From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.9 required=5.0 tests=DKIM_SIGNED, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,T_DKIM_INVALID autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 4E33D7DF86 for ; Mon, 18 Jun 2018 21:45:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933241AbeFRVos (ORCPT ); Mon, 18 Jun 2018 17:44:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:40390 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936510AbeFRVor (ORCPT ); Mon, 18 Jun 2018 17:44:47 -0400 Received: from mail-wm0-f53.google.com (mail-wm0-f53.google.com [74.125.82.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 91AB420836 for ; Mon, 18 Jun 2018 21:44:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1529358286; bh=gDw8i04v+PnkkUDymHS9ykQ+jmxZYRMZE4jHMJO8o/M=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=SGzJCx4MrpeTQuPJDZg1dnUpY6AmYGqyE8U09bxIvEIQbyGhv9effZP8FjAsE2P87 mkzltxoWYRPrOMe5Qmh2tp0ju5p9Z2yHyYz9LBWcORnIBhAu4vC6Vy2PfNGMJHDvoE cMCMky/tdi/OkYNhPbSK9+IEL1BTpMboqG/OstcY= Received: by mail-wm0-f53.google.com with SMTP id o13-v6so16439465wmf.4 for ; Mon, 18 Jun 2018 14:44:46 -0700 (PDT) X-Gm-Message-State: APt69E316nl6E6bFQt0AU3cBxB55YXBPaS49USCa1Gc2jZfOdCz3AoIa NFOrtK1Ks4b1tYDQizxCZfG2ZtiOYEp93NBJimHsWg== X-Google-Smtp-Source: ADUXVKIb8qUh7XC+sL9MOcnqlLKDxU4C6RRWGSqu7pZ/LNB0urpcMNsHJR2ldbkC/H8WuhAjX3zKMHzLUuLV6tgXErc= X-Received: by 2002:a1c:f902:: with SMTP id x2-v6mr9232918wmh.116.1529358285009; Mon, 18 Jun 2018 14:44:45 -0700 (PDT) MIME-Version: 1.0 References: <20180607143807.3611-1-yu-cheng.yu@intel.com> <1528815820.8271.16.camel@2b52.sc.intel.com> <814fc15e80908d8630ff665be690ccbe6e69be88.camel@gmail.com> <1528988176.13101.15.camel@2b52.sc.intel.com> <2b77abb17dfaf58b7c23fac9d8603482e1887337.camel@gmail.com> In-Reply-To: <2b77abb17dfaf58b7c23fac9d8603482e1887337.camel@gmail.com> From: Andy Lutomirski Date: Mon, 18 Jun 2018 14:44:33 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 00/10] Control Flow Enforcement - Part (3) To: Balbir Singh Cc: Yu-cheng Yu , LKML , linux-doc@vger.kernel.org, Linux-MM , linux-arch , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , "H. J. Lu" , "Shanbhogue, Vedvyas" , "Ravi V. Shankar" , Dave Hansen , Jonathan Corbet , Oleg Nesterov , Arnd Bergmann , mike.kravetz@oracle.com Content-Type: text/plain; charset="UTF-8" Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Sat, Jun 16, 2018 at 8:16 PM Balbir Singh wrote: > > On Thu, 2018-06-14 at 07:56 -0700, Yu-cheng Yu wrote: > > On Thu, 2018-06-14 at 11:07 +1000, Balbir Singh wrote: > > > On Tue, 2018-06-12 at 08:03 -0700, Yu-cheng Yu wrote: > > > > On Tue, 2018-06-12 at 20:56 +1000, Balbir Singh wrote: > > > > > > > > > > On 08/06/18 00:37, Yu-cheng Yu wrote: > > > > > > This series introduces CET - Shadow stack > > > > > > > > > > > > At the high level, shadow stack is: > > > > > > > > > > > > Allocated from a task's address space with vm_flags VM_SHSTK; > > > > > > Its PTEs must be read-only and dirty; > > > > > > Fixed sized, but the default size can be changed by sys admin. > > > > > > > > > > > > For a forked child, the shadow stack is duplicated when the next > > > > > > shadow stack access takes place. > > > > > > > > > > > > For a pthread child, a new shadow stack is allocated. > > > > > > > > > > > > The signal handler uses the same shadow stack as the main program. > > > > > > > > > > > > > > > > Even with sigaltstack()? > > > > > > > > > > > > > Yes. > > > > > > I am not convinced that it would work, as we switch stacks, oveflow might > > > be an issue. I also forgot to bring up setcontext(2), I presume those > > > will get new shadow stacks > > > > Do you mean signal stack/sigaltstack overflow or swapcontext in a signal > > handler? > > > > I meant any combination of that. If there is a user space threads implementation that uses sigaltstack for switching threads > Anyone who does that is nuts. The whole point of user space threads is speed, and signals are very slow. For userspace threads to work, we need an API to allocate new shadow stacks, and we need to use the extremely awkwardly defined RSTORSSP stuff to switch. (I assume this is possible on an ISA level. The docs are bad, and the mnemonics for the relevant instructions are nonsensical.) -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html