSQ8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=rkibUktkvDgvPaKzYudHbYv+zssBd9BVnmORpFK5sIM=; b=nBbdx50kVmrmKMPlL0AbD2F+rMV4KddpMlwC204JafADo6eB9xDKiuyt+Lj1XcMPGC sBeuoDSpTsU/l9jOmPjWWpc9mTLbVHiVfuQJoSPdraObHbai3w8bAOaF8yoDC3B6o+fq XiBqfSxvfQBeljWtTp0wf0hWTmlRWzZfINFtEukU4S8EzOUsiMBM23+bDPdEJcS20pkf C6pl/UbRlsFz960/vnpoCKfcNK2L0XWohh3OJXNXEIA/yk4sV/TIO9gAUd1qopRuJpUR 6/4+wzzoRJMLT/x6I8hzWCgRiM9geS7/W4+X3GPkTGs2Bymc18FVlbByt6yeojPCrVAF G8YA== X-Gm-Message-State: APjAAAUw2C3SPk8FMD+7DywTDflxvIizq1p2NVjYPEbxckcWHQAIHowg FZiG5uq+4dvdfcpHsOiXWzJjgZckl1Q= X-Google-Smtp-Source: APXvYqwQNDswXhVN3SaWKfAiYZ9PFI71KTrt+N0THLB/Nq1EPI+5R3W5gBzqamh9PGPVG4SeUiySkA== X-Received: by 2002:aa7:8218:: with SMTP id k24mr35369354pfi.221.1565631483928; Mon, 12 Aug 2019 10:38:03 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id u3sm153514pjn.5.2019.08.12.10.38.03 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 12 Aug 2019 10:38:03 -0700 (PDT) Date: Mon, 12 Aug 2019 10:38:02 -0700 From: Kees Cook To: Paul Chaignon Cc: Andy Lutomirski , Will Drewry , linux-kernel@vger.kernel.org Subject: Re: [PATCH] seccomp: allow BPF_MOD ALU instructions Message-ID: <201908121035.06695C79F@keescook> References: <20190809182621.GA4074@Nover> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 11, 2019 at 10:58:33AM +0200, Paul Chaignon wrote: > On Fri, Aug 9, 2019 at 8:26 PM Paul Chaignon wrote: > > > > We need BPF_MOD to match system calls against whitelists encoded as 32-bit > > bit arrays. The selection of the syscall's bit in the appropriate bit > > array requires a modulo operation such that X = 1 << nr % 32. > > Of course, X = 1 << nr & 0x1F, and we can do without BPF_MOD in our case. > I'll put that on a lack of sleep... No worries! Changing the dialect of seccomp BPF isn't something I'd like to do without really good reason since it creates a split in the filter correctness from userspace (i.e. a filter using BPF_MOD on an older kernel will fail). So there would need to be a distinct flag set somewhere, etc. So, if you do end up discovering later you really want BPF_MOD, we can figure that out, but for now if you can get by with "&", that would be best. :) Thanks! -Kees > > > > > Signed-off-by: Paul Chaignon > > --- > > kernel/seccomp.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/kernel/seccomp.c b/kernel/seccomp.c > > index 811b4a86cdf6..87de6532ff6d 100644 > > --- a/kernel/seccomp.c > > +++ b/kernel/seccomp.c > > @@ -205,6 +205,8 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) > > case BPF_ALU | BPF_MUL | BPF_X: > > case BPF_ALU | BPF_DIV | BPF_K: > > case BPF_ALU | BPF_DIV | BPF_X: > > + case BPF_ALU | BPF_MOD | BPF_K: > > + case BPF_ALU | BPF_MOD | BPF_X: > > case BPF_ALU | BPF_AND | BPF_K: > > case BPF_ALU | BPF_AND | BPF_X: > > case BPF_ALU | BPF_OR | BPF_K: > > -- > > 2.17.1 -- Kees Cook