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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no 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 2C840C432C0 for ; Wed, 20 Nov 2019 20:29:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 03D1D20872 for ; Wed, 20 Nov 2019 20:29:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726454AbfKTU3J (ORCPT ); Wed, 20 Nov 2019 15:29:09 -0500 Received: from out01.mta.xmission.com ([166.70.13.231]:49718 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726044AbfKTU3I (ORCPT ); Wed, 20 Nov 2019 15:29:08 -0500 Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1iXWb4-0007Q3-GX; Wed, 20 Nov 2019 13:29:06 -0700 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1iXWb4-0004NJ-8d; Wed, 20 Nov 2019 13:29:06 -0700 From: ebiederm@xmission.com (Eric W. Biederman) To: Will Deacon Cc: Alexey Dobriyan , Andrew Morton , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, security@kernel.org, ben.dooks@codethink.co.uk References: <20191118145114.GA9228@avx2> <20191118125457.778e44dfd4740d24795484c7@linux-foundation.org> <20191118215227.GA24536@avx2> <20191120191752.GC4799@willie-the-truck> Date: Wed, 20 Nov 2019 14:28:37 -0600 In-Reply-To: <20191120191752.GC4799@willie-the-truck> (Will Deacon's message of "Wed, 20 Nov 2019 19:17:52 +0000") Message-ID: <87d0dm47ii.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1iXWb4-0004NJ-8d;;;mid=<87d0dm47ii.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+83lFIyA5hg1F570AKpaOgIP+SI2XVCJc= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH] exec: warn if process starts with executable stack X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Will Deacon writes: > On Tue, Nov 19, 2019 at 12:52:27AM +0300, Alexey Dobriyan wrote: >> There were few episodes of silent downgrade to an executable stack: >> >> 1) linking innocent looking assembly file >> >> $ cat f.S >> .intel_syntax noprefix >> .text >> .globl f >> f: >> ret >> >> $ cat main.c >> void f(void); >> int main(void) >> { >> f(); >> return 0; >> } >> >> $ gcc main.c f.S >> $ readelf -l ./a.out >> GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000 >> 0x0000000000000000 0x0000000000000000 RWE 0x10 >> >> 2) converting C99 nested function into a closure >> https://nullprogram.com/blog/2019/11/15/ >> >> void intsort2(int *base, size_t nmemb, _Bool invert) >> { >> int cmp(const void *a, const void *b) >> { >> int r = *(int *)a - *(int *)b; >> return invert ? -r : r; >> } >> qsort(base, nmemb, sizeof(*base), cmp); >> } >> >> will silently require stack trampolines while non-closure version will not. >> >> While without a double this behaviour is documented somewhere, add a warning >> so that developers and users can at least notice. After so many years of x86_64 >> having proper executable stack support it should not cause too much problems. >> >> If the system is old or CPU is old, then there will be an early warning >> against init and/or support personnel will write that "uh-oh, our Enterprise >> Software absolutely requires executable stack" and close tickets and customers >> will nod heads and life moves on. >> >> Signed-off-by: Alexey Dobriyan >> --- >> >> fs/exec.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> --- a/fs/exec.c >> +++ b/fs/exec.c >> @@ -762,6 +762,11 @@ int setup_arg_pages(struct linux_binprm *bprm, >> goto out_unlock; >> BUG_ON(prev != vma); >> >> + if (vm_flags & VM_EXEC) { >> + pr_warn_once("process '%s'/%u started with executable stack\n", >> + current->comm, current->pid); >> + } > > Given that this is triggerable by userspace, is there a concern about PID > namespaces here? In what sense? Are you thinking about the printing of the pid? Pretty much by fiat and by definition the kernel log always print things in the initial pid namespace. Which this printk does. Eric