From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id C740E6B0007 for ; Tue, 19 Jun 2018 04:52:42 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id g20-v6so10010916pfi.2 for ; Tue, 19 Jun 2018 01:52:42 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id r7-v6sor4667900ple.150.2018.06.19.01.52.41 for (Google Transport Security); Tue, 19 Jun 2018 01:52:41 -0700 (PDT) Message-ID: <09b7cc16ee5275d4ef3dffb11942e3f2ba44aedd.camel@gmail.com> Subject: Re: [PATCH 00/10] Control Flow Enforcement - Part (3) From: Balbir Singh Date: Tue, 19 Jun 2018 18:52:29 +1000 In-Reply-To: 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> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski 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 On Mon, 2018-06-18 at 14:44 -0700, Andy Lutomirski wrote: > 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.) The whole point was to ensure we don't break applications/code that work today. I think as long as there is a shadow stack allocated corresponding to the user space stack and we can Restore SSP as we switch things should be fine. Balbir Singh.